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2026,38(5):1799-1812, DOI: 10.18307/2026.0500
Abstract:
Urban lakes serve multiple functions, including flood storage, water supply, landscape tourism, and ecological maintenance, thereby holding significant ecological, environmental, and socioeconomic value. The Yangtze River Basin contains approximately 355000 urban lakes, accounting for over 65% of the total water area of China's urban lakes, and these lakes exhibit strong ecological functions. However, urban lakes in the basin currently face prominent challenges such as high non-point source pollution loads during flood seasons, pollution risks associated with ecological water supplementation safety, and limited resilience of aquatic ecosystems. Addressing these issues requires an integrated approach that considers the holistic nature of urban lake ecosystems and the systemic characteristics of river basin management. It is essential to advance coordinated water environment and aquatic ecosystem management under a source-sewer-treatment plant-river-lake integrated framework. This study systematically reviews the research status and development needs related to the coordinated governance of water environment and aquatic ecosystems in urban lakes of the Yangtze River Basin. It synthesizes recent progress in domestic and international research as well as practical engineering applications, and provides an in-depth analysis of the major challenges currently constraining coordinated governance: (1) In certain urban areas, the accumulation of pollutants during dry seasons and the episodic release of contaminants during rainfall events remain prominent, the storm-induced non-point source pollution increasingly becoming a key constraint on the sustained improvement of urban water environments; (2) A critical challenge in using effluents from municipal wastewater treatment plants as ecological replenishment for urban lakes lies in achieving water quality and aquatic ecosystem compatibility between reclaimed water and receiving water bodies; (3) The ecological resilience of lake ecosystems remains weak, and watershed-level systematic governance is still insufficient. Based on this analysis, we summarize targeted strategies and key tasks centered on the framework of "efficient external source control-water supplementation safety-habitat restoration and reconstruction-system optimization and configuration-integrated platform management", aiming to accelerate progress in ecological environment governance of urban lakes in the Yangtze River Basin and provide scientific and technological support for national ecological civilization construction and the implementation of green development strategies.
Urban lakes serve multiple functions, including flood storage, water supply, landscape tourism, and ecological maintenance, thereby holding significant ecological, environmental, and socioeconomic value. The Yangtze River Basin contains approximately 355000 urban lakes, accounting for over 65% of the total water area of China's urban lakes, and these lakes exhibit strong ecological functions. However, urban lakes in the basin currently face prominent challenges such as high non-point source pollution loads during flood seasons, pollution risks associated with ecological water supplementation safety, and limited resilience of aquatic ecosystems. Addressing these issues requires an integrated approach that considers the holistic nature of urban lake ecosystems and the systemic characteristics of river basin management. It is essential to advance coordinated water environment and aquatic ecosystem management under a source-sewer-treatment plant-river-lake integrated framework. This study systematically reviews the research status and development needs related to the coordinated governance of water environment and aquatic ecosystems in urban lakes of the Yangtze River Basin. It synthesizes recent progress in domestic and international research as well as practical engineering applications, and provides an in-depth analysis of the major challenges currently constraining coordinated governance: (1) In certain urban areas, the accumulation of pollutants during dry seasons and the episodic release of contaminants during rainfall events remain prominent, the storm-induced non-point source pollution increasingly becoming a key constraint on the sustained improvement of urban water environments; (2) A critical challenge in using effluents from municipal wastewater treatment plants as ecological replenishment for urban lakes lies in achieving water quality and aquatic ecosystem compatibility between reclaimed water and receiving water bodies; (3) The ecological resilience of lake ecosystems remains weak, and watershed-level systematic governance is still insufficient. Based on this analysis, we summarize targeted strategies and key tasks centered on the framework of "efficient external source control-water supplementation safety-habitat restoration and reconstruction-system optimization and configuration-integrated platform management", aiming to accelerate progress in ecological environment governance of urban lakes in the Yangtze River Basin and provide scientific and technological support for national ecological civilization construction and the implementation of green development strategies.
2026,38(5):1813-1828, DOI: 10.18307/2026.0501
Abstract:
The increasing global demand for biodiversity conservation has made the accurate acquisition of biodiversity data a pressing challenge worldwide. Essential biodiversity variables (EBVs), as core indicators for biodiversity monitoring, provide a scientific foundation for both global and regional conservation policies. While traditional monitoring methods have contributed valuable data, they remain limited by high costs, low efficiency, and sampling difficulties. Environmental DNA (eDNA), as an emerging tool, enables efficient and precise detection of diverse species within environmental samples, thereby supplying richer datasets for the development of EBVs. This paper highlights the potential of eDNA technology in advancing EBVs construction and examines its prospects in biodiversity conservation in China, with the goal of fostering stronger integration between scientific research and policy-making. Using the six classes of EBVs as an analytical framework, this study reviewed 22 national and regional guidelines for aquatic biodiversity monitoring in China. The results revealed a strong dominance of community-level indicators, with approximately 95.5% of guidelines focusing on community composition, while genetic diversity, quantitative population dynamics, and ecosystem structure and function remain poorly represented. Considerable inconsistencies also existed among guidelines issued by different administrative sectors, limiting long-term comparability. Environmental DNA, with its high sensitivity, non-invasive sampling, and broad taxonomic coverage, offers a promising approach to address these structural gaps and support the development of EBVs-aligned aquatic biodiversity monitoring systems.
The increasing global demand for biodiversity conservation has made the accurate acquisition of biodiversity data a pressing challenge worldwide. Essential biodiversity variables (EBVs), as core indicators for biodiversity monitoring, provide a scientific foundation for both global and regional conservation policies. While traditional monitoring methods have contributed valuable data, they remain limited by high costs, low efficiency, and sampling difficulties. Environmental DNA (eDNA), as an emerging tool, enables efficient and precise detection of diverse species within environmental samples, thereby supplying richer datasets for the development of EBVs. This paper highlights the potential of eDNA technology in advancing EBVs construction and examines its prospects in biodiversity conservation in China, with the goal of fostering stronger integration between scientific research and policy-making. Using the six classes of EBVs as an analytical framework, this study reviewed 22 national and regional guidelines for aquatic biodiversity monitoring in China. The results revealed a strong dominance of community-level indicators, with approximately 95.5% of guidelines focusing on community composition, while genetic diversity, quantitative population dynamics, and ecosystem structure and function remain poorly represented. Considerable inconsistencies also existed among guidelines issued by different administrative sectors, limiting long-term comparability. Environmental DNA, with its high sensitivity, non-invasive sampling, and broad taxonomic coverage, offers a promising approach to address these structural gaps and support the development of EBVs-aligned aquatic biodiversity monitoring systems.
2026,38(5):1829-1849, DOI: 10.18307/2026.0502
Abstract:
The Qaidam Basin, located on the northeastern margin of the Tibetan Plateau, is characterized by a “mountain-deep basin” structural framework and Cenozoic sedimentary fill exceeding 10 km, which has given rise to China's largest continental saline-lake potash metallogenic belt, containing over 80% of the nation's proven reserves. Since the Neogene, the basin has experienced multiple phases of tectonic deformation. Under the combined influence of plateau uplift and extreme regional aridification, secondary depressions such as Qarhan, Dalangtan-Heibei, Kunteyi, and Mahai have developed, forming a composite mineralization system dominated by brine-type deposits with the coexistence of solid-liquid mineralization. The potash-forming process is jointly controlled by four-dimensional factors: tectonics, climate, provenance, and sedimentation. Based on a systematic review of tectono-sedimentary evolution and paleoclimate changes, this study reconstructs the spatiotemporal distribution and controlling mechanisms of potash mineralization. The results indicate that tectonic differentiation determined the framework of brine accumulation and storage, climate drove evaporation concentration and mineralization rhythms, while provenance supply promotes continuous potassium enrichment through a “deep-shallow coupling” binary mechanism. Combined with lithofacies-palaeogeographic differentiation, depositional centers migrated multiple times during the Pleistocene, leading to progressive aridification and salinization in the northwestern Qaidam Basin. Based on the comprehensive analysis of metallogenic factors, the evolution of potash mineralization in the Qaidam Basin can be divided into five stages: unified paleolake subsidence, multi-depression differentiation, extreme aridification and concentration, fault-controlled inheritance and metallogenic climax, and modern saline-lake cluster. Furthermore, three metallogenic models are identified: central-sedimentary-center type, foreland thrust-belt-controlled type, and northwestern tectonically controlled type. This evolutionary sequence and model framework not only reveal the dynamic essence of saline-lake potash mineralization under the uplift of the Tibetan Plateau, but also provide a theoretical basis and practical guidance for deep brine exploration and the refinement of metallogenic models in China.
The Qaidam Basin, located on the northeastern margin of the Tibetan Plateau, is characterized by a “mountain-deep basin” structural framework and Cenozoic sedimentary fill exceeding 10 km, which has given rise to China's largest continental saline-lake potash metallogenic belt, containing over 80% of the nation's proven reserves. Since the Neogene, the basin has experienced multiple phases of tectonic deformation. Under the combined influence of plateau uplift and extreme regional aridification, secondary depressions such as Qarhan, Dalangtan-Heibei, Kunteyi, and Mahai have developed, forming a composite mineralization system dominated by brine-type deposits with the coexistence of solid-liquid mineralization. The potash-forming process is jointly controlled by four-dimensional factors: tectonics, climate, provenance, and sedimentation. Based on a systematic review of tectono-sedimentary evolution and paleoclimate changes, this study reconstructs the spatiotemporal distribution and controlling mechanisms of potash mineralization. The results indicate that tectonic differentiation determined the framework of brine accumulation and storage, climate drove evaporation concentration and mineralization rhythms, while provenance supply promotes continuous potassium enrichment through a “deep-shallow coupling” binary mechanism. Combined with lithofacies-palaeogeographic differentiation, depositional centers migrated multiple times during the Pleistocene, leading to progressive aridification and salinization in the northwestern Qaidam Basin. Based on the comprehensive analysis of metallogenic factors, the evolution of potash mineralization in the Qaidam Basin can be divided into five stages: unified paleolake subsidence, multi-depression differentiation, extreme aridification and concentration, fault-controlled inheritance and metallogenic climax, and modern saline-lake cluster. Furthermore, three metallogenic models are identified: central-sedimentary-center type, foreland thrust-belt-controlled type, and northwestern tectonically controlled type. This evolutionary sequence and model framework not only reveal the dynamic essence of saline-lake potash mineralization under the uplift of the Tibetan Plateau, but also provide a theoretical basis and practical guidance for deep brine exploration and the refinement of metallogenic models in China.
2026,38(5):1850-1859, DOI: 10.18307/2026.0511
Abstract:
With climate change, the increasing frequency and intensity of extreme climate events have intensified the outbreak and expansion of cyanobacterial blooms in shallow eutrophic lakes, posing severe threats to the security and water supply safety of lake ecosystems. However, how extreme climate events drive the long-term dynamics of cyanobacterial blooms, as well as the dominant factors and underlying mechanisms, remain unclear. Taking Lake Hongze as a case study, Mann-Kendall trend analysis based on 64 years of meteorological observations revealed a significant warming trend in extreme temperature indices. Since 1991, the total duration and frequency of extreme heat events has increased by approximately 5.33 days and 2 events per decade, respectively. Meanwhile, the Simple Daily Intensity Index and the annual total precipitation from very wet days have increased by 0.38 mm/d and 15.18 mm, respectively. Based on remote-sensing observations from 2003 to 2020, the bloom occurrence rate in Lake Hongze has increased by an average of 1.15% per year, while the maximum bloom extent has expanded by 154.69 km². The bloom onset has advanced by 24.56 days, and the potential bloom duration has extended by an average of 27. 20 days. Further attribution analysis using the SHAP method indicated that the bloom occurrence rate and the maximum bloom extent are the cyanobacterial bloom metrics most sensitive to extreme climate events, with the mean intensity of extreme heat events playing a dominant role. The continued intensification of extreme heat events is expected to further advance the bloom onset and expand the bloom extent. Notably, when temperatures exceed a certain threshold, algal growth may be inhibited due to thermal stress, suggesting a dual "promoting-inhibiting" effect of extreme heat events on cyanobacterial bloom dynamics. This study elucidates the response mechanisms and threshold behaviors of cyanobacterial blooms under extreme climate forcing, providing a theoretical basis and scientific support for the early warning of bloom risks and adaptive watershed management.
With climate change, the increasing frequency and intensity of extreme climate events have intensified the outbreak and expansion of cyanobacterial blooms in shallow eutrophic lakes, posing severe threats to the security and water supply safety of lake ecosystems. However, how extreme climate events drive the long-term dynamics of cyanobacterial blooms, as well as the dominant factors and underlying mechanisms, remain unclear. Taking Lake Hongze as a case study, Mann-Kendall trend analysis based on 64 years of meteorological observations revealed a significant warming trend in extreme temperature indices. Since 1991, the total duration and frequency of extreme heat events has increased by approximately 5.33 days and 2 events per decade, respectively. Meanwhile, the Simple Daily Intensity Index and the annual total precipitation from very wet days have increased by 0.38 mm/d and 15.18 mm, respectively. Based on remote-sensing observations from 2003 to 2020, the bloom occurrence rate in Lake Hongze has increased by an average of 1.15% per year, while the maximum bloom extent has expanded by 154.69 km². The bloom onset has advanced by 24.56 days, and the potential bloom duration has extended by an average of 27. 20 days. Further attribution analysis using the SHAP method indicated that the bloom occurrence rate and the maximum bloom extent are the cyanobacterial bloom metrics most sensitive to extreme climate events, with the mean intensity of extreme heat events playing a dominant role. The continued intensification of extreme heat events is expected to further advance the bloom onset and expand the bloom extent. Notably, when temperatures exceed a certain threshold, algal growth may be inhibited due to thermal stress, suggesting a dual "promoting-inhibiting" effect of extreme heat events on cyanobacterial bloom dynamics. This study elucidates the response mechanisms and threshold behaviors of cyanobacterial blooms under extreme climate forcing, providing a theoretical basis and scientific support for the early warning of bloom risks and adaptive watershed management.
2026,38(5):1860-1870, DOI: 10.18307/2026.0512
Abstract:
Microcystis, the most frequently observed genus in cyanobacterial blooms, exhibits significant morphological diversity and pronounced spatiotemporal variation. However, the seasonal distribution patterns of its distinct morphological characteristics remain unclear. This study systematically analyzed the morphological features, spatiotemporal distribution patterns, and coupling relationships with environmental factors (temperature, nutrients, etc.) of Microcystis in Lake Chaohu from 2022 to 2023. The results indicate that there are significant differences in colony size and cell diameter among Microcystis species. M. panniformis and M. aeruginosa have the largest colony sizes, which are significantly larger than those of M. flos-aquae and M. botrys. M. wesenbergii has the largest cell diameter, which is significantly larger than those of M. botrys, M. aeruginosa, and M. viridis, while M. flos-aquae and M. ichthyoblabe have the smallest diameters. This morphological differentiation was accompanied by differential responses to nutrients (nitrogen and phosphorus) and temperature. Nitrogen and phosphorus were the key nutrients affecting the colony size and cell diameter of Microcystis, with significant differences in occurrence frequency of different species across total phosphorus and temperature ranges. During the cold season, M. viridis and M. pseudofilamentosa had higher frequencies. As water temperatures increased into the warm season, the community shifted toward higher frequencies of M. wesenbergii, M. novacekii, and M. aeruginosa. In the hot season, M. botrys and M. smithii became the most frequent species. Correlation analysis and regression models further revealed the regulatory effects of environmental factors on the cell diameter of Microcystis. Temperature and phosphorus showed significant correlations with cell diameter in most species. This study aims to provide a scientific basis for understanding the ecological adaptation mechanisms of Microcystis in Lake Chaohu and for the management of cyanobacteria in eutrophic lakes.
Microcystis, the most frequently observed genus in cyanobacterial blooms, exhibits significant morphological diversity and pronounced spatiotemporal variation. However, the seasonal distribution patterns of its distinct morphological characteristics remain unclear. This study systematically analyzed the morphological features, spatiotemporal distribution patterns, and coupling relationships with environmental factors (temperature, nutrients, etc.) of Microcystis in Lake Chaohu from 2022 to 2023. The results indicate that there are significant differences in colony size and cell diameter among Microcystis species. M. panniformis and M. aeruginosa have the largest colony sizes, which are significantly larger than those of M. flos-aquae and M. botrys. M. wesenbergii has the largest cell diameter, which is significantly larger than those of M. botrys, M. aeruginosa, and M. viridis, while M. flos-aquae and M. ichthyoblabe have the smallest diameters. This morphological differentiation was accompanied by differential responses to nutrients (nitrogen and phosphorus) and temperature. Nitrogen and phosphorus were the key nutrients affecting the colony size and cell diameter of Microcystis, with significant differences in occurrence frequency of different species across total phosphorus and temperature ranges. During the cold season, M. viridis and M. pseudofilamentosa had higher frequencies. As water temperatures increased into the warm season, the community shifted toward higher frequencies of M. wesenbergii, M. novacekii, and M. aeruginosa. In the hot season, M. botrys and M. smithii became the most frequent species. Correlation analysis and regression models further revealed the regulatory effects of environmental factors on the cell diameter of Microcystis. Temperature and phosphorus showed significant correlations with cell diameter in most species. This study aims to provide a scientific basis for understanding the ecological adaptation mechanisms of Microcystis in Lake Chaohu and for the management of cyanobacteria in eutrophic lakes.
2026,38(5):1871-1881, DOI: 10.18307/2026.0513
Abstract:
Lake ecosystems in cold and arid regions are sensitive to climate change and human disturbances, and the dynamics of their phytoplankton communities serve as important indicators characterizing changes in the aquatic ecological environment. Lake Hulun, a typical shallow lake in the arid and semi-arid regions of northern China, has exhibited eutrophication characteristics following the implementation of the "River Diversion to Lake" project. Therefore, exploring the assembly mechanism of its phytoplankton community and the key environmental driving factors is of great significance for lake ecological restoration and algal bloom prevention and control. In the spring and summer periods of 2024 and 2025, a systematic ecological investigation was conducted at 25 sites in the main lake area and main inflow waters of Lake Hulun, aiming to analyze the seasonal succession patterns, taxonomic beta diversity characteristics of phytoplankton communities, and their coupling relationships with environmental factors. The results indicated that the phytoplankton community structure in Lake Hulun displayed significant seasonal succession. The dominant groups in spring showed significant inter-annual succession, changing from the common dominant groups of Cyanobacteria and Chlorophyta in 2024 to Chlorophyta and Bacillariophyta in 2025; in summer, the absolute dominant group was Cyanobacteria in both years. Microcystis aeruginosa and Anabaena circinalis became the dominant species. The annual average phytoplankton cell abundance was 2.42×105 cells/L, and the seasonal distribution showed that the density in summer (2.95×105−3.20×105 cells/L) was significantly higher than that in spring (1.68×105−1.76×105 cells/L). Although species richness was relatively higher in summer, the Shannon-Wiener diversity index of the community was significantly lower than that in spring. Canonical correspondence analysis showed that the spring community was mainly affected by total phosphorus, turbidity, and dissolved oxygen, while the summer community was mainly driven by factors such as water temperature, total nitrogen, five-day biochemical oxygen demand, and chlorophyll-a. Decomposition of taxonomic beta diversity revealed that the taxonomic beta diversity between seasons and years was dominated by the turnover component, indicating that species replacement is the core process in the assembly of the phytoplankton community in Lake Hulun, reflecting strong environmental filtering effects and habitat heterogeneity. This study demonstrates that environmental filtering is the core driving force affecting the seasonal dynamics of the phytoplankton community in Lake Hulun from two dimensions: species composition and community assembly mechanism. The research results not only identified the key regulatory factors in the eutrophication process of Lake Hulun but also provided an important scientific basis for the aquatic ecological health assessment, cyanobacterial bloom early warning, and ecological restoration practices of this lake and similar cold and arid lakes in northern China.
Lake ecosystems in cold and arid regions are sensitive to climate change and human disturbances, and the dynamics of their phytoplankton communities serve as important indicators characterizing changes in the aquatic ecological environment. Lake Hulun, a typical shallow lake in the arid and semi-arid regions of northern China, has exhibited eutrophication characteristics following the implementation of the "River Diversion to Lake" project. Therefore, exploring the assembly mechanism of its phytoplankton community and the key environmental driving factors is of great significance for lake ecological restoration and algal bloom prevention and control. In the spring and summer periods of 2024 and 2025, a systematic ecological investigation was conducted at 25 sites in the main lake area and main inflow waters of Lake Hulun, aiming to analyze the seasonal succession patterns, taxonomic beta diversity characteristics of phytoplankton communities, and their coupling relationships with environmental factors. The results indicated that the phytoplankton community structure in Lake Hulun displayed significant seasonal succession. The dominant groups in spring showed significant inter-annual succession, changing from the common dominant groups of Cyanobacteria and Chlorophyta in 2024 to Chlorophyta and Bacillariophyta in 2025; in summer, the absolute dominant group was Cyanobacteria in both years. Microcystis aeruginosa and Anabaena circinalis became the dominant species. The annual average phytoplankton cell abundance was 2.42×105 cells/L, and the seasonal distribution showed that the density in summer (2.95×105−3.20×105 cells/L) was significantly higher than that in spring (1.68×105−1.76×105 cells/L). Although species richness was relatively higher in summer, the Shannon-Wiener diversity index of the community was significantly lower than that in spring. Canonical correspondence analysis showed that the spring community was mainly affected by total phosphorus, turbidity, and dissolved oxygen, while the summer community was mainly driven by factors such as water temperature, total nitrogen, five-day biochemical oxygen demand, and chlorophyll-a. Decomposition of taxonomic beta diversity revealed that the taxonomic beta diversity between seasons and years was dominated by the turnover component, indicating that species replacement is the core process in the assembly of the phytoplankton community in Lake Hulun, reflecting strong environmental filtering effects and habitat heterogeneity. This study demonstrates that environmental filtering is the core driving force affecting the seasonal dynamics of the phytoplankton community in Lake Hulun from two dimensions: species composition and community assembly mechanism. The research results not only identified the key regulatory factors in the eutrophication process of Lake Hulun but also provided an important scientific basis for the aquatic ecological health assessment, cyanobacterial bloom early warning, and ecological restoration practices of this lake and similar cold and arid lakes in northern China.
2026,38(5):1882-1898, DOI: 10.18307/2026.0514
Abstract:
Phytoplankton, as the primary producers in lake ecosystems, influence material cycling and energy flow within water bodies. Their community structure and dynamic changes directly reflect the nutrient status and ecological health of the water body. To comprehensively understand phytoplankton variations and influencing factors in tailwater lakes of northern arid-cold regions, the representative Lake Daihai was selected as the study site. Water and sediment samples were collected across all four seasons in 2024 to systematically analyze phytoplankton community structure and its response to environmental factors. Results indicate that during the study period, water body total nitrogen (TN) and total phosphorus (TP) concentrations exceeded Grade Ⅴ and Grade Ⅳ water standards, respectively, while sediment TN and TP contents surpassed the national sediment average. A total of 95 phytoplankton species belonging to 8 phyla were identified, dominated by Chlorophyta, Cyanobacteria, and Bacillariophyta. Phytoplankton cell density, biomass, and Chl. a concentration peaked in winter. Twelve dominant species across 5 phyla were identified, primarily from Chlorophyta and Bacillariophyta, with Microcystis and Chroomonas serving as key dominant genera throughout the year. Results from Shannon diversity index, Pielou evenness index, Margalef richness index, and Simpson dominance index indicated higher phytoplankton community diversity and greater ecosystem stability in spring and summer compared to autumn and winter. Phytoplankton communities in Lake Daihai exhibited low spatial heterogeneity, suggesting that diversity and richness are primarily influenced by seasonal variations. Statistical analysis indicates that water temperature, pH, dissolved oxygen, TN, and dissolved inorganic phosphorus are key factors influencing phytoplankton community structure. Multi-year surveys reveal that the dominant phytoplankton species in Lake Daihai have shifted from Bacillariophyta and Chlorophyta to Cyanobacteria and Cryptophyta. This study uncovers the key mechanisms driving seasonal succession in phytoplankton communities of northern cold-arid lakes, providing a scientific basis for ecological management and conservation of Lake Daihai.
Phytoplankton, as the primary producers in lake ecosystems, influence material cycling and energy flow within water bodies. Their community structure and dynamic changes directly reflect the nutrient status and ecological health of the water body. To comprehensively understand phytoplankton variations and influencing factors in tailwater lakes of northern arid-cold regions, the representative Lake Daihai was selected as the study site. Water and sediment samples were collected across all four seasons in 2024 to systematically analyze phytoplankton community structure and its response to environmental factors. Results indicate that during the study period, water body total nitrogen (TN) and total phosphorus (TP) concentrations exceeded Grade Ⅴ and Grade Ⅳ water standards, respectively, while sediment TN and TP contents surpassed the national sediment average. A total of 95 phytoplankton species belonging to 8 phyla were identified, dominated by Chlorophyta, Cyanobacteria, and Bacillariophyta. Phytoplankton cell density, biomass, and Chl. a concentration peaked in winter. Twelve dominant species across 5 phyla were identified, primarily from Chlorophyta and Bacillariophyta, with Microcystis and Chroomonas serving as key dominant genera throughout the year. Results from Shannon diversity index, Pielou evenness index, Margalef richness index, and Simpson dominance index indicated higher phytoplankton community diversity and greater ecosystem stability in spring and summer compared to autumn and winter. Phytoplankton communities in Lake Daihai exhibited low spatial heterogeneity, suggesting that diversity and richness are primarily influenced by seasonal variations. Statistical analysis indicates that water temperature, pH, dissolved oxygen, TN, and dissolved inorganic phosphorus are key factors influencing phytoplankton community structure. Multi-year surveys reveal that the dominant phytoplankton species in Lake Daihai have shifted from Bacillariophyta and Chlorophyta to Cyanobacteria and Cryptophyta. This study uncovers the key mechanisms driving seasonal succession in phytoplankton communities of northern cold-arid lakes, providing a scientific basis for ecological management and conservation of Lake Daihai.
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Available online: September 11, 2026
Abstract:
Total load control of riverine pollutant transport is critical for safeguarding water environmental quality, particularly under the background of frequent extreme precipitation and intensified hydrological variability, where the relative changes between pollutant loads and discharge directly determine the ultimate concentration levels in rivers. Elucidating the response characteristics of concentration and flux to discharge variations is of great significance for watershed water quality risk assessment. Based on daily monitoring data from 136 representative stations across China""s major river basins during 2021–2024, combined with synchronous hydrological records, this study analyzed the spatiotemporal heterogeneity of total nitrogen (TN) and total phosphorus (TP) concentrations and fluxes, and employed power function regression models to establish concentration-discharge (C-Q) and flux-discharge (F-Q) relationships to decipher their response mechanisms to discharge variations. The results revealed significant spatial inconsistency between concentrations and fluxes of nitrogen and phosphorus in Chinese rivers. Northern basins exhibited a "high concentration-low flux" pattern, with TN concentrations typically sustained between 4.0 and 8.0 mg/L and an average TP concentration of 0.093 mg/L, yet transport fluxes remained low due to limited runoff; conversely, southern basins displayed a "low concentration-high flux" pattern, with average TN and TP fluxes (4.29 kg/km2/d and 0.18 kg/km2/d) significantly exceeding those in the north (3.62 kg/km2/d and 0.12 kg/km2/d). Seasonal fluctuations revealed fundamentally distinct driving mechanisms for nitrogen and phosphorus: TN, predominantly in dissolved form, was governed by dilution effects, exhibiting "high concentration during dry season and high flux during wet season" characteristics, with runoff being the decisive factor for flux variation; TP, primarily in particulate form, was dominated by scouring effects, where intense rainfall during the wet season triggered soil erosion and sediment resuspension, causing concentration and flux to peak synchronously. C-Q analysis indicated that TN concentration was significantly negatively correlated with discharge (northern b = -0.20, southern b = -0.16), dominated by dilution effects, while the relationship between TP concentration and discharge was weak, particularly failing to reach significance in northern basins. F-Q analysis showed no significant regional difference in TN flux sensitivity to discharge, whereas TP flux sensitivity was significantly higher in the north (b"" = 0.41) than in the south (b"" = 0.28), indicating elevated phosphorus export risk in northern basins during extreme rainfall events. In conclusion, region-specific management strategies are recommended: northern basins should prioritize dry-season concentration control and rainy-season particulate phosphorus export prevention, while southern basins should focus on wet-season total load control and early warning systems for concentration rebound risks during low-flow periods.
Total load control of riverine pollutant transport is critical for safeguarding water environmental quality, particularly under the background of frequent extreme precipitation and intensified hydrological variability, where the relative changes between pollutant loads and discharge directly determine the ultimate concentration levels in rivers. Elucidating the response characteristics of concentration and flux to discharge variations is of great significance for watershed water quality risk assessment. Based on daily monitoring data from 136 representative stations across China""s major river basins during 2021–2024, combined with synchronous hydrological records, this study analyzed the spatiotemporal heterogeneity of total nitrogen (TN) and total phosphorus (TP) concentrations and fluxes, and employed power function regression models to establish concentration-discharge (C-Q) and flux-discharge (F-Q) relationships to decipher their response mechanisms to discharge variations. The results revealed significant spatial inconsistency between concentrations and fluxes of nitrogen and phosphorus in Chinese rivers. Northern basins exhibited a "high concentration-low flux" pattern, with TN concentrations typically sustained between 4.0 and 8.0 mg/L and an average TP concentration of 0.093 mg/L, yet transport fluxes remained low due to limited runoff; conversely, southern basins displayed a "low concentration-high flux" pattern, with average TN and TP fluxes (4.29 kg/km2/d and 0.18 kg/km2/d) significantly exceeding those in the north (3.62 kg/km2/d and 0.12 kg/km2/d). Seasonal fluctuations revealed fundamentally distinct driving mechanisms for nitrogen and phosphorus: TN, predominantly in dissolved form, was governed by dilution effects, exhibiting "high concentration during dry season and high flux during wet season" characteristics, with runoff being the decisive factor for flux variation; TP, primarily in particulate form, was dominated by scouring effects, where intense rainfall during the wet season triggered soil erosion and sediment resuspension, causing concentration and flux to peak synchronously. C-Q analysis indicated that TN concentration was significantly negatively correlated with discharge (northern b = -0.20, southern b = -0.16), dominated by dilution effects, while the relationship between TP concentration and discharge was weak, particularly failing to reach significance in northern basins. F-Q analysis showed no significant regional difference in TN flux sensitivity to discharge, whereas TP flux sensitivity was significantly higher in the north (b"" = 0.41) than in the south (b"" = 0.28), indicating elevated phosphorus export risk in northern basins during extreme rainfall events. In conclusion, region-specific management strategies are recommended: northern basins should prioritize dry-season concentration control and rainy-season particulate phosphorus export prevention, while southern basins should focus on wet-season total load control and early warning systems for concentration rebound risks during low-flow periods.
Available online: September 10, 2026
Abstract:
To elucidate the long-term succession characteristics of the zooplankton community in Dianshan Lake and its response to submerged macrophyte restoration, four seasonal surveys were conducted from 2019 to 2024, and the community characteristics and environmental factors were systematically analyzed. Based on UpSet plots, non-metric multidimensional scaling (NMDS), and canonical correspondence analysis (CCA), we quantified the stability of species composition, dominant species patterns, and community succession characteristics. A comprehensive water quality assessment was performed using indicator organisms and diversity indices. A total of 58 zooplankton species were identified, with the annual shared species ratio ranging from 46.34% to 55.88%, indicating a relatively stable community composition. The average abundance and biomass were 99.33 ind./L and 4.87 mg/L, respectively, showing negligible interannual fluctuations but significant seasonal differences (peaking in summer) and high spatial homogeneity. Twelve dominant species were screened out, among which Bosmina longirostris persisted as a dominant taxon for six consecutive years. NMDS results showed strong community structural homogeneity during 2019–2021, with the highest intra-group aggregation occurring in 2020. In contrast, the aggregation degree decreased notably during 2022–2024, closely correlated with the occurrence and decline of cyanobacterial blooms. Regarding seasonal succession, the zooplankton community exhibited a regular succession along the primary axis in winter, whereas the community structures remained similar across the other seasons. CCA results indicated that water temperature, salinity, total nitrogen, pH, and dissolved oxygen were the key environmental factors driving changes in zooplankton community structure. The zooplankton community was characterized by a long-term dominance of small-sized groups and B. longirostris, and the community structure was highly sensitive to bloom events. For the first time, large-scale submerged macrophyte communities were recorded to have re-established and persisted in the southern area of Dianshan Lake since 2024. Indicator organism and diversity assessments revealed that the water quality remained at an α–β mesotrophic level, yet showed a marked improvement trend in 2024. Field observations confirmed a spatio-temporal coupling between the water quality improvement and macrophyte recovery. It is speculated that vegetation restoration indirectly promoted community stability by improving habitat heterogeneity and food web structure; however, its driving effect on water quality requires long-term verification. The " physicochemical–biological–habitat" response mechanism chain constructed in this study provides operable monitoring indicators and decision-making support for eutrophication control and ecological restoration efficiency evaluation.
To elucidate the long-term succession characteristics of the zooplankton community in Dianshan Lake and its response to submerged macrophyte restoration, four seasonal surveys were conducted from 2019 to 2024, and the community characteristics and environmental factors were systematically analyzed. Based on UpSet plots, non-metric multidimensional scaling (NMDS), and canonical correspondence analysis (CCA), we quantified the stability of species composition, dominant species patterns, and community succession characteristics. A comprehensive water quality assessment was performed using indicator organisms and diversity indices. A total of 58 zooplankton species were identified, with the annual shared species ratio ranging from 46.34% to 55.88%, indicating a relatively stable community composition. The average abundance and biomass were 99.33 ind./L and 4.87 mg/L, respectively, showing negligible interannual fluctuations but significant seasonal differences (peaking in summer) and high spatial homogeneity. Twelve dominant species were screened out, among which Bosmina longirostris persisted as a dominant taxon for six consecutive years. NMDS results showed strong community structural homogeneity during 2019–2021, with the highest intra-group aggregation occurring in 2020. In contrast, the aggregation degree decreased notably during 2022–2024, closely correlated with the occurrence and decline of cyanobacterial blooms. Regarding seasonal succession, the zooplankton community exhibited a regular succession along the primary axis in winter, whereas the community structures remained similar across the other seasons. CCA results indicated that water temperature, salinity, total nitrogen, pH, and dissolved oxygen were the key environmental factors driving changes in zooplankton community structure. The zooplankton community was characterized by a long-term dominance of small-sized groups and B. longirostris, and the community structure was highly sensitive to bloom events. For the first time, large-scale submerged macrophyte communities were recorded to have re-established and persisted in the southern area of Dianshan Lake since 2024. Indicator organism and diversity assessments revealed that the water quality remained at an α–β mesotrophic level, yet showed a marked improvement trend in 2024. Field observations confirmed a spatio-temporal coupling between the water quality improvement and macrophyte recovery. It is speculated that vegetation restoration indirectly promoted community stability by improving habitat heterogeneity and food web structure; however, its driving effect on water quality requires long-term verification. The " physicochemical–biological–habitat" response mechanism chain constructed in this study provides operable monitoring indicators and decision-making support for eutrophication control and ecological restoration efficiency evaluation.
GUO Xiaojuan, DENG Wei, WU Shucheng, HUANG Yanan, ZHANG Hao, DENG Danli, LI Yuchen, Li Wenhui, YANG Zhengjian
Available online: September 10, 2026
Abstract:
Algal blooms significantly alter biogeochemical cycling and greenhouse gas (GHG) fluxes in reservoir ecosystems. To investigate the impact of algal blooms on the spatial-temporal dynamics and interfacial transport mechanisms of GHGs, high-resolution monitoring of dissolved CO2, CH4 and N2O concentrations and fluxes were conducted in the Gaobazhou Reservoir during a bloom event. . Dissolved concentrations ranged from 0.12 to 215.82 μmol/L for CO2 (saturation: 1.8% to 1332.9%), 0.01 to 0.41 μmol/L for CH4 (saturation: 1198.2% to 12789.5%), and 17.83 to 48.78 nmol/L for N2O (saturation: 221.8% to 538.5%). Except CO2 in the bloom zone, all monitored GHGs were highly supersaturated. Floating chamber measured CO2, CH4 and N2O fluxes in non-algal bloom areas were 204.39±170.93 mg/(m2·h), 0.36±0.42 mg/(m2·h), and 0.01±0.01 mg/(m2·h), respectively, in the algal bloom areas were -88.42±39.20 mg/(m2·h) for CO2, 0.55±0.51 mg/(m2·h) for CH4, and 0.07±0.05 mg/(m2·h) for N2O. Driven by intense photosynthetic activity in the algal bloom areas, the surface water shifted from a CO2 source to a net sink;, compared to non-bloom areas However, CH4 and N2O emissions increased by 54% and 342%, respectively. Significant methodological discrepancies were found between the flux results of floating chamber and thin boundary layer methods: floating chamber estimations were 3-10 times higher than those derived from the thin boundary layer method, with the maximum divergence (~10×) occurring in the algal bloom regions. Algal blooms altered dissolved gas compositions and induced total dissolved gas (TDG) supersaturation (111.6% to 136.4%). The TDG supersaturation triggered microbubble formation, shifting the dominant gas transfer pathway to a coupled process of molecular diffusion and microbubble-mediated emission, which significantly enhanced CH4 and N2O emissions. This study demonstrates that algal blooms stimulate GHGs emissions by fundamentally altering interfacial gas transfer pathways, providing a new insight for accurate reservoir carbon budgeting and eco-hydraulic management.
Algal blooms significantly alter biogeochemical cycling and greenhouse gas (GHG) fluxes in reservoir ecosystems. To investigate the impact of algal blooms on the spatial-temporal dynamics and interfacial transport mechanisms of GHGs, high-resolution monitoring of dissolved CO2, CH4 and N2O concentrations and fluxes were conducted in the Gaobazhou Reservoir during a bloom event. . Dissolved concentrations ranged from 0.12 to 215.82 μmol/L for CO2 (saturation: 1.8% to 1332.9%), 0.01 to 0.41 μmol/L for CH4 (saturation: 1198.2% to 12789.5%), and 17.83 to 48.78 nmol/L for N2O (saturation: 221.8% to 538.5%). Except CO2 in the bloom zone, all monitored GHGs were highly supersaturated. Floating chamber measured CO2, CH4 and N2O fluxes in non-algal bloom areas were 204.39±170.93 mg/(m2·h), 0.36±0.42 mg/(m2·h), and 0.01±0.01 mg/(m2·h), respectively, in the algal bloom areas were -88.42±39.20 mg/(m2·h) for CO2, 0.55±0.51 mg/(m2·h) for CH4, and 0.07±0.05 mg/(m2·h) for N2O. Driven by intense photosynthetic activity in the algal bloom areas, the surface water shifted from a CO2 source to a net sink;, compared to non-bloom areas However, CH4 and N2O emissions increased by 54% and 342%, respectively. Significant methodological discrepancies were found between the flux results of floating chamber and thin boundary layer methods: floating chamber estimations were 3-10 times higher than those derived from the thin boundary layer method, with the maximum divergence (~10×) occurring in the algal bloom regions. Algal blooms altered dissolved gas compositions and induced total dissolved gas (TDG) supersaturation (111.6% to 136.4%). The TDG supersaturation triggered microbubble formation, shifting the dominant gas transfer pathway to a coupled process of molecular diffusion and microbubble-mediated emission, which significantly enhanced CH4 and N2O emissions. This study demonstrates that algal blooms stimulate GHGs emissions by fundamentally altering interfacial gas transfer pathways, providing a new insight for accurate reservoir carbon budgeting and eco-hydraulic management.
Available online: September 09, 2026
Abstract:
Lakes, as critical carriers of global freshwater resources and key functional units of ecosystems, play a vital role in maintaining biodiversity, supporting sustainable water use, and ensuring the stable provision of multiple ecosystem services. Based on a theoretical framework for characterizing lake ecosystem status, this study systematically reviews the conceptual connotations, indicator construction logic, and applications in ecological health assessment of diversity, integrity, stability, and sustainability (hereafter referred to as the “four dimensions”). In general, diversity and integrity primarily describe community composition and structural characteristics, whereas stability and sustainability emphasize functional processes and the long-term maintenance capacity of ecosystems. Together, these four dimensions constitute an integrated structural–functional framework for assessing lake ecosystem health. At present, the “four-dimension” indicator system has been widely applied in lake ecological health assessment, restoration evaluation, and management decision support. However, several key challenges remain: high sensitivity of indicators to spatial and temporal scales, leading to limited cross-scale comparability; insufficient incorporation of ecological mechanisms in indicator selection; limited representation of functional processes such as energy flow and material cycling; and a lack of long-term continuous observations, which constrains the detection of system trajectories and lagged responses. Further analysis reveals that the four dimensions are not independent but are interconnected through structure–function coupling and feedback mechanisms. Under natural conditions, increased diversity, improved structural integrity, and enhanced ecosystem functioning can jointly promote stability and sustainability via positive feedbacks. However, under conditions of species dominance or environmental homogenization, ecosystems may shift into a “superficially stable” simplified state, characterized by reduced community variability but diminished functional redundancy and response diversity, resulting in short-term stability but long-term vulnerability. Based on these insights, this study highlights the need to develop integrated indicator systems that incorporate multi-scale and multi-taxa information, while simultaneously linking structural attributes with functional processes in both static and dynamic dimensions. Such advancements will improve the characterization of lake ecosystem health and its temporal dynamics, providing a more mechanistic foundation for ecological risk identification, management optimization, and the long-term sustainable development of lake ecosystems.
Lakes, as critical carriers of global freshwater resources and key functional units of ecosystems, play a vital role in maintaining biodiversity, supporting sustainable water use, and ensuring the stable provision of multiple ecosystem services. Based on a theoretical framework for characterizing lake ecosystem status, this study systematically reviews the conceptual connotations, indicator construction logic, and applications in ecological health assessment of diversity, integrity, stability, and sustainability (hereafter referred to as the “four dimensions”). In general, diversity and integrity primarily describe community composition and structural characteristics, whereas stability and sustainability emphasize functional processes and the long-term maintenance capacity of ecosystems. Together, these four dimensions constitute an integrated structural–functional framework for assessing lake ecosystem health. At present, the “four-dimension” indicator system has been widely applied in lake ecological health assessment, restoration evaluation, and management decision support. However, several key challenges remain: high sensitivity of indicators to spatial and temporal scales, leading to limited cross-scale comparability; insufficient incorporation of ecological mechanisms in indicator selection; limited representation of functional processes such as energy flow and material cycling; and a lack of long-term continuous observations, which constrains the detection of system trajectories and lagged responses. Further analysis reveals that the four dimensions are not independent but are interconnected through structure–function coupling and feedback mechanisms. Under natural conditions, increased diversity, improved structural integrity, and enhanced ecosystem functioning can jointly promote stability and sustainability via positive feedbacks. However, under conditions of species dominance or environmental homogenization, ecosystems may shift into a “superficially stable” simplified state, characterized by reduced community variability but diminished functional redundancy and response diversity, resulting in short-term stability but long-term vulnerability. Based on these insights, this study highlights the need to develop integrated indicator systems that incorporate multi-scale and multi-taxa information, while simultaneously linking structural attributes with functional processes in both static and dynamic dimensions. Such advancements will improve the characterization of lake ecosystem health and its temporal dynamics, providing a more mechanistic foundation for ecological risk identification, management optimization, and the long-term sustainable development of lake ecosystems.
Available online: September 09, 2026
Abstract:
Lakes constitute a significant source of atmospheric CH4, yet estimates of their emissions remain highly uncertain, partly due to an incomplete understanding of CH4’s biological sources. The phenomenon of CH4 supersaturation in surface waters, often termed the “methane paradox,” challenges the traditional view that biological CH4 production occurs only under strictly anaerobic conditions, indicating that oxic CH4 production may be possible. To investigate the cause of this surface CH4 supersaturation, this study focused on the eutrophic Gaoyang Lake. Combining field observations with incubation experiments, we examined the spatiotemporal distribution patterns of CH4 in the water column and their driving mechanisms. Field monitoring revealed a pronounced “methane paradox” in summer. CH4 in the surface water was not only supersaturated relative to the atmosphere (approximately 496 times atmospheric concentration) but was also 58% higher than in the bottom water. Incubation experiments indicated that methylphosphonate (MPn) degradation is an important source of lacustrine CH4: (1) The addition of MPn stimulated CH4 production, increasing the CH4 production rate by 68.6% compared to the control; (2) The MPn degradation process was regulated by inorganic phosphorus (Pi), as Pi addition inhibited both MPn degradation and CH4 production; (3) The addition of Pi to aerobic lake water suppressed CH4 production, reducing yield by 28% compared to the control. Furthermore, a significant negative correlation was observed between surface CH4 and soluble reactive phosphorus (SRP) (r = -0.87, p < 0.05), suggesting that decreased SRP promotes the accumulation of CH4 in surface waters. This finding further supports the inference that microbial MPn metabolism drives surface CH4 supersaturation. In summer, substantial depletion of SRP in the surface layer, coupled with thermal stratification hindering vertical nutrient transport, creates favorable conditions for MPn-based CH4 production. This study reveals the impact of phosphonate metabolism on the CH4 cycle in eutrophic lakes, providing new evidence and a theoretical perspective for understanding lake CH4 sources. These findings are significant for refining global lake greenhouse gas emission models and predicting ecosystem responses under climate change.
Lakes constitute a significant source of atmospheric CH4, yet estimates of their emissions remain highly uncertain, partly due to an incomplete understanding of CH4’s biological sources. The phenomenon of CH4 supersaturation in surface waters, often termed the “methane paradox,” challenges the traditional view that biological CH4 production occurs only under strictly anaerobic conditions, indicating that oxic CH4 production may be possible. To investigate the cause of this surface CH4 supersaturation, this study focused on the eutrophic Gaoyang Lake. Combining field observations with incubation experiments, we examined the spatiotemporal distribution patterns of CH4 in the water column and their driving mechanisms. Field monitoring revealed a pronounced “methane paradox” in summer. CH4 in the surface water was not only supersaturated relative to the atmosphere (approximately 496 times atmospheric concentration) but was also 58% higher than in the bottom water. Incubation experiments indicated that methylphosphonate (MPn) degradation is an important source of lacustrine CH4: (1) The addition of MPn stimulated CH4 production, increasing the CH4 production rate by 68.6% compared to the control; (2) The MPn degradation process was regulated by inorganic phosphorus (Pi), as Pi addition inhibited both MPn degradation and CH4 production; (3) The addition of Pi to aerobic lake water suppressed CH4 production, reducing yield by 28% compared to the control. Furthermore, a significant negative correlation was observed between surface CH4 and soluble reactive phosphorus (SRP) (r = -0.87, p < 0.05), suggesting that decreased SRP promotes the accumulation of CH4 in surface waters. This finding further supports the inference that microbial MPn metabolism drives surface CH4 supersaturation. In summer, substantial depletion of SRP in the surface layer, coupled with thermal stratification hindering vertical nutrient transport, creates favorable conditions for MPn-based CH4 production. This study reveals the impact of phosphonate metabolism on the CH4 cycle in eutrophic lakes, providing new evidence and a theoretical perspective for understanding lake CH4 sources. These findings are significant for refining global lake greenhouse gas emission models and predicting ecosystem responses under climate change.
Available online: September 04, 2026
Abstract:
To investigate how deep-water hypoxia induced by seasonal thermal stratification affects fish distribution patterns in both vertical and horizontal dimensions, hydroacoustic surveys and gillnet sampling were conducted in Niutoushan Reservoir in 2025, combined with vertical profiles of water temperature and dissolved oxygen. The compression of vertical fish habitat and changes in spatial aggregation patterns were analyzed. To address the difficulty of distinguishing whether the upward shift of fish distribution resulted from hypoxia avoidance using conventional correlation analyses, null models were constructed to test whether fish utilization of hypoxic layers was lower than random expectations. Meanwhile, horizontal fish aggregation hotspots were transformed into station-scale aggregation intensity metrics, and multiple linear regression models (LMs) were used to examine their relationships with water-depth structure and hypoxia intensity.The results showed that vertical fish allocation patterns differed significantly among the four survey months (PERMANOVA, p = 0.001, R² = 0.277). During the stratified period (May and October), the vertical centroid depth (Zc) of fish distribution became significantly shallower and less dispersed (median: 7.54 m), compared with the mixed period (12.19 m), corresponding to an upward shift of 4.65 m (ΔZc = ?4.65 m). Null-model analyses indicated that fish utilization of deep hypoxic layers was generally lower than random expectations under the 3 mg/L dissolved oxygen threshold. Horizontally, fish aggregation hotspots repeatedly occurred in the river–reservoir transition zone (site S3) across multiple months. The LM results revealed an inverted U-shaped relationship between fish aggregation intensity and water depth, with an estimated optimal depth (D*) of approximately 14.4 m. After accounting for water-depth structure and seasonal differences, oxygen-stress deficit (DOdef) showed a negative association with fish aggregation intensity (β = ?1.151 ± 0.444, p = 0.022).This study establishes an analytical framework integrating null-model testing and aggregation-intensity quantification, providing directional evidence for identifying fish hypoxia avoidance and spatial aggregation responses. The framework may support habitat monitoring and hypoxia-risk assessment for fish communities in similar medium- to deep-water valley-type reservoirs during stratified periods.
To investigate how deep-water hypoxia induced by seasonal thermal stratification affects fish distribution patterns in both vertical and horizontal dimensions, hydroacoustic surveys and gillnet sampling were conducted in Niutoushan Reservoir in 2025, combined with vertical profiles of water temperature and dissolved oxygen. The compression of vertical fish habitat and changes in spatial aggregation patterns were analyzed. To address the difficulty of distinguishing whether the upward shift of fish distribution resulted from hypoxia avoidance using conventional correlation analyses, null models were constructed to test whether fish utilization of hypoxic layers was lower than random expectations. Meanwhile, horizontal fish aggregation hotspots were transformed into station-scale aggregation intensity metrics, and multiple linear regression models (LMs) were used to examine their relationships with water-depth structure and hypoxia intensity.The results showed that vertical fish allocation patterns differed significantly among the four survey months (PERMANOVA, p = 0.001, R² = 0.277). During the stratified period (May and October), the vertical centroid depth (Zc) of fish distribution became significantly shallower and less dispersed (median: 7.54 m), compared with the mixed period (12.19 m), corresponding to an upward shift of 4.65 m (ΔZc = ?4.65 m). Null-model analyses indicated that fish utilization of deep hypoxic layers was generally lower than random expectations under the 3 mg/L dissolved oxygen threshold. Horizontally, fish aggregation hotspots repeatedly occurred in the river–reservoir transition zone (site S3) across multiple months. The LM results revealed an inverted U-shaped relationship between fish aggregation intensity and water depth, with an estimated optimal depth (D*) of approximately 14.4 m. After accounting for water-depth structure and seasonal differences, oxygen-stress deficit (DOdef) showed a negative association with fish aggregation intensity (β = ?1.151 ± 0.444, p = 0.022).This study establishes an analytical framework integrating null-model testing and aggregation-intensity quantification, providing directional evidence for identifying fish hypoxia avoidance and spatial aggregation responses. The framework may support habitat monitoring and hypoxia-risk assessment for fish communities in similar medium- to deep-water valley-type reservoirs during stratified periods.
Liu Linwei, Tang Haoran, Zhao, Xingchen, Xiao Qitao, Zhuang Xinfeng, Wang Jin, Qing Zhengye, Deng Jianming, Hyunbin Jo
Available online: September 03, 2026
Abstract:
Against the backdrop of global warming, extreme high-temperature events are becoming more frequent and intense. Lake heatwaves, as a typical manifestation, can alter the production and emission processes of CO2 in shallow lakes over short time scales, thereby affecting the accuracy of CO2 budget estimates in lake ecosystems. To investigate the effects of short-term heatwaves on CO2 production and emissions in shallow lakes and to explore the response characteristics and related influencing factors, this study conducted experiments using the "Smart Lake" mesocosm simulation system at the Taihu Lake Dongshan Station. A heatwave group (+8°C) and a control group (ambient temperature) were established. Based on observations and estimations during three periods (pre-heatwave, during heatwave, and post-heatwave), we analyzed the variations in pCO2 in surface water and sediment pore water, as well as diffusive CO2 fluxes at the water-air interface and the sediment-water interface. The relationships between surface water pCO2 and major environmental variables were also explored. The results showed that during the heatwave, pCO2 increased in both groups, but the increase was greater in the heatwave group, reaching a mean value of 860 ± 54 μatm, compared to 606 ± 37 μatm in the control group. Meanwhile, the water-air pCO2 flux in the heatwave group was significantly enhanced during the heatwave, at 31.2 ± 3.1 mmol m?² d?¹, higher than that of the control group (19.2 ± 5.0 mmol m?² d?¹). In contrast, the sediment-water interface flux in the heatwave group was relatively small, only 1.3 ± 0.2 mmol m?² d?¹, indicating that CO2 production and emissions from sediments alone cannot explain the enhancement of the water-air CO2 emission flux during the heatwave. Partial correlation analysis showed that after controlling for the effect of water temperature, the correlations between surface water pCO2 and environmental variables in the heatwave group were not significant, suggesting the effects of environment variables in CO? were mainly driven by changes in water temperature. Overall, short-term winter heatwave events can significantly alter CO2 dynamics variability in the water-sediment system of shallow lakes, but the biological metabolic processes and physicochemical mechanisms underlying these responses still require further investigate.
Against the backdrop of global warming, extreme high-temperature events are becoming more frequent and intense. Lake heatwaves, as a typical manifestation, can alter the production and emission processes of CO2 in shallow lakes over short time scales, thereby affecting the accuracy of CO2 budget estimates in lake ecosystems. To investigate the effects of short-term heatwaves on CO2 production and emissions in shallow lakes and to explore the response characteristics and related influencing factors, this study conducted experiments using the "Smart Lake" mesocosm simulation system at the Taihu Lake Dongshan Station. A heatwave group (+8°C) and a control group (ambient temperature) were established. Based on observations and estimations during three periods (pre-heatwave, during heatwave, and post-heatwave), we analyzed the variations in pCO2 in surface water and sediment pore water, as well as diffusive CO2 fluxes at the water-air interface and the sediment-water interface. The relationships between surface water pCO2 and major environmental variables were also explored. The results showed that during the heatwave, pCO2 increased in both groups, but the increase was greater in the heatwave group, reaching a mean value of 860 ± 54 μatm, compared to 606 ± 37 μatm in the control group. Meanwhile, the water-air pCO2 flux in the heatwave group was significantly enhanced during the heatwave, at 31.2 ± 3.1 mmol m?² d?¹, higher than that of the control group (19.2 ± 5.0 mmol m?² d?¹). In contrast, the sediment-water interface flux in the heatwave group was relatively small, only 1.3 ± 0.2 mmol m?² d?¹, indicating that CO2 production and emissions from sediments alone cannot explain the enhancement of the water-air CO2 emission flux during the heatwave. Partial correlation analysis showed that after controlling for the effect of water temperature, the correlations between surface water pCO2 and environmental variables in the heatwave group were not significant, suggesting the effects of environment variables in CO? were mainly driven by changes in water temperature. Overall, short-term winter heatwave events can significantly alter CO2 dynamics variability in the water-sediment system of shallow lakes, but the biological metabolic processes and physicochemical mechanisms underlying these responses still require further investigate.
Luo Mingjie, Zhang Lijuan, Liu Xunjie, Sun Jingying, Yang Yanan, Yang Jianghua, Zhang Yong, Zhang Xiaowei
Available online: September 01, 2026
Abstract:
Environmental DNA (eDNA) has become an important tool for monitoring and studying aquatic biodiversity. However, the consistency of results across different laboratories remains insufficiently evaluated. In this study, three independent laboratories processed and sequenced the same batch of freshwater samples under a unified and standardized framework, with positive controls used to validate workflow reliability. The results showed that no false negatives were detected across laboratories in positive controls, and false-positive sequences accounted for less than 0.5%. For environmental samples, the species detection overlap among laboratories was ≥ 80%, with a coefficient of variation in α-diversity of less than 0.05. The relative abundance of commonly detected species exhibited strong correlations across laboratories (r ≥ 0.94). Although significant differences in community composition were observed (PERMANOVA, R2 = 0.35, p = 0.005), the abundance patterns of dominant species were highly consistent. This study demonstrates that, under standardized key procedures, eDNA metabarcoding can achieve consistent species detection and diversity estimation across laboratories, while highlighting that comparisons of community structure should be interpreted cautiously due to potential laboratory-specific effects.
Environmental DNA (eDNA) has become an important tool for monitoring and studying aquatic biodiversity. However, the consistency of results across different laboratories remains insufficiently evaluated. In this study, three independent laboratories processed and sequenced the same batch of freshwater samples under a unified and standardized framework, with positive controls used to validate workflow reliability. The results showed that no false negatives were detected across laboratories in positive controls, and false-positive sequences accounted for less than 0.5%. For environmental samples, the species detection overlap among laboratories was ≥ 80%, with a coefficient of variation in α-diversity of less than 0.05. The relative abundance of commonly detected species exhibited strong correlations across laboratories (r ≥ 0.94). Although significant differences in community composition were observed (PERMANOVA, R2 = 0.35, p = 0.005), the abundance patterns of dominant species were highly consistent. This study demonstrates that, under standardized key procedures, eDNA metabarcoding can achieve consistent species detection and diversity estimation across laboratories, while highlighting that comparisons of community structure should be interpreted cautiously due to potential laboratory-specific effects.
Available online: September 01, 2026
Abstract:
To identify indicator species of aquatic macrophytes and elucidate their responses to environmental gradients and spatial processes in typical tributaries of the middle and lower Yangtze River, we investigated the Xiangjiang, Hanjiang, and Ganjiang Rivers using environmental DNA (eDNA) metabarcoding combined with water-quality, bioclimatic, and topographic variables. Community structure, indicator species distribution patterns, and their driving mechanisms were systematically analyzed.The results revealed significant differences in aquatic macrophyte community composition among the three tributaries. After controlling for spatial structure, ammonium nitrogen remained the only significant environmental variable associated with community variation. Variation partitioning showed that the independent contribution of spatial variables exceeded that of environmental variables, and significant residual spatial autocorrelation was detected, indicating an important role of spatial processes in community assembly.Indicator species analysis (IndVal) identified three significant taxa, including Stuckenia pectinata in the Xiangjiang River and Typha latifolia and Trapa bicornis in the Hanjiang River. Generalized linear models (GLM) and random forest (RF) models consistently demonstrated species-specific responses to environmental and spatial factors. S. pectinata was primarily associated with the ammonium-nitrogen gradient, whereas T. latifolia was mainly structured by spatial variables. T. bicornis responded to both environmental and spatial factors but exhibited relatively weak explanatory relationships. Both modeling approaches showed satisfactory predictive performance, indicating that the integrated framework of environmental and spatial variables effectively explained indicator-species distribution patterns.In addition, although eDNA metabarcoding showed relatively low consistency with traditional field surveys, it exhibited strong complementarity and substantially expanded species detection coverage.Overall, our findings suggest that the distribution of aquatic macrophyte communities and their indicator species is jointly shaped by environmental filtering and spatial processes rather than solely by local environmental conditions. Spatial structure plays a critical role in modulating environmental signals and influencing species distributions. This study provides a theoretical basis for indicator-species identification, understanding community assembly mechanisms, and applying eDNA metabarcoding in riverine ecological monitoring.
To identify indicator species of aquatic macrophytes and elucidate their responses to environmental gradients and spatial processes in typical tributaries of the middle and lower Yangtze River, we investigated the Xiangjiang, Hanjiang, and Ganjiang Rivers using environmental DNA (eDNA) metabarcoding combined with water-quality, bioclimatic, and topographic variables. Community structure, indicator species distribution patterns, and their driving mechanisms were systematically analyzed.The results revealed significant differences in aquatic macrophyte community composition among the three tributaries. After controlling for spatial structure, ammonium nitrogen remained the only significant environmental variable associated with community variation. Variation partitioning showed that the independent contribution of spatial variables exceeded that of environmental variables, and significant residual spatial autocorrelation was detected, indicating an important role of spatial processes in community assembly.Indicator species analysis (IndVal) identified three significant taxa, including Stuckenia pectinata in the Xiangjiang River and Typha latifolia and Trapa bicornis in the Hanjiang River. Generalized linear models (GLM) and random forest (RF) models consistently demonstrated species-specific responses to environmental and spatial factors. S. pectinata was primarily associated with the ammonium-nitrogen gradient, whereas T. latifolia was mainly structured by spatial variables. T. bicornis responded to both environmental and spatial factors but exhibited relatively weak explanatory relationships. Both modeling approaches showed satisfactory predictive performance, indicating that the integrated framework of environmental and spatial variables effectively explained indicator-species distribution patterns.In addition, although eDNA metabarcoding showed relatively low consistency with traditional field surveys, it exhibited strong complementarity and substantially expanded species detection coverage.Overall, our findings suggest that the distribution of aquatic macrophyte communities and their indicator species is jointly shaped by environmental filtering and spatial processes rather than solely by local environmental conditions. Spatial structure plays a critical role in modulating environmental signals and influencing species distributions. This study provides a theoretical basis for indicator-species identification, understanding community assembly mechanisms, and applying eDNA metabarcoding in riverine ecological monitoring.
Available online: August 31, 2026
Abstract:
Dissolved organic matter (DOM) in sediments constitutes a vital active component of the lake carbon pool. Chemodiversity of DOM groups is crucial for understanding lake carbon cycling and ecological functions. This study focused on the middle and lower reaches of the Yangtze River and Huaihe River basins, where 80 surface sediment samples were collected from 38 lakes. Using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), DOM was classified into molecular groups according to molecular compositional characteristics. We then investigated chemodiversity of different DOM groups and their driving factors under eutrophication stress. The results showed significant differences in molecular richness and composition among DOM groups. Lignin-like (39.63%) and protein-like (31.63%) compounds were the major components of sediment DOM. Their α diversity (molecular richness) was significantly higher than that of the other groups (P < 0.05), with mean values of 1125.75 and 783.73, respectively. Both groups also exhibited the lowest β diversity, as measured by Bray-Curtis dissimilarity, with mean values of 0.30 and 0.38, respectively, indicating the most uniform composition in spatial distribution. The molecular richness of most DOM groups was significantly associated with sediment physicochemical properties and land-use variables, whereas neither molecular richness nor compositional variation exhibited significant relationships with the trophic state index. Random forest analysis further quantified the relative importance of individual variables in explaining molecular richness, DOM in sediment was identified as the dominant factor for seven groups, and ammonium nitrogen (NH4+) in sediment mainly drove bioavailable groups such as carbohydrate- and amino sugar-like compounds. These results indicate that sediment physicochemical factors act as the primary drivers of molecular richness for most DOM groups. Furthermore, land-use variables such as the proportion of cropland area (Cropland%) contributed more to lignin-, tannin-, and polycyclic aromatic hydrocarbon-like groups. This may suggest that agricultural activities promote the accumulation of various recalcitrant molecules in lake sediments. Redundancy analysis showed that compositional variation in most groups was mainly explained by sediment physicochemical factors. Whereas tannin- and polycyclic aromatic hydrocarbon-like compounds were also influenced by land-use (e.g., Cropland%) and socioeconomic development (e.g., gross domestic product) factors. It indicates that natural and anthropogenic factors jointly regulate the changes of chemodiversity of DOM groups. This study enhances the understanding of chemodiversity of sediment DOM groups and their primary drivers, providing a molecular-level scientific basis for lake carbon sink management and watershed-scale carbon pool stability assessment under eutrophication.
Dissolved organic matter (DOM) in sediments constitutes a vital active component of the lake carbon pool. Chemodiversity of DOM groups is crucial for understanding lake carbon cycling and ecological functions. This study focused on the middle and lower reaches of the Yangtze River and Huaihe River basins, where 80 surface sediment samples were collected from 38 lakes. Using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), DOM was classified into molecular groups according to molecular compositional characteristics. We then investigated chemodiversity of different DOM groups and their driving factors under eutrophication stress. The results showed significant differences in molecular richness and composition among DOM groups. Lignin-like (39.63%) and protein-like (31.63%) compounds were the major components of sediment DOM. Their α diversity (molecular richness) was significantly higher than that of the other groups (P < 0.05), with mean values of 1125.75 and 783.73, respectively. Both groups also exhibited the lowest β diversity, as measured by Bray-Curtis dissimilarity, with mean values of 0.30 and 0.38, respectively, indicating the most uniform composition in spatial distribution. The molecular richness of most DOM groups was significantly associated with sediment physicochemical properties and land-use variables, whereas neither molecular richness nor compositional variation exhibited significant relationships with the trophic state index. Random forest analysis further quantified the relative importance of individual variables in explaining molecular richness, DOM in sediment was identified as the dominant factor for seven groups, and ammonium nitrogen (NH4+) in sediment mainly drove bioavailable groups such as carbohydrate- and amino sugar-like compounds. These results indicate that sediment physicochemical factors act as the primary drivers of molecular richness for most DOM groups. Furthermore, land-use variables such as the proportion of cropland area (Cropland%) contributed more to lignin-, tannin-, and polycyclic aromatic hydrocarbon-like groups. This may suggest that agricultural activities promote the accumulation of various recalcitrant molecules in lake sediments. Redundancy analysis showed that compositional variation in most groups was mainly explained by sediment physicochemical factors. Whereas tannin- and polycyclic aromatic hydrocarbon-like compounds were also influenced by land-use (e.g., Cropland%) and socioeconomic development (e.g., gross domestic product) factors. It indicates that natural and anthropogenic factors jointly regulate the changes of chemodiversity of DOM groups. This study enhances the understanding of chemodiversity of sediment DOM groups and their primary drivers, providing a molecular-level scientific basis for lake carbon sink management and watershed-scale carbon pool stability assessment under eutrophication.
Available online: August 28, 2026
Abstract:
Changes in dominant plant communities in reservoir water-level-fluctuation zones are important indicators of river ecosystem evolution and provide a key basis for wetland ecological management. However, efficient methods for rapidly and accurately obtaining information on dominant vegetation remain limited. Therefore, taking the dominant herbaceous communities in the water-level-fluctuation zone of Ertan Reservoir as the research object, this study systematically evaluated the performance of three mainstream deep learning models—U-Net, PSPNet, and DeepLabV3+—combined with different convolutional neural network backbones in the automatic identification of typical herbaceous community types in the water-level-fluctuation zone, and compared them with a feature engineering-based stacking ensemble machine learning method. The results showed that: (1) the U-Net–ResNet50 combination achieved the best overall performance, with an overall accuracy of 0.918 and the highest F1 score, and performed particularly well in identifying dominant herbaceous community types such as the Cynodon dactylon community (F1 = 0.941) and the Abutilon theophrasti community. Its encoder–decoder structure effectively fused multi-level semantic information and spatial details, thereby enhancing recognition stability in complex vegetation scenes. (2) PSPNet and DeepLabV3+ exhibited relatively large fluctuations in validation loss in some combinations. For example, PSPNet–ResNet50 showed pronounced loss fluctuations during the early training stage, which may be related to the sensitivity of its multi-scale module to network depth. Nevertheless, both models showed higher training efficiency and shorter inference time, making them suitable for large-scale vegetation monitoring. (3) Compared with traditional methods, deep learning showed comparable performance in identifying dominant herbaceous community types. For example, the stacking ensemble model achieved an overall accuracy of 0.931, which was close to that of U-Net–ResNet50. However, for the “other herbaceous communities” category with relatively few samples, the F1 scores of traditional methods were generally higher than those of deep learning models; even the lowest value among the traditional methods (0.672) was still higher than the highest value among the deep learning models (0.539). Despite this, deep learning has the advantage of automatic feature extraction, significantly reducing dependence on manual feature engineering and showing strong potential for cross-regional transfer. Overall, deep learning models have promising application prospects for herbaceous community classification in reservoir water-level-fluctuation zones. Future studies should further expand sample size, integrate multi-source remote sensing data, and incorporate transfer learning methods to build an intelligent recognition framework that synergistically optimizes “data–model–application”, thereby supporting refined monitoring and management of wetland ecosystems.
Changes in dominant plant communities in reservoir water-level-fluctuation zones are important indicators of river ecosystem evolution and provide a key basis for wetland ecological management. However, efficient methods for rapidly and accurately obtaining information on dominant vegetation remain limited. Therefore, taking the dominant herbaceous communities in the water-level-fluctuation zone of Ertan Reservoir as the research object, this study systematically evaluated the performance of three mainstream deep learning models—U-Net, PSPNet, and DeepLabV3+—combined with different convolutional neural network backbones in the automatic identification of typical herbaceous community types in the water-level-fluctuation zone, and compared them with a feature engineering-based stacking ensemble machine learning method. The results showed that: (1) the U-Net–ResNet50 combination achieved the best overall performance, with an overall accuracy of 0.918 and the highest F1 score, and performed particularly well in identifying dominant herbaceous community types such as the Cynodon dactylon community (F1 = 0.941) and the Abutilon theophrasti community. Its encoder–decoder structure effectively fused multi-level semantic information and spatial details, thereby enhancing recognition stability in complex vegetation scenes. (2) PSPNet and DeepLabV3+ exhibited relatively large fluctuations in validation loss in some combinations. For example, PSPNet–ResNet50 showed pronounced loss fluctuations during the early training stage, which may be related to the sensitivity of its multi-scale module to network depth. Nevertheless, both models showed higher training efficiency and shorter inference time, making them suitable for large-scale vegetation monitoring. (3) Compared with traditional methods, deep learning showed comparable performance in identifying dominant herbaceous community types. For example, the stacking ensemble model achieved an overall accuracy of 0.931, which was close to that of U-Net–ResNet50. However, for the “other herbaceous communities” category with relatively few samples, the F1 scores of traditional methods were generally higher than those of deep learning models; even the lowest value among the traditional methods (0.672) was still higher than the highest value among the deep learning models (0.539). Despite this, deep learning has the advantage of automatic feature extraction, significantly reducing dependence on manual feature engineering and showing strong potential for cross-regional transfer. Overall, deep learning models have promising application prospects for herbaceous community classification in reservoir water-level-fluctuation zones. Future studies should further expand sample size, integrate multi-source remote sensing data, and incorporate transfer learning methods to build an intelligent recognition framework that synergistically optimizes “data–model–application”, thereby supporting refined monitoring and management of wetland ecosystems.
Qinguangxiong, Yuanxiaolong, Changzheng, Suweigang, Gaoping, Zhaozhen, Chenhuijuan, Zhudengxian, Limengling, Zhangxiying
Available online: August 28, 2026
Abstract:
As a crucial strategy for the sustainable exploitation of potassium resources in salt lakes, water-replenishment-induced mineral dissolution plays a vital role in safeguarding national strategic interests. This study conducted a combined investigation of the mineral composition of brine-storing layers and the spatiotemporal distribution of brine hydrochemistry in the Dabuxun segment of Qarhan Salt Lake. The results indicate that the brine-storing layers exhibit distinct vertical mineral zonation: the shallow zone (0 – 4 m) is dominated by halite, with a maximum content of 95%; the middle zone (4 – 9 m) is enriched in carnallite (10% – 31% content), accompanied by bischofite; and the deep zone (>8 m) shows an increase in detrital minerals. Brine differentiation is controlled by Na?, Mg2?, and K?. The horizontal high-value belt of K? between the water-replenishment channel and the brine-extraction channel, as well as the vertical “chemical inflection point” where Mg2?, Cl?, and K? increase synchronously, reveal that water level dynamics are the key factors regulating the vertical migration and enrichment of potassium. Two brine replenishment methods exist in the study area: natural lake water recharge and artificial channel replenishment. The former has a broad influence range and long duration, with a significant dissolution effect on solid potassium salts in the shallow and middle layers. The latter extends the replenishment coverage, characterized by strong directionality but limited spatial scope. Overall, the study demonstrates that mineral dissolution induced by current artificial water replenishment still holds great potential in the shallow and middle layers. Therefore, it is necessary to optimize the replenishment layout and enhance the penetration capacity of low-mineralization water into target layers to improve the dissolution and extraction efficiency of potassium salt resources. This research elucidates the coupling mechanism among mineralogy, hydrochemistry, and hydrodynamics, providing a fundamental scientific basis for water-replenishment-induced mineral dissolution in Qarhan Salt Lake.
As a crucial strategy for the sustainable exploitation of potassium resources in salt lakes, water-replenishment-induced mineral dissolution plays a vital role in safeguarding national strategic interests. This study conducted a combined investigation of the mineral composition of brine-storing layers and the spatiotemporal distribution of brine hydrochemistry in the Dabuxun segment of Qarhan Salt Lake. The results indicate that the brine-storing layers exhibit distinct vertical mineral zonation: the shallow zone (0 – 4 m) is dominated by halite, with a maximum content of 95%; the middle zone (4 – 9 m) is enriched in carnallite (10% – 31% content), accompanied by bischofite; and the deep zone (>8 m) shows an increase in detrital minerals. Brine differentiation is controlled by Na?, Mg2?, and K?. The horizontal high-value belt of K? between the water-replenishment channel and the brine-extraction channel, as well as the vertical “chemical inflection point” where Mg2?, Cl?, and K? increase synchronously, reveal that water level dynamics are the key factors regulating the vertical migration and enrichment of potassium. Two brine replenishment methods exist in the study area: natural lake water recharge and artificial channel replenishment. The former has a broad influence range and long duration, with a significant dissolution effect on solid potassium salts in the shallow and middle layers. The latter extends the replenishment coverage, characterized by strong directionality but limited spatial scope. Overall, the study demonstrates that mineral dissolution induced by current artificial water replenishment still holds great potential in the shallow and middle layers. Therefore, it is necessary to optimize the replenishment layout and enhance the penetration capacity of low-mineralization water into target layers to improve the dissolution and extraction efficiency of potassium salt resources. This research elucidates the coupling mechanism among mineralogy, hydrochemistry, and hydrodynamics, providing a fundamental scientific basis for water-replenishment-induced mineral dissolution in Qarhan Salt Lake.
Available online: August 27, 2026
Abstract:
After the Three Gorges Dam operation, the systematic scouring response of the downstream riverbed has resulted in a heterogeneous coarsening pattern of bed sediment, accompanied by structural modifications to the longitudinal replenishment mechanism of bed sediment for suspended load. Based on measured hydrological and sediment data from the Zhicheng, Shashi, and Jianli hydrological stations between 2003 and 2019, this study adopts Markov chain theory to develop a new formula for calculating sediment transport capacity that incorporates transition probabilities. This formula is then used to analyze suspended sediment concentration and cross-sectional erosion and deposition in the Jingjiang Reach below the Three Gorges Dam, revealing the changing characteristics and influencing mechanisms of suspended sediment transport in this reach after the reservoir"s operation. The results show that: (i) using a three-dimensional sediment transition probability matrix, a new formula for calculating the sediment-carrying capacity of cross-sections in the Jingjiang Reach of the Middle Yangtze River has been developed. The new formula demonstrates higher predictive accuracy than traditional formulas, with Nash-Sutcliffe efficiency (NSE) coefficients exceeding 0.716 at all stations; (ii) suspended sediment transport is predominantly concentrated during the flood season. The proportion of flood season sediment transport decreased from 98%, 93%, and 90% in 2003 to 93%, 87%, and 77% in 2019 at Zhicheng, Shashi, and Jianli stations, respectively, indicating a more nonuniform intra-annual distribution of sediment transport; (iii) under unchanged other conditions, the sediment transfer probability (P13) increases with flow discharge but decreases rapidly with increasing bed sediment grain size, approaching zero when the grain size exceeds 5 mm. When sediment concentration is below 0.2 kg/m3, P13 increases rapidly and then stabilizes; (iv) between 2003 and 2019, a positive correlation was observed between the sediment transition probability P13 and sediment transport rate. At the Zhicheng cross-section, P13 decreased from 0.469 to 0, while at Shashi and Jianli, it declined from 0.691 to 0.496 and from 0.789 to 0.742, respectively, reflecting a reduced capacity for suspended sediment supply due to bed coarsening in the reaches closer to the dam. The findings of this study provide a theoretical foundation for analyzing water-sediment transport and channel evolution in the near-dam reaches of the Middle Yangtze River.
After the Three Gorges Dam operation, the systematic scouring response of the downstream riverbed has resulted in a heterogeneous coarsening pattern of bed sediment, accompanied by structural modifications to the longitudinal replenishment mechanism of bed sediment for suspended load. Based on measured hydrological and sediment data from the Zhicheng, Shashi, and Jianli hydrological stations between 2003 and 2019, this study adopts Markov chain theory to develop a new formula for calculating sediment transport capacity that incorporates transition probabilities. This formula is then used to analyze suspended sediment concentration and cross-sectional erosion and deposition in the Jingjiang Reach below the Three Gorges Dam, revealing the changing characteristics and influencing mechanisms of suspended sediment transport in this reach after the reservoir"s operation. The results show that: (i) using a three-dimensional sediment transition probability matrix, a new formula for calculating the sediment-carrying capacity of cross-sections in the Jingjiang Reach of the Middle Yangtze River has been developed. The new formula demonstrates higher predictive accuracy than traditional formulas, with Nash-Sutcliffe efficiency (NSE) coefficients exceeding 0.716 at all stations; (ii) suspended sediment transport is predominantly concentrated during the flood season. The proportion of flood season sediment transport decreased from 98%, 93%, and 90% in 2003 to 93%, 87%, and 77% in 2019 at Zhicheng, Shashi, and Jianli stations, respectively, indicating a more nonuniform intra-annual distribution of sediment transport; (iii) under unchanged other conditions, the sediment transfer probability (P13) increases with flow discharge but decreases rapidly with increasing bed sediment grain size, approaching zero when the grain size exceeds 5 mm. When sediment concentration is below 0.2 kg/m3, P13 increases rapidly and then stabilizes; (iv) between 2003 and 2019, a positive correlation was observed between the sediment transition probability P13 and sediment transport rate. At the Zhicheng cross-section, P13 decreased from 0.469 to 0, while at Shashi and Jianli, it declined from 0.691 to 0.496 and from 0.789 to 0.742, respectively, reflecting a reduced capacity for suspended sediment supply due to bed coarsening in the reaches closer to the dam. The findings of this study provide a theoretical foundation for analyzing water-sediment transport and channel evolution in the near-dam reaches of the Middle Yangtze River.
Available online: August 27, 2026
Abstract:
The potential for fish passage facilities to induce “reservoir ecological traps for fish” represents an issue that urgently requires in-depth examination and discussion in China’s fish passage research. Current research on fish passage technology focuses primarily on two questions: how fish downstream of dams pass upstream and how many fish can pass through fish passage facilities. Systematic investigations into post-passage survival, reproduction, and downstream migration of fish remain scarce, making it difficult to determine whether reservoirs function as ecological traps. Focusing on ecological traps encountered by fish after dam passage, this study synthesizes relevant literature and engineering reports on post-passage ecological traps, reviews the relationship between hydraulic engineering projects and fish passage facilities, summarizes the requirements and ecological effects of fish dam passage, delineates the ecological challenges faced by fish after passage and the mechanisms by which they may become trapped, develops an ecological trap assessment framework aligned with the life-history requirements of migratory fishes, elucidates the impacts of ecological traps on key life-history behaviors, and emphasizes that future research should adopt a multidimensional perspective integrating upstream and downstream migration, fish behavior, hydroecology, and habitat suitability to comprehensively evaluate the ecological effects of fish passage facilities and promote a shift toward ecosystem-oriented design and management to enhance their effectiveness in maintaining river connectivity and conserving migratory fish populations.
The potential for fish passage facilities to induce “reservoir ecological traps for fish” represents an issue that urgently requires in-depth examination and discussion in China’s fish passage research. Current research on fish passage technology focuses primarily on two questions: how fish downstream of dams pass upstream and how many fish can pass through fish passage facilities. Systematic investigations into post-passage survival, reproduction, and downstream migration of fish remain scarce, making it difficult to determine whether reservoirs function as ecological traps. Focusing on ecological traps encountered by fish after dam passage, this study synthesizes relevant literature and engineering reports on post-passage ecological traps, reviews the relationship between hydraulic engineering projects and fish passage facilities, summarizes the requirements and ecological effects of fish dam passage, delineates the ecological challenges faced by fish after passage and the mechanisms by which they may become trapped, develops an ecological trap assessment framework aligned with the life-history requirements of migratory fishes, elucidates the impacts of ecological traps on key life-history behaviors, and emphasizes that future research should adopt a multidimensional perspective integrating upstream and downstream migration, fish behavior, hydroecology, and habitat suitability to comprehensively evaluate the ecological effects of fish passage facilities and promote a shift toward ecosystem-oriented design and management to enhance their effectiveness in maintaining river connectivity and conserving migratory fish populations.
Available online: August 26, 2026
Abstract:
To address the critical lack of monitoring data on hydrological processes and landscape changes within sub-lake groups of large floodplain wetlands and to explore the relationship between their water recession processes and associated landscape dynamics, this study focused on nine dish-shaped lakes in the Poyang Lake National Nature Reserve as a case study. By integrating remote sensing, geographic information systems (GIS), and spatiotemporal analysis, we investigated the influence of the water recession process in these lakes on the structural characteristics of overwintering waterbird habitats, examining three key factors: natural precipitation, anthropogenic regulation, and lake topography. The main conclusions are as follows: (1) Satellite remote sensing technology enables the synchronous monitoring of water surface area and landscape composition across numerous lakes, effectively resolving the data scarcity issue for sub-lakes in large floodplain wetlands. (2) The impact of natural precipitation on the water recession process occurs primarily before the dish-shaped lakes become hydrologically disconnected from the main lake body, determining the timing of sandbar exposure. In contrast, the effects of anthropogenic regulation and lake topography manifest after this disconnection. Human regulation slows the recession process compared to natural conditions, while lake topography governs water retention capacity and the potential for water level control. (3) Both floods and droughts significantly reduce the availability of foraging habitats for overwintering waterbirds. However, as extreme hydrological events typically conclude by autumn, they do not affect the foraging habitat area in winter. During periods of abnormal precipitation, landscapes in naturally receding lakes exhibit greater fluctuation than those in artificially regulated lakes. Extreme flood events have a more pronounced impact on the landscape of topographically low-lying lakes, whereas extreme droughts exert a stronger influence on higher-elevation lakes. The findings of this study provide valuable insights for the conservation of overwintering waterbirds in Poyang Lake and support the implementation of targeted wetland management strategies, such as the "one lake, one policy" approach.
To address the critical lack of monitoring data on hydrological processes and landscape changes within sub-lake groups of large floodplain wetlands and to explore the relationship between their water recession processes and associated landscape dynamics, this study focused on nine dish-shaped lakes in the Poyang Lake National Nature Reserve as a case study. By integrating remote sensing, geographic information systems (GIS), and spatiotemporal analysis, we investigated the influence of the water recession process in these lakes on the structural characteristics of overwintering waterbird habitats, examining three key factors: natural precipitation, anthropogenic regulation, and lake topography. The main conclusions are as follows: (1) Satellite remote sensing technology enables the synchronous monitoring of water surface area and landscape composition across numerous lakes, effectively resolving the data scarcity issue for sub-lakes in large floodplain wetlands. (2) The impact of natural precipitation on the water recession process occurs primarily before the dish-shaped lakes become hydrologically disconnected from the main lake body, determining the timing of sandbar exposure. In contrast, the effects of anthropogenic regulation and lake topography manifest after this disconnection. Human regulation slows the recession process compared to natural conditions, while lake topography governs water retention capacity and the potential for water level control. (3) Both floods and droughts significantly reduce the availability of foraging habitats for overwintering waterbirds. However, as extreme hydrological events typically conclude by autumn, they do not affect the foraging habitat area in winter. During periods of abnormal precipitation, landscapes in naturally receding lakes exhibit greater fluctuation than those in artificially regulated lakes. Extreme flood events have a more pronounced impact on the landscape of topographically low-lying lakes, whereas extreme droughts exert a stronger influence on higher-elevation lakes. The findings of this study provide valuable insights for the conservation of overwintering waterbirds in Poyang Lake and support the implementation of targeted wetland management strategies, such as the "one lake, one policy" approach.
Available online: August 24, 2026
Abstract:
The Taipu Sluice is a key regulation structure in the Taihu Basin, and accurate forecasting of its discharge is crucial for coordinated flood control, water supply, and ecological regulation in the basin. However, conventional forecasting approaches suffered from issues such as fixed parameters, unclear response mechanisms to multi-source driving factors, and ambiguous nonlinear precipitation and water level thresholds. To address these limitations, this study integrated principal component analysis, corrected stochasticity rate method, and K-means clustering to develop a forecasting model for Taipu Sluice discharge driven by multiple factors and to establish a threshold identification system for the response of Pingwang water level to precipitation. The results showed that: (1) The key factors affecting Taipu Sluice discharge were summarized into three principal components: regional water-level synergy, rainfall-runoff effect, and upstream-downstream water-level antagonism, with a cumulative contribution rate of 93.47%. The variable importance ranking indicated that the 8:00 water level at Pingwang contributed the most. (2) A simplified multiple regression model based on the water levels at Pingwang, Wangjiangjing, and Chenmu stations achieved relatively high forecasting accuracy. Under high water level conditions in Taihu Lake (water level > 3.80 m), the discharge of Taipu Sluice exhibited a strong linear relationship with the Taihu-Pingwang water-level difference (R = 0.92). (3) Corrected stochasticity analysis demonstrated that when the daily variation amplitude of Pingwang water level was ≥0.10 m, deterministic processes dominated; otherwise, stochastic fluctuations prevailed. Through K-means clustering, a regional precipitation threshold of 25.0 mm, which triggered a significant change in Pingwang water level, was identified and could serve as an early-warning indicator for Pingwang water level, with high classification accuracy. The precipitation threshold and the water level variation threshold together formed a dual-threshold early-warning system, providing proactive decision support for adaptive regulation of Taipu Sluice and risk avoidance during heavy precipitation events. The coupled framework proposed in this study, which integrated principal component dimensionality reduction, regression modeling, and clustering-based threshold identification, offers a data-driven paradigm that can be referenced for hydrological forecasting and refined regulation under complex engineering control in plain tidal river network regions.
The Taipu Sluice is a key regulation structure in the Taihu Basin, and accurate forecasting of its discharge is crucial for coordinated flood control, water supply, and ecological regulation in the basin. However, conventional forecasting approaches suffered from issues such as fixed parameters, unclear response mechanisms to multi-source driving factors, and ambiguous nonlinear precipitation and water level thresholds. To address these limitations, this study integrated principal component analysis, corrected stochasticity rate method, and K-means clustering to develop a forecasting model for Taipu Sluice discharge driven by multiple factors and to establish a threshold identification system for the response of Pingwang water level to precipitation. The results showed that: (1) The key factors affecting Taipu Sluice discharge were summarized into three principal components: regional water-level synergy, rainfall-runoff effect, and upstream-downstream water-level antagonism, with a cumulative contribution rate of 93.47%. The variable importance ranking indicated that the 8:00 water level at Pingwang contributed the most. (2) A simplified multiple regression model based on the water levels at Pingwang, Wangjiangjing, and Chenmu stations achieved relatively high forecasting accuracy. Under high water level conditions in Taihu Lake (water level > 3.80 m), the discharge of Taipu Sluice exhibited a strong linear relationship with the Taihu-Pingwang water-level difference (R = 0.92). (3) Corrected stochasticity analysis demonstrated that when the daily variation amplitude of Pingwang water level was ≥0.10 m, deterministic processes dominated; otherwise, stochastic fluctuations prevailed. Through K-means clustering, a regional precipitation threshold of 25.0 mm, which triggered a significant change in Pingwang water level, was identified and could serve as an early-warning indicator for Pingwang water level, with high classification accuracy. The precipitation threshold and the water level variation threshold together formed a dual-threshold early-warning system, providing proactive decision support for adaptive regulation of Taipu Sluice and risk avoidance during heavy precipitation events. The coupled framework proposed in this study, which integrated principal component dimensionality reduction, regression modeling, and clustering-based threshold identification, offers a data-driven paradigm that can be referenced for hydrological forecasting and refined regulation under complex engineering control in plain tidal river network regions.
yinkailag, Li Shanze, Wang Yuchun, Huang Wei, Xu Xuming, Wang Xuan, Bao Yufei, Wen Jie, Yin Chunxue, Chen Qingkong
Available online: August 24, 2026
Abstract:
The superimposed hydrological regulation of cascade reservoirs significantly alters the structure and function of river ecosystems. Identifying the spatiotemporal variations in phytoplankton communities and their key environmental drivers in the lower reaches of the Jinsha River can provide scientific basis for ecological restoration and management of cascade reservoirs in this region. Phytoplankton surveys were conducted in March 2025 (low-water period) and July 2025 (high-water period), during which taxonomic composition, density and biomass, diversity, dominant taxa, and niche attributes were quantified; Pearson correlation and redundancy analysis (RDA) were subsequently applied to examine relationships between dominant taxa and environmental variables. In total, 104 phytoplankton species (83 genera, 9 phyla) were recorded across the cascade reservoirs, with Chlorophyta, Bacillariophyta, and Cyanobacteria as the predominant groups. Species richness was significantly higher in the high-water period than in the low-water period (P<0.01) but remained relatively uniform among reservoirs. By contrast, phytoplankton density ranged from 0.14×105 to 362.37×105 cells/L and biomass from 0.01 to 19.05 mg/L, and neither exhibited significant spatiotemporal variation. Diversity metrics showed no significant differences among reservoirs; however, the richness, Shannon–Wiener, and Simpson indices were significantly higher in the high-water period than in the low-water period, whereas evenness did not vary significantly between seasons. The diversity-based assessment further indicated that the study area overall corresponded to an α–β mesosaprobic (moderately polluted) level. During the low-water period, diatoms predominated and exhibited relatively narrow? niche breadth, whereas the high-water period was characterized by co-dominance of multiple taxonomic groups and an overall increase in niche breadth. Notably, Cyclotella remained consistently dominant in both seasons, while Cryptomonas exhibited concurrent increases in dominance and niche breadth in the high-water period. At the community level, niche overlap was generally higher in the high-water period than in the low-water period: overlap patterns were relatively even across dominance classes in the low-water period, whereas the high-water period showed an increased proportion of dominant-taxon pairs with low overlap. Permanganate index (CODMn), pH, and dissolved oxygen (DO) were consistently identified by Pearson correlation and RDA as the primary environmental drivers shaping the spatiotemporal patterns of dominant phytoplankton taxa.
The superimposed hydrological regulation of cascade reservoirs significantly alters the structure and function of river ecosystems. Identifying the spatiotemporal variations in phytoplankton communities and their key environmental drivers in the lower reaches of the Jinsha River can provide scientific basis for ecological restoration and management of cascade reservoirs in this region. Phytoplankton surveys were conducted in March 2025 (low-water period) and July 2025 (high-water period), during which taxonomic composition, density and biomass, diversity, dominant taxa, and niche attributes were quantified; Pearson correlation and redundancy analysis (RDA) were subsequently applied to examine relationships between dominant taxa and environmental variables. In total, 104 phytoplankton species (83 genera, 9 phyla) were recorded across the cascade reservoirs, with Chlorophyta, Bacillariophyta, and Cyanobacteria as the predominant groups. Species richness was significantly higher in the high-water period than in the low-water period (P<0.01) but remained relatively uniform among reservoirs. By contrast, phytoplankton density ranged from 0.14×105 to 362.37×105 cells/L and biomass from 0.01 to 19.05 mg/L, and neither exhibited significant spatiotemporal variation. Diversity metrics showed no significant differences among reservoirs; however, the richness, Shannon–Wiener, and Simpson indices were significantly higher in the high-water period than in the low-water period, whereas evenness did not vary significantly between seasons. The diversity-based assessment further indicated that the study area overall corresponded to an α–β mesosaprobic (moderately polluted) level. During the low-water period, diatoms predominated and exhibited relatively narrow? niche breadth, whereas the high-water period was characterized by co-dominance of multiple taxonomic groups and an overall increase in niche breadth. Notably, Cyclotella remained consistently dominant in both seasons, while Cryptomonas exhibited concurrent increases in dominance and niche breadth in the high-water period. At the community level, niche overlap was generally higher in the high-water period than in the low-water period: overlap patterns were relatively even across dominance classes in the low-water period, whereas the high-water period showed an increased proportion of dominant-taxon pairs with low overlap. Permanganate index (CODMn), pH, and dissolved oxygen (DO) were consistently identified by Pearson correlation and RDA as the primary environmental drivers shaping the spatiotemporal patterns of dominant phytoplankton taxa.
Available online: August 24, 2026
Abstract:
With the progress of Chinese dual-carbon strategy, scientifically assessing greenhouse gas (GHG) emission characteristics from reservoirs is essential for objectively evaluating the climate effects of hydropower projects and supporting the low-carbon attributes of the hydropower sector. Riverine reservoirs integrate longitudinal riverine transport, reservoir retention and sedimentation, and engineering regulation. Their greenhouse gas emissions are controlled not only by internal carbon transformation processes, but also by reservoir impoundment, water-level regulation, dam-discharge degassing, and alternating wetting and drying processes in water-level fluctuation zones. Identifying emission pathways, dynamic variations, and upscaling approaches for reservoir greenhouse gases is therefore critical for evaluating the climate effects and low-carbon attributes of riverine hydropower reservoirs. This review focuses on the identification of major riverine reservoir greenhouse gas emission pathways and related assessment requirements. It systematically summarizes key processes and monitoring needs, including carbon pulses during impoundment, reservoir-operation-driven source-sink shifts, air-water interface diffusion, ebullition, degassing during dam discharge, and non-steady emissions from water-level fluctuation zone. The applicability and limitations of major monitoring techniques, including chamber methods, thin boundary layer models, eddy covariance, acoustic sensing, and remote sensing–based spatial identification, are further reviewed. Taking the Three Gorges Reservoir as a representative case, this paper summarizes the practical evolution and major challenges of greenhouse gas monitoring technologies in large riverine reservoirs. The synthesis indicates that current riverine reservoir greenhouse gas monitoring still faces several challenges, including insufficient resolution of coupled emission processes, unclear interfaces among different methods, high uncertainty in key emission pathways, difficulties in characterizing non-steady emissions from water-level fluctuation zones, and limited capacity for multi-scale data integration. Future work should shift from single-method applications toward monitoring-target-driven method combinations, build multi-parameter collaborative monitoring networks and standardized datasets, strengthen remote sensing-based spatial constraints and mechanistic constraints, and promote the integration of process-based models with data-driven approaches. These developments will provide methodological support for whole-reservoir dynamic assessment, carbon footprint accounting, and low-carbon operation management of large riverine reservoirs.
With the progress of Chinese dual-carbon strategy, scientifically assessing greenhouse gas (GHG) emission characteristics from reservoirs is essential for objectively evaluating the climate effects of hydropower projects and supporting the low-carbon attributes of the hydropower sector. Riverine reservoirs integrate longitudinal riverine transport, reservoir retention and sedimentation, and engineering regulation. Their greenhouse gas emissions are controlled not only by internal carbon transformation processes, but also by reservoir impoundment, water-level regulation, dam-discharge degassing, and alternating wetting and drying processes in water-level fluctuation zones. Identifying emission pathways, dynamic variations, and upscaling approaches for reservoir greenhouse gases is therefore critical for evaluating the climate effects and low-carbon attributes of riverine hydropower reservoirs. This review focuses on the identification of major riverine reservoir greenhouse gas emission pathways and related assessment requirements. It systematically summarizes key processes and monitoring needs, including carbon pulses during impoundment, reservoir-operation-driven source-sink shifts, air-water interface diffusion, ebullition, degassing during dam discharge, and non-steady emissions from water-level fluctuation zone. The applicability and limitations of major monitoring techniques, including chamber methods, thin boundary layer models, eddy covariance, acoustic sensing, and remote sensing–based spatial identification, are further reviewed. Taking the Three Gorges Reservoir as a representative case, this paper summarizes the practical evolution and major challenges of greenhouse gas monitoring technologies in large riverine reservoirs. The synthesis indicates that current riverine reservoir greenhouse gas monitoring still faces several challenges, including insufficient resolution of coupled emission processes, unclear interfaces among different methods, high uncertainty in key emission pathways, difficulties in characterizing non-steady emissions from water-level fluctuation zones, and limited capacity for multi-scale data integration. Future work should shift from single-method applications toward monitoring-target-driven method combinations, build multi-parameter collaborative monitoring networks and standardized datasets, strengthen remote sensing-based spatial constraints and mechanistic constraints, and promote the integration of process-based models with data-driven approaches. These developments will provide methodological support for whole-reservoir dynamic assessment, carbon footprint accounting, and low-carbon operation management of large riverine reservoirs.
Available online: August 24, 2026
Abstract:
The Lower Jingjiang Reach exhibits inherent meandering tendency and natural cutoff characteristics. As a key node for river regime control in the middle Yangtze River, the Qigongling Bend, if subjected to natural cutoff, would impose significant adverse impacts on river channel stability, river-lake relations, and port and waterway safety. To clarify the natural cutoff process of this bend, this study conducted in-depth investigation on its dominant cutoff modes, defined the extreme hydrological conditions triggering natural cutoff, and quantitatively revealed the dynamic evolution process of natural cutoff, through analysis of measured hydrological data and theoretical formula calculations.The results show that cut-through cutoff and composite cutoff induced by extreme floods are the possible cutoff modes of the Qigongling Bend. The corresponding extreme hydrological combination is a discharge of 40,512 m3/s at Jianli Station, 23,688 m3/s at Chenglingji Station, and a water level of 31.12 m at Luoshan Station. There is a significant positive correlation between cutoff duration and channel roughness coefficient: within the roughness range of 0.025 to 0.037, the cutoff duration ranges from 65 h to 113 h. A scenario simulation with daily decreasing discharge after the extreme hydrological event was performed, which showed that the maximum erosion at the narrow neck exceeded the critical threshold for cutoff at the end of the 4th day, verifying the possibility of natural cutoff.This extreme hydrological combination corresponds to a discharge of approximately 54,000 m3/s at Zhicheng Station. The unfavorable combination of upstream large floods and low inflow in the middle reach is prone to inducing cutoff risk. This study presents preliminary findings, and further research is required to deepen hydrological frequency analysis and refined numerical simulations. Such hydrological combinations can serve as key concern scenarios for Three Gorges Reservoir operation and river channel inspections.
The Lower Jingjiang Reach exhibits inherent meandering tendency and natural cutoff characteristics. As a key node for river regime control in the middle Yangtze River, the Qigongling Bend, if subjected to natural cutoff, would impose significant adverse impacts on river channel stability, river-lake relations, and port and waterway safety. To clarify the natural cutoff process of this bend, this study conducted in-depth investigation on its dominant cutoff modes, defined the extreme hydrological conditions triggering natural cutoff, and quantitatively revealed the dynamic evolution process of natural cutoff, through analysis of measured hydrological data and theoretical formula calculations.The results show that cut-through cutoff and composite cutoff induced by extreme floods are the possible cutoff modes of the Qigongling Bend. The corresponding extreme hydrological combination is a discharge of 40,512 m3/s at Jianli Station, 23,688 m3/s at Chenglingji Station, and a water level of 31.12 m at Luoshan Station. There is a significant positive correlation between cutoff duration and channel roughness coefficient: within the roughness range of 0.025 to 0.037, the cutoff duration ranges from 65 h to 113 h. A scenario simulation with daily decreasing discharge after the extreme hydrological event was performed, which showed that the maximum erosion at the narrow neck exceeded the critical threshold for cutoff at the end of the 4th day, verifying the possibility of natural cutoff.This extreme hydrological combination corresponds to a discharge of approximately 54,000 m3/s at Zhicheng Station. The unfavorable combination of upstream large floods and low inflow in the middle reach is prone to inducing cutoff risk. This study presents preliminary findings, and further research is required to deepen hydrological frequency analysis and refined numerical simulations. Such hydrological combinations can serve as key concern scenarios for Three Gorges Reservoir operation and river channel inspections.
Liu Bao Gui, LI Ning Yu, Qian Jie Qiong, Yang Fei, Zhou Rui Juan, Liang Xue Yuan, Zheng Wan Ying, Hu Jie, Wang Ying Bin
Available online: August 18, 2026
Abstract:
Arid and semi-arid regions account for approximately half of China""s total land area. However, under the background of climate change, our understanding of the impacts of drought stress on aquatic organisms remains poorly understood. To investigate the effects of drought-related hydrological factors (DHFs) on phytoplankton, this study selected the Ningxia section of the Yellow River Basin - a typical area of aquatic ecological evolution in the arid and semi-arid regions of northwest China - as the research object. A total of 66 sampling sites were established in the main stream, tributaries, and affiliated lakes and reservoirs of this region in autumn (October) 2023, and an aquatic ecological survey was conducted. Hierarchical cluster analysis, non-metric multidimensional scaling (NMDS), and analysis of similarity (ANOSIM) were used to investigate the spatial distribution pattern of phytoplankton communities and the differences among groups. Multiple statistical methods, including Mantel test, redundancy analysis (RDA), and variance partitioning, were employed to systematically decipher the response mechanisms of phytoplankton to DHFs. As a result, a total of 143 phytoplankton species (including varieties) belonging to 7 phyla and 81 genera were identified. The community structure exhibited typical diatom-chlorophyte characteristics, with diatoms accounting for 39% of total species and 47% of total biomass. Significant spatial heterogeneity of DHFs was observed in the study area, with coefficients of variation (CV) for turbidity, TN/TP mass ratio, and total dissolved solids (TDS) reaching as high as 2.04, 2.03, and 1.66, respectively. Correspondingly, the CVs of phytoplankton cell density and biomass were 1.84 and 1.42, respectively. The average TN/TP mass ratio in the study area was 91.15, indicating clear phosphorus limitation. Hierarchical cluster analysis based on Bray-Curtis distances divided the phytoplankton communities into four groups with highly significant spatial heterogeneity (ANOSIM: R=0.783, p=0.001), and all DHFs differed significantly among groups. Mantel test and RDA results indicated that pH, turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were key drivers of changes in phytoplankton community structure. Variance partitioning showed that DHFs alone explained 12% of the community variation, which was six times the explanatory power of other factors (e.g., traditional nutrients, 2%). This study confirms the potential impact of drought on changes in phytoplankton community structure and provides a new perspective on the mechanisms underlying spatial pattern formation of phytoplankton communities in arid regions.
Arid and semi-arid regions account for approximately half of China""s total land area. However, under the background of climate change, our understanding of the impacts of drought stress on aquatic organisms remains poorly understood. To investigate the effects of drought-related hydrological factors (DHFs) on phytoplankton, this study selected the Ningxia section of the Yellow River Basin - a typical area of aquatic ecological evolution in the arid and semi-arid regions of northwest China - as the research object. A total of 66 sampling sites were established in the main stream, tributaries, and affiliated lakes and reservoirs of this region in autumn (October) 2023, and an aquatic ecological survey was conducted. Hierarchical cluster analysis, non-metric multidimensional scaling (NMDS), and analysis of similarity (ANOSIM) were used to investigate the spatial distribution pattern of phytoplankton communities and the differences among groups. Multiple statistical methods, including Mantel test, redundancy analysis (RDA), and variance partitioning, were employed to systematically decipher the response mechanisms of phytoplankton to DHFs. As a result, a total of 143 phytoplankton species (including varieties) belonging to 7 phyla and 81 genera were identified. The community structure exhibited typical diatom-chlorophyte characteristics, with diatoms accounting for 39% of total species and 47% of total biomass. Significant spatial heterogeneity of DHFs was observed in the study area, with coefficients of variation (CV) for turbidity, TN/TP mass ratio, and total dissolved solids (TDS) reaching as high as 2.04, 2.03, and 1.66, respectively. Correspondingly, the CVs of phytoplankton cell density and biomass were 1.84 and 1.42, respectively. The average TN/TP mass ratio in the study area was 91.15, indicating clear phosphorus limitation. Hierarchical cluster analysis based on Bray-Curtis distances divided the phytoplankton communities into four groups with highly significant spatial heterogeneity (ANOSIM: R=0.783, p=0.001), and all DHFs differed significantly among groups. Mantel test and RDA results indicated that pH, turbidity, chemical oxygen demand (COD), and total phosphorus (TP) were key drivers of changes in phytoplankton community structure. Variance partitioning showed that DHFs alone explained 12% of the community variation, which was six times the explanatory power of other factors (e.g., traditional nutrients, 2%). This study confirms the potential impact of drought on changes in phytoplankton community structure and provides a new perspective on the mechanisms underlying spatial pattern formation of phytoplankton communities in arid regions.
Available online: August 18, 2026
Abstract:
Sediment accretion and drought often occur concurrently in floodplain wetlands, and both affect plant growth and distribution. However, the combined effects of these two factors remain poorly understood. In this study, we examined the effects of water levels (0 cm，?20cm，and?40 cm) and sediment burial depths (0 cm，3 cm, and 6 cm) on the growth of Phalaris arundinacea L. within populations of the dominant species Carex thunbergii Steud. (1 P. arundinacea : 25 C. thunbergii individuals) in the Shengjin Lake wetland. Upon high sediment burial (6 cm), a reduction in the water level from 0 cm to -20 cm significantly increased the biomass, plant height, and root length of P. arundinacea (P < 0.05) , but significantly reduced the plant height of C. thunbergii (P < 0.05). This indicated that moderate drought enhanced the growth of P. arundinacea upon high sediment burial. Under moderate drought (?20 cm), an increase in sediment burial from 0 cm to 6 cm significantly increased the aboveground biomass of P. arundinacea (P < 0.05), but significantly decreased underground biomass of C. thunbergii (P < 0.05). In addition, moderate drought and high sediment burial increased the aboveground biomass ratio of P. arundinacea within total aboveground biomass (C. thunbergii + P. arundinacea) (P < 0.05). These results suggested that moderate drought combined with high sediment deposition may enhance the growth of P. arundinacea within C. thunbergii grasslands. Management measures such as water level regulation and sedimentation alleviation may help maintain the structure and function of wetland vegetation.
Sediment accretion and drought often occur concurrently in floodplain wetlands, and both affect plant growth and distribution. However, the combined effects of these two factors remain poorly understood. In this study, we examined the effects of water levels (0 cm，?20cm，and?40 cm) and sediment burial depths (0 cm，3 cm, and 6 cm) on the growth of Phalaris arundinacea L. within populations of the dominant species Carex thunbergii Steud. (1 P. arundinacea : 25 C. thunbergii individuals) in the Shengjin Lake wetland. Upon high sediment burial (6 cm), a reduction in the water level from 0 cm to -20 cm significantly increased the biomass, plant height, and root length of P. arundinacea (P < 0.05) , but significantly reduced the plant height of C. thunbergii (P < 0.05). This indicated that moderate drought enhanced the growth of P. arundinacea upon high sediment burial. Under moderate drought (?20 cm), an increase in sediment burial from 0 cm to 6 cm significantly increased the aboveground biomass of P. arundinacea (P < 0.05), but significantly decreased underground biomass of C. thunbergii (P < 0.05). In addition, moderate drought and high sediment burial increased the aboveground biomass ratio of P. arundinacea within total aboveground biomass (C. thunbergii + P. arundinacea) (P < 0.05). These results suggested that moderate drought combined with high sediment deposition may enhance the growth of P. arundinacea within C. thunbergii grasslands. Management measures such as water level regulation and sedimentation alleviation may help maintain the structure and function of wetland vegetation.
Long Mengqiao, Cao Mingsong, Lv Hongjian, Zhang Yu, Chen Shasha, Ma Weisong, Xie Mingdi, Shen Yankun, Fu Mei, Yao Weizhi
Available online: August 18, 2026
Abstract:
The Qijiang River is a typical cascade-developed tributary in the upper Yangtze River, where successive dams have reshaped longitudinal river connectivity, yet empirical evidence remains limited regarding their effects on the population genetic patterns of small resident fishes. In this study, Saurogobio punctatus was selected as the target species, and concatenated mitochondrial cytochrome b (Cyt b), cytochrome oxidase subunit I (CO I), and control region (D-loop) sequences from nine geographical populations were analyzed to characterize the genetic diversity and genetic structure of this species under the barrier effects of cascade dams. The results showed that: (1) A total of 36 variant sites and 18 haplotypes were identified from 185 individuals, and the overall haplotype diversity and nucleotide diversity were 0.787 ± 0.019 and 0.0020 ± 0.0002, respectively. No regular pattern of genetic diversity variation was observed among populations from different river sections. (2) Analysis of the genetic differentiation index (Fst) and gene flow (Nm) indicated moderate to high genetic differentiation between the uppermost S9 population and all other populations, although some degree of gene exchange was still maintained. (3) The Analysis of Molecular Variance (AMOVA) showed that only 1.72% of the molecular variation occurred among populations, whereas 98.28% occurred within populations, and neither the haplotype phylogenetic trees nor the haplotype network exhibited obvious signatures of dam-induced isolation. (4) Mismatch distribution and neutrality tests detected no clear signal of population expansion in either the total population or populations from different river sections. Taken together, these results indicate that the cascade dams in the Qijiang River have not yet caused a significant decline in the overall genetic diversity of S. punctatus and have had only limited effects on its overall genetic structure. However, a certain degree of local differentiation has emerged in the uppermost population, suggesting that this species can still maintain relatively stable population connectivity over the short term under conditions of high-density cascade damming. This study provides basic data and scientific support for research on population genetic differentiation of small omnivorous fishes under cascade hydropower development.
The Qijiang River is a typical cascade-developed tributary in the upper Yangtze River, where successive dams have reshaped longitudinal river connectivity, yet empirical evidence remains limited regarding their effects on the population genetic patterns of small resident fishes. In this study, Saurogobio punctatus was selected as the target species, and concatenated mitochondrial cytochrome b (Cyt b), cytochrome oxidase subunit I (CO I), and control region (D-loop) sequences from nine geographical populations were analyzed to characterize the genetic diversity and genetic structure of this species under the barrier effects of cascade dams. The results showed that: (1) A total of 36 variant sites and 18 haplotypes were identified from 185 individuals, and the overall haplotype diversity and nucleotide diversity were 0.787 ± 0.019 and 0.0020 ± 0.0002, respectively. No regular pattern of genetic diversity variation was observed among populations from different river sections. (2) Analysis of the genetic differentiation index (Fst) and gene flow (Nm) indicated moderate to high genetic differentiation between the uppermost S9 population and all other populations, although some degree of gene exchange was still maintained. (3) The Analysis of Molecular Variance (AMOVA) showed that only 1.72% of the molecular variation occurred among populations, whereas 98.28% occurred within populations, and neither the haplotype phylogenetic trees nor the haplotype network exhibited obvious signatures of dam-induced isolation. (4) Mismatch distribution and neutrality tests detected no clear signal of population expansion in either the total population or populations from different river sections. Taken together, these results indicate that the cascade dams in the Qijiang River have not yet caused a significant decline in the overall genetic diversity of S. punctatus and have had only limited effects on its overall genetic structure. However, a certain degree of local differentiation has emerged in the uppermost population, suggesting that this species can still maintain relatively stable population connectivity over the short term under conditions of high-density cascade damming. This study provides basic data and scientific support for research on population genetic differentiation of small omnivorous fishes under cascade hydropower development.
Ma Jinpan, Zhu Yao, Zhang Yuepeng, Xiao Peng, Cheng Yao, Jiao Meng, Li Chaoyang, Zhang He, Yang Siyu, Li Renhui, Zuo Jun
Available online: August 18, 2026
Abstract:
Dredging is a common measure for ecological restoration in reservoirs, but it may also affect phytoplankton community structure. Human Reservoir, an important drinking water source in Wenling City, has experienced blooms of Raphidiopsis raciborskii in recent years. To reduce internal nutrient loading and improve water quality, whole-reservoir dredging was conducted from February to September 2024. To evaluate the effects of dredging on the phytoplankton community, this study monitored R. raciborskii blooms in Human Reservoir from October 2023 to September 2025. Phytoplankton community composition, diversity, niche, and their relationships with environmental factors were analyzed across different periods defined by bloom stages and the dredging process. The results showed that nutrient concentrations decreased significantly after dredging. A total of 55 phytoplankton genera belonging to seven phyla were identified during the monitoring period. Total phytoplankton cell abundance declined markedly during dredging but increased again after dredging. The dominant cyanobacterial taxa were Raphidiopsis and Pseudanabaena, showing a temporal succession from Raphidiopsis to Pseudanabaena. The abundance of R. raciborskii was highest before dredging, reaching 2.56×10?cells/L, decreased during dredging, and increased again after dredging. Phytoplankton diversity was relatively low before dredging but increased markedly after dredging. Redundancy analysis indicated that the phytoplankton community was positively correlated with nutrient concentrations before dredging, whereas this relationship weakened after dredging. The random forest model showed that bloom stage and dredging process were the key factors influencing phytoplankton community structure, followed by ammonium nitrogen. The niche breadth of R. raciborskii narrowed during dredging and widened after dredging. Multivariate homogeneity of group dispersions (PERMDISP) tests indicated that the phytoplankton community structure gradually returned to its pre-dredging state within one year after dredging. These results suggest that dredging can improve water quality and suppress R. raciborskii blooms in the short term; however, its effect is limited in duration, as the phytoplankton community gradually recovers and the bloom rapidly rebounds after dredging.
Dredging is a common measure for ecological restoration in reservoirs, but it may also affect phytoplankton community structure. Human Reservoir, an important drinking water source in Wenling City, has experienced blooms of Raphidiopsis raciborskii in recent years. To reduce internal nutrient loading and improve water quality, whole-reservoir dredging was conducted from February to September 2024. To evaluate the effects of dredging on the phytoplankton community, this study monitored R. raciborskii blooms in Human Reservoir from October 2023 to September 2025. Phytoplankton community composition, diversity, niche, and their relationships with environmental factors were analyzed across different periods defined by bloom stages and the dredging process. The results showed that nutrient concentrations decreased significantly after dredging. A total of 55 phytoplankton genera belonging to seven phyla were identified during the monitoring period. Total phytoplankton cell abundance declined markedly during dredging but increased again after dredging. The dominant cyanobacterial taxa were Raphidiopsis and Pseudanabaena, showing a temporal succession from Raphidiopsis to Pseudanabaena. The abundance of R. raciborskii was highest before dredging, reaching 2.56×10?cells/L, decreased during dredging, and increased again after dredging. Phytoplankton diversity was relatively low before dredging but increased markedly after dredging. Redundancy analysis indicated that the phytoplankton community was positively correlated with nutrient concentrations before dredging, whereas this relationship weakened after dredging. The random forest model showed that bloom stage and dredging process were the key factors influencing phytoplankton community structure, followed by ammonium nitrogen. The niche breadth of R. raciborskii narrowed during dredging and widened after dredging. Multivariate homogeneity of group dispersions (PERMDISP) tests indicated that the phytoplankton community structure gradually returned to its pre-dredging state within one year after dredging. These results suggest that dredging can improve water quality and suppress R. raciborskii blooms in the short term; however, its effect is limited in duration, as the phytoplankton community gradually recovers and the bloom rapidly rebounds after dredging.
Available online: August 11, 2026
Abstract:
Wetland restoration represents a key technical strategy for reversing lake ecosystem degradation and restoring ecological functions. By enhancing hydrological connectivity and optimizing landscape patterns, it can substantially improve habitat quality for waterbirds. Huangpi Lake is a small shallow lake in the middle and lower Yangtze River floodplain that has experienced severe landscape fragmentation and ecological degradation due to long-term anthropogenic disturbances such as aquaculture reclamation. The wetland restoration project was carried out in the study area between June 2023 and June 2024. However, a systematic assessment of its ecological impacts is still lacking. From the perspective of waterbird functional groups, this study systematically examined the dynamics of wintering waterbird communities before and after restoration, and evaluated the effects of landscape pattern changes on waterbird assemblages by integrating landscape configuration and composition. The results demonstrated that the landscape pattern of the lake wetland was substantially optimized following restoration. During the early wintering period, overall patch density decreased by 48.93%, water area expanded by 53.49%, and the number of mudflat patches declined by 53.89%; in the mid-wintering period, the number of water patches decreased by 71.31%; and in the late wintering period, the vegetation aggregation index increased by 12.45%. Waterbird functional groups showed differential responses to variations in landscape patterns. Increases in the water area aggregation index promoted population growth in predatory diving waterbirds (G1); higher mudflat aggregation index effectively increased colony size in herbivorous waterbirds (G5); whereas an elevated shallow-water aggregation index caused habitat homogenization, leading to population declines in small benthivorous waders (G3), which depend on such heterogeneous patches. Generalized Additive Model (GAM) analysis indicated that patch density represented the key landscape configuration factor governing the population dynamics of G5, whereas water area and aggregation index served as the dominant drivers shaping the distribution of diving waterbirds and large waders. To restore small shallow lake wetlands, landscape patterns should be optimized by enhancing hydrological connectivity and staged water level regulation to meet the wintering needs of different waterbird functional groups. This study highlights the importance of constructing heterogeneous habitat mosaics during wetland restoration for the effective conservation of wintering waterbirds, and provides theoretical support and practical implications for the scientific restoration of heavily human-disturbed wetlands and the protection of waterbird habitats in the middle and lower Yangtze River floodplain.
Wetland restoration represents a key technical strategy for reversing lake ecosystem degradation and restoring ecological functions. By enhancing hydrological connectivity and optimizing landscape patterns, it can substantially improve habitat quality for waterbirds. Huangpi Lake is a small shallow lake in the middle and lower Yangtze River floodplain that has experienced severe landscape fragmentation and ecological degradation due to long-term anthropogenic disturbances such as aquaculture reclamation. The wetland restoration project was carried out in the study area between June 2023 and June 2024. However, a systematic assessment of its ecological impacts is still lacking. From the perspective of waterbird functional groups, this study systematically examined the dynamics of wintering waterbird communities before and after restoration, and evaluated the effects of landscape pattern changes on waterbird assemblages by integrating landscape configuration and composition. The results demonstrated that the landscape pattern of the lake wetland was substantially optimized following restoration. During the early wintering period, overall patch density decreased by 48.93%, water area expanded by 53.49%, and the number of mudflat patches declined by 53.89%; in the mid-wintering period, the number of water patches decreased by 71.31%; and in the late wintering period, the vegetation aggregation index increased by 12.45%. Waterbird functional groups showed differential responses to variations in landscape patterns. Increases in the water area aggregation index promoted population growth in predatory diving waterbirds (G1); higher mudflat aggregation index effectively increased colony size in herbivorous waterbirds (G5); whereas an elevated shallow-water aggregation index caused habitat homogenization, leading to population declines in small benthivorous waders (G3), which depend on such heterogeneous patches. Generalized Additive Model (GAM) analysis indicated that patch density represented the key landscape configuration factor governing the population dynamics of G5, whereas water area and aggregation index served as the dominant drivers shaping the distribution of diving waterbirds and large waders. To restore small shallow lake wetlands, landscape patterns should be optimized by enhancing hydrological connectivity and staged water level regulation to meet the wintering needs of different waterbird functional groups. This study highlights the importance of constructing heterogeneous habitat mosaics during wetland restoration for the effective conservation of wintering waterbirds, and provides theoretical support and practical implications for the scientific restoration of heavily human-disturbed wetlands and the protection of waterbird habitats in the middle and lower Yangtze River floodplain.
Available online: August 11, 2026
Abstract:
Lake Merzbacher, located in the central Tian Shan Mountains, experiences frequent outbursts. The resulting glacial lake outburst floods (GLOFs) pose a severe threat to the water resource security of the downstream basin. To address the gaps in existing research regarding the response mechanisms and early warning indicators of GLOFs, this study integrated multi-source remote sensing imagery, meteorological reanalysis data, and runoff observation data from hydrological stations spanning 1990 to 2022. Utilizing a combination of the NDWI and visual interpretation, we constructed a high-precision, high-temporal-resolution dataset of glacial lake boundaries over the past three decades and extracted GLOF events to analyze the evolutionary characteristics of the glacial lake and its outburst floods. The results reveal that the evolution of the glacial lake area can be divided into three stages: a rapid expansion phase (1990–1996), a relatively stable phase (1997–2010), and a structural transformation phase (2011–2022). GLOF events predominantly occurred in July and August (accounting for 96% of occurrences) and exhibited an advancing trend in timing (7 days/decade). The peak discharge demonstrated an increasing trend (approximately 66 m3/s per decade) with heightened abruptness (flood duration shortened by 1.1 days/decade), and the overall flood magnitude has intensified since 2010. Furthermore, we quantitatively analyzed the relationships among the maximum pre-outburst area, lake drainage volume, net peak discharge, and total flood volume. By incorporating the pre-outburst glacial lake area, floating ice coverage, and changes in the altitude of the 0°C level height, we proposed a set of multi-dimensional early warning indicators capable of evaluating outburst timing and flood magnitude. These findings provide a scientific basis and reference for enhancing forecasting and early warning capabilities, as well as disaster risk assessment for GLOFs.
Lake Merzbacher, located in the central Tian Shan Mountains, experiences frequent outbursts. The resulting glacial lake outburst floods (GLOFs) pose a severe threat to the water resource security of the downstream basin. To address the gaps in existing research regarding the response mechanisms and early warning indicators of GLOFs, this study integrated multi-source remote sensing imagery, meteorological reanalysis data, and runoff observation data from hydrological stations spanning 1990 to 2022. Utilizing a combination of the NDWI and visual interpretation, we constructed a high-precision, high-temporal-resolution dataset of glacial lake boundaries over the past three decades and extracted GLOF events to analyze the evolutionary characteristics of the glacial lake and its outburst floods. The results reveal that the evolution of the glacial lake area can be divided into three stages: a rapid expansion phase (1990–1996), a relatively stable phase (1997–2010), and a structural transformation phase (2011–2022). GLOF events predominantly occurred in July and August (accounting for 96% of occurrences) and exhibited an advancing trend in timing (7 days/decade). The peak discharge demonstrated an increasing trend (approximately 66 m3/s per decade) with heightened abruptness (flood duration shortened by 1.1 days/decade), and the overall flood magnitude has intensified since 2010. Furthermore, we quantitatively analyzed the relationships among the maximum pre-outburst area, lake drainage volume, net peak discharge, and total flood volume. By incorporating the pre-outburst glacial lake area, floating ice coverage, and changes in the altitude of the 0°C level height, we proposed a set of multi-dimensional early warning indicators capable of evaluating outburst timing and flood magnitude. These findings provide a scientific basis and reference for enhancing forecasting and early warning capabilities, as well as disaster risk assessment for GLOFs.
Available online: August 11, 2026
Abstract:
Seasonal floodplain wetlands, as dynamic transitional ecosystems between terrestrial and aquatic environments, play a pivotal role in maintaining regional ecological balance and regulating hydrological processes. However, their spatiotemporally variable inundation regimes and heterogeneous land cover pose significant challenges for remote sensing-based water body extraction. Notably, the intricate coupling of hydrological dynamics and spectral responses constrains the applicability of single spectral indices, leading to inconsistent accuracy and limited monitoring efficacy. Focusing on the Poyang Lake floodplain as a representative case, this study aims to investigate the adaptability of multiple spectral indices to hydrological fluctuations and land cover complexity in seasonal floodplain wetlands, with the primary objective of developing optimized, context-specific extraction strategies tailored to distinct hydrological scenarios and surface conditions.The research was conducted in the Poyang Lake National Nature Reserve, a typical seasonal floodplain wetland in China. Sentinel-2 MSI imagery was selected as the core data source, leveraging its high spatial and spectral resolution. Eight representative spectral indices were constructed, including normalized indices (NDWI, MNDWI), multi-band indices (MBWI, SWI), and auxiliary indices (NDVI, TCB, TCG, TCW). Water body extraction was performed under both wet (July 2021) and dry (March 2021) hydrological conditions using K-means clustering on the Google Earth Engine (GEE) platform. Ground truth data were derived from high-resolution GF-1/2 PMS imagery, with random forest classification employed for validation. Extraction accuracy was evaluated using multiple metrics: Overall Accuracy (OA), Producer’s Accuracy (PA), User’s Accuracy (UA), and Kappa coefficient. Additionally, stratified assessments were conducted for distinct water body types, encompassing permanent waters, seasonal dish-shaped lakes, and paddy fields.Results indicate that hydrological variation exerts a significant regulatory effect on the performance of spectral indices. During the wet season, NDWI achieved the highest extraction accuracy (OA = 95.4%), whereas TCB performed poorest (OA = 73.5%) due to interference from high-moisture vegetation. In the dry season, SWI (OA = 97.4%) and NDWI (OA = 97.2%) demonstrated strong discriminative capacity in mixed spectral environments, while TCW exhibited high spectral confusion with mudflats (OA=75.7%). For different water body types, SWI yielded the best results for seasonal dish-shaped lakes (OA=98.5%); NDWI and TCB performed optimally for permanent water bodies (OA=99%); and only MBWI maintained high accuracy for paddy fields (OA=94%). Boxplot analyses and spectral curve comparisons confirmed that the adaptability of spectral indices is closely linked to their ability to enhance intra-class spectral homogeneity and inter-class separability.This study confirms that no single spectral index can effectively capture water bodies across all seasonal and land cover conditions in floodplain wetlands. The efficacy of each index is strongly modulated by hydrological stages and the spectral characteristics of specific surface types. Thus, adopting a differentiated extraction strategy based on hydrological context and target land cover types is imperative. This study identifies the optimal matching patterns of spectral indices under varying hydrological conditions and water body types. It provides a scientific and technical framework for dynamic monitoring of water bodies in seasonal floodplain wetlands and holds significant practical implications for enhancing wetland ecosystem conservation and refined water resource management.
Seasonal floodplain wetlands, as dynamic transitional ecosystems between terrestrial and aquatic environments, play a pivotal role in maintaining regional ecological balance and regulating hydrological processes. However, their spatiotemporally variable inundation regimes and heterogeneous land cover pose significant challenges for remote sensing-based water body extraction. Notably, the intricate coupling of hydrological dynamics and spectral responses constrains the applicability of single spectral indices, leading to inconsistent accuracy and limited monitoring efficacy. Focusing on the Poyang Lake floodplain as a representative case, this study aims to investigate the adaptability of multiple spectral indices to hydrological fluctuations and land cover complexity in seasonal floodplain wetlands, with the primary objective of developing optimized, context-specific extraction strategies tailored to distinct hydrological scenarios and surface conditions.The research was conducted in the Poyang Lake National Nature Reserve, a typical seasonal floodplain wetland in China. Sentinel-2 MSI imagery was selected as the core data source, leveraging its high spatial and spectral resolution. Eight representative spectral indices were constructed, including normalized indices (NDWI, MNDWI), multi-band indices (MBWI, SWI), and auxiliary indices (NDVI, TCB, TCG, TCW). Water body extraction was performed under both wet (July 2021) and dry (March 2021) hydrological conditions using K-means clustering on the Google Earth Engine (GEE) platform. Ground truth data were derived from high-resolution GF-1/2 PMS imagery, with random forest classification employed for validation. Extraction accuracy was evaluated using multiple metrics: Overall Accuracy (OA), Producer’s Accuracy (PA), User’s Accuracy (UA), and Kappa coefficient. Additionally, stratified assessments were conducted for distinct water body types, encompassing permanent waters, seasonal dish-shaped lakes, and paddy fields.Results indicate that hydrological variation exerts a significant regulatory effect on the performance of spectral indices. During the wet season, NDWI achieved the highest extraction accuracy (OA = 95.4%), whereas TCB performed poorest (OA = 73.5%) due to interference from high-moisture vegetation. In the dry season, SWI (OA = 97.4%) and NDWI (OA = 97.2%) demonstrated strong discriminative capacity in mixed spectral environments, while TCW exhibited high spectral confusion with mudflats (OA=75.7%). For different water body types, SWI yielded the best results for seasonal dish-shaped lakes (OA=98.5%); NDWI and TCB performed optimally for permanent water bodies (OA=99%); and only MBWI maintained high accuracy for paddy fields (OA=94%). Boxplot analyses and spectral curve comparisons confirmed that the adaptability of spectral indices is closely linked to their ability to enhance intra-class spectral homogeneity and inter-class separability.This study confirms that no single spectral index can effectively capture water bodies across all seasonal and land cover conditions in floodplain wetlands. The efficacy of each index is strongly modulated by hydrological stages and the spectral characteristics of specific surface types. Thus, adopting a differentiated extraction strategy based on hydrological context and target land cover types is imperative. This study identifies the optimal matching patterns of spectral indices under varying hydrological conditions and water body types. It provides a scientific and technical framework for dynamic monitoring of water bodies in seasonal floodplain wetlands and holds significant practical implications for enhancing wetland ecosystem conservation and refined water resource management.
Huang Siao, Mi Juntao, Zhang Chenxue, Zheng Jianan, Zhao Yu, Qin Bo, Li Guozhan, Chen Guangjie, Wang Rong
Available online: July 31, 2026
Abstract:
The eutrophication of shallow lakes has become a global environmental issue. Phosphorus (P) is a key driver of lake eutrophication, and its distribution within sediments, as well as the transformation among its different fractions, directly influences the potential for internal P release and the trajectory of ecological restoration. While existing studies predominantly focus on internal phosphorus (P) release in shallow lakes, the long-term alterations in sedimentary P speciation driven by eutrophication and the underlying ecological feedback mechanisms remain poorly understood. In this study, 37 shallow lakes in the Eastern Plain of China were selected as research subjects. Based on sediment core records and combined with contemporary physicochemical water quality observations, we reconstructed the centennial evolutionary history of P fractions in lake sediments and explored their environmental implications. The results indicate that eutrophication has led to an increase in algal biomass, leading to an increase in the content and proportion of high-release-risk active phosphorus in surface sediments, alongside a decrease in the content and proportion of relatively stable calcium-bound phosphorus (Ca-P). Furthermore, the ratio of Ca-P to calcium (Ca) continuously decreased over the time series, indicating a gradual weakening of phosphorus fixation processes associated with calcium carbonate. These processes include the substitution of phosphate ions (PO43-) for partial carbonate ions (CO32-) within the crystal structure of calcium carbonate (CaCO3), as well as the formation of insoluble calcium-phosphate minerals on the surface or within the interior of CaCO3 crystals. This further suggests that the accumulation capacity for inert phosphorus in shallow lake sediments may be impaired under eutrophic conditions. This study concludes that the elevated proportion of labile P in sediments will exacerbate the risk of internal P release and intensify the positive feedback loop of the turbid water state, thereby making the restoration of lake ecosystems significantly more difficult.
The eutrophication of shallow lakes has become a global environmental issue. Phosphorus (P) is a key driver of lake eutrophication, and its distribution within sediments, as well as the transformation among its different fractions, directly influences the potential for internal P release and the trajectory of ecological restoration. While existing studies predominantly focus on internal phosphorus (P) release in shallow lakes, the long-term alterations in sedimentary P speciation driven by eutrophication and the underlying ecological feedback mechanisms remain poorly understood. In this study, 37 shallow lakes in the Eastern Plain of China were selected as research subjects. Based on sediment core records and combined with contemporary physicochemical water quality observations, we reconstructed the centennial evolutionary history of P fractions in lake sediments and explored their environmental implications. The results indicate that eutrophication has led to an increase in algal biomass, leading to an increase in the content and proportion of high-release-risk active phosphorus in surface sediments, alongside a decrease in the content and proportion of relatively stable calcium-bound phosphorus (Ca-P). Furthermore, the ratio of Ca-P to calcium (Ca) continuously decreased over the time series, indicating a gradual weakening of phosphorus fixation processes associated with calcium carbonate. These processes include the substitution of phosphate ions (PO43-) for partial carbonate ions (CO32-) within the crystal structure of calcium carbonate (CaCO3), as well as the formation of insoluble calcium-phosphate minerals on the surface or within the interior of CaCO3 crystals. This further suggests that the accumulation capacity for inert phosphorus in shallow lake sediments may be impaired under eutrophic conditions. This study concludes that the elevated proportion of labile P in sediments will exacerbate the risk of internal P release and intensify the positive feedback loop of the turbid water state, thereby making the restoration of lake ecosystems significantly more difficult.
Available online: July 31, 2026
Abstract:
Understanding the spatiotemporal dynamics of fish communities and their associations with environmental gradients in large reservoirs is of great significance for formulating scientific fisheries resource conservation and management strategies and optimizing hydrological operations in cascade reservoirs at the watershed scale. This study focused on the Nuozhadu Reservoir, a key control project on the main stem of the Lancang River. Quarterly fish surveys were conducted at 11 sampling sites in July, October, and December 2024 and April 2025, combined with water environmental factors, to systematically examine fish community structure, α-diversity patterns, and their environmental associations after reservoir impoundment. A total of 43 fish species were recorded, with Cypriniformes as the dominant group. Non-native species (e.g., Hemiculter leucisculus, Parachromis managuensis, and Coptodon zillii) consistently dominated throughout the year, whereas local endemic species mostly occurred as marginal components of the community, with low abundance and low index of relative importance (IRI). From the perspective of species composition, the fish community was characterized by a high proportion of resident (76.74%), lentic (58.14%), and omnivorous (58.14%) species. Fish α-diversity remained overall stable over time but exhibited pronounced spatial differentiation along the longitudinal gradient from near-dam to far-dam areas, with significantly higher diversity in the reservoir tail than in the reservoir head. Joint analyses using generalized linear models (GLM) and generalized additive models (GAM) revealed that fish diversity was statistically associated with multiple environmental variables, among which distance from the dam had relatively high explanatory power and was positively associated with fish diversity. In addition, fish diversity was also statistically associated with dissolved oxygen, total nitrogen (increasing first and then decreasing), and water depth (decreasing). This study systematically revealed the structural characteristics, spatiotemporal dynamics, and environmental driving associations of fish communities in the Nuozhadu Reservoir after impoundment. These findings provide a scientific basis for the conservation and management of fishery resources in large reservoirs in China.
Understanding the spatiotemporal dynamics of fish communities and their associations with environmental gradients in large reservoirs is of great significance for formulating scientific fisheries resource conservation and management strategies and optimizing hydrological operations in cascade reservoirs at the watershed scale. This study focused on the Nuozhadu Reservoir, a key control project on the main stem of the Lancang River. Quarterly fish surveys were conducted at 11 sampling sites in July, October, and December 2024 and April 2025, combined with water environmental factors, to systematically examine fish community structure, α-diversity patterns, and their environmental associations after reservoir impoundment. A total of 43 fish species were recorded, with Cypriniformes as the dominant group. Non-native species (e.g., Hemiculter leucisculus, Parachromis managuensis, and Coptodon zillii) consistently dominated throughout the year, whereas local endemic species mostly occurred as marginal components of the community, with low abundance and low index of relative importance (IRI). From the perspective of species composition, the fish community was characterized by a high proportion of resident (76.74%), lentic (58.14%), and omnivorous (58.14%) species. Fish α-diversity remained overall stable over time but exhibited pronounced spatial differentiation along the longitudinal gradient from near-dam to far-dam areas, with significantly higher diversity in the reservoir tail than in the reservoir head. Joint analyses using generalized linear models (GLM) and generalized additive models (GAM) revealed that fish diversity was statistically associated with multiple environmental variables, among which distance from the dam had relatively high explanatory power and was positively associated with fish diversity. In addition, fish diversity was also statistically associated with dissolved oxygen, total nitrogen (increasing first and then decreasing), and water depth (decreasing). This study systematically revealed the structural characteristics, spatiotemporal dynamics, and environmental driving associations of fish communities in the Nuozhadu Reservoir after impoundment. These findings provide a scientific basis for the conservation and management of fishery resources in large reservoirs in China.
Available online: July 31, 2026
Abstract:
Mountainous urban rivers are subject to prominent water pollution problems due to the combined effects of complex topography and high-intensity human activities. Characterizing water quality spatiotemporal features and identifying pollution sources are therefore essential for refined watershed management. This study focuses on the Yanjin Stream, a first-order tributary of the Chishui River. We characterize its water quality spatiotemporal features, quantitatively evaluate pollutant overloading through environmental capacity calculations, and apply the Positive Matrix Factorization (PMF) model to identify major pollution sources and their contribution variations under different hydrological conditions, thereby elucidating pollution pattern formation mechanisms driven by the joint effects of hydrological processes and land-use structure.The results indicate that: (1) Except for the TN concentration, which generally shows an upward trend with increasing flow, the changes of other water quality indicators in each flow interval are not significant; pollutant fluxes increase with rising flow and exhibit differentiated reduction requirements across different flow intervals. DOC requires reduction throughout all flow intervals, with reduction ratios of 23.76%~30.93% (25.00~427.93 kg/d). CODMn requires reduction under low-to-medium flow conditions, with a reduction amount of 40.93 kg/d (11.93%). No reduction requirements are identified for NH4+?N or TP. The reduction demand for TN is relatively lower compared with that of regional background rivers, ranging from 80.50 to 416.14 kg/d (14.32%~98.21%) in different flow intervals and from 142.56 to 686.25 kg/d (29.77%~41.38%) in different river sections. (2) Pronounced spatial differentiation of water quality is observed, with overall deterioration from upstream to mid-downstream reaches. The middle reaches exhibit the highest pollutant overloading and reduction demand. DOC and CODMn require substantial reductions of 241.67 kg/d and 92.81 kg/d, corresponding to reduction ratios of 92.80% and 84.79%, respectively. NH4+?N and TP require reductions of 51.30 kg/d (86.16%) and 10.27 kg/d (55.58%). The proportion of built-up land significantly enhances TN, NH4+?N, and TP levels, whereas land-use effects on DOC and CODMn are relatively limited at the macro scale. (3) PMF source apportionment shows that during dry season, domestic sewage and industrial wastewater together contribute more than 60% of total pollution. Domestic sewage predominantly contributes NH4+?N (68.97%) and TP (91.66%), while industrial wastewater is mainly characterized by CODMn (60.11%) and electrical conductivity (62.80%). During wet season, point-source contributions weaken while non-point source contributions intensify, resulting in a more complex pollution source structure. Surface runoff contributes 15.37%, primarily characterized by DOC (43.44%) and TN (28.06%), whereas combined industrial and aquaculture wastewater contributes 26.84%, mainly characterized by TP (32.44%) and CODMn (63.34%). Overall, this study demonstrates that water pollution patterns in the Yanjin Stream are jointly regulated by hydrological variability and land-use structure, providing a scientific basis for water environment regulation and management in mountainous urban rivers.
Mountainous urban rivers are subject to prominent water pollution problems due to the combined effects of complex topography and high-intensity human activities. Characterizing water quality spatiotemporal features and identifying pollution sources are therefore essential for refined watershed management. This study focuses on the Yanjin Stream, a first-order tributary of the Chishui River. We characterize its water quality spatiotemporal features, quantitatively evaluate pollutant overloading through environmental capacity calculations, and apply the Positive Matrix Factorization (PMF) model to identify major pollution sources and their contribution variations under different hydrological conditions, thereby elucidating pollution pattern formation mechanisms driven by the joint effects of hydrological processes and land-use structure.The results indicate that: (1) Except for the TN concentration, which generally shows an upward trend with increasing flow, the changes of other water quality indicators in each flow interval are not significant; pollutant fluxes increase with rising flow and exhibit differentiated reduction requirements across different flow intervals. DOC requires reduction throughout all flow intervals, with reduction ratios of 23.76%~30.93% (25.00~427.93 kg/d). CODMn requires reduction under low-to-medium flow conditions, with a reduction amount of 40.93 kg/d (11.93%). No reduction requirements are identified for NH4+?N or TP. The reduction demand for TN is relatively lower compared with that of regional background rivers, ranging from 80.50 to 416.14 kg/d (14.32%~98.21%) in different flow intervals and from 142.56 to 686.25 kg/d (29.77%~41.38%) in different river sections. (2) Pronounced spatial differentiation of water quality is observed, with overall deterioration from upstream to mid-downstream reaches. The middle reaches exhibit the highest pollutant overloading and reduction demand. DOC and CODMn require substantial reductions of 241.67 kg/d and 92.81 kg/d, corresponding to reduction ratios of 92.80% and 84.79%, respectively. NH4+?N and TP require reductions of 51.30 kg/d (86.16%) and 10.27 kg/d (55.58%). The proportion of built-up land significantly enhances TN, NH4+?N, and TP levels, whereas land-use effects on DOC and CODMn are relatively limited at the macro scale. (3) PMF source apportionment shows that during dry season, domestic sewage and industrial wastewater together contribute more than 60% of total pollution. Domestic sewage predominantly contributes NH4+?N (68.97%) and TP (91.66%), while industrial wastewater is mainly characterized by CODMn (60.11%) and electrical conductivity (62.80%). During wet season, point-source contributions weaken while non-point source contributions intensify, resulting in a more complex pollution source structure. Surface runoff contributes 15.37%, primarily characterized by DOC (43.44%) and TN (28.06%), whereas combined industrial and aquaculture wastewater contributes 26.84%, mainly characterized by TP (32.44%) and CODMn (63.34%). Overall, this study demonstrates that water pollution patterns in the Yanjin Stream are jointly regulated by hydrological variability and land-use structure, providing a scientific basis for water environment regulation and management in mountainous urban rivers.
Available online: July 30, 2026
Abstract:
Zooplankton community structure is a key indicator of lake ecosystem health. Understanding its spatiotemporal dynamics and environmental drivers is of great significance for ecological conservation and water environment management. The Huayanghe Lakes, located in the middle and lower reaches of the Yangtze River, is a typical sluice-controlled river-connected lake group and an important regional drinking water source. Clarifying the spatiotemporal variations and driving mechanisms of metazoan zooplankton community structure in this lake group is therefore important for lake ecological protection, water quality improvement, and drinking water source management. In this study, systematic investigations of metazoan zooplankton community structure and physicochemical water parameters were conducted in the Huayanghe Lakes in April 2023 (spring), July 2023 (summer), October 2023 (autumn), and January 2024 (winter). Redundancy analysis (RDA) and variation partitioning analysis (VPA) were used to explore the main driving factors of community structure. During the survey period, a total of 67 metazoan zooplankton species belonging to 50 genera were identified, including 37 Rotifer species from 23 genera, 15 Cladoceran species from 14 genera, and 15 Copepod species from 13 genera. The abundance and biomass ranged from 21 to 956 ind./L and 2.83 to 17.09 mg/L, respectively. Temporally, metazoan zooplankton community structure showed obvious seasonal differences. Abundance was highest in autumn, biomass was highest in spring, and both abundance and biomass were lowest in summer. The number of dominant species, Shannon-Wiener diversity index, and Pielou evenness index were higher in autumn and winter than in spring and summer, whereas the Margalef richness index reached its maximum in summer. Spatially, metazoan zooplankton abundance and biomass followed the pattern: Longgan Lake > Huangda Lake > Bo Lake, while Margalef richness, Shannon–Wiener diversity, and Pielou’s evenness indices showed the opposite pattern: Bo Lake > Huangda Lake > Longgan Lake. Environmental driving analysis indicated that the key factors influencing metazoan zooplankton community structure varied across temporal and spatial scales. Temporally, zooplankton communities were positively correlated with suspended solids (SS) and ammonium nitrogen (NH4+-N) in spring, dissolved total phosphorus (DTP) and phosphate (PO?3?–P) in summer, phosphate (PO?3?–P) and permanganate index (CODMn) in autumn, and total phosphorus (TP) and dissolved oxygen (DO) in winter. Spatially, SS, PO?3?–P, and water transparency (SD) were the primary factors driving the community structure in Longgan Lake, Huangda Lake, and Bo Lake, respectively. The VPA results showed that water environmental factors and sluice-controlled hydrological factors jointly explained 54.7% of the variation in metazoan zooplankton community structure, with independent explanation rates of 28.1% for water environmental factors and 17.4% for hydrological factors, and a shared explanation rate of 9.2%. These results indicate that sluice-controlled water level processes play an important role in shaping community structure by affecting water exchange, suspended sediment transport, and nutrient distribution. Seasonally, the Huayanghe Lakes were in an oligotrophic–mesotrophic and oligosaprobic condition in summer, while eutrophic and α-mesosaprobic conditions were observed in spring, autumn, and winter. Spatially, Bo Lake was classified as oligotrophic–mesotrophic and oligosaprobic, Huangda Lake as mesotrophic and α-mesosaprobic, and Longgan Lake as eutrophic and β-mesosaprobic. Overall, the zooplankton community structure in the Huayanghe Lakes exhibited significant spatiotemporal heterogeneity, driven by multiple environmental factors, including nutrients, suspended solids, and dissolved oxygen. These findings provide a scientific basis for ecological protection, eutrophication control, and drinking water source management in the Huayanghe Lakes.
Zooplankton community structure is a key indicator of lake ecosystem health. Understanding its spatiotemporal dynamics and environmental drivers is of great significance for ecological conservation and water environment management. The Huayanghe Lakes, located in the middle and lower reaches of the Yangtze River, is a typical sluice-controlled river-connected lake group and an important regional drinking water source. Clarifying the spatiotemporal variations and driving mechanisms of metazoan zooplankton community structure in this lake group is therefore important for lake ecological protection, water quality improvement, and drinking water source management. In this study, systematic investigations of metazoan zooplankton community structure and physicochemical water parameters were conducted in the Huayanghe Lakes in April 2023 (spring), July 2023 (summer), October 2023 (autumn), and January 2024 (winter). Redundancy analysis (RDA) and variation partitioning analysis (VPA) were used to explore the main driving factors of community structure. During the survey period, a total of 67 metazoan zooplankton species belonging to 50 genera were identified, including 37 Rotifer species from 23 genera, 15 Cladoceran species from 14 genera, and 15 Copepod species from 13 genera. The abundance and biomass ranged from 21 to 956 ind./L and 2.83 to 17.09 mg/L, respectively. Temporally, metazoan zooplankton community structure showed obvious seasonal differences. Abundance was highest in autumn, biomass was highest in spring, and both abundance and biomass were lowest in summer. The number of dominant species, Shannon-Wiener diversity index, and Pielou evenness index were higher in autumn and winter than in spring and summer, whereas the Margalef richness index reached its maximum in summer. Spatially, metazoan zooplankton abundance and biomass followed the pattern: Longgan Lake > Huangda Lake > Bo Lake, while Margalef richness, Shannon–Wiener diversity, and Pielou’s evenness indices showed the opposite pattern: Bo Lake > Huangda Lake > Longgan Lake. Environmental driving analysis indicated that the key factors influencing metazoan zooplankton community structure varied across temporal and spatial scales. Temporally, zooplankton communities were positively correlated with suspended solids (SS) and ammonium nitrogen (NH4+-N) in spring, dissolved total phosphorus (DTP) and phosphate (PO?3?–P) in summer, phosphate (PO?3?–P) and permanganate index (CODMn) in autumn, and total phosphorus (TP) and dissolved oxygen (DO) in winter. Spatially, SS, PO?3?–P, and water transparency (SD) were the primary factors driving the community structure in Longgan Lake, Huangda Lake, and Bo Lake, respectively. The VPA results showed that water environmental factors and sluice-controlled hydrological factors jointly explained 54.7% of the variation in metazoan zooplankton community structure, with independent explanation rates of 28.1% for water environmental factors and 17.4% for hydrological factors, and a shared explanation rate of 9.2%. These results indicate that sluice-controlled water level processes play an important role in shaping community structure by affecting water exchange, suspended sediment transport, and nutrient distribution. Seasonally, the Huayanghe Lakes were in an oligotrophic–mesotrophic and oligosaprobic condition in summer, while eutrophic and α-mesosaprobic conditions were observed in spring, autumn, and winter. Spatially, Bo Lake was classified as oligotrophic–mesotrophic and oligosaprobic, Huangda Lake as mesotrophic and α-mesosaprobic, and Longgan Lake as eutrophic and β-mesosaprobic. Overall, the zooplankton community structure in the Huayanghe Lakes exhibited significant spatiotemporal heterogeneity, driven by multiple environmental factors, including nutrients, suspended solids, and dissolved oxygen. These findings provide a scientific basis for ecological protection, eutrophication control, and drinking water source management in the Huayanghe Lakes.
Available online: July 29, 2026
Abstract:
The river-lake-reservoir-pond composite water system in the middle and lower reaches of the Yangtze River represents a critical medium through which watershed hydrological connectivity interacts with ecological processes. However, the coordinated evolutionary dynamics of its multiple components and their underlying driving mechanisms remain inadequately understood. Most existing studies have focused on individual water-body types, which limits a systematic understanding of the dynamic interactions among components within the composite system and the coupled effects of multiple driving factors. Using thematic datasets derived from multi-source remote sensing imagery, this study integrates landscape pattern analysis with the Geographical Detector model to systematically characterize the spatiotemporal differentiation of composite water landscapes in the middle and lower reaches of the Yangtze River. In addition, the interactive effects of natural and anthropogenic driving factors are quantitatively identified. The results show that: (1) During the study period, the total area of composite water landscapes exhibited an overall increasing trend, while their internal structure underwent pronounced differentiation. Areas of rivers and channels, reservoirs and ponds, and shoal lands expanded, whereas lakes, tidal flats, and marsh wetlands continued to decline, highlighting the substantial restructuring of water systems driven by human activities. (2) Significant dynamic transitions occurred among landscape components within the composite water system. Some components experienced net gains, whereas others showed net losses, revealing complex trade-off relationships among water-landscape elements. (3) The overall landscape pattern became increasingly fragmented and complex. Indicators including the number of patches (NP), patch density (PD), edge density (ED), landscape shape index (LSI), Shannon’s diversity index (SHDI), and Shannon’s evenness index (SHEI) increased continuously, whereas the aggregation index (AI) declined. The responses of landscape metrics varied significantly among different water-body types, reflecting divergent evolutionary pathways. (4) The evolution of the composite water landscape was jointly driven by natural conditions and anthropogenic disturbances. Temperature and precipitation established the fundamental regional pattern, while changes in population density exerted particularly strong influences on processes such as lake shrinkage and marsh degradation. Overall, this study elucidates the structural evolution and driving mechanisms of the composite water system in the middle and lower reaches of the Yangtze River, providing a scientific basis for integrated watershed water-resource management, ecological restoration, and territorial spatial planning.
The river-lake-reservoir-pond composite water system in the middle and lower reaches of the Yangtze River represents a critical medium through which watershed hydrological connectivity interacts with ecological processes. However, the coordinated evolutionary dynamics of its multiple components and their underlying driving mechanisms remain inadequately understood. Most existing studies have focused on individual water-body types, which limits a systematic understanding of the dynamic interactions among components within the composite system and the coupled effects of multiple driving factors. Using thematic datasets derived from multi-source remote sensing imagery, this study integrates landscape pattern analysis with the Geographical Detector model to systematically characterize the spatiotemporal differentiation of composite water landscapes in the middle and lower reaches of the Yangtze River. In addition, the interactive effects of natural and anthropogenic driving factors are quantitatively identified. The results show that: (1) During the study period, the total area of composite water landscapes exhibited an overall increasing trend, while their internal structure underwent pronounced differentiation. Areas of rivers and channels, reservoirs and ponds, and shoal lands expanded, whereas lakes, tidal flats, and marsh wetlands continued to decline, highlighting the substantial restructuring of water systems driven by human activities. (2) Significant dynamic transitions occurred among landscape components within the composite water system. Some components experienced net gains, whereas others showed net losses, revealing complex trade-off relationships among water-landscape elements. (3) The overall landscape pattern became increasingly fragmented and complex. Indicators including the number of patches (NP), patch density (PD), edge density (ED), landscape shape index (LSI), Shannon’s diversity index (SHDI), and Shannon’s evenness index (SHEI) increased continuously, whereas the aggregation index (AI) declined. The responses of landscape metrics varied significantly among different water-body types, reflecting divergent evolutionary pathways. (4) The evolution of the composite water landscape was jointly driven by natural conditions and anthropogenic disturbances. Temperature and precipitation established the fundamental regional pattern, while changes in population density exerted particularly strong influences on processes such as lake shrinkage and marsh degradation. Overall, this study elucidates the structural evolution and driving mechanisms of the composite water system in the middle and lower reaches of the Yangtze River, providing a scientific basis for integrated watershed water-resource management, ecological restoration, and territorial spatial planning.
Guo Song, Peng Kaida, Xu Dong, Ji Yachan, Dai Anni, Gao Yinwei, Zhang Hui, Liao Mingjun, Wan Liang, Gao Jian
Available online: July 21, 2026
Abstract:
Lake Nanhu, a typical shallow urban lake in the middle and lower reaches of the Yangtze River, has undergone ecological evolution characterized by typical urban eutrophication due to long?term intensive anthropogenic activities. To reveal its long?term ecological response under continuous restoration efforts, this study integrated historical literature data from 1991-2022 with systematic field monitoring conducted from February 2023 to January 2025, analyzing the evolving trends, current status, and influencing factors of water quality and phytoplankton. Long?term data indicate that nitrogen and phosphorus concentrations followed three distinct phases: (1) a fluctuating rise beginning in the 1990s; (2) persistently high levels from 2003 to 2020, nitrogen and phosphorus concentrations persistently exceeded the Grade?V standard of China’s “Environmental Quality Standards for Surface Water” (GB 3838?2002); and (3) a downward trend after 2020, reflecting the initial effectiveness of implemented governance measures. Accordingly, phytoplankton abundance reached a peak of 1191.94 × 10? cells/L in summer 2017-2018 but declined markedly during 2023-2025. Nevertheless, the annual mean chlorophyll?a concentration remained high (61.08 μg/?L), indicating a continued risk of algal blooms. Recent monitoring showed that phytoplankton in Lake Nanhu were dominated by Cyanobacteria such as Pseudoanabaena and Microcystis in summer and autumn, with potentially toxigenic algae contributing up to 81% of total abundance, while Bacillariophyta, mainly represented by Cyclotella, prevailed in winter and spring. Both Pearson correlation and redundancy analysis (RDA) identified total phosphorus and water temperature as key environmental factors driving phytoplankton biomass and the dynamics of potentially toxigenic cyanobacteria. The results demonstrate that although long?term management has sub-stantially reduced nitrogen and phosphorus concentrations, phosphorus loading and its synergistic effect with water tem-perature remain critical in regulating algal biomass and sustaining the competitive advantage of toxigenic cyanobacteria. Therefore, future strategies must continue to strengthen the control of external phosphorus inputs and the suppression of internal phosphorus release.
Lake Nanhu, a typical shallow urban lake in the middle and lower reaches of the Yangtze River, has undergone ecological evolution characterized by typical urban eutrophication due to long?term intensive anthropogenic activities. To reveal its long?term ecological response under continuous restoration efforts, this study integrated historical literature data from 1991-2022 with systematic field monitoring conducted from February 2023 to January 2025, analyzing the evolving trends, current status, and influencing factors of water quality and phytoplankton. Long?term data indicate that nitrogen and phosphorus concentrations followed three distinct phases: (1) a fluctuating rise beginning in the 1990s; (2) persistently high levels from 2003 to 2020, nitrogen and phosphorus concentrations persistently exceeded the Grade?V standard of China’s “Environmental Quality Standards for Surface Water” (GB 3838?2002); and (3) a downward trend after 2020, reflecting the initial effectiveness of implemented governance measures. Accordingly, phytoplankton abundance reached a peak of 1191.94 × 10? cells/L in summer 2017-2018 but declined markedly during 2023-2025. Nevertheless, the annual mean chlorophyll?a concentration remained high (61.08 μg/?L), indicating a continued risk of algal blooms. Recent monitoring showed that phytoplankton in Lake Nanhu were dominated by Cyanobacteria such as Pseudoanabaena and Microcystis in summer and autumn, with potentially toxigenic algae contributing up to 81% of total abundance, while Bacillariophyta, mainly represented by Cyclotella, prevailed in winter and spring. Both Pearson correlation and redundancy analysis (RDA) identified total phosphorus and water temperature as key environmental factors driving phytoplankton biomass and the dynamics of potentially toxigenic cyanobacteria. The results demonstrate that although long?term management has sub-stantially reduced nitrogen and phosphorus concentrations, phosphorus loading and its synergistic effect with water tem-perature remain critical in regulating algal biomass and sustaining the competitive advantage of toxigenic cyanobacteria. Therefore, future strategies must continue to strengthen the control of external phosphorus inputs and the suppression of internal phosphorus release.
Available online: July 20, 2026
Abstract:
Influenced by eutrophication and water system connectivity in typical lake-dominated water network areas (e.g., Taihu Lake), the invasive species Pomacea canaliculata frequently outbreaks in lakeside wetlands, park lakes, and rural water bodies. Due to its strong reproductive capacity and high environmental adaptability, Pomacea canaliculata has become widely established and continues to spread in this region, posing a serious threat to freshwater and agricultural ecosystems. Previous detection studies mainly relied on a single Unmanned Aerial Vehicle (UAV) or Unmanned Surface Vehicle (USV) platform, which struggled to balance large-scale screening and fine-grained identification due to limitations in viewing angle and operational efficiency. This study employs UAV–USV collaborative monitoring technology combined with deep learning methods to construct an “aerial screening–area projection–close-range verification” collaborative detection framework. Two independent datasets are established from UAV aerial imagery and USV close-range observations, covering typical water bodies, including lakeside zones, wetland parks, and rural villages. The results show that: (1) the proposed DBSCAN (Density-Based Spatial Clustering of Applications with Noise) density clustering method effectively generates community-level annotations, improving detection accuracy for dense small targets; (2) the improved UAV-side and USV-side models achieve mAP@0.5 values of 0.946 and 0.968, respectively, maintaining stable detection performance under complex water environments; (3) the air–water collaborative framework fully leverages the complementary advantages of UAV wide-area coverage and USV fine-scale observation, significantly improving detection efficiency and spatial localization accuracy. This study provides technical support for the precise prevention and control of Pomacea canaliculata in typical lake-dominated water network areas and offers a methodological reference for monitoring other aquatic invasive species in the future.
Influenced by eutrophication and water system connectivity in typical lake-dominated water network areas (e.g., Taihu Lake), the invasive species Pomacea canaliculata frequently outbreaks in lakeside wetlands, park lakes, and rural water bodies. Due to its strong reproductive capacity and high environmental adaptability, Pomacea canaliculata has become widely established and continues to spread in this region, posing a serious threat to freshwater and agricultural ecosystems. Previous detection studies mainly relied on a single Unmanned Aerial Vehicle (UAV) or Unmanned Surface Vehicle (USV) platform, which struggled to balance large-scale screening and fine-grained identification due to limitations in viewing angle and operational efficiency. This study employs UAV–USV collaborative monitoring technology combined with deep learning methods to construct an “aerial screening–area projection–close-range verification” collaborative detection framework. Two independent datasets are established from UAV aerial imagery and USV close-range observations, covering typical water bodies, including lakeside zones, wetland parks, and rural villages. The results show that: (1) the proposed DBSCAN (Density-Based Spatial Clustering of Applications with Noise) density clustering method effectively generates community-level annotations, improving detection accuracy for dense small targets; (2) the improved UAV-side and USV-side models achieve mAP@0.5 values of 0.946 and 0.968, respectively, maintaining stable detection performance under complex water environments; (3) the air–water collaborative framework fully leverages the complementary advantages of UAV wide-area coverage and USV fine-scale observation, significantly improving detection efficiency and spatial localization accuracy. This study provides technical support for the precise prevention and control of Pomacea canaliculata in typical lake-dominated water network areas and offers a methodological reference for monitoring other aquatic invasive species in the future.
Available online: July 17, 2026
Abstract:
Reactive oxygen species (ROS) are a class of highly reactive oxygen-containing intermediates that are ubiquitous in lake waters, mainly including superoxide radical (O2?·), hydrogen peroxide (H2O2), hydroxyl radical (·OH), singlet oxygen (1O2), and triplet excited dissolved organic matter (3DOM*). In lake ecosystems, ROS can be generated through multiple pathways, including photochemical reactions, microbial metabolism, metal-mediated redox reactions, and sediment–water interface processes, and are jointly regulated by water depth, thermal stratification, dissolved organic matter composition, as well as inorganic ions and metal cycling. In shallow lakes, stronger light penetration and more intensive water mixing facilitate the dispersion of ROS throughout the water column and support relatively high concentration levels. In contrast, ROS in deep stratified lakes usually exhibit pronounced vertical heterogeneity, with photochemical production dominating in the surface layer, whereas interface-related processes and dark biological processes become increasingly important in the thermocline and bottom waters. ROS play important roles in lake water quality and ecosystem evolution. They participate in the cycling of biogenic elements, including carbon, nitrogen, phosphorus, iron, and manganese, influence the attenuation and transformation of pollutants, and affect lake ecosystem structure by regulating community composition and biological metabolism. Owing to their strong oxidative capacity and environmental compatibility, ROS also show broad application potential in lake pollution control and ecological restoration, including ROS-enhanced degradation and purification of water contaminants, as well as targeted ROS generation for precise regulation and restoration of lake ecosystems. It should be noted that the behavior and eco-environmental effects of ROS in lakes are closely related to their formation pathways, steady-state concentrations, and dominant species. Differences among ROS in oxidative capacity, reaction selectivity, and spatial distribution determine their distinct roles in lake waters. This review systematically summarizes the spatiotemporal occurrence characteristics, biotic and abiotic formation mechanisms, and eco-environmental effects of ROS in lake waters, and further discusses future research directions, with the aim of providing theoretical guidance and technical support for understanding lake habitat evolution, assessing ecosystem status, and improving the control and management of polluted lakes.
Reactive oxygen species (ROS) are a class of highly reactive oxygen-containing intermediates that are ubiquitous in lake waters, mainly including superoxide radical (O2?·), hydrogen peroxide (H2O2), hydroxyl radical (·OH), singlet oxygen (1O2), and triplet excited dissolved organic matter (3DOM*). In lake ecosystems, ROS can be generated through multiple pathways, including photochemical reactions, microbial metabolism, metal-mediated redox reactions, and sediment–water interface processes, and are jointly regulated by water depth, thermal stratification, dissolved organic matter composition, as well as inorganic ions and metal cycling. In shallow lakes, stronger light penetration and more intensive water mixing facilitate the dispersion of ROS throughout the water column and support relatively high concentration levels. In contrast, ROS in deep stratified lakes usually exhibit pronounced vertical heterogeneity, with photochemical production dominating in the surface layer, whereas interface-related processes and dark biological processes become increasingly important in the thermocline and bottom waters. ROS play important roles in lake water quality and ecosystem evolution. They participate in the cycling of biogenic elements, including carbon, nitrogen, phosphorus, iron, and manganese, influence the attenuation and transformation of pollutants, and affect lake ecosystem structure by regulating community composition and biological metabolism. Owing to their strong oxidative capacity and environmental compatibility, ROS also show broad application potential in lake pollution control and ecological restoration, including ROS-enhanced degradation and purification of water contaminants, as well as targeted ROS generation for precise regulation and restoration of lake ecosystems. It should be noted that the behavior and eco-environmental effects of ROS in lakes are closely related to their formation pathways, steady-state concentrations, and dominant species. Differences among ROS in oxidative capacity, reaction selectivity, and spatial distribution determine their distinct roles in lake waters. This review systematically summarizes the spatiotemporal occurrence characteristics, biotic and abiotic formation mechanisms, and eco-environmental effects of ROS in lake waters, and further discusses future research directions, with the aim of providing theoretical guidance and technical support for understanding lake habitat evolution, assessing ecosystem status, and improving the control and management of polluted lakes.
Available online: July 17, 2026
Abstract:
Gate-controlled operation is a crucial strategy for water resources management in coastal plain river networks. However, the strong hydrodynamic disturbances it triggers can easily induce sediment resuspension, leading to a surge in Sediment Oxygen Demand (SOD), which subsequently alters dissolved oxygen (DO) dynamics and induces hypoxia risks. To reveal the response mechanism between hydrodynamics and SOD under gated conditions, this study takes Jinhuigang River in Shanghai as a case study. Based on in-situ hydrological and water quality monitoring and sediment sampling, a one-dimensional hydrodynamic model considering tributary effects was constructed. Combined with an SOD prediction model established via sediment oxygen consumption kinetic experiments, the coupling characteristics of hydrodynamic conditions and SOD under different water diversion intensities were systematically analyzed. The results indicate that: (1) The constructed one-dimensional model effectively simulates the hydrodynamic evolution process in the gated channel, accurately capturing the longitudinal propagation and lag effects of hydrodynamic disturbances; (2) Gate-controlled water diversion significantly enhances channel hydrodynamic intensity, with SOD showing an overall increasing trend as the diversion scale increases, while exhibiting significant spatial heterogeneity; (3) Under strong hydrodynamic disturbances, SOD shows a stable positive linear response to flow velocity. Flow velocity acts as the dominant mechanism amplifying SOD by increasing the equivalent suspended sediment thickness (hs) and accelerating the exposure and release of oxygen-consuming substances. This study reveals the key response chain of "hydrodynamic enhancement—sediment resuspension—SOD amplification" under gated scenarios, providing a theoretical basis for refined water quality operation and hypoxia risk prevention in plain gated rivers.
Gate-controlled operation is a crucial strategy for water resources management in coastal plain river networks. However, the strong hydrodynamic disturbances it triggers can easily induce sediment resuspension, leading to a surge in Sediment Oxygen Demand (SOD), which subsequently alters dissolved oxygen (DO) dynamics and induces hypoxia risks. To reveal the response mechanism between hydrodynamics and SOD under gated conditions, this study takes Jinhuigang River in Shanghai as a case study. Based on in-situ hydrological and water quality monitoring and sediment sampling, a one-dimensional hydrodynamic model considering tributary effects was constructed. Combined with an SOD prediction model established via sediment oxygen consumption kinetic experiments, the coupling characteristics of hydrodynamic conditions and SOD under different water diversion intensities were systematically analyzed. The results indicate that: (1) The constructed one-dimensional model effectively simulates the hydrodynamic evolution process in the gated channel, accurately capturing the longitudinal propagation and lag effects of hydrodynamic disturbances; (2) Gate-controlled water diversion significantly enhances channel hydrodynamic intensity, with SOD showing an overall increasing trend as the diversion scale increases, while exhibiting significant spatial heterogeneity; (3) Under strong hydrodynamic disturbances, SOD shows a stable positive linear response to flow velocity. Flow velocity acts as the dominant mechanism amplifying SOD by increasing the equivalent suspended sediment thickness (hs) and accelerating the exposure and release of oxygen-consuming substances. This study reveals the key response chain of "hydrodynamic enhancement—sediment resuspension—SOD amplification" under gated scenarios, providing a theoretical basis for refined water quality operation and hypoxia risk prevention in plain gated rivers.
Available online: July 15, 2026
Abstract:
Cylindrospermopsis raciborskii is a bloom-forming cyanobacterium that has attracted global attention following Microcystis and is currently expanding rapidly in southern China. To investigate the distribution patterns and driving factors of C. raciborskii in this area, a field survey was conducted during the dry season in 100 reservoirs across seven river basins of Guangdong Province. The abundance of C. raciborskii was quantified using Real-time quantitative PCR targeting the rpoC1 gene. The results showed that C. raciborskii was detected in all collected samples, with abundances ranging from 4.98×10? to 4.23×10? cells/L. The abundance varied by up to four orders of magnitude among reservoirs, indicating substantial spatial variability in population size. Principal component analysis revealed that spatial variation in environmental factors among reservoirs across river basins in Guangdong Province was primarily driven by nitrogen, phosphorus, and water temperature. At the basin scale, the mean abundance of C. raciborskii in the Pearl River Delta and the western Guangdong coastal river basins was significantly higher than that in the Xijiang, Hanjiang, and Beijiang basins. These two basins were also the most severely affected by C. raciborskii blooms, with heavy blooms occurring in 10 reservoirs. According to the Australian risk classification system for cyanobacterial blooms based on C. raciborskii abundance, 53% of the surveyed reservoirs were categorized as low risk, whereas 23% were classified as Alert Level 2. The binary classification machine learning models of Extreme Gradient Boosting (XGBoost) and Random Forest (RF) together with multiple linear stepwise regression analysis indicated a significant positive relationship between the C. raciborskii abundance and trophic state index (TSI). These results suggest that eutrophication level is the primary driver of the spatial variation in C. raciborskii abundance among reservoirs in Guangdong Province.
Cylindrospermopsis raciborskii is a bloom-forming cyanobacterium that has attracted global attention following Microcystis and is currently expanding rapidly in southern China. To investigate the distribution patterns and driving factors of C. raciborskii in this area, a field survey was conducted during the dry season in 100 reservoirs across seven river basins of Guangdong Province. The abundance of C. raciborskii was quantified using Real-time quantitative PCR targeting the rpoC1 gene. The results showed that C. raciborskii was detected in all collected samples, with abundances ranging from 4.98×10? to 4.23×10? cells/L. The abundance varied by up to four orders of magnitude among reservoirs, indicating substantial spatial variability in population size. Principal component analysis revealed that spatial variation in environmental factors among reservoirs across river basins in Guangdong Province was primarily driven by nitrogen, phosphorus, and water temperature. At the basin scale, the mean abundance of C. raciborskii in the Pearl River Delta and the western Guangdong coastal river basins was significantly higher than that in the Xijiang, Hanjiang, and Beijiang basins. These two basins were also the most severely affected by C. raciborskii blooms, with heavy blooms occurring in 10 reservoirs. According to the Australian risk classification system for cyanobacterial blooms based on C. raciborskii abundance, 53% of the surveyed reservoirs were categorized as low risk, whereas 23% were classified as Alert Level 2. The binary classification machine learning models of Extreme Gradient Boosting (XGBoost) and Random Forest (RF) together with multiple linear stepwise regression analysis indicated a significant positive relationship between the C. raciborskii abundance and trophic state index (TSI). These results suggest that eutrophication level is the primary driver of the spatial variation in C. raciborskii abundance among reservoirs in Guangdong Province.
Available online: July 14, 2026
Abstract:
Current is the core driver of energy and material transport in lake systems and exerts a decisive influence on the distribution of pollutants, algae, and fish. Clarifying the spatiotemporal variability of lake currents is essential for understanding the mechanisms underlying lake ecological and environmental problems and for supporting precise management strategies. Based on high-frequency synchronous observations of wind and current fields from 20 automatic monitoring stations in Lake Chaohu in 2024, this study systematically analyzed the spatiotemporal characteristics of the wind and current fields and explored their response relationships and driving mechanisms. Vector decomposition, Pearson correlation analysis, and circular statistical methods were employed to construct indices including the coefficient of variation of current velocity, directional dispersion coefficient, and composite current velocity ratio, thereby quantitatively evaluating current stability and dynamic characteristics across multiple temporal scales.The results indicate that the wind field over Lake Chaohu is controlled by the East Asian monsoon circulation and exhibits pronounced seasonal transition characteristics. In 2024, the basin-wide mean wind speed was approximately 3.4 m/s, with easterly winds prevailing in spring, southerly winds in summer, northeasterly winds in autumn, and northerly winds in winter. The current field in Lake Chaohu generally exhibited a weak “west-in–east-out” transport pattern, with mean current velocities at individual stations ranging from 3.75 to 9.27 cm/s and a basin-wide mean of 5.18 cm/s. High-velocity zones were mainly distributed in river inflow and outflow estuaries and flow passages on both sides of Laoshan Island, whereas the northwestern lake region, central lake area, and some nearshore zones remained under low-velocity conditions.Vertical current velocities in Lake Chaohu were only on the order of mm/s, indicating limited vertical exchange capacity. The current field exhibited significant fluctuations across seasonal, monthly, and daily scales. Basin-wide vector-averaged current velocities in spring and summer were 0.92 cm/s and 0.89 cm/s, respectively, both substantially higher than the 0.53 cm/s observed in autumn and winter. During the “Yangtze River-to-Lake Chaohu Water Diversion Project” period, daily mean current velocities in the Zhao River inflow region remained between 9.69 and 14.82 cm/s. At eight national monitoring stations, the mean coefficient of variation of current velocity reached 94.06%, the directional dispersion coefficient ranged from 73.5% to 95.8%, and the mean composite current velocity ratio was only 0.28, indicating that the Lake Chaohu current field is characterized by “low velocity, high variability, and strong directional dispersion.”Wind speed and current velocity showed a significant positive correlation overall (p < 0.01), indicating that wind forcing is the primary driver controlling current variability in Lake Chaohu. However, substantial differences were observed in the response intensity of currents to wind forcing among different sites, suggesting that the current field structure is jointly influenced by multiple factors, including lake basin morphology and inflow–outflow discharge conditions. These findings provide a scientific basis for hydrodynamic regulation, identification of weak-flow retention zones, and the prevention and control of eutrophication and algal blooms in shallow lakes.
Current is the core driver of energy and material transport in lake systems and exerts a decisive influence on the distribution of pollutants, algae, and fish. Clarifying the spatiotemporal variability of lake currents is essential for understanding the mechanisms underlying lake ecological and environmental problems and for supporting precise management strategies. Based on high-frequency synchronous observations of wind and current fields from 20 automatic monitoring stations in Lake Chaohu in 2024, this study systematically analyzed the spatiotemporal characteristics of the wind and current fields and explored their response relationships and driving mechanisms. Vector decomposition, Pearson correlation analysis, and circular statistical methods were employed to construct indices including the coefficient of variation of current velocity, directional dispersion coefficient, and composite current velocity ratio, thereby quantitatively evaluating current stability and dynamic characteristics across multiple temporal scales.The results indicate that the wind field over Lake Chaohu is controlled by the East Asian monsoon circulation and exhibits pronounced seasonal transition characteristics. In 2024, the basin-wide mean wind speed was approximately 3.4 m/s, with easterly winds prevailing in spring, southerly winds in summer, northeasterly winds in autumn, and northerly winds in winter. The current field in Lake Chaohu generally exhibited a weak “west-in–east-out” transport pattern, with mean current velocities at individual stations ranging from 3.75 to 9.27 cm/s and a basin-wide mean of 5.18 cm/s. High-velocity zones were mainly distributed in river inflow and outflow estuaries and flow passages on both sides of Laoshan Island, whereas the northwestern lake region, central lake area, and some nearshore zones remained under low-velocity conditions.Vertical current velocities in Lake Chaohu were only on the order of mm/s, indicating limited vertical exchange capacity. The current field exhibited significant fluctuations across seasonal, monthly, and daily scales. Basin-wide vector-averaged current velocities in spring and summer were 0.92 cm/s and 0.89 cm/s, respectively, both substantially higher than the 0.53 cm/s observed in autumn and winter. During the “Yangtze River-to-Lake Chaohu Water Diversion Project” period, daily mean current velocities in the Zhao River inflow region remained between 9.69 and 14.82 cm/s. At eight national monitoring stations, the mean coefficient of variation of current velocity reached 94.06%, the directional dispersion coefficient ranged from 73.5% to 95.8%, and the mean composite current velocity ratio was only 0.28, indicating that the Lake Chaohu current field is characterized by “low velocity, high variability, and strong directional dispersion.”Wind speed and current velocity showed a significant positive correlation overall (p < 0.01), indicating that wind forcing is the primary driver controlling current variability in Lake Chaohu. However, substantial differences were observed in the response intensity of currents to wind forcing among different sites, suggesting that the current field structure is jointly influenced by multiple factors, including lake basin morphology and inflow–outflow discharge conditions. These findings provide a scientific basis for hydrodynamic regulation, identification of weak-flow retention zones, and the prevention and control of eutrophication and algal blooms in shallow lakes.
Available online: July 13, 2026
Abstract:
Studying water-level amplitude in plateau shallow lakes provides a critical perspective for understanding human–environment interactions and associated ecological risks. However, long-term continuous records of lake-level variation are scarce due to the relatively late establishment of modern monitoring. Using Qilu Lake in Yunnan Province as a case study, this research synthesizes multiple lines of evidence—including settlement distribution, palaeoshoreline geomorphology, historical documents, early maps, and remote sensing—to reconstruct seasonal lake extents (wet and dry seasons) for six representative years (1284, 1523, 1691, 1798, 1894, and 1937). Combined with documentary records, we further derive a characteristic series of water-level amplitude for the period 1284–1955. The results show that the main basin morphology remained generally stable under topographic constraints, while changes in lake extent were concentrated in reclamation-prone areas such as the shoals and deltaic margins along the western shore and the southern and northern shores. These changes are manifested as outward advancement of embankment lines and progressive enclosure of bays, with a gradual reduction in the space available for wet-season lake expansion. Over the past 600 years, the water-level amplitude of Qilu Lake exhibits a step-like decline superimposed on internal variability. Two notable downward shifts occurred around 1523 and 1691, marking phase changes in amplitude, whereas strong human intervention in outflow channels around 1894 did not trigger such a shift. Mechanism analysis indicates that variations in water-level amplitude were jointly driven by climatic windows and engineered interventions, with governance capacity acting as a key mediator. Specifically, warm–dry climatic phases provided implementation windows for reclamation, dredging, and outlet modification by lowering lake levels and promoting the stabilization of exposed lakebeds. Whether a downward shift in amplitude occurred depended on whether institutions could translate such short-term interventions into sustained engineering practices and maintain their effects over time. This study offers a traceable, process-based framework for identifying historical phase shifts and evaluating governance pathways in plateau shallow lakes.
Studying water-level amplitude in plateau shallow lakes provides a critical perspective for understanding human–environment interactions and associated ecological risks. However, long-term continuous records of lake-level variation are scarce due to the relatively late establishment of modern monitoring. Using Qilu Lake in Yunnan Province as a case study, this research synthesizes multiple lines of evidence—including settlement distribution, palaeoshoreline geomorphology, historical documents, early maps, and remote sensing—to reconstruct seasonal lake extents (wet and dry seasons) for six representative years (1284, 1523, 1691, 1798, 1894, and 1937). Combined with documentary records, we further derive a characteristic series of water-level amplitude for the period 1284–1955. The results show that the main basin morphology remained generally stable under topographic constraints, while changes in lake extent were concentrated in reclamation-prone areas such as the shoals and deltaic margins along the western shore and the southern and northern shores. These changes are manifested as outward advancement of embankment lines and progressive enclosure of bays, with a gradual reduction in the space available for wet-season lake expansion. Over the past 600 years, the water-level amplitude of Qilu Lake exhibits a step-like decline superimposed on internal variability. Two notable downward shifts occurred around 1523 and 1691, marking phase changes in amplitude, whereas strong human intervention in outflow channels around 1894 did not trigger such a shift. Mechanism analysis indicates that variations in water-level amplitude were jointly driven by climatic windows and engineered interventions, with governance capacity acting as a key mediator. Specifically, warm–dry climatic phases provided implementation windows for reclamation, dredging, and outlet modification by lowering lake levels and promoting the stabilization of exposed lakebeds. Whether a downward shift in amplitude occurred depended on whether institutions could translate such short-term interventions into sustained engineering practices and maintain their effects over time. This study offers a traceable, process-based framework for identifying historical phase shifts and evaluating governance pathways in plateau shallow lakes.
Available online: July 13, 2026
Abstract:
Potential evapotranspiration (PET) is a key parameter in hydrological cycle and ecological process research, and is currently mostly calculated using the Penman-Monteith (P-M) equation. However, direct measurement of PET is usually difficult, resulting in a lack of empirical verification for calculation results and unknown uncertainty. Based on the underlying surface characteristics of the Poyang Lake floodplain wetland, this study used latent heat flux observation data from an eddy covariance system, drew on Granger"s (1989) conceptual analysis of potential evapotranspiration, and combined multiple accuracy evaluation indicators to test the calculation results of the P-M equation under different temperature input conditions. Comprehensive analysis shows that the PET values calculated by different methods are highly consistent with the measured data, but the PET using surface temperature as input is closest to the observed latent heat flux and can better reflect the temporal variation characteristics of potential evapotranspiration. This research result helps to further clarify the sensitivity of potential evapotranspiration to temperature, improve the reliability of calculation results, and has positive theoretical significance and practical reference value.
Potential evapotranspiration (PET) is a key parameter in hydrological cycle and ecological process research, and is currently mostly calculated using the Penman-Monteith (P-M) equation. However, direct measurement of PET is usually difficult, resulting in a lack of empirical verification for calculation results and unknown uncertainty. Based on the underlying surface characteristics of the Poyang Lake floodplain wetland, this study used latent heat flux observation data from an eddy covariance system, drew on Granger"s (1989) conceptual analysis of potential evapotranspiration, and combined multiple accuracy evaluation indicators to test the calculation results of the P-M equation under different temperature input conditions. Comprehensive analysis shows that the PET values calculated by different methods are highly consistent with the measured data, but the PET using surface temperature as input is closest to the observed latent heat flux and can better reflect the temporal variation characteristics of potential evapotranspiration. This research result helps to further clarify the sensitivity of potential evapotranspiration to temperature, improve the reliability of calculation results, and has positive theoretical significance and practical reference value.
Ke Senfan, ZHU Shilong, LI Dongqing, Duan Xinbin, Yu Lixiong, Gao Shenghui, JIAO Yilin, HU Yizhong, Cheng Bixin, Shi Xiaotao
Available online: July 13, 2026
Abstract:
The upstream post-dam movement strategies of fish constitute an important basis for evaluating habitat suitability in dam-affected river reaches. In particular, how the typical abrupt hydraulic characteristics of mountainous rivers influence post-dam upstream migration behaviour remains an urgent question to be addressed. In this study, two representative loach species from the Heishui River in the Jinsha River basin, the red-tailed loach Paracobitis variegatus and the short-bodied loach Paracobitis potanini, were selected as target species. Fish resources of the target species were investigated using net-capture surveys, and radio frequency identification (RFID) technology was applied to evaluate the post-dam upstream migration performance of the two loach species. A quantitative evaluation model of post-dam upstream migration performance for loaches was developed by coupling hydrological and hydrodynamic factors of the reservoir area, in order to identify the key factors influencing post-dam upstream migration performance and to establish response curves between upstream migration success and these key factors. The results showed that: (1) the fishway passage rates of the two loach species in 2022, 2023, and 2024 were 22.92%, 9.01%, and 7.00%, respectively; (2) after dam passage, loaches exhibited different proportions of habitat selection, with 85% remaining in the near-dam reservoir area, 15% continuing upstream to 0.7 km above the dam, and no loaches migrating to 1.3 km above the dam; (3) the dominant factors affecting post-dam upstream migration performance were fish species, river discharge, and river water temperature; (4) post-dam upstream migration success was significantly negatively correlated with river discharge and water temperature (P < 0.05), and the upstream migration success of P. potanini was significantly higher than that of P. variegatus (P < 0.05); and (5) surveys of post-dam loach distribution and substrate characteristics indicated that loaches were mainly distributed in areas characterized by mixed cobble and silt substrates. This study provides an important reference for ecological operation of small hydropower stations and post-dam habitat restoration in the Jinsha River basin.
The upstream post-dam movement strategies of fish constitute an important basis for evaluating habitat suitability in dam-affected river reaches. In particular, how the typical abrupt hydraulic characteristics of mountainous rivers influence post-dam upstream migration behaviour remains an urgent question to be addressed. In this study, two representative loach species from the Heishui River in the Jinsha River basin, the red-tailed loach Paracobitis variegatus and the short-bodied loach Paracobitis potanini, were selected as target species. Fish resources of the target species were investigated using net-capture surveys, and radio frequency identification (RFID) technology was applied to evaluate the post-dam upstream migration performance of the two loach species. A quantitative evaluation model of post-dam upstream migration performance for loaches was developed by coupling hydrological and hydrodynamic factors of the reservoir area, in order to identify the key factors influencing post-dam upstream migration performance and to establish response curves between upstream migration success and these key factors. The results showed that: (1) the fishway passage rates of the two loach species in 2022, 2023, and 2024 were 22.92%, 9.01%, and 7.00%, respectively; (2) after dam passage, loaches exhibited different proportions of habitat selection, with 85% remaining in the near-dam reservoir area, 15% continuing upstream to 0.7 km above the dam, and no loaches migrating to 1.3 km above the dam; (3) the dominant factors affecting post-dam upstream migration performance were fish species, river discharge, and river water temperature; (4) post-dam upstream migration success was significantly negatively correlated with river discharge and water temperature (P < 0.05), and the upstream migration success of P. potanini was significantly higher than that of P. variegatus (P < 0.05); and (5) surveys of post-dam loach distribution and substrate characteristics indicated that loaches were mainly distributed in areas characterized by mixed cobble and silt substrates. This study provides an important reference for ecological operation of small hydropower stations and post-dam habitat restoration in the Jinsha River basin.
Available online: July 08, 2026
Abstract:
Intense climate change and intensified human activities have profoundly altered river hydrological processes, exerting significant impacts on the health and security of fluvial aquatic ecosystems. Following the research paradigm of “spatiotemporal evolution?driving mechanism?causal pathways”, this study systematically analyzes the spatiotemporal variation characteristics and driving mechanisms of hydrological regime indices at 18 hydrological stations across the Nan?Beipan River Basin. The Bayesian Estimation of Abrupt change, Seasonality and Trend (BEAST) method is employed to identify non?stationarity and abrupt changes in runoff series, while the Indicators of Hydrologic Alteration?Range of Variability Approach (IHA?RVA) is used to quantify the degree of hydrological regime alteration before and after dam construction. Combined with Extreme Gradient Boosting?SHapley Additive exPlanations (XGBoost?SHAP), Optimal Multivariate Stratified Geodetector (OMGD) and Partial Least Squares?Structural Equation Modeling (PLS?SEM), this study further distinguishes single?factor, multi?factor effects and impact pathways of natural factors and human activities across the whole basin, regulated basins and natural basins. The results show that: (1) Abrupt runoff changes are highly consistent with regional drought and flood events; (2) Reservoir dams induce hydrological regime shifts characterized by decreased high?flow magnitudes and increased low?flow magnitudes, with dam?induced impacts gradually weakening with increasing distance; (3) XGBoost?SHAP results reveal that climatic factors dominate hydrological regime variations in different basins, whereas both OMGD and PLS?SEM indicate that coupled interactions between climate and river network/landscape/human activities are the primary controlling factors for the whole basin, regulated basins and natural basins respectively. Topography, lithology, soil and other factors only affect partial hydrological regime indices. Overall, hydrological regime indices in the karst Nan?Beipan River Basin exhibit nonlinear responses to climatic and underlying surface factors. Regulated basins are mainly governed by the “climate?landscape” coupling mode, while natural basins are dominated by the “climate?human activity” coupling mode. Both modes demonstrate high sensitivity to climate change. Enhanced human disturbances may increase vulnerability risks in natural basins, highlighting the urgent need to monitor and regulate anthropogenic impacts. Future basin water resource management should prioritize extreme hydrological events triggered by climate change, and pay close attention to potential ecological impacts of reservoir regulation and land?use changes (human activities).
Intense climate change and intensified human activities have profoundly altered river hydrological processes, exerting significant impacts on the health and security of fluvial aquatic ecosystems. Following the research paradigm of “spatiotemporal evolution?driving mechanism?causal pathways”, this study systematically analyzes the spatiotemporal variation characteristics and driving mechanisms of hydrological regime indices at 18 hydrological stations across the Nan?Beipan River Basin. The Bayesian Estimation of Abrupt change, Seasonality and Trend (BEAST) method is employed to identify non?stationarity and abrupt changes in runoff series, while the Indicators of Hydrologic Alteration?Range of Variability Approach (IHA?RVA) is used to quantify the degree of hydrological regime alteration before and after dam construction. Combined with Extreme Gradient Boosting?SHapley Additive exPlanations (XGBoost?SHAP), Optimal Multivariate Stratified Geodetector (OMGD) and Partial Least Squares?Structural Equation Modeling (PLS?SEM), this study further distinguishes single?factor, multi?factor effects and impact pathways of natural factors and human activities across the whole basin, regulated basins and natural basins. The results show that: (1) Abrupt runoff changes are highly consistent with regional drought and flood events; (2) Reservoir dams induce hydrological regime shifts characterized by decreased high?flow magnitudes and increased low?flow magnitudes, with dam?induced impacts gradually weakening with increasing distance; (3) XGBoost?SHAP results reveal that climatic factors dominate hydrological regime variations in different basins, whereas both OMGD and PLS?SEM indicate that coupled interactions between climate and river network/landscape/human activities are the primary controlling factors for the whole basin, regulated basins and natural basins respectively. Topography, lithology, soil and other factors only affect partial hydrological regime indices. Overall, hydrological regime indices in the karst Nan?Beipan River Basin exhibit nonlinear responses to climatic and underlying surface factors. Regulated basins are mainly governed by the “climate?landscape” coupling mode, while natural basins are dominated by the “climate?human activity” coupling mode. Both modes demonstrate high sensitivity to climate change. Enhanced human disturbances may increase vulnerability risks in natural basins, highlighting the urgent need to monitor and regulate anthropogenic impacts. Future basin water resource management should prioritize extreme hydrological events triggered by climate change, and pay close attention to potential ecological impacts of reservoir regulation and land?use changes (human activities).
Available online: July 08, 2026
Abstract:
Benthic diatoms are important primary producers in river ecosystems and serve as sensitive indicators of nutrient dynamics and ecological health. To elucidate the spatiotemporal distribution patterns of benthic diatom communities and their responses to environmental factors in the mainstream of the Fenhe River, seasonal surveys were conducted at 25 sampling sites along the mainstream during four seasons from April 2021 to January 2022. Community composition, diversity, and relationships with physicochemical variables were systematically investigated. The results indicated pronounced seasonal and spatial variations in benthic diatom communities. Diatoma moniliformis dominated in spring, autumn, and winter, whereas the abundance of Cyclotella meneghiniana increased markedly in summer. Although α-diversity indices showed no significant overall differences among seasons, clear spatial patterns were observed, with significantly higher values in the upstream reaches than in the middle and downstream reaches. β-diversity analyses demonstrated that both season (R2 = 0.143, P = 0.001) and river reach (R2 = 0.136, P = 0.001) exerted significant effects on community structure. Redundancy analysis (RDA) further revealed that water temperature, pH, dissolved oxygen, total dissolved solids, and total phosphorus were the principal environmental factors driving the distribution of benthic diatom communities.
Benthic diatoms are important primary producers in river ecosystems and serve as sensitive indicators of nutrient dynamics and ecological health. To elucidate the spatiotemporal distribution patterns of benthic diatom communities and their responses to environmental factors in the mainstream of the Fenhe River, seasonal surveys were conducted at 25 sampling sites along the mainstream during four seasons from April 2021 to January 2022. Community composition, diversity, and relationships with physicochemical variables were systematically investigated. The results indicated pronounced seasonal and spatial variations in benthic diatom communities. Diatoma moniliformis dominated in spring, autumn, and winter, whereas the abundance of Cyclotella meneghiniana increased markedly in summer. Although α-diversity indices showed no significant overall differences among seasons, clear spatial patterns were observed, with significantly higher values in the upstream reaches than in the middle and downstream reaches. β-diversity analyses demonstrated that both season (R2 = 0.143, P = 0.001) and river reach (R2 = 0.136, P = 0.001) exerted significant effects on community structure. Redundancy analysis (RDA) further revealed that water temperature, pH, dissolved oxygen, total dissolved solids, and total phosphorus were the principal environmental factors driving the distribution of benthic diatom communities.
Available online: July 02, 2026
Abstract:
This study investigates whether environmental stress alters the mechanisms by which biodiversity sustains ecosystem functioning and stability. To address this question, we established 48 freshwater mesocosms with submerged macrophyte communities and exposed them to two stressors: warming and pulsed surface runoff pollution. Results show that warming significantly increased the net biodiversity effect (NBE), whereas runoff pollution had no significant impact on functioning or its components. Complementarity effects remained the primary mechanism driving ecosystem functioning, with their positive relationship to functioning being unaffected by either stressor. Selection effects played a similarly important role in driving ecosystem functioning, but their correlation with functioning showed a weakening trend under pollution. Regarding stability, warming maintained overall ecosystem stability by reducing species asynchrony while simultaneously increasing average species stability, without altering the positive relationships between overall stability and these two components. Further analysis revealed that average species stability contributed more strongly to overall stability than species asynchrony, highlighting the dominant role of key species in stability maintenance. Path analysis indicated that warming indirectly buffered its potential negative effects on stability primarily by enhancing ecosystem functioning. While pollution induced a certain degree of species asynchrony, this positive regulatory effect was overridden by the pronounced biomass dominance of key species within the experimental scale. Overall, these findings suggest that the mechanisms by which biodiversity maintains ecosystem functioning and stability may shift under environmental stress, although these mechanisms still exhibited strong robustness under relatively moderate stress intensities. This study advances the understanding of how freshwater ecosystems respond to global change in terms of functioning and stability mechanisms, and provides a theoretical basis for ecosystem management and ecological risk assessment.
This study investigates whether environmental stress alters the mechanisms by which biodiversity sustains ecosystem functioning and stability. To address this question, we established 48 freshwater mesocosms with submerged macrophyte communities and exposed them to two stressors: warming and pulsed surface runoff pollution. Results show that warming significantly increased the net biodiversity effect (NBE), whereas runoff pollution had no significant impact on functioning or its components. Complementarity effects remained the primary mechanism driving ecosystem functioning, with their positive relationship to functioning being unaffected by either stressor. Selection effects played a similarly important role in driving ecosystem functioning, but their correlation with functioning showed a weakening trend under pollution. Regarding stability, warming maintained overall ecosystem stability by reducing species asynchrony while simultaneously increasing average species stability, without altering the positive relationships between overall stability and these two components. Further analysis revealed that average species stability contributed more strongly to overall stability than species asynchrony, highlighting the dominant role of key species in stability maintenance. Path analysis indicated that warming indirectly buffered its potential negative effects on stability primarily by enhancing ecosystem functioning. While pollution induced a certain degree of species asynchrony, this positive regulatory effect was overridden by the pronounced biomass dominance of key species within the experimental scale. Overall, these findings suggest that the mechanisms by which biodiversity maintains ecosystem functioning and stability may shift under environmental stress, although these mechanisms still exhibited strong robustness under relatively moderate stress intensities. This study advances the understanding of how freshwater ecosystems respond to global change in terms of functioning and stability mechanisms, and provides a theoretical basis for ecosystem management and ecological risk assessment.
Available online: June 30, 2026
Abstract:
he lakes in the Qinghai-Tibet Plateau are greatly affected by climate change. The lake expansion and salinity decline caused by rapid warming are changing the physical environment inside the lake, which in turn affects its ecological process. However, the differences in the vertical distribution of phytoplankton biomass between the thermal stratification period and the mixing period in plateau lakes are still not fully understood. Based on the comprehensive observation data of 10 large lakes in the plateau during the thermal stratification period and the mixing period from 2024 to 2025, combined with the historical high-resolution and continuous lake water temperature profile, this study analyzed the difference of phytoplankton biomass ( represented by chlorophyll a ) between the thermal stratification period and the mixing period, and discussed the regulation mechanism of thermal stability and density barrier driven by salinity gradient on the temporal and spatial displacement of chlorophyll a. The results showed that the change of lake thermal structure dominated the vertical differentiation of chlorophyll a, and the concentration of chlorophyll a in most lakes during the thermal mixing period was significantly lower than that during the thermal stratification period. During the thermal stratification period, the chlorophyll a in the lakes of Bamu Co, Selin Co and Zhari Namco showed a typical deep chlorophyll maximum ( DCM ) phenomenon in the vertical direction ( the peak concentration of chlorophyll a in Bamu Co was 6.15 μg / L and 4.10 μg / L in 2024 and 2025, respectively ). In 2024, the peak concentration of chlorophyll a in Zhari Namco was 7.10 μg / L ; in 2024, the peak concentration of chlorophyll a in Selin Co was 3.97 μg / L ), that is, the surface concentration was low, and a significant peak was formed in the thermocline with the increase of depth and reached the maximum value, and then gradually decreased in the deep water layer. Not all lakes follow this rule. For example, although there is thermal stratification in Peiku Co and Tangra Yumco, there is no significant difference in the vertical distribution of chlorophyll a concentration. In the thermal mixing period, the vertical distribution of chlorophyll a concentration in the lake was in a uniform distribution state, and the overall chlorophyll a concentration was at a low level ( the maximum chlorophyll a concentration in the mixing period of Zhari Namco in 2025 was 2.61 μg / L, and the maximum chlorophyll a concentration in Selin Co was 2.40 μg / L ). In addition, the high-salinity water in the lower layer ( below 20 m ) of Dagze Co formed a stable salinity thermocline, resulting in the lake maintaining a density stratification state throughout the year. This unique physical structure makes the vertical distribution pattern of chlorophyll a significantly different from other lakes only controlled by thermal stratification. The results of this study show that the change of thermal structure controls the vertical distribution pattern of chlorophyll a in plateau lakes, while the stable salinity stratification of Dagze Co can form a perennial effective physical barrier and dominate its unique vertical distribution pattern. Therefore, the vertical distribution characteristics of phytoplankton biomass in plateau lakes are determined by the thermal stratification and high salinity of lakes.
he lakes in the Qinghai-Tibet Plateau are greatly affected by climate change. The lake expansion and salinity decline caused by rapid warming are changing the physical environment inside the lake, which in turn affects its ecological process. However, the differences in the vertical distribution of phytoplankton biomass between the thermal stratification period and the mixing period in plateau lakes are still not fully understood. Based on the comprehensive observation data of 10 large lakes in the plateau during the thermal stratification period and the mixing period from 2024 to 2025, combined with the historical high-resolution and continuous lake water temperature profile, this study analyzed the difference of phytoplankton biomass ( represented by chlorophyll a ) between the thermal stratification period and the mixing period, and discussed the regulation mechanism of thermal stability and density barrier driven by salinity gradient on the temporal and spatial displacement of chlorophyll a. The results showed that the change of lake thermal structure dominated the vertical differentiation of chlorophyll a, and the concentration of chlorophyll a in most lakes during the thermal mixing period was significantly lower than that during the thermal stratification period. During the thermal stratification period, the chlorophyll a in the lakes of Bamu Co, Selin Co and Zhari Namco showed a typical deep chlorophyll maximum ( DCM ) phenomenon in the vertical direction ( the peak concentration of chlorophyll a in Bamu Co was 6.15 μg / L and 4.10 μg / L in 2024 and 2025, respectively ). In 2024, the peak concentration of chlorophyll a in Zhari Namco was 7.10 μg / L ; in 2024, the peak concentration of chlorophyll a in Selin Co was 3.97 μg / L ), that is, the surface concentration was low, and a significant peak was formed in the thermocline with the increase of depth and reached the maximum value, and then gradually decreased in the deep water layer. Not all lakes follow this rule. For example, although there is thermal stratification in Peiku Co and Tangra Yumco, there is no significant difference in the vertical distribution of chlorophyll a concentration. In the thermal mixing period, the vertical distribution of chlorophyll a concentration in the lake was in a uniform distribution state, and the overall chlorophyll a concentration was at a low level ( the maximum chlorophyll a concentration in the mixing period of Zhari Namco in 2025 was 2.61 μg / L, and the maximum chlorophyll a concentration in Selin Co was 2.40 μg / L ). In addition, the high-salinity water in the lower layer ( below 20 m ) of Dagze Co formed a stable salinity thermocline, resulting in the lake maintaining a density stratification state throughout the year. This unique physical structure makes the vertical distribution pattern of chlorophyll a significantly different from other lakes only controlled by thermal stratification. The results of this study show that the change of thermal structure controls the vertical distribution pattern of chlorophyll a in plateau lakes, while the stable salinity stratification of Dagze Co can form a perennial effective physical barrier and dominate its unique vertical distribution pattern. Therefore, the vertical distribution characteristics of phytoplankton biomass in plateau lakes are determined by the thermal stratification and high salinity of lakes.
Available online: June 30, 2026
Abstract:
Huayang Lake Complex is a typical wetland system in the middle and lower reaches of the Yangtze River, with core ecological functions including waterbird protection, hydrological connectivity and water quality purification, as well as social production guarantee functions such as water supply and flood control. Current water level regulation focuses on single factors and lacks an annual dynamic process curve, which is difficult to fully support the stable exertion of its core ecological functions. Based on nearly 50 years of hydrological, topographic, water quality and habitat data, this study establishes a multi-factor collaborative calculation framework of “hydrology–morphology–water quality–habitat” by using the IHA-RVA method, ArcGIS spatial analysis, hydrodynamic-water quality model and habitat suitability area method, and proposes an annual optimal ecological water level hydrograph to satisfy the hydrological stability and ecological health of the lake complex. The results show that the optimal ecological water level ranges from 11.86 m (April) to 13.53 m (September), with a threshold range of 11.56 m (March) to 14.87 m (August). It presents a temporal distribution characteristic of "convergence in winter and spring, expansion in summer and autumn", and the seasonal water levels adapt to the demands of biological habitats, hydrological rhythms and water quality improvement. This scheme can guarantee the overwintering of key waterbirds, inhabitation of aquatic organisms and water quality purification, and provide a scientific reference for ecological water level regulation of similar gate-controlled lakes or lake groups in the middle and lower reaches of the Yangtze River.
Huayang Lake Complex is a typical wetland system in the middle and lower reaches of the Yangtze River, with core ecological functions including waterbird protection, hydrological connectivity and water quality purification, as well as social production guarantee functions such as water supply and flood control. Current water level regulation focuses on single factors and lacks an annual dynamic process curve, which is difficult to fully support the stable exertion of its core ecological functions. Based on nearly 50 years of hydrological, topographic, water quality and habitat data, this study establishes a multi-factor collaborative calculation framework of “hydrology–morphology–water quality–habitat” by using the IHA-RVA method, ArcGIS spatial analysis, hydrodynamic-water quality model and habitat suitability area method, and proposes an annual optimal ecological water level hydrograph to satisfy the hydrological stability and ecological health of the lake complex. The results show that the optimal ecological water level ranges from 11.86 m (April) to 13.53 m (September), with a threshold range of 11.56 m (March) to 14.87 m (August). It presents a temporal distribution characteristic of "convergence in winter and spring, expansion in summer and autumn", and the seasonal water levels adapt to the demands of biological habitats, hydrological rhythms and water quality improvement. This scheme can guarantee the overwintering of key waterbirds, inhabitation of aquatic organisms and water quality purification, and provide a scientific reference for ecological water level regulation of similar gate-controlled lakes or lake groups in the middle and lower reaches of the Yangtze River.
He Shufeng, She Xingyuan, Feng Tao, Ma Yiming, Wu Biqiong, Du Mingcheng, Sun Huimin, He Mengnan, Chen Qiuwen
Available online: June 29, 2026
Abstract:
Abstract: Dongting Lake, as the second largest natural lake connected to the Yangtze River in the middle and lower reaches, is an important habitat for the four major Chinese carps in the Yangtze River and possesses irreplaceable ecological functions and economic value. Based on the hydrological and topographic data of Dongting Lake from 2016 to 2020, this study constructed a two-dimensional hydrodynamic model of Dongting Lake, simulated the flow velocity and water depth distribution of Dongting Lake from 2016 to 2020, and established the flow velocity and water depth suitability curves for the fattening of juvenile and adult fish of the four major Chinese carps in combination with literature data. The changes of Habitat Suitability Index (HSI) and Weighted Usable Area (WUA) from July to October 2016-2020 were calculated, and the relationship between WUA and the water level of Chenglingji in Dongting Lake was fitted. The suitable ecological water level of Dongting Lake has been determined. The results show that: (1) The optimal flow rate for fattening juvenile fish of the four major Chinese carps in Dongting Lake by rope feed is 0.1-0.2 m/s, and the optimal water depth is 0.7-1.6 m. The optimal flow rate for fattening adult fish by rope feed is 0.1-0.3 m/s, and the optimal water depth is 2.0-4.0 m. (2) From 2016 to 2020, the average monthly flow velocity and water depth of Dongting Lake from July to October basically showed a gradually decreasing trend. The flow velocity of South Dongting Lake was relatively high, while that of East Dongting Lake was relatively high. In 2020, the overall average monthly flow velocity and water depth were relatively high compared with other years. (3) From 2016 to 2020, the average monthly HSI and WUA ranges of juvenile fish of the four major Chinese carps in Dongting Lake during July and August were 0.004-0.14 and 12-402 km2 respectively, and those of adult fish during September and October were 0.05-0.23 and 146-683 km2 respectively. Juvenile and adult fish have the highest suitability in the non-mainstream area of South Dongting Lake. (4) The suitable ecological water level for fattening juvenile fish of the four major Chinese carps in Dongting Lake by using bait is 26.9-28.0 m, corresponding to a WUA of 342 km2, accounting for 13% of the total area. The suitable ecological water level for fattening adult fish by using bait is 29.0-30.0 m, corresponding to a WUA of 832 km2, accounting for 32% of the total area. The research results provide a reference for the protection of the Dongting Lake ecosystem. Key words: Dongting Lake; The four major Chinese carps; Feeding and Fattening of Juvenile fish; Feeding and Fattening of adult fish; Ecological water level
Abstract: Dongting Lake, as the second largest natural lake connected to the Yangtze River in the middle and lower reaches, is an important habitat for the four major Chinese carps in the Yangtze River and possesses irreplaceable ecological functions and economic value. Based on the hydrological and topographic data of Dongting Lake from 2016 to 2020, this study constructed a two-dimensional hydrodynamic model of Dongting Lake, simulated the flow velocity and water depth distribution of Dongting Lake from 2016 to 2020, and established the flow velocity and water depth suitability curves for the fattening of juvenile and adult fish of the four major Chinese carps in combination with literature data. The changes of Habitat Suitability Index (HSI) and Weighted Usable Area (WUA) from July to October 2016-2020 were calculated, and the relationship between WUA and the water level of Chenglingji in Dongting Lake was fitted. The suitable ecological water level of Dongting Lake has been determined. The results show that: (1) The optimal flow rate for fattening juvenile fish of the four major Chinese carps in Dongting Lake by rope feed is 0.1-0.2 m/s, and the optimal water depth is 0.7-1.6 m. The optimal flow rate for fattening adult fish by rope feed is 0.1-0.3 m/s, and the optimal water depth is 2.0-4.0 m. (2) From 2016 to 2020, the average monthly flow velocity and water depth of Dongting Lake from July to October basically showed a gradually decreasing trend. The flow velocity of South Dongting Lake was relatively high, while that of East Dongting Lake was relatively high. In 2020, the overall average monthly flow velocity and water depth were relatively high compared with other years. (3) From 2016 to 2020, the average monthly HSI and WUA ranges of juvenile fish of the four major Chinese carps in Dongting Lake during July and August were 0.004-0.14 and 12-402 km2 respectively, and those of adult fish during September and October were 0.05-0.23 and 146-683 km2 respectively. Juvenile and adult fish have the highest suitability in the non-mainstream area of South Dongting Lake. (4) The suitable ecological water level for fattening juvenile fish of the four major Chinese carps in Dongting Lake by using bait is 26.9-28.0 m, corresponding to a WUA of 342 km2, accounting for 13% of the total area. The suitable ecological water level for fattening adult fish by using bait is 29.0-30.0 m, corresponding to a WUA of 832 km2, accounting for 32% of the total area. The research results provide a reference for the protection of the Dongting Lake ecosystem. Key words: Dongting Lake; The four major Chinese carps; Feeding and Fattening of Juvenile fish; Feeding and Fattening of adult fish; Ecological water level
Available online: June 25, 2026
Abstract:
The Tianshan Mountains serve as a crucial water resource formation zone in China"s arid northwest region. Understanding the hydrological processes within this area holds significant implications for water resource management in arid zones. The northern slope of the Tianshan Mountains lies at the heart of the Eurasian continent, encompassing primarily the region north of the Tianshan range and the southern edge of the Junggar Basin. It exhibits a typical temperate continental climate. While previous studies have primarily focused on precipitation and groundwater isotopes in arid regions, systematic investigations of river water hydrogen and oxygen stable isotopes across the entire northern slope of the Tianshan Mountains remain scarce. To reveal the stable isotope characteristics of river water on the northern slope of the Tianshan Mountains in the arid northwest region and their implications for the hydrological cycle, this study systematically collected river water samples from major rivers on the northern slope of the Tianshan Mountains between 2022 and 2025. Based on hydrogen and oxygen stable isotope data from 225 samples, it combined isotope analysis with remote sensing technology to elucidate the spatiotemporal variation characteristics of hydrogen and oxygen stable isotope compositions in river water. The study also analyzed the influence of river water physicochemical properties and environmental factors on these isotope compositions. The results indicate:(1) River water hydrogen and oxygen stable isotope compositions exhibit distinct spatiotemporal variation patterns. The ranges of δ2H and δ1?O values for rivers on the northern slope of the Tianshan Mountains were ?117.2‰ to ?46.4‰ and ?17.84‰ to?7.10‰, respectively, with regional averages of ?78.3‰ and ?13.27‰. The temporal variability in the stable hydrogen and oxygen isotope composition is relatively small. Spatially, significant regional differentiation is evident: the western, central, and eastern regions exhibit average δ2H and δ18O values of ?85.8‰,?14.16‰ and ?71.0‰,?12.28‰ and ?81.0‰, ?13.74‰, respectively, forming a spatial distribution pattern with higher values in the central area and lower values in the eastern and western wings.(2) The regional river water line (EL) equation is δ2H = 4.31δ18O? 21.94 (R2=0.72, n=225), with a slope (4.31) significantly lower than that of the local atmospheric precipitation line (slope 7.51) and the global atmospheric precipitation line (slope 8); The hydrogen and oxygen stable isotope compositions of rivers in the western and central regions are primarily dominated by precipitation recharge, while eastern rivers exhibit a strong signal of evaporative fractionation.(3) Hydrogen and oxygen stable isotope compositions in rivers on the northern slope of the Tianshan Mountains are influenced by multiple factors. The physicochemical properties of the river water itself contribute to its isotopic characteristics. Additionally, environmental factors such as precipitation, evapotranspiration, surface temperature, and vegetation cover influence river isotope compositions by regulating local hydrological processes. This study elucidates the spatiotemporal variation patterns of stable hydrogen and oxygen isotopes in river water along the northern slope of the Tianshan Mountains. Through field sampling and remote sensing techniques, it quantitatively identifies the primary factors influencing the stable hydrogen and oxygen isotope composition of regional river water. This research fills a gap in studies using stable hydrogen and oxygen isotopes in river water to indicate hydrological processes across the entire mountain range scale of the northern Tianshan slope, providing isotopic evidence for a deeper understanding of water cycle processes in the Tianshan region"s watersheds.
The Tianshan Mountains serve as a crucial water resource formation zone in China"s arid northwest region. Understanding the hydrological processes within this area holds significant implications for water resource management in arid zones. The northern slope of the Tianshan Mountains lies at the heart of the Eurasian continent, encompassing primarily the region north of the Tianshan range and the southern edge of the Junggar Basin. It exhibits a typical temperate continental climate. While previous studies have primarily focused on precipitation and groundwater isotopes in arid regions, systematic investigations of river water hydrogen and oxygen stable isotopes across the entire northern slope of the Tianshan Mountains remain scarce. To reveal the stable isotope characteristics of river water on the northern slope of the Tianshan Mountains in the arid northwest region and their implications for the hydrological cycle, this study systematically collected river water samples from major rivers on the northern slope of the Tianshan Mountains between 2022 and 2025. Based on hydrogen and oxygen stable isotope data from 225 samples, it combined isotope analysis with remote sensing technology to elucidate the spatiotemporal variation characteristics of hydrogen and oxygen stable isotope compositions in river water. The study also analyzed the influence of river water physicochemical properties and environmental factors on these isotope compositions. The results indicate:(1) River water hydrogen and oxygen stable isotope compositions exhibit distinct spatiotemporal variation patterns. The ranges of δ2H and δ1?O values for rivers on the northern slope of the Tianshan Mountains were ?117.2‰ to ?46.4‰ and ?17.84‰ to?7.10‰, respectively, with regional averages of ?78.3‰ and ?13.27‰. The temporal variability in the stable hydrogen and oxygen isotope composition is relatively small. Spatially, significant regional differentiation is evident: the western, central, and eastern regions exhibit average δ2H and δ18O values of ?85.8‰,?14.16‰ and ?71.0‰,?12.28‰ and ?81.0‰, ?13.74‰, respectively, forming a spatial distribution pattern with higher values in the central area and lower values in the eastern and western wings.(2) The regional river water line (EL) equation is δ2H = 4.31δ18O? 21.94 (R2=0.72, n=225), with a slope (4.31) significantly lower than that of the local atmospheric precipitation line (slope 7.51) and the global atmospheric precipitation line (slope 8); The hydrogen and oxygen stable isotope compositions of rivers in the western and central regions are primarily dominated by precipitation recharge, while eastern rivers exhibit a strong signal of evaporative fractionation.(3) Hydrogen and oxygen stable isotope compositions in rivers on the northern slope of the Tianshan Mountains are influenced by multiple factors. The physicochemical properties of the river water itself contribute to its isotopic characteristics. Additionally, environmental factors such as precipitation, evapotranspiration, surface temperature, and vegetation cover influence river isotope compositions by regulating local hydrological processes. This study elucidates the spatiotemporal variation patterns of stable hydrogen and oxygen isotopes in river water along the northern slope of the Tianshan Mountains. Through field sampling and remote sensing techniques, it quantitatively identifies the primary factors influencing the stable hydrogen and oxygen isotope composition of regional river water. This research fills a gap in studies using stable hydrogen and oxygen isotopes in river water to indicate hydrological processes across the entire mountain range scale of the northern Tianshan slope, providing isotopic evidence for a deeper understanding of water cycle processes in the Tianshan region"s watersheds.
Available online: June 22, 2026
Abstract:
Phytoplankton in cold-region lakes are key carriers of material cycling and energy flow in lake ecosystems. Compared with phytoplankton in lakes at mid-to-low latitudes, their community structure exhibits higher sensitivity to climate change and anthropogenic stress. To elucidate the spatio-temporal characteristics of phytoplankton community structure and its key driving forces in cold-region lakes, this study used samples from January, May, July and September to represent winter, spring, summer and autumn, respectively. Plankton community and water quality samples were collected from Lake Chagan in 2024 and subjected to laboratory analysis.The results showed that the water trophic state of Chagan Lake was mesotrophic in spring, summer, and winter (34.20≤TLI≤47.16), while it was eutrophic in autumn (48.85≤TLI≤59.56). A total of 175 phytoplankton species belonging to 8 phyla were identified, with Bacillariophyta having the highest biomass and Cyanophyta the highest cell density. There were 12 dominant phytoplankton species from 5 phyla; the absolute dominant species (with the highest dominance) in spring, summer, autumn, and winter were Synedra acus (Bacillariophyta), Tribonema ulothrichoides (Xanthophyta), Dolichospermum spiroides (Cyanophyta), and Synedra acus var. angustissima (Bacillariophyta), respectively. The Shannon-Wiener diversity index, Simpson diversity index, Pielou evenness index, and Margalef richness index of the phytoplankton community were generally low, indicating weak resistance to external and internal environmental changes. Based on Pearson correlation analysis, redundancy analysis (RDA), and Mantel tests, it was clarified that WT, TP, TN, NH??-N, NO??-N, and DO were the main controlling factors affecting phytoplankton cell density in Chagan Lake. Among these, WT, TN, TP, and NO??-N were the main factors influencing phytoplankton dominance, while TN, NH??-N, and DO dominated changes in phytoplankton community structure. Notably, low temperature, low light (ice cover) and weakened hydrodynamic mixing in winter and spring promoted Bacillariophyta to become the absolute dominant species, whereas high TN and NO??-N in summer and autumn facilitated Xanthophyta and Cyanophyta to become the absolute dominant species. To effectively prevent Cyanophyta from becoming the absolute dominant species across all seasons in Chagan Lake, it is urgent to reduce the concentration of nutrient salts (TN and NO??-N) input in summer and autumn to address the threats posed by climate warming. This study reveals the driving mechanism of phytoplankton community structure in northern cold-region lakes, providing a scientific basis for the aquatic ecological protection of Chagan Lake and similar cold-region lakes.
Phytoplankton in cold-region lakes are key carriers of material cycling and energy flow in lake ecosystems. Compared with phytoplankton in lakes at mid-to-low latitudes, their community structure exhibits higher sensitivity to climate change and anthropogenic stress. To elucidate the spatio-temporal characteristics of phytoplankton community structure and its key driving forces in cold-region lakes, this study used samples from January, May, July and September to represent winter, spring, summer and autumn, respectively. Plankton community and water quality samples were collected from Lake Chagan in 2024 and subjected to laboratory analysis.The results showed that the water trophic state of Chagan Lake was mesotrophic in spring, summer, and winter (34.20≤TLI≤47.16), while it was eutrophic in autumn (48.85≤TLI≤59.56). A total of 175 phytoplankton species belonging to 8 phyla were identified, with Bacillariophyta having the highest biomass and Cyanophyta the highest cell density. There were 12 dominant phytoplankton species from 5 phyla; the absolute dominant species (with the highest dominance) in spring, summer, autumn, and winter were Synedra acus (Bacillariophyta), Tribonema ulothrichoides (Xanthophyta), Dolichospermum spiroides (Cyanophyta), and Synedra acus var. angustissima (Bacillariophyta), respectively. The Shannon-Wiener diversity index, Simpson diversity index, Pielou evenness index, and Margalef richness index of the phytoplankton community were generally low, indicating weak resistance to external and internal environmental changes. Based on Pearson correlation analysis, redundancy analysis (RDA), and Mantel tests, it was clarified that WT, TP, TN, NH??-N, NO??-N, and DO were the main controlling factors affecting phytoplankton cell density in Chagan Lake. Among these, WT, TN, TP, and NO??-N were the main factors influencing phytoplankton dominance, while TN, NH??-N, and DO dominated changes in phytoplankton community structure. Notably, low temperature, low light (ice cover) and weakened hydrodynamic mixing in winter and spring promoted Bacillariophyta to become the absolute dominant species, whereas high TN and NO??-N in summer and autumn facilitated Xanthophyta and Cyanophyta to become the absolute dominant species. To effectively prevent Cyanophyta from becoming the absolute dominant species across all seasons in Chagan Lake, it is urgent to reduce the concentration of nutrient salts (TN and NO??-N) input in summer and autumn to address the threats posed by climate warming. This study reveals the driving mechanism of phytoplankton community structure in northern cold-region lakes, providing a scientific basis for the aquatic ecological protection of Chagan Lake and similar cold-region lakes.
Available online: June 22, 2026
Abstract:
Molecular species identification and environmental DNA (eDNA) technologies have developed rapidly in recent years. They are widely used in biodiversity surveys and environmental monitoring because they are efficient and non-invasive. However, their performance and accuracy depend strongly on the completeness and reliability of reference databases, especially DNA barcode libraries. In China, most river basins still lack systematic, standardized, and comprehensive barcode resources. This limitation restricts the application of molecular methods in ecological assessment and biodiversity conservation. The Yarlung Tsangpo River is one of the highest-altitude large transboundary rivers in the world. Its unique climate and complex hydrological and geomorphological conditions support rich and distinctive freshwater fish diversity. However, a basin-wide DNA barcode reference library for fish is still lacking. Systematic genetic data remain insufficient, which limits the use of molecular monitoring approaches in this region. In this study, we compiled DNA sequences from fish specimens collected by our research team across the Yarlung Tsangpo River basin from 1998 to 2024. We also incorporated sequences from public databases. All data were processed using standardized methods, followed by strict quality control and reliability assessment based on genetic distances. Based on these steps, we established the first comprehensive DNA barcode reference dataset covering the entire basin. The dataset contains 3,174 high-quality DNA sequences. Among them, 2,890 sequences (91.1%) were newly generated, and 284 sequences (8.9%) were obtained from public databases. Samples were collected from 82 sites, including the main stem, major tributaries, and associated lakes and wetlands. The elevation range spans from 155 to 4,600 m. The dataset includes 78 species from 49 genera, 21 families, and 8 orders. These species comprise 62 native species and 16 non-native species. The dataset covers 69% of endemic fish species in the basin and 100% of fish species in the reach upstream of the Lhagu River confluence. The average sequence length is approximately 813 bp. The main molecular markers are cytochrome c oxidase subunit I (COI) and cytochrome b (Cyt b). Their sequence length ranges are 461-1779 bp and 798-1390 bp, respectively. Most species show clear DNA barcode gaps, which support reliable species-level identification. The dataset adopts a “metadata-sequence data” separation framework. It follows the FAIR (Findable, Accessible, Interoperable, Reusable) and CARE (Collective Benefit, Authority to Control, Responsibility, Ethics) principles. It includes standardized information on taxonomy, voucher specimens, distribution, sampling time, collectors, and sequence sources. Color photographs are available for some species. The dataset is openly accessible through the Science Data Bank(ScienceDB; DOI：10.57760/sciencedb.36688). This dataset fills a key gap in DNA barcode reference resources for fish in the Yarlung Tsangpo River basin. It supports species identification, biodiversity inventory, non-native species monitoring, and eDNA metabarcoding studies. It also provides essential data support for the conservation and management of plateau river ecosystems.
Molecular species identification and environmental DNA (eDNA) technologies have developed rapidly in recent years. They are widely used in biodiversity surveys and environmental monitoring because they are efficient and non-invasive. However, their performance and accuracy depend strongly on the completeness and reliability of reference databases, especially DNA barcode libraries. In China, most river basins still lack systematic, standardized, and comprehensive barcode resources. This limitation restricts the application of molecular methods in ecological assessment and biodiversity conservation. The Yarlung Tsangpo River is one of the highest-altitude large transboundary rivers in the world. Its unique climate and complex hydrological and geomorphological conditions support rich and distinctive freshwater fish diversity. However, a basin-wide DNA barcode reference library for fish is still lacking. Systematic genetic data remain insufficient, which limits the use of molecular monitoring approaches in this region. In this study, we compiled DNA sequences from fish specimens collected by our research team across the Yarlung Tsangpo River basin from 1998 to 2024. We also incorporated sequences from public databases. All data were processed using standardized methods, followed by strict quality control and reliability assessment based on genetic distances. Based on these steps, we established the first comprehensive DNA barcode reference dataset covering the entire basin. The dataset contains 3,174 high-quality DNA sequences. Among them, 2,890 sequences (91.1%) were newly generated, and 284 sequences (8.9%) were obtained from public databases. Samples were collected from 82 sites, including the main stem, major tributaries, and associated lakes and wetlands. The elevation range spans from 155 to 4,600 m. The dataset includes 78 species from 49 genera, 21 families, and 8 orders. These species comprise 62 native species and 16 non-native species. The dataset covers 69% of endemic fish species in the basin and 100% of fish species in the reach upstream of the Lhagu River confluence. The average sequence length is approximately 813 bp. The main molecular markers are cytochrome c oxidase subunit I (COI) and cytochrome b (Cyt b). Their sequence length ranges are 461-1779 bp and 798-1390 bp, respectively. Most species show clear DNA barcode gaps, which support reliable species-level identification. The dataset adopts a “metadata-sequence data” separation framework. It follows the FAIR (Findable, Accessible, Interoperable, Reusable) and CARE (Collective Benefit, Authority to Control, Responsibility, Ethics) principles. It includes standardized information on taxonomy, voucher specimens, distribution, sampling time, collectors, and sequence sources. Color photographs are available for some species. The dataset is openly accessible through the Science Data Bank(ScienceDB; DOI：10.57760/sciencedb.36688). This dataset fills a key gap in DNA barcode reference resources for fish in the Yarlung Tsangpo River basin. It supports species identification, biodiversity inventory, non-native species monitoring, and eDNA metabarcoding studies. It also provides essential data support for the conservation and management of plateau river ecosystems.
Available online: June 16, 2026
Abstract:
Since the impoundment of the Three Gorges Reservoir (TGR) and the joint regulation of upstream cascade reservoirs, the sediment transport environment of the TGR, particularly within the variable backwater zone, has undergone significant changes. As a sensitive reach subject to alternating river–reservoir influences, the evolution of suspended sediment vertical distribution in this zone directly affects sediment management strategies at the reservoir tail and navigational maintenance. Based on long-term field observations from 2009 to 2020, this study systematically identifies suspended sediment vertical distribution patterns in the variable backwater zone using the K-means clustering algorithm and quantitatively evaluates the applicability of the classical Rouse equation and the Han Qiangwei non-equilibrium sediment transport formula. A total of 267 measured vertical profiles are classified into three typical patterns: low-concentration weak-gradient pattern (Pattern 0, 67.8%), medium-concentration positive-gradient pattern (Pattern 1, 28.8%), and high-concentration quasi-uniform pattern (Pattern 2, 3.4%). The results reveal pronounced temporal differentiation among the distribution patterns. On the intra-annual scale, the patterns are closely associated with flood-season hydrological processes: Pattern 0 predominates during the pre- and post-flood periods, whereas the other patterns mainly occur during the main flood season (July–August). On the interannual scale, the low-concentration pattern increased steadily during 2009–2020 and became the dominant distribution in the variable backwater zone after 2014 under cascade reservoir regulation. This evolution is consistent with the intensified clear-water release effect induced by the operation of the TGR and the Jinsha River cascade reservoirs, indicating a persistent non-equilibrium sediment transport regime in which sediment transport capacity substantially exceeds sediment supply. In terms of formula performance, the Rouse equation and the Han formula yield comparable results for calculating depth-averaged suspended sediment concentration. However, for unit-width sediment discharge, the Han formula effectively corrects the systematic underestimation under Pattern 0 by introducing a non-equilibrium coefficient, showing significantly higher accuracy and stability than the Rouse equation. Both formulas exhibit limited capability in representing near-bed high-concentration layers. Future studies should focus on improving diffusion coefficient parameterization under unsteady flow conditions in variable backwater zones and incorporating fine-sediment flocculation processes to enhance sediment transport predictions under complex hydraulic conditions. The findings provide important theoretical support for understanding sediment transport mechanisms and optimizing regulation strategies in variable backwater zones of large reservoirs.
Since the impoundment of the Three Gorges Reservoir (TGR) and the joint regulation of upstream cascade reservoirs, the sediment transport environment of the TGR, particularly within the variable backwater zone, has undergone significant changes. As a sensitive reach subject to alternating river–reservoir influences, the evolution of suspended sediment vertical distribution in this zone directly affects sediment management strategies at the reservoir tail and navigational maintenance. Based on long-term field observations from 2009 to 2020, this study systematically identifies suspended sediment vertical distribution patterns in the variable backwater zone using the K-means clustering algorithm and quantitatively evaluates the applicability of the classical Rouse equation and the Han Qiangwei non-equilibrium sediment transport formula. A total of 267 measured vertical profiles are classified into three typical patterns: low-concentration weak-gradient pattern (Pattern 0, 67.8%), medium-concentration positive-gradient pattern (Pattern 1, 28.8%), and high-concentration quasi-uniform pattern (Pattern 2, 3.4%). The results reveal pronounced temporal differentiation among the distribution patterns. On the intra-annual scale, the patterns are closely associated with flood-season hydrological processes: Pattern 0 predominates during the pre- and post-flood periods, whereas the other patterns mainly occur during the main flood season (July–August). On the interannual scale, the low-concentration pattern increased steadily during 2009–2020 and became the dominant distribution in the variable backwater zone after 2014 under cascade reservoir regulation. This evolution is consistent with the intensified clear-water release effect induced by the operation of the TGR and the Jinsha River cascade reservoirs, indicating a persistent non-equilibrium sediment transport regime in which sediment transport capacity substantially exceeds sediment supply. In terms of formula performance, the Rouse equation and the Han formula yield comparable results for calculating depth-averaged suspended sediment concentration. However, for unit-width sediment discharge, the Han formula effectively corrects the systematic underestimation under Pattern 0 by introducing a non-equilibrium coefficient, showing significantly higher accuracy and stability than the Rouse equation. Both formulas exhibit limited capability in representing near-bed high-concentration layers. Future studies should focus on improving diffusion coefficient parameterization under unsteady flow conditions in variable backwater zones and incorporating fine-sediment flocculation processes to enhance sediment transport predictions under complex hydraulic conditions. The findings provide important theoretical support for understanding sediment transport mechanisms and optimizing regulation strategies in variable backwater zones of large reservoirs.
Available online: June 16, 2026
Abstract:
Varved lake sediments serve as a crucial archive for high-resolution paleoclimate and paleoenvironmental research. Owing to their interannual to even seasonal temporal resolution, they provide a high-precision chronological framework for climate reconstruction. Investigating the formation mechanism of varves is essential for understanding their depositional processes and for accurately interpreting the climatic and environmental information they record. This study focuses on the laminated sediments of Rena Co in the central Tibetan Plateau. By integratingS210Pb/137Cs dating with varve counting results, it confirms that these laminations are varves. Based on microscopic observations of varve thin sections, micro-X-ray fluorescence (μ-XRF) elemental mapping of varve thin sections, X-ray diffraction (XRD) analysis of core sediments, and scanning electron microscopy (SEM) observations of surface microtextures on coarse-grained particles, we systematically analyzed the structural, compositional, and morphological characteristics of the varves from Rena Co, and further explored their formation processes and underlying mechanisms. The results indicate that the varves of Rena Co consist of alternating light and dark layers. The light-colored layers form during summer and are mainly composed of fine-grained, Ca-rich authigenic carbonate (such as aragonite), together with abundant cladoceran fragments remains. In contrast, the dark-colored layers develop during winter following lake ice formation and comprise fine-grained, Fe-rich clay minerals that slowly settle beneath the ice, along with coarse-grained, Si-rich aeolian materials (e.g., quartz and feldspar) that accumulate on the ice surface and are subsequently deposited on the lakebed during ice melt.
Varved lake sediments serve as a crucial archive for high-resolution paleoclimate and paleoenvironmental research. Owing to their interannual to even seasonal temporal resolution, they provide a high-precision chronological framework for climate reconstruction. Investigating the formation mechanism of varves is essential for understanding their depositional processes and for accurately interpreting the climatic and environmental information they record. This study focuses on the laminated sediments of Rena Co in the central Tibetan Plateau. By integratingS210Pb/137Cs dating with varve counting results, it confirms that these laminations are varves. Based on microscopic observations of varve thin sections, micro-X-ray fluorescence (μ-XRF) elemental mapping of varve thin sections, X-ray diffraction (XRD) analysis of core sediments, and scanning electron microscopy (SEM) observations of surface microtextures on coarse-grained particles, we systematically analyzed the structural, compositional, and morphological characteristics of the varves from Rena Co, and further explored their formation processes and underlying mechanisms. The results indicate that the varves of Rena Co consist of alternating light and dark layers. The light-colored layers form during summer and are mainly composed of fine-grained, Ca-rich authigenic carbonate (such as aragonite), together with abundant cladoceran fragments remains. In contrast, the dark-colored layers develop during winter following lake ice formation and comprise fine-grained, Fe-rich clay minerals that slowly settle beneath the ice, along with coarse-grained, Si-rich aeolian materials (e.g., quartz and feldspar) that accumulate on the ice surface and are subsequently deposited on the lakebed during ice melt.
Available online: June 16, 2026
Abstract:
River network routing is a crucial component of watershed hydrological modeling, with the Muskingum method being one of the most widely used approaches. However, traditional applications of the Muskingum method typically rely on discrete difference equations, which not only introduce numerical errors but also hinder seamless temporal-scale coupling with hydrological models formulated in differential form. To address this limitation, this study develops a differential form of the Muskingum river routing method by assembling the governing ordinary differential equations (ODEs) for all river segments using a matrix-based approach. A connectivity matrix is introduced to identify upstream inflows for each channel, leading to the formulation of the Muskingum-based Ordinary Differential Equation River-network Routing method (ODE-MR). The ODE-MR is further coupled with the differential form of the Xinanjiang hydrological model to construct a fully differential hydrological modeling framework.Comparative experiments between differential and difference forms demonstrate that, with analytical solutions as reference, the root mean square error of ODE-MR is on the order of 10??, significantly reducing the numerical inaccuracies of the traditional difference-based Muskingum method. Additional experiments comparing the coupling strategies with differential hydrological models show that, as the time step decreases, the results of the hybrid differential-difference coupling approach gradually converge toward those of the fully differential coupling method, indicating superior modeling accuracy of the fully differential coupling method approach. Real-world application in the Tunxi River Basin further validates the model, at the daily scale, with the ODE-MR-based fully differential coupling model improving the multi-year average Nash-Sutcliffe efficiency coefficient by 0.04, demonstrating enhanced predictive performance. This study provides a valuable reference for hydrological modeling and cross-disciplinary model integration within a unified differential equation framework.
River network routing is a crucial component of watershed hydrological modeling, with the Muskingum method being one of the most widely used approaches. However, traditional applications of the Muskingum method typically rely on discrete difference equations, which not only introduce numerical errors but also hinder seamless temporal-scale coupling with hydrological models formulated in differential form. To address this limitation, this study develops a differential form of the Muskingum river routing method by assembling the governing ordinary differential equations (ODEs) for all river segments using a matrix-based approach. A connectivity matrix is introduced to identify upstream inflows for each channel, leading to the formulation of the Muskingum-based Ordinary Differential Equation River-network Routing method (ODE-MR). The ODE-MR is further coupled with the differential form of the Xinanjiang hydrological model to construct a fully differential hydrological modeling framework.Comparative experiments between differential and difference forms demonstrate that, with analytical solutions as reference, the root mean square error of ODE-MR is on the order of 10??, significantly reducing the numerical inaccuracies of the traditional difference-based Muskingum method. Additional experiments comparing the coupling strategies with differential hydrological models show that, as the time step decreases, the results of the hybrid differential-difference coupling approach gradually converge toward those of the fully differential coupling method, indicating superior modeling accuracy of the fully differential coupling method approach. Real-world application in the Tunxi River Basin further validates the model, at the daily scale, with the ODE-MR-based fully differential coupling model improving the multi-year average Nash-Sutcliffe efficiency coefficient by 0.04, demonstrating enhanced predictive performance. This study provides a valuable reference for hydrological modeling and cross-disciplinary model integration within a unified differential equation framework.
Available online: June 16, 2026
Abstract:
After the completion and operation of Quanzhou Bailai Water Control Project, the water supply capacity of Jinji sluice will be improved, resulting in the decrease of downstream water volume. In order to analyze the impact of the project on the estuary water environment, a two-dimensional unsteady water environment mathematical model of Jinjiang estuary is constructed by using MIKE21, and the tidal current field, salinity upstream distance, along-the-way change and diluted water area of the estuary before and after the construction of Bailai Reservoir are simulated. After analysis, the discharge of Jinji Gate is reduced by 53.4% at the maximum after the construction of the reservoir, and the prediction results show that the basic shape of tidal current field in Jinjiang estuary and coastal waters has not changed before and after the construction of the reservoir. The maximum increment of the upstream distance of the saltwater tide in Jinjiang Estuary is 0.66km, and the areas with obvious changes are mainly 2.6~12.3km in the upper reaches of Jinjiang Estuary, and the salinity variation is basically below 3.4‰. The area of diluted water in the experimental area of Quanzhou Bay Estuary Wetland Nature Reserve decreased by 3.4% at the maximum, but the core area and buffer area basically had no effect. Generally speaking, the Bailai Reservoir has little influence on tidal current field and salinity field in Jinjiang estuary after the reservoir is built. The research results can provide a basis for the protection and management of water environment in Jinjiang estuary, and can also provide some reference for the impact analysis of water environment in other estuary projects.
After the completion and operation of Quanzhou Bailai Water Control Project, the water supply capacity of Jinji sluice will be improved, resulting in the decrease of downstream water volume. In order to analyze the impact of the project on the estuary water environment, a two-dimensional unsteady water environment mathematical model of Jinjiang estuary is constructed by using MIKE21, and the tidal current field, salinity upstream distance, along-the-way change and diluted water area of the estuary before and after the construction of Bailai Reservoir are simulated. After analysis, the discharge of Jinji Gate is reduced by 53.4% at the maximum after the construction of the reservoir, and the prediction results show that the basic shape of tidal current field in Jinjiang estuary and coastal waters has not changed before and after the construction of the reservoir. The maximum increment of the upstream distance of the saltwater tide in Jinjiang Estuary is 0.66km, and the areas with obvious changes are mainly 2.6~12.3km in the upper reaches of Jinjiang Estuary, and the salinity variation is basically below 3.4‰. The area of diluted water in the experimental area of Quanzhou Bay Estuary Wetland Nature Reserve decreased by 3.4% at the maximum, but the core area and buffer area basically had no effect. Generally speaking, the Bailai Reservoir has little influence on tidal current field and salinity field in Jinjiang estuary after the reservoir is built. The research results can provide a basis for the protection and management of water environment in Jinjiang estuary, and can also provide some reference for the impact analysis of water environment in other estuary projects.
Available online: June 16, 2026
Abstract:
Riverbed armoring in gravel-sand rivers involves complex interactions among suspended load, bed load, and bed material, forming a non-steady “scour–armoring–exchange” process. Traditional prediction methods often oversimplify these mechanisms and neglect sediment exchange, leading to limited accuracy and applicability. This study aims to develop a new riverbed armoring calculation method that explicitly incorporates sediment exchange between suspended load, bed load, and bed material to improve prediction performance. Four representative domestic and international riverbed armoring models were first compared under different hydraulic and sediment conditions to identify their limitations. Based on sediment transport statistical theory and an improved active-layer sediment mass conservation equation, a new method was proposed that considers the coupled “suspended load–bed load–bed material” exchange process. The model was validated against both flume experiments and field data from the downstream reaches of the Danjiangkou and Three Gorges Reservoirs. The results show that compared with the traditional methods, the proposed method significantly improves the prediction accuracy. The calculation accuracy of the new method is considerably higher than that of conventional approaches in both natural rivers and flume experiments. When applied to natural rivers, the RMSE and MAE values are 4.9% and 3.3%, respectively, while for flume tests they are 5.5% and 2.5%, respectively. It effectively reproduced the dynamic feedback between flow scour and bed armoring, accurately simulating both the gradation of the armoring layer and the depth of bed scour. Sensitivity analyses demonstrated that dynamic variation of the active-layer thickness and appropriate definition of armoring stability are essential for accurate modeling. The newly developed method, grounded in sediment transport statistics and active-layer balance theory, provides a physically-based and reliable approach for predicting armoring in gravel-sand beds. It addresses key limitations of conventional models by coupling multiple sediment transport modes and dynamic bed evolution. The results enhance understanding of riverbed armoring mechanisms and offer a robust tool for forecasting downstream channel adjustment below large dams.
Riverbed armoring in gravel-sand rivers involves complex interactions among suspended load, bed load, and bed material, forming a non-steady “scour–armoring–exchange” process. Traditional prediction methods often oversimplify these mechanisms and neglect sediment exchange, leading to limited accuracy and applicability. This study aims to develop a new riverbed armoring calculation method that explicitly incorporates sediment exchange between suspended load, bed load, and bed material to improve prediction performance. Four representative domestic and international riverbed armoring models were first compared under different hydraulic and sediment conditions to identify their limitations. Based on sediment transport statistical theory and an improved active-layer sediment mass conservation equation, a new method was proposed that considers the coupled “suspended load–bed load–bed material” exchange process. The model was validated against both flume experiments and field data from the downstream reaches of the Danjiangkou and Three Gorges Reservoirs. The results show that compared with the traditional methods, the proposed method significantly improves the prediction accuracy. The calculation accuracy of the new method is considerably higher than that of conventional approaches in both natural rivers and flume experiments. When applied to natural rivers, the RMSE and MAE values are 4.9% and 3.3%, respectively, while for flume tests they are 5.5% and 2.5%, respectively. It effectively reproduced the dynamic feedback between flow scour and bed armoring, accurately simulating both the gradation of the armoring layer and the depth of bed scour. Sensitivity analyses demonstrated that dynamic variation of the active-layer thickness and appropriate definition of armoring stability are essential for accurate modeling. The newly developed method, grounded in sediment transport statistics and active-layer balance theory, provides a physically-based and reliable approach for predicting armoring in gravel-sand beds. It addresses key limitations of conventional models by coupling multiple sediment transport modes and dynamic bed evolution. The results enhance understanding of riverbed armoring mechanisms and offer a robust tool for forecasting downstream channel adjustment below large dams.
Available online: June 15, 2026
Abstract:
To elucidate the spatiotemporal succession patterns and environmental driving mechanisms of bacterial communities across different habitats in reservoirs within the semi-arid region of southern Ningxia, water and sediment samples were collected from eight typical reservoirs in Guyuan City during April, July, and October 2025. By integrating 16S rRNA gene high-throughput sequencing with the Trophic Level Index (TLI), Mantel tests, and Redundancy Analysis (RDA), this study investigated community structure, seasonal dynamics, and their relationships with environmental factors.The results indicated that the eight reservoirs exhibited a complete environmental gradient ranging from mesotrophic (Site S6) to hyper-eutrophic (Site S1) status based on TLI evaluation. Proteobacteria was the predominant phylum in both water (31.68%–36.49%) and sediment (38.16%–43.48%) habitats. In July, high temperatures and strong irradiance drove an explosive enrichment of Cyanobacteriota and its constituent order Synechococcales in the water column, resulting in a simplified community structure and a decline in α-diversity. In contrast, the sediment habitat remained relatively stable, enriching benthic-specific taxa such as Acidobacteriota and Chloroflexi, with α-diversity exhibiting a trend of seasonal accumulation.The environmental driving mechanisms demonstrated distinct habitat specificity. Water bacterial communities were significantly influenced by Total Nitrogen (TN), Total Phosphorus (TP), Permanganate Index (CODMn), and Nitrate Nitrogen (NO3-N) (P<0.01), while high summer temperatures and pH were identified as key physical factors reshaping community structure. Conversely, the succession of sediment communities was primarily regulated by Ammonium Nitrogen (NH4+-N), TP, and Salinity (SAL). This study systematically elucidates the seasonal variations in microbial community structures across different habitats in arid-region reservoirs, providing a scientific basis for regional water environment management.
To elucidate the spatiotemporal succession patterns and environmental driving mechanisms of bacterial communities across different habitats in reservoirs within the semi-arid region of southern Ningxia, water and sediment samples were collected from eight typical reservoirs in Guyuan City during April, July, and October 2025. By integrating 16S rRNA gene high-throughput sequencing with the Trophic Level Index (TLI), Mantel tests, and Redundancy Analysis (RDA), this study investigated community structure, seasonal dynamics, and their relationships with environmental factors.The results indicated that the eight reservoirs exhibited a complete environmental gradient ranging from mesotrophic (Site S6) to hyper-eutrophic (Site S1) status based on TLI evaluation. Proteobacteria was the predominant phylum in both water (31.68%–36.49%) and sediment (38.16%–43.48%) habitats. In July, high temperatures and strong irradiance drove an explosive enrichment of Cyanobacteriota and its constituent order Synechococcales in the water column, resulting in a simplified community structure and a decline in α-diversity. In contrast, the sediment habitat remained relatively stable, enriching benthic-specific taxa such as Acidobacteriota and Chloroflexi, with α-diversity exhibiting a trend of seasonal accumulation.The environmental driving mechanisms demonstrated distinct habitat specificity. Water bacterial communities were significantly influenced by Total Nitrogen (TN), Total Phosphorus (TP), Permanganate Index (CODMn), and Nitrate Nitrogen (NO3-N) (P<0.01), while high summer temperatures and pH were identified as key physical factors reshaping community structure. Conversely, the succession of sediment communities was primarily regulated by Ammonium Nitrogen (NH4+-N), TP, and Salinity (SAL). This study systematically elucidates the seasonal variations in microbial community structures across different habitats in arid-region reservoirs, providing a scientific basis for regional water environment management.
Available online: June 12, 2026
Abstract:
The dynamics of total phosphorus (TP) concentrations in shallow lakes are collectively driven by multiple environmental factors. The complexity of these underlying mechanisms is closely related to the lake"s physicochemical properties. Based on high-frequency data from national water quality, hydrological, and meteorological monitoring stations in the Lake Chaohu basin from 2021 to 2024, this study employed principal component analysis (PCA) and time-lag correlation analysis to elucidate the variation patterns of TP concentrations, identify the primary driving factors, and determine the risk threshold grades of environmental factors associated with TP exceedance or abrupt changes. The results indicated that water temperature (WT), dissolved oxygen (DO), and algal density (AD) were the dominant environmental drivers governing TP fluctuations in Lake Chaohu, with a cumulative contribution rate exceeding 50%. Wind speed (WD) was identified as a key meteorological factor. Furthermore, this study identified a cascading driving process of TP dynamics with distinct time-lag effects in Lake Chaohu. Specifically, a rise in WT during summer was followed by an increase in algal density after 4 days, accompanied by a significant decline in DO. The decrease in DO rapidly induced an elevation in water TP concentration within 24 hours, indicating a rapid response of phosphorus release at the sediment-water microinterface. The peak impact of AD on TP concentration occurred with a 3-day lag, attributable to both direct phosphorus release during algal growth and senescence, and indirect effects via DO consumption. Based on these findings, risk threshold grades for DO (7.69, 7.08, 6.72 mg/L) and AD (9.80, 15.64, 21.14 × 10? cells/L) were established for different TP concentration intervals in Lake Chaohu: (0.05, 0.075], (0.075, 0.1], and >0.1 mg/L. These results provide a crucial temporal decision-making basis for TP risk early warning and precision management in Lake Chaohu.
The dynamics of total phosphorus (TP) concentrations in shallow lakes are collectively driven by multiple environmental factors. The complexity of these underlying mechanisms is closely related to the lake"s physicochemical properties. Based on high-frequency data from national water quality, hydrological, and meteorological monitoring stations in the Lake Chaohu basin from 2021 to 2024, this study employed principal component analysis (PCA) and time-lag correlation analysis to elucidate the variation patterns of TP concentrations, identify the primary driving factors, and determine the risk threshold grades of environmental factors associated with TP exceedance or abrupt changes. The results indicated that water temperature (WT), dissolved oxygen (DO), and algal density (AD) were the dominant environmental drivers governing TP fluctuations in Lake Chaohu, with a cumulative contribution rate exceeding 50%. Wind speed (WD) was identified as a key meteorological factor. Furthermore, this study identified a cascading driving process of TP dynamics with distinct time-lag effects in Lake Chaohu. Specifically, a rise in WT during summer was followed by an increase in algal density after 4 days, accompanied by a significant decline in DO. The decrease in DO rapidly induced an elevation in water TP concentration within 24 hours, indicating a rapid response of phosphorus release at the sediment-water microinterface. The peak impact of AD on TP concentration occurred with a 3-day lag, attributable to both direct phosphorus release during algal growth and senescence, and indirect effects via DO consumption. Based on these findings, risk threshold grades for DO (7.69, 7.08, 6.72 mg/L) and AD (9.80, 15.64, 21.14 × 10? cells/L) were established for different TP concentration intervals in Lake Chaohu: (0.05, 0.075], (0.075, 0.1], and >0.1 mg/L. These results provide a crucial temporal decision-making basis for TP risk early warning and precision management in Lake Chaohu.
Available online: June 12, 2026
Abstract:
The operation of the Three Gorges Reservoir (TGR) has altered water and sediment processes in the middle and lower reaches of the Yangtze River, affecting the adjustment characteristics of scouring and sedimentation in the branch channels as well as the flow distribution relationships among relatively balanced channels. Thereby exerting a cascading impact on flood control, navigation, and river management. Given the current limitations in understanding the adjustment patterns of branch channels under the influence of water and sediment conditions altered by the operation of cascade reservoi, this study utilizes measured hydrological and topographic data from 2003 to 2023. Taking eleven typical distributary channels in the Chenglingji to Jiujiang section as examples, it employs a distributary channel classification method based on dynamic diversion ratios to investigate channel type conversion phenomena and analyze their driving mechanisms. The study reveals：（1）The method for classifying branch channels based on dynamic diversion ratios demonstrates good adaptability in classifying branch channels in the middle and lower reaches of the Yangtze River and identifying their typological transitions under different operating modes of the TGR（2）Following the TGR impoundment, the branch channels exhibited different adjustment patterns during various periods. Since 2013, the section from Chenglingji to Jiujiang has been dominated by Type I branch channels (where the main channel corresponds to a low-flow-dominant branch channel), while in Type II branch channels (where the main channel corresponds to a low-flow-prone branch), the Jiepaoxin Sandbar branch section, Luxi Kou, Jiayu, and Yanzowo channels have transitioned to Type I branch channels, shifting from a “main channel shortening, branch channel lengthening” pattern to a “main channel lengthening, branch channel shortening” pattern;（3）For the transformation of Type II distributary channels into Type I channels, altered hydrological and sediment conditions were the primary driver. Navigation improvement projects demonstrated a promoting effect on this transformation in most distributary channels. After 2013, the frequency and duration of flow levels between 20,000 and 30,000 m3/s increased, leading to intensified scouring in the main channel branch at these flow levels. with some branches evolving into Class I distributary channels. It is foreseeable that branched river systems in the middle and lower reaches of the Yangtze River will predominantly shift toward Class I, characterized by an adjustment pattern where the main channel grows while tributaries diminish.
The operation of the Three Gorges Reservoir (TGR) has altered water and sediment processes in the middle and lower reaches of the Yangtze River, affecting the adjustment characteristics of scouring and sedimentation in the branch channels as well as the flow distribution relationships among relatively balanced channels. Thereby exerting a cascading impact on flood control, navigation, and river management. Given the current limitations in understanding the adjustment patterns of branch channels under the influence of water and sediment conditions altered by the operation of cascade reservoi, this study utilizes measured hydrological and topographic data from 2003 to 2023. Taking eleven typical distributary channels in the Chenglingji to Jiujiang section as examples, it employs a distributary channel classification method based on dynamic diversion ratios to investigate channel type conversion phenomena and analyze their driving mechanisms. The study reveals：（1）The method for classifying branch channels based on dynamic diversion ratios demonstrates good adaptability in classifying branch channels in the middle and lower reaches of the Yangtze River and identifying their typological transitions under different operating modes of the TGR（2）Following the TGR impoundment, the branch channels exhibited different adjustment patterns during various periods. Since 2013, the section from Chenglingji to Jiujiang has been dominated by Type I branch channels (where the main channel corresponds to a low-flow-dominant branch channel), while in Type II branch channels (where the main channel corresponds to a low-flow-prone branch), the Jiepaoxin Sandbar branch section, Luxi Kou, Jiayu, and Yanzowo channels have transitioned to Type I branch channels, shifting from a “main channel shortening, branch channel lengthening” pattern to a “main channel lengthening, branch channel shortening” pattern;（3）For the transformation of Type II distributary channels into Type I channels, altered hydrological and sediment conditions were the primary driver. Navigation improvement projects demonstrated a promoting effect on this transformation in most distributary channels. After 2013, the frequency and duration of flow levels between 20,000 and 30,000 m3/s increased, leading to intensified scouring in the main channel branch at these flow levels. with some branches evolving into Class I distributary channels. It is foreseeable that branched river systems in the middle and lower reaches of the Yangtze River will predominantly shift toward Class I, characterized by an adjustment pattern where the main channel grows while tributaries diminish.
Available online: June 12, 2026
Abstract:
In river ecosystems, environmental filtering selects for aquatic biological functional traits that exhibit specific responses to catchment-scale land use patterns. To elucidate the mechanisms by which spatial land use configurations influence the distribution of aquatic biological functional traits, this study conducted systematic surveys at 30 sampling sites in the Chishui River Basin from 2022 to 2024. Four macroinvertebrate functional groups were identified through functional trait matrix analysis and cluster analysis. Significant traits for each functional group were screened using Gini coefficients derived from random forest models. Multiple linear regression analysis was employed to examine the variation in explanatory power (R2) of habitat factors within buffer zones of 50, 100, 250, 500, 1000, and 2000 m. Based on the principle of R2 maximization, a 500-m circular buffer zone was determined as the optimal spatial scale for each sampling site. Generalized additive models were subsequently applied to identify the response intervals of buffer zone land use structure that maintain stability of each functional assemblage: forest land 15.21%–44.89%, cropland <5.29%, built-up land 1.21%–9.00%, bare land >32.49%, and water body 0.64%–10.89%, along with critical habitat parameter ranges (water temperature 15–24℃, pH 5.02–8.81, NH?-N 0.31–0.45 mg/L, substrate particle size 36–188 mm). This study further quantified the effects of natural land proportion on the suitability of each functional group: a 10% increase in natural land corresponded to suitability increases of 0.33 and 0.34 units for scrapers and predators, respectively; filters and collectors also exhibited significant suitability improvements with elevated natural land proportion. These findings reveal the response relationships and underlying mechanisms among land use, habitat factors, and macroinvertebrate functional groups, providing quantitative foundations for catchment ecological conservation and land management.
In river ecosystems, environmental filtering selects for aquatic biological functional traits that exhibit specific responses to catchment-scale land use patterns. To elucidate the mechanisms by which spatial land use configurations influence the distribution of aquatic biological functional traits, this study conducted systematic surveys at 30 sampling sites in the Chishui River Basin from 2022 to 2024. Four macroinvertebrate functional groups were identified through functional trait matrix analysis and cluster analysis. Significant traits for each functional group were screened using Gini coefficients derived from random forest models. Multiple linear regression analysis was employed to examine the variation in explanatory power (R2) of habitat factors within buffer zones of 50, 100, 250, 500, 1000, and 2000 m. Based on the principle of R2 maximization, a 500-m circular buffer zone was determined as the optimal spatial scale for each sampling site. Generalized additive models were subsequently applied to identify the response intervals of buffer zone land use structure that maintain stability of each functional assemblage: forest land 15.21%–44.89%, cropland <5.29%, built-up land 1.21%–9.00%, bare land >32.49%, and water body 0.64%–10.89%, along with critical habitat parameter ranges (water temperature 15–24℃, pH 5.02–8.81, NH?-N 0.31–0.45 mg/L, substrate particle size 36–188 mm). This study further quantified the effects of natural land proportion on the suitability of each functional group: a 10% increase in natural land corresponded to suitability increases of 0.33 and 0.34 units for scrapers and predators, respectively; filters and collectors also exhibited significant suitability improvements with elevated natural land proportion. These findings reveal the response relationships and underlying mechanisms among land use, habitat factors, and macroinvertebrate functional groups, providing quantitative foundations for catchment ecological conservation and land management.
Available online: June 11, 2026
Abstract:
Lakes are important ecosystems that support water conservation, climate regulation, and biodiversity conservation. Jiangsu Province is located in the lower reaches of the Yangtze and Huaihe Rivers and represents a typical shallow lake region in China. Lake eutrophication remains a major environmental issue in this area. Northern and Southern Jiangsu differ markedly in natural geography and socioeconomic development. As a result, the trophic status of lakes and their driving factors show clear regional differences. Using long-term monthly monitoring data from 2011 to 2023, this study analyzed the spatial and temporal changes in water quality parameters and the comprehensive Trophic Level Index (TLI) of seven typical lakes. These lakes include Lake Luoma, Lake Hongze, Lake Baima, and Lake Gaoyou in Northern Jiangsu, and Lake Gehu, Lake Changdang, and Lake Gucheng in Southern Jiangsu. The study used Random Forest models and Pearson correlation analysis to quantify the relevant driving mechanisms. The results show that the water quality of typical lakes in Jiangsu exhibited clear regional differences over the past decade. Regarding trophic status, Lake Gehu and Lake Changdang had the most serious eutrophication, with status between light and moderate eutrophication. Lake Baima, Lake Hongze, and Lake Gaoyou were lightly eutrophic. Lake Luoma and Lake Gucheng were in the transition from mesotrophic to lightly eutrophic. Trend analysis indicates that water quality improved significantly in Southern Jiangsu lakes, especially in Lake Gehu and Lake Changdang, which were moderately eutrophic in the past. In Lake Gehu, TN concentration decreased by 1.96 mg/L and TP concentration decreased by 0.087 mg/L. Its TLI value decreased by 9.4. In contrast, water quality worsened in Northern Jiangsu lakes. Lake Luoma changed from mesotrophic to lightly eutrophic, with its TLI rising by 7.4. The TLI of Lake Hongze and Lake Gaoyou increased by 6.6 and 5.4, respectively. The TLI values of all study lakes ranged from 47.36 to 61.01. Southern lakes generally had higher trophic levels, but their pollution control effects were more remarkable. In terms of seasonal variation, Northern lakes showed distinct differences between flood and dry seasons. Their TLI values were much higher in flood seasons. Seasonal changes in TLI were weak in Southern lakes. Driving factor analysis shows that the water quality of Northern lakes was strongly affected by hydrometeorological conditions. More rainfall leads to larger inflows and brings in large amounts of external nutrients. High temperature and wind disturbance also intensify internal nutrient release. The water quality improvement in Southern lakes mainly benefited from optimized land use and rigorous pollution management. Reduced farmland area cuts pollutant sources, while restored forests and wetlands act as pollutant sinks to intercept runoff pollution. This study reveals the complex challenges of lake governance under climate change and non-point source pollution. The results can provide scientific support for targeted eutrophication control and regional water security management in Jiangsu Province.
Lakes are important ecosystems that support water conservation, climate regulation, and biodiversity conservation. Jiangsu Province is located in the lower reaches of the Yangtze and Huaihe Rivers and represents a typical shallow lake region in China. Lake eutrophication remains a major environmental issue in this area. Northern and Southern Jiangsu differ markedly in natural geography and socioeconomic development. As a result, the trophic status of lakes and their driving factors show clear regional differences. Using long-term monthly monitoring data from 2011 to 2023, this study analyzed the spatial and temporal changes in water quality parameters and the comprehensive Trophic Level Index (TLI) of seven typical lakes. These lakes include Lake Luoma, Lake Hongze, Lake Baima, and Lake Gaoyou in Northern Jiangsu, and Lake Gehu, Lake Changdang, and Lake Gucheng in Southern Jiangsu. The study used Random Forest models and Pearson correlation analysis to quantify the relevant driving mechanisms. The results show that the water quality of typical lakes in Jiangsu exhibited clear regional differences over the past decade. Regarding trophic status, Lake Gehu and Lake Changdang had the most serious eutrophication, with status between light and moderate eutrophication. Lake Baima, Lake Hongze, and Lake Gaoyou were lightly eutrophic. Lake Luoma and Lake Gucheng were in the transition from mesotrophic to lightly eutrophic. Trend analysis indicates that water quality improved significantly in Southern Jiangsu lakes, especially in Lake Gehu and Lake Changdang, which were moderately eutrophic in the past. In Lake Gehu, TN concentration decreased by 1.96 mg/L and TP concentration decreased by 0.087 mg/L. Its TLI value decreased by 9.4. In contrast, water quality worsened in Northern Jiangsu lakes. Lake Luoma changed from mesotrophic to lightly eutrophic, with its TLI rising by 7.4. The TLI of Lake Hongze and Lake Gaoyou increased by 6.6 and 5.4, respectively. The TLI values of all study lakes ranged from 47.36 to 61.01. Southern lakes generally had higher trophic levels, but their pollution control effects were more remarkable. In terms of seasonal variation, Northern lakes showed distinct differences between flood and dry seasons. Their TLI values were much higher in flood seasons. Seasonal changes in TLI were weak in Southern lakes. Driving factor analysis shows that the water quality of Northern lakes was strongly affected by hydrometeorological conditions. More rainfall leads to larger inflows and brings in large amounts of external nutrients. High temperature and wind disturbance also intensify internal nutrient release. The water quality improvement in Southern lakes mainly benefited from optimized land use and rigorous pollution management. Reduced farmland area cuts pollutant sources, while restored forests and wetlands act as pollutant sinks to intercept runoff pollution. This study reveals the complex challenges of lake governance under climate change and non-point source pollution. The results can provide scientific support for targeted eutrophication control and regional water security management in Jiangsu Province.
Available online: June 11, 2026
Abstract:
Sediment nitrogen and phosphorus pollution has become a critical factor limiting the sustained improvement of lake water quality in China. To address this issue, this study reviewed domestic and international literature and monitoring data from 2000 to 2022, obtaining surface sediment data from 131 lakes within China"s five major lake zones—Eastern Plain Lakes (EPL), Northeast Plain & Mountain Lakes (NPML), Inner Mongolia-Xinjiang Plateau Lakes (IXML), Yunnan-Guizhou Plateau Lakes (YGPL), and Tibetan Plateau Lakes (TPL). The Single Pollution Index (Pi) method was employed to evaluate the pollution status and spatial differentiation characteristics of Total Nitrogen (TN) and Total Phosphorus (TP). Furthermore, by incorporating case studies, this research systematically reviews the nearly 70-year evolution of management paradigms for lake sediments in China. The key findings are as follows: (1) TN pollution in lake sediments is relatively severe overall (Average Pi = 4.54), reaching a heavy pollution level, with a spatial pattern showing higher levels in the northeast and southwest and lower levels in central and western regions. The pollution degree across lake zones, in descending order, is: NPML Pi = 6.90 > YGPL (5.89) > IXML (5.08) > EPL (4.09) > TPL (4.08). In contrast, TP pollution is relatively lighter overall (Average Pi = 1.41), with the order YGPL Pi = 2.26 > NPML (1.96) > IXML (1.32) > EPL (1.27) > TPL (0.94), at a light pollution level. This indicates that the relatively severe TN pollution and the TP pollution in Chinese lakes are primarily influenced by localized anthropogenic inputs and regional natural backgrounds. (2) The management of sediment pollution in China has undergone a clear three-stage developmental progression: from engineering dredging (1950–1998) to environmental dredging (1998–2015), and then to the current stage of systematic governance (2015–present). (3) For future management, a systematic approach guided by the principle of "zoning, classification, and gradation" must be implemented. Efforts should focus on strengthening foundational surveys and database construction, promoting the classified recycling and utilization of sediments based on pollution characteristics, and establishing long-term guarantee mechanisms, to achieve effective internal pollution control and the long-term restoration of lake ecosystems in China.
Sediment nitrogen and phosphorus pollution has become a critical factor limiting the sustained improvement of lake water quality in China. To address this issue, this study reviewed domestic and international literature and monitoring data from 2000 to 2022, obtaining surface sediment data from 131 lakes within China"s five major lake zones—Eastern Plain Lakes (EPL), Northeast Plain & Mountain Lakes (NPML), Inner Mongolia-Xinjiang Plateau Lakes (IXML), Yunnan-Guizhou Plateau Lakes (YGPL), and Tibetan Plateau Lakes (TPL). The Single Pollution Index (Pi) method was employed to evaluate the pollution status and spatial differentiation characteristics of Total Nitrogen (TN) and Total Phosphorus (TP). Furthermore, by incorporating case studies, this research systematically reviews the nearly 70-year evolution of management paradigms for lake sediments in China. The key findings are as follows: (1) TN pollution in lake sediments is relatively severe overall (Average Pi = 4.54), reaching a heavy pollution level, with a spatial pattern showing higher levels in the northeast and southwest and lower levels in central and western regions. The pollution degree across lake zones, in descending order, is: NPML Pi = 6.90 > YGPL (5.89) > IXML (5.08) > EPL (4.09) > TPL (4.08). In contrast, TP pollution is relatively lighter overall (Average Pi = 1.41), with the order YGPL Pi = 2.26 > NPML (1.96) > IXML (1.32) > EPL (1.27) > TPL (0.94), at a light pollution level. This indicates that the relatively severe TN pollution and the TP pollution in Chinese lakes are primarily influenced by localized anthropogenic inputs and regional natural backgrounds. (2) The management of sediment pollution in China has undergone a clear three-stage developmental progression: from engineering dredging (1950–1998) to environmental dredging (1998–2015), and then to the current stage of systematic governance (2015–present). (3) For future management, a systematic approach guided by the principle of "zoning, classification, and gradation" must be implemented. Efforts should focus on strengthening foundational surveys and database construction, promoting the classified recycling and utilization of sediments based on pollution characteristics, and establishing long-term guarantee mechanisms, to achieve effective internal pollution control and the long-term restoration of lake ecosystems in China.
Available online: June 10, 2026
Abstract:
The global attention to the pollution of nutrients and per-and polyfluoroalkyl substances (PFAS) is increasing, which requires the development of more efficient and low-cost remediation strategies. This study focuses on the remediation of nitrogen, phosphorus, and various PFAS components by aquatic plants, representing a sustainable alternative to traditional physical and chemical methods. In order to overcome the limitations of traditional experimental methods, we constructed a comprehensive dataset by systematically searching for literature in databases such as CNKI, Science Direct, and Web of Science from 2015 to 2025. The final database contains 128 independent experimental records, covering pollutant remediation data under different experimental conditions, ensuring the universality of research conclusions. The input features cover 14 dimensions, including aquatic plant types (submerged, emergent, and floating), planting density, environmental temperature, and initial concentrations of nitrogen, phosphorus, and eight specific PFAS components (such as PFOS, PFOA, PFBA). In order to mitigate inherent systematic biases in multi-source literature data, this study implemented strict quality control protocols. For missing values of secondary environmental parameters, RF-based imputation is used for processing, which can better preserve the nonlinear structure of the data than simple mean replacement. All numerical features are standardized using StandardScaler to eliminate dimensional deviations. In addition, data heterogeneity was quantitatively evaluated using one-way analysis of variance (ANOVA) and effect measures (η2). The results indicate that planting density and temperature are the main sources of statistical heterogeneity, explaining 41.67% and 41.47% of the total variation, respectively (P<0.001). We comprehensively evaluated the impact of various factors on the removal rate of PFAS using Multi-objective Random Forest (MTRF), Multilayer Perceptron (MLP), Random Forest (RF), and Extreme Gradient Boosting (XGBoost) algorithms.?Use R2 and Root Mean Square Err (RMSE) as evaluation metrics for different models.The MTRF model achieved average R2 values of 0.68 and 0.72 in nitrogen removal and PFNA prediction, respectively, demonstrating substantial predictive ability significantly better than the MLP model with negative R2 values and inability to capture complex patterns. The in-depth mechanism explanation using the SHAP framework reveals that initial phosphorus concentration has a positive effect on nitrogen absorption, and phosphorus can promote nitrogen absorption by improving plant metabolic capacity. For PFAS, a threshold suppression effect was observed; Due to oxidative stress and enzyme activity inhibition caused by reactive oxygen species (ROS), high initial concentrations and extreme temperatures are negatively correlated with removal efficiency. Through virtual screening, Vallisneria natans was identified as the dominant species, possibly due to its strong root to stem transport ability and high bioaccumulation factor for PFAS. By optimizing the operating conditions, the optimal planting density for removing nutrients from Vallisneria natans is 19 plants/m2, and the optimal restoration time is 69 days; The optimal planting density for removing PFAS is 59 plants/m2, and the optimal restoration time is 34 days. The machine learning model established in this study not only provides accurate predictions for plant remediation efficiency under complex water quality conditions, but also provides theoretical basis and engineering decision support for low-cost and systematic treatment of water composite pollution.
The global attention to the pollution of nutrients and per-and polyfluoroalkyl substances (PFAS) is increasing, which requires the development of more efficient and low-cost remediation strategies. This study focuses on the remediation of nitrogen, phosphorus, and various PFAS components by aquatic plants, representing a sustainable alternative to traditional physical and chemical methods. In order to overcome the limitations of traditional experimental methods, we constructed a comprehensive dataset by systematically searching for literature in databases such as CNKI, Science Direct, and Web of Science from 2015 to 2025. The final database contains 128 independent experimental records, covering pollutant remediation data under different experimental conditions, ensuring the universality of research conclusions. The input features cover 14 dimensions, including aquatic plant types (submerged, emergent, and floating), planting density, environmental temperature, and initial concentrations of nitrogen, phosphorus, and eight specific PFAS components (such as PFOS, PFOA, PFBA). In order to mitigate inherent systematic biases in multi-source literature data, this study implemented strict quality control protocols. For missing values of secondary environmental parameters, RF-based imputation is used for processing, which can better preserve the nonlinear structure of the data than simple mean replacement. All numerical features are standardized using StandardScaler to eliminate dimensional deviations. In addition, data heterogeneity was quantitatively evaluated using one-way analysis of variance (ANOVA) and effect measures (η2). The results indicate that planting density and temperature are the main sources of statistical heterogeneity, explaining 41.67% and 41.47% of the total variation, respectively (P<0.001). We comprehensively evaluated the impact of various factors on the removal rate of PFAS using Multi-objective Random Forest (MTRF), Multilayer Perceptron (MLP), Random Forest (RF), and Extreme Gradient Boosting (XGBoost) algorithms.?Use R2 and Root Mean Square Err (RMSE) as evaluation metrics for different models.The MTRF model achieved average R2 values of 0.68 and 0.72 in nitrogen removal and PFNA prediction, respectively, demonstrating substantial predictive ability significantly better than the MLP model with negative R2 values and inability to capture complex patterns. The in-depth mechanism explanation using the SHAP framework reveals that initial phosphorus concentration has a positive effect on nitrogen absorption, and phosphorus can promote nitrogen absorption by improving plant metabolic capacity. For PFAS, a threshold suppression effect was observed; Due to oxidative stress and enzyme activity inhibition caused by reactive oxygen species (ROS), high initial concentrations and extreme temperatures are negatively correlated with removal efficiency. Through virtual screening, Vallisneria natans was identified as the dominant species, possibly due to its strong root to stem transport ability and high bioaccumulation factor for PFAS. By optimizing the operating conditions, the optimal planting density for removing nutrients from Vallisneria natans is 19 plants/m2, and the optimal restoration time is 69 days; The optimal planting density for removing PFAS is 59 plants/m2, and the optimal restoration time is 34 days. The machine learning model established in this study not only provides accurate predictions for plant remediation efficiency under complex water quality conditions, but also provides theoretical basis and engineering decision support for low-cost and systematic treatment of water composite pollution.
Available online: June 10, 2026
Abstract:
As global climate change intensifies, hydrological cycles are exhibiting increasingly pronounced non-stationary, multi-scale, and highly nonlinear behaviors. Traditional mechanistic models face significant challenges in fully capturing the meteorological–runoff response mechanisms, while deep learning approaches still struggle with long-term dependency modeling, spatial correlations, and sequence decoupling. To address these issues, we propose a hybrid forecasting model, JMD-Gformer, which combines Jump plus AM-FM Mode Decomposition (JMD), sparse directed graph networks, and Transformer-based architectures. In this framework, JMD decomposes the non-stationary runoff time series into jump components (representing abrupt runoff events) and periodic components (capturing seasonal and inter-annual fluctuations), effectively mitigating noise and mode aliasing. Additionally, we construct a sparse directed graph based on meteorology-hydrology nodes to represent the upstream-downstream interactions. The model further incorporates a multi-head self-attention mechanism for long-range temporal dependencies. Experiments conducted on multi-time-scale runoff predictions in the Daliao River Basin demonstrate that, compared to the second-best benchmark model, JMD-Gformer reduces MAPE and RMSE by 36.4% and 41.2%, respectively, and shows strong robustness and predictive accuracy under complex hydrological conditions. This model provides a promising new approach for smart watershed management.
As global climate change intensifies, hydrological cycles are exhibiting increasingly pronounced non-stationary, multi-scale, and highly nonlinear behaviors. Traditional mechanistic models face significant challenges in fully capturing the meteorological–runoff response mechanisms, while deep learning approaches still struggle with long-term dependency modeling, spatial correlations, and sequence decoupling. To address these issues, we propose a hybrid forecasting model, JMD-Gformer, which combines Jump plus AM-FM Mode Decomposition (JMD), sparse directed graph networks, and Transformer-based architectures. In this framework, JMD decomposes the non-stationary runoff time series into jump components (representing abrupt runoff events) and periodic components (capturing seasonal and inter-annual fluctuations), effectively mitigating noise and mode aliasing. Additionally, we construct a sparse directed graph based on meteorology-hydrology nodes to represent the upstream-downstream interactions. The model further incorporates a multi-head self-attention mechanism for long-range temporal dependencies. Experiments conducted on multi-time-scale runoff predictions in the Daliao River Basin demonstrate that, compared to the second-best benchmark model, JMD-Gformer reduces MAPE and RMSE by 36.4% and 41.2%, respectively, and shows strong robustness and predictive accuracy under complex hydrological conditions. This model provides a promising new approach for smart watershed management.
Ye Zili, Zhi Mingqiang, Zhang Wenyu, Li Yuanhe, Shi Yuanzhi, Zhang Chunmin, Zhang Huajun, Huang Wei, Liu Cheng, Yin Hongbin
Available online: June 09, 2026
Abstract:
This study selected East Lake Taihu as the research object. It systematically investigated the physicochemical properties, nutrient distribution, and pollutant release characteristics of sediments in historical aquaculture areas and aquatic vegetation zones. This study adopted the single-factor pollution index method and the comprehensive pollution index method to assess sediment pollution levels. The research clarifies the pollution status and release characteristics of sediments in historical aquaculture areas of East Lake Taihu. The results indicate obvious differences in sediment physicochemical properties and nutrient contents between the two functional zones. In the 0–10 cm and 10–20 cm surface sediment layers of aquaculture areas, pH values (7.19 and 7.23) and moisture contents (65.84% and 54.31%) were significantly higher than those in aquatic vegetation zones. Sediment pH generally increased with the increase of sediment depth, while moisture content decreased with the increase of depth. The average contents of total nitrogen (TN), total phosphorus (TP), and organic matter (OM) in 0–10 cm surface sediments of aquaculture areas were 1610 mg/kg, 665 mg/kg, and 4.26%, respectively, which were 1.22, 1.43, and 1.51 times the corresponding values in aquatic vegetation zones. Nutrients in aquaculture areas mainly accumulate in surface sediment layers. The average TN release flux of aquaculture areas (31.63 mg/(m2·d)) was substantially higher than that of aquatic vegetation zones (-3.99 mg/(m2·d)), indicating a continuous nitrogen release process in aquaculture area sediments. By comparison, the TP release flux showed no significant difference between the two zones. The concentrations of ammonia nitrogen and ferrous iron in pore water, as well as the release fluxes calculated by Fick''s Law, were significantly higher in aquaculture areas than in aquatic vegetation zones. The average concentration of diffusive gradients in thin films–extractable phosphorus (DGT-P) in aquaculture areas was 0.026 mg/L, 1.5 times the value of 0.017 mg/L in aquatic vegetation zones, which demonstrates a stronger labile phosphorus release capacity in aquaculture areas. Sediment pollution assessment results reveal that sediment pollution presents vertical decreasing trends and regional differentiation characteristics. In the 0–10 cm sediment layer, the proportion of heavily polluted sites reached 17.4% for TN and 35.5% for the comprehensive pollution index (FF). This proportion dropped to 26.1% in the 10–20 cm layer. The 20–30 cm layer was mainly dominated by slight FF pollution, with a proportion of 37.4%. In the 0–10 and 10–20 cm layers, aquaculture areas showed significantly higher pollution indices than aquatic vegetation zones, while the difference narrowed in the 20–30 cm layer. Heavily polluted sites were mostly concentrated in historical aquaculture areas. This study’s findings provide a scientific basis for the targeted control of internal sediment pollution in the aquaculture areas of East Lake Taihu.
This study selected East Lake Taihu as the research object. It systematically investigated the physicochemical properties, nutrient distribution, and pollutant release characteristics of sediments in historical aquaculture areas and aquatic vegetation zones. This study adopted the single-factor pollution index method and the comprehensive pollution index method to assess sediment pollution levels. The research clarifies the pollution status and release characteristics of sediments in historical aquaculture areas of East Lake Taihu. The results indicate obvious differences in sediment physicochemical properties and nutrient contents between the two functional zones. In the 0–10 cm and 10–20 cm surface sediment layers of aquaculture areas, pH values (7.19 and 7.23) and moisture contents (65.84% and 54.31%) were significantly higher than those in aquatic vegetation zones. Sediment pH generally increased with the increase of sediment depth, while moisture content decreased with the increase of depth. The average contents of total nitrogen (TN), total phosphorus (TP), and organic matter (OM) in 0–10 cm surface sediments of aquaculture areas were 1610 mg/kg, 665 mg/kg, and 4.26%, respectively, which were 1.22, 1.43, and 1.51 times the corresponding values in aquatic vegetation zones. Nutrients in aquaculture areas mainly accumulate in surface sediment layers. The average TN release flux of aquaculture areas (31.63 mg/(m2·d)) was substantially higher than that of aquatic vegetation zones (-3.99 mg/(m2·d)), indicating a continuous nitrogen release process in aquaculture area sediments. By comparison, the TP release flux showed no significant difference between the two zones. The concentrations of ammonia nitrogen and ferrous iron in pore water, as well as the release fluxes calculated by Fick''s Law, were significantly higher in aquaculture areas than in aquatic vegetation zones. The average concentration of diffusive gradients in thin films–extractable phosphorus (DGT-P) in aquaculture areas was 0.026 mg/L, 1.5 times the value of 0.017 mg/L in aquatic vegetation zones, which demonstrates a stronger labile phosphorus release capacity in aquaculture areas. Sediment pollution assessment results reveal that sediment pollution presents vertical decreasing trends and regional differentiation characteristics. In the 0–10 cm sediment layer, the proportion of heavily polluted sites reached 17.4% for TN and 35.5% for the comprehensive pollution index (FF). This proportion dropped to 26.1% in the 10–20 cm layer. The 20–30 cm layer was mainly dominated by slight FF pollution, with a proportion of 37.4%. In the 0–10 and 10–20 cm layers, aquaculture areas showed significantly higher pollution indices than aquatic vegetation zones, while the difference narrowed in the 20–30 cm layer. Heavily polluted sites were mostly concentrated in historical aquaculture areas. This study’s findings provide a scientific basis for the targeted control of internal sediment pollution in the aquaculture areas of East Lake Taihu.
Chen Weijing, Fu Yu, Teng Jiakun, Xie Tian, Lu Xiuming, Yu Hailing, Che Chunguang, Duan Houlang, Yu Xiubo
Available online: June 09, 2026
Abstract:
Hydrology and vegetation are important components of the landscape structure of freshwater wetlands. Changes in the water and sediment regimes of the Yellow River, along with reduced freshwater input, have impacted waterbird diversity in the Shandong Yellow River Delta National Nature Reserve (hereinafter referred to as the "Nature Reserve"). In response, the Nature Reserve has implemented consecutive years of freshwater wetland ecological water supplement projects, regulating the distribution area of open water and shallow water, and improving plant community composition. However, quantitative research on waterbird diversity and its relationship with wetland landscape patterns following this ecological intervention has been lacking. This study utilizes waterbird survey data, Sentinel-2 satellite remote sensing data, and water level monitoring data collected during field investigations in 2023 and 2024. The aim is to elucidate the composition and numerical changes of waterbird communities in the wetland restoration area and to reveal the quantitative relationships between waterbird diversity and the areal extent of key wetland landscape elements. The results showed that a total of 126 waterbird species belonging to 15 families and 7 orders were recorded in the study area. Waterbird species richness and individual abundance exhibited significant monthly fluctuations, with peaks during migration periods in March and November. During migration seasons, ducks and shorebirds dominated in terms of species proportion, while ducks, cranes, and storks dominated in terms of individual abundance. Within the 10,000-mu wetland restoration area of the Nature Reserve, the areas of shallow water (water depth 0-30 cm) and open water were largest. Specifically, the shallow water area was greatest in winter (1888 m2), while the open water area was relatively larger in spring and autumn (2933 m2). The vegetation area exhibited a trend of "expansion in summer, contraction in winter," increasing by 26% in 2024 compared to 2023. The abundance of geese and ducks showed a unimodal relationship with the proportions of both open water area and vegetation area. Goose abundance peaked when the ratio of water area to vegetation area was approximately 2:1 (n = 44, df = 40, p < 0.01, R2 = 0.14; n = 44, df = 40, p < 0.01, R2 = 0.28). Duck abundance peaked when this ratio was approximately 1.5:1 (n = 118, df = 114, p < 0.01, R2 = 0.02; n = 118, df = 114, p < 0.01, R2 = 0.002). The abundance of shorebirds was significantly positively correlated with the proportion of shallow water area (n = 24, df = 22, p < 0.05, R2 = 0.29) but significantly negatively correlated with the proportion of vegetation area (n = 24, df = 22, p < 0.05, R2 = 0.17).
Hydrology and vegetation are important components of the landscape structure of freshwater wetlands. Changes in the water and sediment regimes of the Yellow River, along with reduced freshwater input, have impacted waterbird diversity in the Shandong Yellow River Delta National Nature Reserve (hereinafter referred to as the "Nature Reserve"). In response, the Nature Reserve has implemented consecutive years of freshwater wetland ecological water supplement projects, regulating the distribution area of open water and shallow water, and improving plant community composition. However, quantitative research on waterbird diversity and its relationship with wetland landscape patterns following this ecological intervention has been lacking. This study utilizes waterbird survey data, Sentinel-2 satellite remote sensing data, and water level monitoring data collected during field investigations in 2023 and 2024. The aim is to elucidate the composition and numerical changes of waterbird communities in the wetland restoration area and to reveal the quantitative relationships between waterbird diversity and the areal extent of key wetland landscape elements. The results showed that a total of 126 waterbird species belonging to 15 families and 7 orders were recorded in the study area. Waterbird species richness and individual abundance exhibited significant monthly fluctuations, with peaks during migration periods in March and November. During migration seasons, ducks and shorebirds dominated in terms of species proportion, while ducks, cranes, and storks dominated in terms of individual abundance. Within the 10,000-mu wetland restoration area of the Nature Reserve, the areas of shallow water (water depth 0-30 cm) and open water were largest. Specifically, the shallow water area was greatest in winter (1888 m2), while the open water area was relatively larger in spring and autumn (2933 m2). The vegetation area exhibited a trend of "expansion in summer, contraction in winter," increasing by 26% in 2024 compared to 2023. The abundance of geese and ducks showed a unimodal relationship with the proportions of both open water area and vegetation area. Goose abundance peaked when the ratio of water area to vegetation area was approximately 2:1 (n = 44, df = 40, p < 0.01, R2 = 0.14; n = 44, df = 40, p < 0.01, R2 = 0.28). Duck abundance peaked when this ratio was approximately 1.5:1 (n = 118, df = 114, p < 0.01, R2 = 0.02; n = 118, df = 114, p < 0.01, R2 = 0.002). The abundance of shorebirds was significantly positively correlated with the proportion of shallow water area (n = 24, df = 22, p < 0.05, R2 = 0.29) but significantly negatively correlated with the proportion of vegetation area (n = 24, df = 22, p < 0.05, R2 = 0.17).
Available online: June 08, 2026
Abstract:
To explore the spatiotemporal coupling mechanism of the water network in the Erhai Basin under the combined influence of natural and social drivers, and to reveal the mediating role of topological features between driving factors and water system elements, this study integrates four phases of remote sensing and geographic data within the framework of complex network theory. Nine topological indicators were selected to characterize the structural features of the basin’s water network，to overcome the limitation of traditional regression that it is difficult to simultaneously handle driver collinearity, spatial overflow and mechanism decomposition, this paper constructs a （Partial Least Squares）PLS-（Spatial Durbin Model）SDM-（Mediation effect）MED framework that can handle multi-driver collinearity, simultaneously characterize spatial overflow, and decompose the total effect into direct effects and indirect effects conducted through topological structure, thereby more accurately identifying key intermediate paths. The results show that:(1) From 2001 to 2023, the Erhai water network evolved from a multi-source redundant configuration to a stable state characterized by a clear mainstem and relatively high efficiency.(2) Among a total of 216 paths, 68 significant X-M-Y paths were identified, with mediation efficiencies mainly ranging between 40% and 80%. Betweenness centrality of edges, compactness, global efficiency, and algebraic connectivity were identified as the core mediating indicators.(3) Social factors primarily exerted high-proportion negative effects on hydrological elements through the mediating role of network topology, while natural factors generally displayed moderately strong and stable positive effects, with a few pathways showing structural suppressing effects.The proposed PLS–SDM–Med analytical framework provides a transferable approach for identifying key structural units and risk pathways in plateau lake basins, offering a theoretical basis for zoning control and ecological restoration in the Erhai Basin and other similar highland lake watersheds.
To explore the spatiotemporal coupling mechanism of the water network in the Erhai Basin under the combined influence of natural and social drivers, and to reveal the mediating role of topological features between driving factors and water system elements, this study integrates four phases of remote sensing and geographic data within the framework of complex network theory. Nine topological indicators were selected to characterize the structural features of the basin’s water network，to overcome the limitation of traditional regression that it is difficult to simultaneously handle driver collinearity, spatial overflow and mechanism decomposition, this paper constructs a （Partial Least Squares）PLS-（Spatial Durbin Model）SDM-（Mediation effect）MED framework that can handle multi-driver collinearity, simultaneously characterize spatial overflow, and decompose the total effect into direct effects and indirect effects conducted through topological structure, thereby more accurately identifying key intermediate paths. The results show that:(1) From 2001 to 2023, the Erhai water network evolved from a multi-source redundant configuration to a stable state characterized by a clear mainstem and relatively high efficiency.(2) Among a total of 216 paths, 68 significant X-M-Y paths were identified, with mediation efficiencies mainly ranging between 40% and 80%. Betweenness centrality of edges, compactness, global efficiency, and algebraic connectivity were identified as the core mediating indicators.(3) Social factors primarily exerted high-proportion negative effects on hydrological elements through the mediating role of network topology, while natural factors generally displayed moderately strong and stable positive effects, with a few pathways showing structural suppressing effects.The proposed PLS–SDM–Med analytical framework provides a transferable approach for identifying key structural units and risk pathways in plateau lake basins, offering a theoretical basis for zoning control and ecological restoration in the Erhai Basin and other similar highland lake watersheds.
Available online: June 08, 2026
Abstract:
PME (Phosphate monoesters) are key components of dissolved organic phosphorus, characterized by relatively high abundance and pronounced photoactivity; however, their photochemical dephosphorylation mechanisms in aquatic systems remain to be systematically elucidated. The study systematically investigated the photochemical behavior of the phosphate monoester G6P (Glucose-6-phosphate) by combining experimental investigations with DFT (Density Functional Theory) calculations. The results indicated that the light absorption of G6P is primarily in the 200–290?nm range, with higher photolysis efficiency under shorter-wavelength irradiation. Analysis of energy and electron transfer processes revealed that interactions between G6P and DO (Dissolved Oxygen), DOM (Dissolved Organic Matter), and major anions (e.g., NO3-, HCO3-) do not serve as the main pathways driving its photolysis. Instead, photodegradation relies more on the attack of RIs (Reactive Intermediates) on electron-rich sites, such as the extended region of the glycosyl–phosphate linkage, which triggers molecular destabilization and ultimately leads to IP (Inorganic Phosphate) release. Photolysis experiments further confirmed this mechanism, showing that 3DOM* plays a predominant role in promoting G6P degradation in DOM-containing systems. From an environmental perspective, significant differences were observed in the photolysis of PME between freshwater and seawater systems. The photolysis rate constants of G6P were determined to be (2.00–5.60)?×10-3?h-1 in freshwater and (1.60–3.30)?×10-3?h-1 in seawater. Freshwater systems favor oxidation-dominated pathways with higher thermodynamic driving force, whereas seawater systems, under high salinity and halide-rich conditions, exhibit more pronounced halogen substitution and addition characteristics. Overall, this study demonstrates that the photolysis of PME is co-determined by its molecular structure and ambient aqueous conditions, which collectively govern the pathways and efficiency of its photochemical transformation. These findings provide a new mechanistic perspective for understanding the abiotic mineralization and environmental behavior of DOP (Dissolved Organic Phosphorus) in aquatic systems.
PME (Phosphate monoesters) are key components of dissolved organic phosphorus, characterized by relatively high abundance and pronounced photoactivity; however, their photochemical dephosphorylation mechanisms in aquatic systems remain to be systematically elucidated. The study systematically investigated the photochemical behavior of the phosphate monoester G6P (Glucose-6-phosphate) by combining experimental investigations with DFT (Density Functional Theory) calculations. The results indicated that the light absorption of G6P is primarily in the 200–290?nm range, with higher photolysis efficiency under shorter-wavelength irradiation. Analysis of energy and electron transfer processes revealed that interactions between G6P and DO (Dissolved Oxygen), DOM (Dissolved Organic Matter), and major anions (e.g., NO3-, HCO3-) do not serve as the main pathways driving its photolysis. Instead, photodegradation relies more on the attack of RIs (Reactive Intermediates) on electron-rich sites, such as the extended region of the glycosyl–phosphate linkage, which triggers molecular destabilization and ultimately leads to IP (Inorganic Phosphate) release. Photolysis experiments further confirmed this mechanism, showing that 3DOM* plays a predominant role in promoting G6P degradation in DOM-containing systems. From an environmental perspective, significant differences were observed in the photolysis of PME between freshwater and seawater systems. The photolysis rate constants of G6P were determined to be (2.00–5.60)?×10-3?h-1 in freshwater and (1.60–3.30)?×10-3?h-1 in seawater. Freshwater systems favor oxidation-dominated pathways with higher thermodynamic driving force, whereas seawater systems, under high salinity and halide-rich conditions, exhibit more pronounced halogen substitution and addition characteristics. Overall, this study demonstrates that the photolysis of PME is co-determined by its molecular structure and ambient aqueous conditions, which collectively govern the pathways and efficiency of its photochemical transformation. These findings provide a new mechanistic perspective for understanding the abiotic mineralization and environmental behavior of DOP (Dissolved Organic Phosphorus) in aquatic systems.
Available online: June 05, 2026
Abstract:
Rivers entering the lake constitute the primary pathways for external nutrient inputs, and variations in nitrogen (N) and phosphorus (P) fluxes directly influence lake eutrophication and the risk of algal blooms. To accurately assess the pollutant export characteristics and driving mechanisms of typical inflow rivers in the Chaohu Basin, this study focuses on the Hangbu River, the largest tributary discharging into Chaohu Lake. Using the period-average flux method, the Load Estimator (LOADEST) model, and the WRTDS model, fluxes and long-term trends were estimated for hydrological and water-quality data from 2019 to 2024 at four stations along the river: Yaojiahe (upstream), Hekou Bridge (midstream), Sanhe Town Bridge (mid-downstream), and Beizhadukou (downstream). The period-average method is computationally simple but produces large errors. In comparison, the LOADEST model performs better in the Chaohu Basin and achieves substantially higher agreement with observed daily fluxes than the WRTDS model. The results show that LOADEST performs best under conditions of continuous discharge records and relatively sparse water-quality measurements, with R2 values of 0.89 to 0.97 and NSE values of 0.84 to 0.98, allowing stable reconstruction of continuous flux series. Based on LOADEST, the estimated total nitrogen (TN) and total phosphorus (TP) fluxes exhibit strong temporal and spatial variability. At the lake-inlet section, the wet season from May to September contributes 68 to 77 percent of annual TN flux and 72 to 81 percent of annual TP flux. A single storm event with 61.8 mm of rainfall can generate as much as 73 percent of the monthly flux, revealing a pronounced pulse-like export pattern. Spatially, TN and TP fluxes increase progressively from upstream to downstream, and the annual fluxes at the Beizhadukou section reach 4.24×106 kg N per year and 2.25×105 kg P per year, which are 10 to 17 times higher than those upstream. Trend decomposition indicates that TN flux into the lake has continued to rise over the past five years, whereas TP flux shows a slight decline, suggesting persistent nitrogen accumulation but a temporary easing of phosphorus export. Overall, flux variations are jointly driven by hydrological processes and human activities. Intense rainfall events amplify the contributions of agricultural and urban pollution to nutrient loading at downstream sections. These findings provide scientific support for external load assessment, pollution control, and algal bloom risk management in the Chaohu Basin under current environmental conditions.
Rivers entering the lake constitute the primary pathways for external nutrient inputs, and variations in nitrogen (N) and phosphorus (P) fluxes directly influence lake eutrophication and the risk of algal blooms. To accurately assess the pollutant export characteristics and driving mechanisms of typical inflow rivers in the Chaohu Basin, this study focuses on the Hangbu River, the largest tributary discharging into Chaohu Lake. Using the period-average flux method, the Load Estimator (LOADEST) model, and the WRTDS model, fluxes and long-term trends were estimated for hydrological and water-quality data from 2019 to 2024 at four stations along the river: Yaojiahe (upstream), Hekou Bridge (midstream), Sanhe Town Bridge (mid-downstream), and Beizhadukou (downstream). The period-average method is computationally simple but produces large errors. In comparison, the LOADEST model performs better in the Chaohu Basin and achieves substantially higher agreement with observed daily fluxes than the WRTDS model. The results show that LOADEST performs best under conditions of continuous discharge records and relatively sparse water-quality measurements, with R2 values of 0.89 to 0.97 and NSE values of 0.84 to 0.98, allowing stable reconstruction of continuous flux series. Based on LOADEST, the estimated total nitrogen (TN) and total phosphorus (TP) fluxes exhibit strong temporal and spatial variability. At the lake-inlet section, the wet season from May to September contributes 68 to 77 percent of annual TN flux and 72 to 81 percent of annual TP flux. A single storm event with 61.8 mm of rainfall can generate as much as 73 percent of the monthly flux, revealing a pronounced pulse-like export pattern. Spatially, TN and TP fluxes increase progressively from upstream to downstream, and the annual fluxes at the Beizhadukou section reach 4.24×106 kg N per year and 2.25×105 kg P per year, which are 10 to 17 times higher than those upstream. Trend decomposition indicates that TN flux into the lake has continued to rise over the past five years, whereas TP flux shows a slight decline, suggesting persistent nitrogen accumulation but a temporary easing of phosphorus export. Overall, flux variations are jointly driven by hydrological processes and human activities. Intense rainfall events amplify the contributions of agricultural and urban pollution to nutrient loading at downstream sections. These findings provide scientific support for external load assessment, pollution control, and algal bloom risk management in the Chaohu Basin under current environmental conditions.
Available online: June 05, 2026
Abstract:
Semi-arid closed lakes are critical nodes where ecological, climate, and human factors intertwine. Their multifunctionality plays an important supporting role in regional sustainable development. This study focuses on the ecological function maintenance of closed lakes in semi-arid regions, with Lake Daihai, a typical inland closed saline lake in the Mongolian Plateau, as the research subject. Given the ongoing deterioration of its water environment, this study conducts a systematic analysis based on continuous monitoring data from 2020 to 2024. Using Principal Component Analysis/Factor Analysis (PCA/FA), five key water quality parameters—dissolved oxygen (DO), chemical oxygen demand (CODCr), total nitrogen (TN), total phosphorus (TP), and salinity (Sal)—were selected from the multidimensional water quality dataset. The spatiotemporal variation patterns of the water environment parameters in Lake Daihai were systematically analyzed, and the Water Quality Index (WQI) was used for quantitative assessment. Pollution source apportionment was carried out using a comparative analysis of the Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR) and Positive Matrix Factorization (PMF) models. The results show that the PMF model exhibited better performance in pollution source identification. The source apportionment results revealed that the main pollution sources in Lake Daihai are as follows, with their contribution rates: rural domestic pollution (23.5%), planktonic endogenous release (22.5%), livestock farming pollution (20.1%), surface runoff pollution (19.6%), and agricultural cultivation pollution (14.4%). This study quantifies the contribution rates of pollution sources in Lake Daihai, providing a theoretical basis for targeted management and ecological restoration of Daihai and similar lakes in semi-arid regions.
Semi-arid closed lakes are critical nodes where ecological, climate, and human factors intertwine. Their multifunctionality plays an important supporting role in regional sustainable development. This study focuses on the ecological function maintenance of closed lakes in semi-arid regions, with Lake Daihai, a typical inland closed saline lake in the Mongolian Plateau, as the research subject. Given the ongoing deterioration of its water environment, this study conducts a systematic analysis based on continuous monitoring data from 2020 to 2024. Using Principal Component Analysis/Factor Analysis (PCA/FA), five key water quality parameters—dissolved oxygen (DO), chemical oxygen demand (CODCr), total nitrogen (TN), total phosphorus (TP), and salinity (Sal)—were selected from the multidimensional water quality dataset. The spatiotemporal variation patterns of the water environment parameters in Lake Daihai were systematically analyzed, and the Water Quality Index (WQI) was used for quantitative assessment. Pollution source apportionment was carried out using a comparative analysis of the Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR) and Positive Matrix Factorization (PMF) models. The results show that the PMF model exhibited better performance in pollution source identification. The source apportionment results revealed that the main pollution sources in Lake Daihai are as follows, with their contribution rates: rural domestic pollution (23.5%), planktonic endogenous release (22.5%), livestock farming pollution (20.1%), surface runoff pollution (19.6%), and agricultural cultivation pollution (14.4%). This study quantifies the contribution rates of pollution sources in Lake Daihai, providing a theoretical basis for targeted management and ecological restoration of Daihai and similar lakes in semi-arid regions.
Available online: June 04, 2026
Abstract:
Over the past half-century of evolution in the Yangtze River-Dongting Lake water network, the regulating and storage function of Dongting Lake over the Yangtze River and the Xiang, Zi, Yuan, and Li Rivers in Hunan has gradually shifted from flood retention and sedimentation to flood regulation and sediment replenishment. This transition marks a new phase in the relationship between rivers and lakes, necessitating updated perspectives for their governance and protection. This study, based on comprehensive prototype observation data of the Yangtze River main stream and the Dongting Lake water system, thoroughly analyzes the developmental process, distribution characteristics, and driving factors of sedimentation to sediment replenishment in Dongting Lake. It reveals the macroscopic response of hydrological conditions (flood and dry seasons) in the lake region to changes in sediment deposition status. Results indicate that Dongting Lake has sequentially undergone three developmental stages: the sediment retention weakening phase, the sediment retention stabilization phase, and the sediment replenishment enhancement phase. Sediment deposition progresses from west to east, while sediment replenishment moves from east to west, maintaining the seasonal pattern of deposition during flood periods and replenishment during non-flood periods. Sediment replenishment is primarily dominated by extremely fine particles, which do not contribute to bed formation in the Yangtze River main stream but facilitate the replenishment of nutrient materials. High sediment inflow and weak hydrodynamic conditions are the primary causes of sediment deposition. The sustained decline in sediment concentration of lake inflow, driven by the operation of controlling reservoir groups and soil conservation projects, serves as the core driving factor for sediment replenishment. However, the level of sediment replenishment in the lake region remains low and shows limited potential for further development. Sediment deposition is one of the main factors behind the widespread elevation of the highest water levels in the lake region prior to the impoundment of the Three Gorges Reservoir. The water replenishment regulation of the Three Gorges Reservoir downstream of the dam struggles to mitigate the declining trend of the lowest water levels in the Dongting Lake region. While changes in sediment deposition status will improve flood control conditions in Dongting Lake, the hydrological situation during dry seasons in the lake region is becoming increasingly strained.
Over the past half-century of evolution in the Yangtze River-Dongting Lake water network, the regulating and storage function of Dongting Lake over the Yangtze River and the Xiang, Zi, Yuan, and Li Rivers in Hunan has gradually shifted from flood retention and sedimentation to flood regulation and sediment replenishment. This transition marks a new phase in the relationship between rivers and lakes, necessitating updated perspectives for their governance and protection. This study, based on comprehensive prototype observation data of the Yangtze River main stream and the Dongting Lake water system, thoroughly analyzes the developmental process, distribution characteristics, and driving factors of sedimentation to sediment replenishment in Dongting Lake. It reveals the macroscopic response of hydrological conditions (flood and dry seasons) in the lake region to changes in sediment deposition status. Results indicate that Dongting Lake has sequentially undergone three developmental stages: the sediment retention weakening phase, the sediment retention stabilization phase, and the sediment replenishment enhancement phase. Sediment deposition progresses from west to east, while sediment replenishment moves from east to west, maintaining the seasonal pattern of deposition during flood periods and replenishment during non-flood periods. Sediment replenishment is primarily dominated by extremely fine particles, which do not contribute to bed formation in the Yangtze River main stream but facilitate the replenishment of nutrient materials. High sediment inflow and weak hydrodynamic conditions are the primary causes of sediment deposition. The sustained decline in sediment concentration of lake inflow, driven by the operation of controlling reservoir groups and soil conservation projects, serves as the core driving factor for sediment replenishment. However, the level of sediment replenishment in the lake region remains low and shows limited potential for further development. Sediment deposition is one of the main factors behind the widespread elevation of the highest water levels in the lake region prior to the impoundment of the Three Gorges Reservoir. The water replenishment regulation of the Three Gorges Reservoir downstream of the dam struggles to mitigate the declining trend of the lowest water levels in the Dongting Lake region. While changes in sediment deposition status will improve flood control conditions in Dongting Lake, the hydrological situation during dry seasons in the lake region is becoming increasingly strained.
Available online: June 04, 2026
Abstract:
Runoff simulation and forecasting are essential for watershed flood hazard mitigation and optimal utilization of regional water resources. A key factor affecting these processes is the structural heterogeneity of precipitation inputs. As the primary source of precipitation data derived from ground observations, rain gauges can substantially improve rainfall-runoff modeling accuracy when deployed with appropriate density and spatial distribution. This study constructs a spatio-temporal graph neural network framework that integrates Long Short-Term Memory (LSTM) and Graph Neural Network (GNN) approaches to jointly capture the temporal dynamics of hydrological variables and the spatial topological structure among stations for watershed runoff simulation. Meanwhile, the effects of rain gauge density and spatial distribution on model performance are systematically assessed using multiple mean areal precipitation (MAP) estimation methods. The results revealed that: (1) Rain gauge samples selected through clustering form four density distribution scenarios, representing 100%, 72.22%, 50%, and 27.78% of the full network respectively. Across four distributions, the average Nash-Sutcliffe efficiency (NSE) values exceeded 0.93. The runoff simulation associated with Distribution 3 yielded the best performance (NSE=0.967, mean absolute error MAE=175.5m3/s, relative bias BIAS=0.01, and coefficient of determination R2=0.98) under both high-flow and low-flow conditions; (2) Among all the MAP methods, the clustering weight method produced the most robust results, achieving the highest NSE, relatively low MAE, and BIAS closest to 0. Additionally, Distribution 3 maintained the best overall performance, with the smallest simulation errors and biases. The optimization of the rain gauge network combined with the selection of appropriate MAP approaches can enhance the efficiency and adaptability and simulation accuracy of runoff simulation models, offering a solid scientific foundation for hydrological forecasting.
Runoff simulation and forecasting are essential for watershed flood hazard mitigation and optimal utilization of regional water resources. A key factor affecting these processes is the structural heterogeneity of precipitation inputs. As the primary source of precipitation data derived from ground observations, rain gauges can substantially improve rainfall-runoff modeling accuracy when deployed with appropriate density and spatial distribution. This study constructs a spatio-temporal graph neural network framework that integrates Long Short-Term Memory (LSTM) and Graph Neural Network (GNN) approaches to jointly capture the temporal dynamics of hydrological variables and the spatial topological structure among stations for watershed runoff simulation. Meanwhile, the effects of rain gauge density and spatial distribution on model performance are systematically assessed using multiple mean areal precipitation (MAP) estimation methods. The results revealed that: (1) Rain gauge samples selected through clustering form four density distribution scenarios, representing 100%, 72.22%, 50%, and 27.78% of the full network respectively. Across four distributions, the average Nash-Sutcliffe efficiency (NSE) values exceeded 0.93. The runoff simulation associated with Distribution 3 yielded the best performance (NSE=0.967, mean absolute error MAE=175.5m3/s, relative bias BIAS=0.01, and coefficient of determination R2=0.98) under both high-flow and low-flow conditions; (2) Among all the MAP methods, the clustering weight method produced the most robust results, achieving the highest NSE, relatively low MAE, and BIAS closest to 0. Additionally, Distribution 3 maintained the best overall performance, with the smallest simulation errors and biases. The optimization of the rain gauge network combined with the selection of appropriate MAP approaches can enhance the efficiency and adaptability and simulation accuracy of runoff simulation models, offering a solid scientific foundation for hydrological forecasting.
Available online: June 02, 2026
Abstract:
While there is a wealth of research on the water quality improvement effects of lake ecological restoration projects, a systematic assessment of the dynamic changes in endogenous pollution in sediments and the mechanisms of nitrogen and phosphorus release is lacking. In particular, the seasonal characteristics of nutrient release at the sediment-water interface after ecological restoration of eutrophic lakes in the plateau region remain unclear. This study takes Dapokou, a typical eutrophic water area in the Caohai Lake of Dianchi Lake, as the research object. By comparing the water environment characteristics, sediment nitrogen and phosphorus occurrence forms, and interface release fluxes in the ecological restoration area and the unrestored area during the rainy season (peak growth period of submerged plants) and the dry season (decline period of submerged plants), the study systematically elucidates the spatiotemporal distribution characteristics of nitrogen and phosphorus in the overlying water-sediment system and the seasonal evolution of interface release fluxes in the ecological restoration area. The results show that ecological restoration improved the quality of the overlying water environment, with the water structure exhibiting a transformation from algal to grass-like patterns. During the rainy season, the total nitrogen (TN) and total phosphorus (TP) concentrations in the restored area decreased by 53.9% and 43.2%, respectively, compared to the unrestored area, while transparency (SD) significantly improved, and dissolved oxygen (DO) returned from supersaturation to normal levels. Regarding sediment occurrence, the remediation area exhibited differentiated evolutionary characteristics: total sediment nitrogen (STN) was significantly reduced by about 50% compared to the unremediation area, and convertible nitrogen (TTN) accounted for only 0.01%–0.02% of total nitrogen, with nitrogen mainly in stable form; however, bioavailable phosphorus (BAP) was enriched in the surface layer of the remediation area (reaching 468.72–534.35 mg/kg), forming a high potential releasable phosphorus reservoir. Regarding nitrogen and phosphorus release characteristics, the release flux at the sediment-water interface exhibits a clear seasonal shift: during the rainy season, when submerged plants are thriving, the interface is dominated by net adsorption, with a sediment-phosphorus (SRP) release flux of -1.08 mg/(m2·d). During the dry season, the decomposition of plant remains alters the sediment microenvironment, significantly increasing the interfacial release flux. At some sites, the ammonia nitrogen (NH4+-N) release flux reaches 86.31–91.53 mg/(m2·d), more than seven times that of the unrestored area, and SRP also shifts to a release state. In summary, the Dapokou ecological restoration project demonstrates improved water quality and net adsorption at the interface during the plant growth period, but there is a risk of nitrogen and phosphorus re-release due to remains decomposition during the dry season. Given the significant fluctuations in water levels and the concentrated seasonal decline of vegetation in shallow plateau lakes, submerged plant restoration measures should be combined with management methods such as dry season debris removal, water level regulation, and bottom sediment oxidation maintenance to control the intensity of seasonal endogenous release and provide a scientific basis and engineering reference for the treatment of endogenous pollution in Dianchi Lake and similar plateau lakes.
While there is a wealth of research on the water quality improvement effects of lake ecological restoration projects, a systematic assessment of the dynamic changes in endogenous pollution in sediments and the mechanisms of nitrogen and phosphorus release is lacking. In particular, the seasonal characteristics of nutrient release at the sediment-water interface after ecological restoration of eutrophic lakes in the plateau region remain unclear. This study takes Dapokou, a typical eutrophic water area in the Caohai Lake of Dianchi Lake, as the research object. By comparing the water environment characteristics, sediment nitrogen and phosphorus occurrence forms, and interface release fluxes in the ecological restoration area and the unrestored area during the rainy season (peak growth period of submerged plants) and the dry season (decline period of submerged plants), the study systematically elucidates the spatiotemporal distribution characteristics of nitrogen and phosphorus in the overlying water-sediment system and the seasonal evolution of interface release fluxes in the ecological restoration area. The results show that ecological restoration improved the quality of the overlying water environment, with the water structure exhibiting a transformation from algal to grass-like patterns. During the rainy season, the total nitrogen (TN) and total phosphorus (TP) concentrations in the restored area decreased by 53.9% and 43.2%, respectively, compared to the unrestored area, while transparency (SD) significantly improved, and dissolved oxygen (DO) returned from supersaturation to normal levels. Regarding sediment occurrence, the remediation area exhibited differentiated evolutionary characteristics: total sediment nitrogen (STN) was significantly reduced by about 50% compared to the unremediation area, and convertible nitrogen (TTN) accounted for only 0.01%–0.02% of total nitrogen, with nitrogen mainly in stable form; however, bioavailable phosphorus (BAP) was enriched in the surface layer of the remediation area (reaching 468.72–534.35 mg/kg), forming a high potential releasable phosphorus reservoir. Regarding nitrogen and phosphorus release characteristics, the release flux at the sediment-water interface exhibits a clear seasonal shift: during the rainy season, when submerged plants are thriving, the interface is dominated by net adsorption, with a sediment-phosphorus (SRP) release flux of -1.08 mg/(m2·d). During the dry season, the decomposition of plant remains alters the sediment microenvironment, significantly increasing the interfacial release flux. At some sites, the ammonia nitrogen (NH4+-N) release flux reaches 86.31–91.53 mg/(m2·d), more than seven times that of the unrestored area, and SRP also shifts to a release state. In summary, the Dapokou ecological restoration project demonstrates improved water quality and net adsorption at the interface during the plant growth period, but there is a risk of nitrogen and phosphorus re-release due to remains decomposition during the dry season. Given the significant fluctuations in water levels and the concentrated seasonal decline of vegetation in shallow plateau lakes, submerged plant restoration measures should be combined with management methods such as dry season debris removal, water level regulation, and bottom sediment oxidation maintenance to control the intensity of seasonal endogenous release and provide a scientific basis and engineering reference for the treatment of endogenous pollution in Dianchi Lake and similar plateau lakes.
Available online: June 02, 2026
Abstract:
Per- and polyfluoroalkyl substances (PFASs) in peri-urban shallow lakes have attracted increasing scientific attention due to their complex environmental behavior and potential health risks. This study investigated the occurrence, bioaccumulation, and trophic magnification of 15 PFASs in water and tissues (muscle and viscera) of 11 fish species from Luoma Lake (a representative peri-urban shallow lake in eastern China), and conducted a preliminary human health risk assessment associated with fish consumption. Results showed that nine PFASs were detected in surface water (∑PFASs: 58.80~90.59 ng/L), while all 15 target compounds were present in both muscle and visceral tissues (∑PFASs: 166.59~417.65 ng/g dw in muscle; 76.04~897.83 ng/g dw in viscera). PFBA, PFOA, and PFHpA were the predominant congeners in water, muscle, and viscera, respectively. PFASs exhibited pronounced tissue-specific accumulation, with concentrations following the order: kidney > liver > gill > muscle > intestine > brain, indicating preferential enrichment in excretory and metabolic organs. A significant urban-rural gradient was observed: PFASs concentrations in muscle, kidney, liver, and gill of fish from urban zone were significantly higher than those from rural zone, whereas no significant differences were found in brain and intestine. Long-chain PFASs generally displayed higher bioaccumulation factors (BAFs) than short-chain analogues. Trophic transfer analysis revealed that long-chain PFASs underwent significant biomagnification (trophic magnification factor, TMF > 1), whereas short-chain PFASs tended to be biodiluted (TMF < 1). Health risk assessment indicated that current dietary exposure to PFASs via consumption of Luoma Lake fish is within acceptable limits (HR < 1). Nevertheless, potential risks from long-term low-dose exposure and the relatively high cumulative toxicity in rural zones warrant further attention. These findings provide valuable insights into the environmental fate, ecological effects, and health risk management of PFASs in peri-urban shallow lake ecosystems.
Per- and polyfluoroalkyl substances (PFASs) in peri-urban shallow lakes have attracted increasing scientific attention due to their complex environmental behavior and potential health risks. This study investigated the occurrence, bioaccumulation, and trophic magnification of 15 PFASs in water and tissues (muscle and viscera) of 11 fish species from Luoma Lake (a representative peri-urban shallow lake in eastern China), and conducted a preliminary human health risk assessment associated with fish consumption. Results showed that nine PFASs were detected in surface water (∑PFASs: 58.80~90.59 ng/L), while all 15 target compounds were present in both muscle and visceral tissues (∑PFASs: 166.59~417.65 ng/g dw in muscle; 76.04~897.83 ng/g dw in viscera). PFBA, PFOA, and PFHpA were the predominant congeners in water, muscle, and viscera, respectively. PFASs exhibited pronounced tissue-specific accumulation, with concentrations following the order: kidney > liver > gill > muscle > intestine > brain, indicating preferential enrichment in excretory and metabolic organs. A significant urban-rural gradient was observed: PFASs concentrations in muscle, kidney, liver, and gill of fish from urban zone were significantly higher than those from rural zone, whereas no significant differences were found in brain and intestine. Long-chain PFASs generally displayed higher bioaccumulation factors (BAFs) than short-chain analogues. Trophic transfer analysis revealed that long-chain PFASs underwent significant biomagnification (trophic magnification factor, TMF > 1), whereas short-chain PFASs tended to be biodiluted (TMF < 1). Health risk assessment indicated that current dietary exposure to PFASs via consumption of Luoma Lake fish is within acceptable limits (HR < 1). Nevertheless, potential risks from long-term low-dose exposure and the relatively high cumulative toxicity in rural zones warrant further attention. These findings provide valuable insights into the environmental fate, ecological effects, and health risk management of PFASs in peri-urban shallow lake ecosystems.
Zhang Wenting, Zhang Xia, Yan Xingcheng, Feng Tao, Qiao Ruxia, Wang Li, Chen Qiuwen, Zhang Xin, Cao Rui
Available online: June 01, 2026
Abstract:
Dissolved inorganic phosphorus (DIP) is a key limiting nutrient in freshwater ecosystems, and its excessive input poses a serious threat to lake water quality and ecological stability. Previous studies have primarily focused on identifying DIP sources in surface waters such as rivers and lakes, while systematic understanding of the spatiotemporal distribution and source contributions of groundwater DIP remains limited. In this study, the Taihu Basin was selected as a representative case. Groundwater samples were systematically collected during the normal, wet, and dry water period in 2024 to analyze DIP concentrations, hydrochemical characteristics, and phosphate oxygen isotope compositions for source apportionment. The results showed that groundwater levels across the basin generally exhibited a spatial pattern of higher values in the west and lower values in the east, with a central depression zone. During the wet water period, groundwater levels were higher and primarily discharged into Lake Taihu, whereas during the dry water period, groundwater levels declined and the flow direction reversed toward discharge-dominated conditions. Spatially, groundwater DIP concentrations were higher in the central and southern regions of the basin and lower in the western and eastern regions. Temporally, DIP concentrations followed the order wet > normal > dry water period. Hydrochemical analyses indicated that groundwater was mainly affected by agricultural activities and domestic sewage during the wet and normal water period, while industrial activities exerted stronger influence during the dry water period. Source apportionment based on phosphate oxygen isotopes revealed that, during the normal season, the contributions of industrial effluents, domestic sewage, and agricultural wastewater were comparable, accounting for 34%, 31%, and 30%, respectively, while forest runoff contributed the least (5%). During the wet water period, agricultural wastewater became the dominant source, accounting for 37%, whereas domestic sewage and industrial effluents decreased to 28% and 25%, respectively, and forest runoff slightly increased to 10%. In contrast, during the dry water period, the agricultural contribution further increased to 42%, followed by domestic sewage (31%), while forest runoff rose significantly to 18% and industrial effluents declined to 9%. Overall, this study provides the comprehensive characterization of the spatiotemporal patterns and seasonal variations in groundwater DIP sources across the Taihu Basin. The findings offer new insights into identifying dominant groundwater phosphorus sources and provide a scientific basis for developing differentiated strategies for water quality management and eutrophication control in large lake basins.
Dissolved inorganic phosphorus (DIP) is a key limiting nutrient in freshwater ecosystems, and its excessive input poses a serious threat to lake water quality and ecological stability. Previous studies have primarily focused on identifying DIP sources in surface waters such as rivers and lakes, while systematic understanding of the spatiotemporal distribution and source contributions of groundwater DIP remains limited. In this study, the Taihu Basin was selected as a representative case. Groundwater samples were systematically collected during the normal, wet, and dry water period in 2024 to analyze DIP concentrations, hydrochemical characteristics, and phosphate oxygen isotope compositions for source apportionment. The results showed that groundwater levels across the basin generally exhibited a spatial pattern of higher values in the west and lower values in the east, with a central depression zone. During the wet water period, groundwater levels were higher and primarily discharged into Lake Taihu, whereas during the dry water period, groundwater levels declined and the flow direction reversed toward discharge-dominated conditions. Spatially, groundwater DIP concentrations were higher in the central and southern regions of the basin and lower in the western and eastern regions. Temporally, DIP concentrations followed the order wet > normal > dry water period. Hydrochemical analyses indicated that groundwater was mainly affected by agricultural activities and domestic sewage during the wet and normal water period, while industrial activities exerted stronger influence during the dry water period. Source apportionment based on phosphate oxygen isotopes revealed that, during the normal season, the contributions of industrial effluents, domestic sewage, and agricultural wastewater were comparable, accounting for 34%, 31%, and 30%, respectively, while forest runoff contributed the least (5%). During the wet water period, agricultural wastewater became the dominant source, accounting for 37%, whereas domestic sewage and industrial effluents decreased to 28% and 25%, respectively, and forest runoff slightly increased to 10%. In contrast, during the dry water period, the agricultural contribution further increased to 42%, followed by domestic sewage (31%), while forest runoff rose significantly to 18% and industrial effluents declined to 9%. Overall, this study provides the comprehensive characterization of the spatiotemporal patterns and seasonal variations in groundwater DIP sources across the Taihu Basin. The findings offer new insights into identifying dominant groundwater phosphorus sources and provide a scientific basis for developing differentiated strategies for water quality management and eutrophication control in large lake basins.
minjialing, yujinxiang, raorongcheng, huanyi, liufangning, meizhigang, yangying, weilingxia, yinheng, zhangyun, lindanqing, chenyukuan, huaqi, licaigang, quejianglong
Available online: May 28, 2026
Abstract:
To investigate the distribution dynamics of Yangtze finless porpoises (YFPs) in Poyang Lake and its tributaries during the middle of the fishing ban, we conducted ten surveys at different water levels between 2022 and 2025. The results indicate that the YFP population is primarily concentrated in the Laoye Temple-Zhuxi Estuary-Piaotou and Duchang-Piaoshan-Meixizui waters. The high water level period is scattered and widely distributed in the lake area, with less distribution in the waterway connecting the Yangtze River and tributaries; The low water level period is concentrated in the main channel and increases in the distribution of sand pits, the waterway connecting the Yangtze River, and tributary tails. The tributaries Gan River, Xin River, Rao River, Fu River, and Xiu River all have distribution of YFPs. Stable, year-round populations were observed in the Gan River (Yangzizhou) and Xin River (Xiniuwan). Migration activities of YFPs are related to seasons and water levels. During winter/low water periods, they migrate from the lake area to the tail of tributaries, while during summer/high water periods, they migrate from the tail of tributaries to the lake area. And as the low water level continues, the distance of migration towards the tail of the tributary may increase for search of resources and space. The KDE model results indicate that the 50% KDE distribution of the YFPs is mainly continuous in the central part of the lake area during the high water level period, while it is fragmented in the lake area and tributary tails during the low water level period. The 50% KDE area decreases with declining water levels, exhibiting a significant positive linear correlation (R=0.721, P<0.05). The fishing ban has led to an expanded distribution range for the YFPs in Poyang Lake. However, the habitat area has decreased and become fragmented due to the normalization of low water levels which may be an important risk factor for the population. The research results suggest that the protection of YFPs in Poyang Lake should focus on the protection of core home range and the connectivity of ecological corridors under the background of normalized low water levels.
To investigate the distribution dynamics of Yangtze finless porpoises (YFPs) in Poyang Lake and its tributaries during the middle of the fishing ban, we conducted ten surveys at different water levels between 2022 and 2025. The results indicate that the YFP population is primarily concentrated in the Laoye Temple-Zhuxi Estuary-Piaotou and Duchang-Piaoshan-Meixizui waters. The high water level period is scattered and widely distributed in the lake area, with less distribution in the waterway connecting the Yangtze River and tributaries; The low water level period is concentrated in the main channel and increases in the distribution of sand pits, the waterway connecting the Yangtze River, and tributary tails. The tributaries Gan River, Xin River, Rao River, Fu River, and Xiu River all have distribution of YFPs. Stable, year-round populations were observed in the Gan River (Yangzizhou) and Xin River (Xiniuwan). Migration activities of YFPs are related to seasons and water levels. During winter/low water periods, they migrate from the lake area to the tail of tributaries, while during summer/high water periods, they migrate from the tail of tributaries to the lake area. And as the low water level continues, the distance of migration towards the tail of the tributary may increase for search of resources and space. The KDE model results indicate that the 50% KDE distribution of the YFPs is mainly continuous in the central part of the lake area during the high water level period, while it is fragmented in the lake area and tributary tails during the low water level period. The 50% KDE area decreases with declining water levels, exhibiting a significant positive linear correlation (R=0.721, P<0.05). The fishing ban has led to an expanded distribution range for the YFPs in Poyang Lake. However, the habitat area has decreased and become fragmented due to the normalization of low water levels which may be an important risk factor for the population. The research results suggest that the protection of YFPs in Poyang Lake should focus on the protection of core home range and the connectivity of ecological corridors under the background of normalized low water levels.
Available online: May 22, 2026
Abstract:
The Qarhan Salt Lake plays a crucial role in China"s potassium fertilizer production, highlighting the essential relationship of water-salt (Here, the term “water-salt” refers to the coupled mass balance of water (liquid) and potash (solid + dissolved) in the Qarhan playa-lake system)for sustainable resource management and potassium fertilizer supply. This research investigates the complex evolutionary mechanisms governing the water-salt relationship in the mining region, influenced by climate change and human activities. This study utilised a comprehensive set of hydrometeorological data collected over a period of nearly three decades (1990–2024) to identify the evolving trends in the key factors influencing the water-salt relationship in the Qarhan Salt Lake mining area. Pearson correlation analysis was employed to reveal the evolution patterns and driving factors of the water-salt system in this region. The results indicate that over the past two decades (2000-2024), the climate in the mining area has transitioned from "warm and dry" to a "warm and humid". The volume of runoff of the recharged river has increased by more than 20%, accompanied by a temperature increasing of 1.5-2.0 °C. Conversely, a reduction of 18.5% has been noted in evaporation rates. Large-scale resource development activities have adversely affected water replenishment in the mining area, leading to a significant decline in the level of confined brine and a reduction in KCl grade. The implementation of artificial water replenishment and mineral dissolution has been shown to alleviate the severity of these negative impacts. The evolution of water-mineral interactions can be divided into three distinct stages. Initially, there is a transition from a naturally "hydrometeorological-dominated" state to a phase characterized by "combined natural and human influences." This is subsequently followed by a shift to a "human-dominated" trajectory. The key drivers of this transformation include climate warming, brine mining, and artificial water recharge for mineral dissolution. It is clear that brine extraction and artificial water recharge serve as the essential conditions for regulating the water-salt balance. These findings offer a scientific foundation for achieving effective water-salt balance and management in the Qarhan Salt Lake mining area.
The Qarhan Salt Lake plays a crucial role in China"s potassium fertilizer production, highlighting the essential relationship of water-salt (Here, the term “water-salt” refers to the coupled mass balance of water (liquid) and potash (solid + dissolved) in the Qarhan playa-lake system)for sustainable resource management and potassium fertilizer supply. This research investigates the complex evolutionary mechanisms governing the water-salt relationship in the mining region, influenced by climate change and human activities. This study utilised a comprehensive set of hydrometeorological data collected over a period of nearly three decades (1990–2024) to identify the evolving trends in the key factors influencing the water-salt relationship in the Qarhan Salt Lake mining area. Pearson correlation analysis was employed to reveal the evolution patterns and driving factors of the water-salt system in this region. The results indicate that over the past two decades (2000-2024), the climate in the mining area has transitioned from "warm and dry" to a "warm and humid". The volume of runoff of the recharged river has increased by more than 20%, accompanied by a temperature increasing of 1.5-2.0 °C. Conversely, a reduction of 18.5% has been noted in evaporation rates. Large-scale resource development activities have adversely affected water replenishment in the mining area, leading to a significant decline in the level of confined brine and a reduction in KCl grade. The implementation of artificial water replenishment and mineral dissolution has been shown to alleviate the severity of these negative impacts. The evolution of water-mineral interactions can be divided into three distinct stages. Initially, there is a transition from a naturally "hydrometeorological-dominated" state to a phase characterized by "combined natural and human influences." This is subsequently followed by a shift to a "human-dominated" trajectory. The key drivers of this transformation include climate warming, brine mining, and artificial water recharge for mineral dissolution. It is clear that brine extraction and artificial water recharge serve as the essential conditions for regulating the water-salt balance. These findings offer a scientific foundation for achieving effective water-salt balance and management in the Qarhan Salt Lake mining area.
Deng Guoping, Fang Dian, Ding Yuting, Yuan Jia, Zhang Xizhao, Zhou Yanfeng, Xu Dongpo, Tang Fujiang, You Yang
Available online: May 22, 2026
Abstract:
In the 1980s, a fishery transplant was carried out nationwide using the H. nipponensis from the Yalu River system as the source population, which achieved significant economic benefits. However, the genetic diversity of the initial small population established by transplantation has not received due attention due to the subsequent effects of different transplantation behaviors (repeated introduction, mixing of other sources, and unintentional transplantation) and adaptation to the habitat. In this study, 439 individuals were collected from 15 transplanted populations across China’s main production regions (Northeast, North, Northwest and Southwest). Mitochondrial cytochrome c oxidase I (CO I) sequences were used to assess genetic diversity and differentiation. The analysis results showed that a total of 47 haplotypes were detected in 15 populations, Overall haplotype diversity (Hd=0.690) and nucleotide diversity (Pi=0.00290) exhibit species characteristics of high haplotype diversity (Hd) and low nucleotide diversity (Pi). Group Evolutionary Tree, haplotype networks and AMOVA showed that most molecular variance occurred within populations (65.06 %, versus 34.94 % among populations). Populations from Miyun Reservoir (MY) and Panjiakou Reservoir (PJK) in North China formed a separate clade and were highly differentiated from all others (Fst > 0.5), probably reflecting repeated introductions from native Japanese sources. The Dahushi Reservoir (DHS) population showed marked diversity loss, likely attributable to accidental transplantation of a very small founder group. The diversity levels of the four populations in Northeast China, which are connected to the water system of their source areas, are relatively balanced. The populations in Northwest and Southwest China, exhibit moderate to high levels of diversity, which demonstrated the potential adaptation of fish species to the new habitat. Neutrality tests, mismatch distributions and Bayesian skyline plots all indicated a historical population expansion. Based on the current research results, it is recommended to identify the biological management units and core population germplasm resources in China as soon as possible, implement necessary genetic monitoring in a timely manner, and then carry out orderly germplasm use strategies, block based resource management, and fishery production management measures to promote the sustainable and healthy development of the industry.
In the 1980s, a fishery transplant was carried out nationwide using the H. nipponensis from the Yalu River system as the source population, which achieved significant economic benefits. However, the genetic diversity of the initial small population established by transplantation has not received due attention due to the subsequent effects of different transplantation behaviors (repeated introduction, mixing of other sources, and unintentional transplantation) and adaptation to the habitat. In this study, 439 individuals were collected from 15 transplanted populations across China’s main production regions (Northeast, North, Northwest and Southwest). Mitochondrial cytochrome c oxidase I (CO I) sequences were used to assess genetic diversity and differentiation. The analysis results showed that a total of 47 haplotypes were detected in 15 populations, Overall haplotype diversity (Hd=0.690) and nucleotide diversity (Pi=0.00290) exhibit species characteristics of high haplotype diversity (Hd) and low nucleotide diversity (Pi). Group Evolutionary Tree, haplotype networks and AMOVA showed that most molecular variance occurred within populations (65.06 %, versus 34.94 % among populations). Populations from Miyun Reservoir (MY) and Panjiakou Reservoir (PJK) in North China formed a separate clade and were highly differentiated from all others (Fst > 0.5), probably reflecting repeated introductions from native Japanese sources. The Dahushi Reservoir (DHS) population showed marked diversity loss, likely attributable to accidental transplantation of a very small founder group. The diversity levels of the four populations in Northeast China, which are connected to the water system of their source areas, are relatively balanced. The populations in Northwest and Southwest China, exhibit moderate to high levels of diversity, which demonstrated the potential adaptation of fish species to the new habitat. Neutrality tests, mismatch distributions and Bayesian skyline plots all indicated a historical population expansion. Based on the current research results, it is recommended to identify the biological management units and core population germplasm resources in China as soon as possible, implement necessary genetic monitoring in a timely manner, and then carry out orderly germplasm use strategies, block based resource management, and fishery production management measures to promote the sustainable and healthy development of the industry.
Available online: May 20, 2026
Abstract:
<sub>:</sub> <sub>This study investigated the driving mechanisms of methane (CH?) emission flux (</sub><sub>F</sub><sub>CH?</sub><sub>) through controlled laboratory experiments simulating the decomposition process of submerged plant (Potamogeton</sub><sub> pectinatus) residues in a eutrophic lake. Four treatment groups were established: a no-plant control (CK), and low (300 g), medium (500 g), and high (1000 g) plant residue addition groups. Constant-temperature incubation was used to simulate environments during both the ice-covered period (0–4°C) and the ice-melt period (10–15°C), with continuous monitoring employed to reveal the dynamics of</sub><sub> F</sub><sub>CH? </sub><sub>and key environmental parameters.The results indicated that plant residue decomposition released dissolved organic carbon (DOC) and total organic carbon (TOC) into the water-sediment system. Their subsequent mineralization produced dissolved inorganic </sub><sub>carbon (DIC) and total inorganic carbon (TIC). The decomposition process concurrently consumed dissolved oxygen (DO), causing DO concentrations to rapidly decline below 2 mg/L and forming a strongly reducing anaerobic environment, which significantly increased</sub><sub> the abundance of methanogens. During the ice-covered period, FCH? increased significantly with the amount of plant residues added, with the FCH? in the high plant group being 3.7 times that of the control group. This confirms that the synergistic effe</sub><sub>ct o</sub><sub>f </sub><sub>“</sub><sub>carbon source input–anoxic environment</sub><sub>”</sub><sub>drove the increase in </sub><sub>F</sub><sub>CH? </sub><sub>during the ice-covered period.Rising temperatures further accelerated organic matter mineralization and CH? production. During this period, </sub><sub>F</sub><sub>CH? </sub><sub> remained significantly positively correla</sub><sub>ted with the amount of plant residue added (</sub><sub>r</sub><sub> = 0.86, </sub><sub>p</sub><sub><</sub><sub>0.001), indicating that climate warming may amplify the promoting effect of plant input on CH? emissions. In conclusion, the decomposition of plant residues in macrophyte-dominated eutrophic lakes jointly promotes CH? production by supplying organic carbon sources and creating anaerobic conditions, while global climate warming—leading to shorter ice-covered periods and higher temperatures—further exacerbates CH? emissions. This study provides an import</sub><sub>ant theoretical basis for the management of eutrophic lakes under global climate change.</sub>
<sub>:</sub> <sub>This study investigated the driving mechanisms of methane (CH?) emission flux (</sub><sub>F</sub><sub>CH?</sub><sub>) through controlled laboratory experiments simulating the decomposition process of submerged plant (Potamogeton</sub><sub> pectinatus) residues in a eutrophic lake. Four treatment groups were established: a no-plant control (CK), and low (300 g), medium (500 g), and high (1000 g) plant residue addition groups. Constant-temperature incubation was used to simulate environments during both the ice-covered period (0–4°C) and the ice-melt period (10–15°C), with continuous monitoring employed to reveal the dynamics of</sub><sub> F</sub><sub>CH? </sub><sub>and key environmental parameters.The results indicated that plant residue decomposition released dissolved organic carbon (DOC) and total organic carbon (TOC) into the water-sediment system. Their subsequent mineralization produced dissolved inorganic </sub><sub>carbon (DIC) and total inorganic carbon (TIC). The decomposition process concurrently consumed dissolved oxygen (DO), causing DO concentrations to rapidly decline below 2 mg/L and forming a strongly reducing anaerobic environment, which significantly increased</sub><sub> the abundance of methanogens. During the ice-covered period, FCH? increased significantly with the amount of plant residues added, with the FCH? in the high plant group being 3.7 times that of the control group. This confirms that the synergistic effe</sub><sub>ct o</sub><sub>f </sub><sub>“</sub><sub>carbon source input–anoxic environment</sub><sub>”</sub><sub>drove the increase in </sub><sub>F</sub><sub>CH? </sub><sub>during the ice-covered period.Rising temperatures further accelerated organic matter mineralization and CH? production. During this period, </sub><sub>F</sub><sub>CH? </sub><sub> remained significantly positively correla</sub><sub>ted with the amount of plant residue added (</sub><sub>r</sub><sub> = 0.86, </sub><sub>p</sub><sub><</sub><sub>0.001), indicating that climate warming may amplify the promoting effect of plant input on CH? emissions. In conclusion, the decomposition of plant residues in macrophyte-dominated eutrophic lakes jointly promotes CH? production by supplying organic carbon sources and creating anaerobic conditions, while global climate warming—leading to shorter ice-covered periods and higher temperatures—further exacerbates CH? emissions. This study provides an import</sub><sub>ant theoretical basis for the management of eutrophic lakes under global climate change.</sub>
Available online: May 20, 2026
Abstract:
Arid-zone lakes serve as key indicators of watershed ecological and environmental changes, playing vital hydrological and ecological roles in maintaining regional water-cycle balance and ecosystem stability. This study examines lake dynamics and their climatic responses in the Hunshandake Sandy Land, a climate-sensitive region in northern China characterized by pronounced aridification and ecological fragility. By integrating multi-source datasets including Landsat, Sentinel, Global Surface Water (GSW), and Global Land Analysis and Discovery (GLAD), water extent was mapped applying the water-index method, water classification enhancement approach, and random-forest classification. Changes in water storage were estimated by combining stage-area relationships and volume-area empirical curves. Based on these methods, we quantified monthly and annual changes in lake area (＞0.01 km2) and water storage from 2003 to 2023, while analyzing relevant meteorological factors. Results indicate significant intra-annual seasonality, exhibiting a single-peak trend in lake extent from May to October. At the interannual scale, the lake system has undergone persistent degradation trend over the 21-year record. Total lake area had decreased by 37.17% compared to 2003. The number of lakes declined from 1,198 to 466, primarily driven by losses of small, shallow lakes and widespread drying. Under regional climatic aridity conditions, 8% of formerly permanent water bodies converted to seasonal status, while 86% of seasonal water bodies experienced episodic drying. Net water storage decreased at a rate of -0.005 km3·yr?1, with medium-to-large lakes (≥1km2) accounting for 60% of the storage loss. Climate-driven mechanisms indicate that precipitation, vapor pressure deficit (VPD), and air temperature exhibit spatiotemporal lags of 0-2 months, with precipitation and VPD both peaking at a 1-month lag. VPD emerges as primary negative factor influencing annual and monthly water body area, while precipitation dominates the interannual regulation of seasonal water body area and, jointly governs positively monthly fluctuations with potential evapotranspiration (ET). Temperature indirectly affects lake dynamics by increasing the VPD and evapotranspiration demand. This regional-scale study elucidates the response mechanisms and spatiotemporal heterogeneity of arid-region lakes under climate change, providing data support for adaptive water-resource management in ecologically fragile areas.
Arid-zone lakes serve as key indicators of watershed ecological and environmental changes, playing vital hydrological and ecological roles in maintaining regional water-cycle balance and ecosystem stability. This study examines lake dynamics and their climatic responses in the Hunshandake Sandy Land, a climate-sensitive region in northern China characterized by pronounced aridification and ecological fragility. By integrating multi-source datasets including Landsat, Sentinel, Global Surface Water (GSW), and Global Land Analysis and Discovery (GLAD), water extent was mapped applying the water-index method, water classification enhancement approach, and random-forest classification. Changes in water storage were estimated by combining stage-area relationships and volume-area empirical curves. Based on these methods, we quantified monthly and annual changes in lake area (＞0.01 km2) and water storage from 2003 to 2023, while analyzing relevant meteorological factors. Results indicate significant intra-annual seasonality, exhibiting a single-peak trend in lake extent from May to October. At the interannual scale, the lake system has undergone persistent degradation trend over the 21-year record. Total lake area had decreased by 37.17% compared to 2003. The number of lakes declined from 1,198 to 466, primarily driven by losses of small, shallow lakes and widespread drying. Under regional climatic aridity conditions, 8% of formerly permanent water bodies converted to seasonal status, while 86% of seasonal water bodies experienced episodic drying. Net water storage decreased at a rate of -0.005 km3·yr?1, with medium-to-large lakes (≥1km2) accounting for 60% of the storage loss. Climate-driven mechanisms indicate that precipitation, vapor pressure deficit (VPD), and air temperature exhibit spatiotemporal lags of 0-2 months, with precipitation and VPD both peaking at a 1-month lag. VPD emerges as primary negative factor influencing annual and monthly water body area, while precipitation dominates the interannual regulation of seasonal water body area and, jointly governs positively monthly fluctuations with potential evapotranspiration (ET). Temperature indirectly affects lake dynamics by increasing the VPD and evapotranspiration demand. This regional-scale study elucidates the response mechanisms and spatiotemporal heterogeneity of arid-region lakes under climate change, providing data support for adaptive water-resource management in ecologically fragile areas.
Available online: May 20, 2026
Abstract:
Submerged macrophytes are critical component in ecological restoration of lakes, which harbor epiphytic microbes that play important roles in nutrient cycling and water quality improvement in aquatic ecosystems. However, the responses of planktonic and epiphytic microbial communities to different restoration strategies, as well as the underlying mechanisms, remain largely unknown. To address this gap, we investigated bacterial and microeukaryotic communities in both water column and phyllosphere of Vallisneria natans (V. natans) across three areas of the urban Lake Xuanwu: a near-natural restoration (NR) area, an enclosure restoration (ER) area, and an unrestored (UR) area, to uncover how ecological restoration shapes microbial communities and their potential functions. The results showed that the NR area exhibited higher coverage and greater species richness of submerged macrophytes, along with lower concentrations of total nitrogen (TN), total phosphorus (TP), turbidity (Turb), and chlorophyll a (Chl a). The diversity of both planktonic and phyllosphere microbial communities was significantly higher in the NR area than in the ER and UR areas. The dominant microbial taxa in the phyllosphere of V. natans differed from those in the surrounding water, with obvious compositional differences among the three restoration areas. Variations in microbial community structure were primarily driven by differences in TN, TP, Turb, and Chl a, with bacterial communities being more strongly influenced by environmental factors than microeukaryotic communities. Functional bacterial groups involved in nitrification and nitrate ammonification were selectively enriched in the phyllosphere of V. natans, and the abundance of nitrogen-cycling populations was significantly correlated with ambient nitrogen concentrations in the water. The microbial co-occurrence networks in the NR area displayed greater complexity and stability than those in the ER and UR areas. Compared with the microeukaryotic network, the bacterial network contained more nodes and edges connecting nodes with environmental factors, reflecting a stronger susceptible to environmental influence for the bacterial community. Moreover, based on functional predictions, the key bacterial genera within the phyllosphere network of Vallisneria natans may play important roles in carbon and nitrogen cycling. This study elucidates the mechanisms by which submerged macrophytes regulate microbial community structure, interaction networks, and keystone functional taxa during ecological restoration to improve water quality, thereby providing scientific support for the ecological restoration of eutrophic lakes.
Submerged macrophytes are critical component in ecological restoration of lakes, which harbor epiphytic microbes that play important roles in nutrient cycling and water quality improvement in aquatic ecosystems. However, the responses of planktonic and epiphytic microbial communities to different restoration strategies, as well as the underlying mechanisms, remain largely unknown. To address this gap, we investigated bacterial and microeukaryotic communities in both water column and phyllosphere of Vallisneria natans (V. natans) across three areas of the urban Lake Xuanwu: a near-natural restoration (NR) area, an enclosure restoration (ER) area, and an unrestored (UR) area, to uncover how ecological restoration shapes microbial communities and their potential functions. The results showed that the NR area exhibited higher coverage and greater species richness of submerged macrophytes, along with lower concentrations of total nitrogen (TN), total phosphorus (TP), turbidity (Turb), and chlorophyll a (Chl a). The diversity of both planktonic and phyllosphere microbial communities was significantly higher in the NR area than in the ER and UR areas. The dominant microbial taxa in the phyllosphere of V. natans differed from those in the surrounding water, with obvious compositional differences among the three restoration areas. Variations in microbial community structure were primarily driven by differences in TN, TP, Turb, and Chl a, with bacterial communities being more strongly influenced by environmental factors than microeukaryotic communities. Functional bacterial groups involved in nitrification and nitrate ammonification were selectively enriched in the phyllosphere of V. natans, and the abundance of nitrogen-cycling populations was significantly correlated with ambient nitrogen concentrations in the water. The microbial co-occurrence networks in the NR area displayed greater complexity and stability than those in the ER and UR areas. Compared with the microeukaryotic network, the bacterial network contained more nodes and edges connecting nodes with environmental factors, reflecting a stronger susceptible to environmental influence for the bacterial community. Moreover, based on functional predictions, the key bacterial genera within the phyllosphere network of Vallisneria natans may play important roles in carbon and nitrogen cycling. This study elucidates the mechanisms by which submerged macrophytes regulate microbial community structure, interaction networks, and keystone functional taxa during ecological restoration to improve water quality, thereby providing scientific support for the ecological restoration of eutrophic lakes.
Available online: May 20, 2026
Abstract:
As one of the most advanced ensemble learning technologies, Stacking is an important way to improve the performance of runoff prediction. The existing researches of Stacking-based runoff prediction mostly focus on the accuracy evaluation under few basins and few lead times. Applicability evaluation and influencing factors analysis under multiple basins and multiple lead times remains unexplored. In this study, Support Vector Regression (SVR) and Random Forest (RF) were used as individual learners, and Ridge Regression was used as a meta-learner, and runoff prediction models based on Stacking were constructed. Taking 200 basins in CAMELS dataset as the study area, and taking 1~7 days as the lead times, the accuracy, stability and applicability of Stacking-based runoff prediction were systematically evaluated, and the correlation between the effectiveness of Stacking and the characteristics of basins and the accuracy of individual learners were analyzed. The main results are as follows: (1) The overall accuracy and stability of Stacking are higher than those of the individual learners. (2) Stacking can improve the accuracy of runoff prediction in most basins in the continental United States. The improvement effect is more significant in the basins with heavy precipitation and high temperature, but the effect is relatively limited in the basins with light precipitation and low temperature. (3) Stacking tends to improve prediction accuracy in the basins with low accuracy of the individual learners, but it is difficult to improve the prediction accuracy in the basins with high accuracy of the individual learners. This study can provide a reference for the application of Stacking in runoff prediction.
As one of the most advanced ensemble learning technologies, Stacking is an important way to improve the performance of runoff prediction. The existing researches of Stacking-based runoff prediction mostly focus on the accuracy evaluation under few basins and few lead times. Applicability evaluation and influencing factors analysis under multiple basins and multiple lead times remains unexplored. In this study, Support Vector Regression (SVR) and Random Forest (RF) were used as individual learners, and Ridge Regression was used as a meta-learner, and runoff prediction models based on Stacking were constructed. Taking 200 basins in CAMELS dataset as the study area, and taking 1~7 days as the lead times, the accuracy, stability and applicability of Stacking-based runoff prediction were systematically evaluated, and the correlation between the effectiveness of Stacking and the characteristics of basins and the accuracy of individual learners were analyzed. The main results are as follows: (1) The overall accuracy and stability of Stacking are higher than those of the individual learners. (2) Stacking can improve the accuracy of runoff prediction in most basins in the continental United States. The improvement effect is more significant in the basins with heavy precipitation and high temperature, but the effect is relatively limited in the basins with light precipitation and low temperature. (3) Stacking tends to improve prediction accuracy in the basins with low accuracy of the individual learners, but it is difficult to improve the prediction accuracy in the basins with high accuracy of the individual learners. This study can provide a reference for the application of Stacking in runoff prediction.
Available online: April 28, 2026
Abstract:
Dissolved gases are key byproducts of biogeochemical reactions and serve as critical indicators for the evolution of aquatic ecosystems. However, traditional headspace equilibrium sampling methods are prone to air contamination, decompression-induced degassing, and limited measurement precision. To address these challenges, this study developed an in-situ system for the simultaneous determination of multiple dissolved gases in deep waters. The method was applied to characterize the distribution of dissolved gases in the Three Gorges Reservoir. Results demonstrated that the proposed method achieves high-precision, simultaneous in-situ measurements of five key gases—methane (CH4), nitrogen (N2), oxygen (O2), argon (Ar), and carbon dioxide (CO2)—at depths of up to 100 meters. High-precision calibration models were established for these five gases through systematic multi-temperature and multi-concentration calibration, achieving a measurement resolution of 1 ppm. Compared to traditional headspace sampling, this approach effectively eliminates air interference and decompression degassing, significantly enhancing data fidelity. Field validation against commercial high-precision instruments (Picarro greenhouse gas analyzer and multi-parameter water quality sondes) demonstrated exceptional consistency (R2 > 0.96; Concordance Correlation Coefficient [CCC] > 0.98), confirming the accuracy and reliability of the measurements. Furthermore, the proposed method surpasses traditional techniques in terms of real-time performance, spatial resolution, and monitoring efficiency. Field application in the Pengxi River Bay of the Three Gorges Reservoir successfully generated high-resolution two-dimensional distribution profiles along a 42-km longitudinal section. The results clearly revealed distinct vertical stratification, extensive bottom water hypoxia, and coupled accumulation of CO2 and CH4 during summer and autumn, effectively identifying hotspots of intense biogeochemical activity. This in-situ monitoring technology matches the accuracy of traditional laboratory methods while offering superior data fidelity, spatiotemporal resolution, and monitoring efficiency. It provides innovative technical support for greenhouse gas emission assessment, water quality management, aquatic nitrogen cycling, and the study of material cycling and ecological evolution in complex aquatic environments.
Dissolved gases are key byproducts of biogeochemical reactions and serve as critical indicators for the evolution of aquatic ecosystems. However, traditional headspace equilibrium sampling methods are prone to air contamination, decompression-induced degassing, and limited measurement precision. To address these challenges, this study developed an in-situ system for the simultaneous determination of multiple dissolved gases in deep waters. The method was applied to characterize the distribution of dissolved gases in the Three Gorges Reservoir. Results demonstrated that the proposed method achieves high-precision, simultaneous in-situ measurements of five key gases—methane (CH4), nitrogen (N2), oxygen (O2), argon (Ar), and carbon dioxide (CO2)—at depths of up to 100 meters. High-precision calibration models were established for these five gases through systematic multi-temperature and multi-concentration calibration, achieving a measurement resolution of 1 ppm. Compared to traditional headspace sampling, this approach effectively eliminates air interference and decompression degassing, significantly enhancing data fidelity. Field validation against commercial high-precision instruments (Picarro greenhouse gas analyzer and multi-parameter water quality sondes) demonstrated exceptional consistency (R2 > 0.96; Concordance Correlation Coefficient [CCC] > 0.98), confirming the accuracy and reliability of the measurements. Furthermore, the proposed method surpasses traditional techniques in terms of real-time performance, spatial resolution, and monitoring efficiency. Field application in the Pengxi River Bay of the Three Gorges Reservoir successfully generated high-resolution two-dimensional distribution profiles along a 42-km longitudinal section. The results clearly revealed distinct vertical stratification, extensive bottom water hypoxia, and coupled accumulation of CO2 and CH4 during summer and autumn, effectively identifying hotspots of intense biogeochemical activity. This in-situ monitoring technology matches the accuracy of traditional laboratory methods while offering superior data fidelity, spatiotemporal resolution, and monitoring efficiency. It provides innovative technical support for greenhouse gas emission assessment, water quality management, aquatic nitrogen cycling, and the study of material cycling and ecological evolution in complex aquatic environments.
zhao rui, Lu Mansheng, Huang Junteng, Li Shengping, Liu Wanxin, Zhang Shulin, Tang Jiaxin, Zheng Jiazhong, Yong Bin, Wang Weiguang
Available online: April 28, 2026
Abstract:
River discharge serves as a critical variable in basin hydrological processes, playing a vital role in flood control, water resource planning, and management. Due to harsh natural environments and climatic conditions, discharge observation stations are scarce in the Yangtze River source region located on the eastern edge of the Qinghai-Tibet Plateau, making it a typical data-deficient area. Therefore, conducting discharge estimation in this region is of significant importance for ensuring water security in the Yangtze River basin and protecting regional ecosystems. This study establishes virtual stations upstream and downstream of the Zhimenda hydrological station in the Yangtze headwaters (ZMD_1 and ZMD_2) as reference points. Utilizing Sentinel-2 and Jason-3, and Sentinel-3A satellite remote sensing data. A novel quantile matching approach was employed to fuse remotely sensed water level and river width data. The Manning"s equation was modified based on generalized cross-section profiles to conduct quantitative discharge estimation for the Yangtze headwaters. Results indicate that the new method achieves high esti-mation accuracy at both virtual stations, with Nash"s efficiency coefficients (NSE) exceeding 0.74. The root mean square error (RMSE) of estimated discharges was 302.13 m3/s and 316.46 m3/s, respectively, with relative root mean square errors (RRMSE) of 30.0% and 32.8%. Overall, discharge estimation accuracy at the ZMD_1 virtual station outperformed that at ZMD_2. The ZMD_2 virtual station results exhibited significant fluctuations, primarily due to the presence of mid-channel bars within the ZMD_2 buffer zone, which compromised the accuracy of flow inversion at the virtual station. This study, based on multi-source satellite remote sensing for estimating river flows in the Yangtze River source region, provides theoretical methods and technical references for flow estimation in data-scarce areas.
River discharge serves as a critical variable in basin hydrological processes, playing a vital role in flood control, water resource planning, and management. Due to harsh natural environments and climatic conditions, discharge observation stations are scarce in the Yangtze River source region located on the eastern edge of the Qinghai-Tibet Plateau, making it a typical data-deficient area. Therefore, conducting discharge estimation in this region is of significant importance for ensuring water security in the Yangtze River basin and protecting regional ecosystems. This study establishes virtual stations upstream and downstream of the Zhimenda hydrological station in the Yangtze headwaters (ZMD_1 and ZMD_2) as reference points. Utilizing Sentinel-2 and Jason-3, and Sentinel-3A satellite remote sensing data. A novel quantile matching approach was employed to fuse remotely sensed water level and river width data. The Manning"s equation was modified based on generalized cross-section profiles to conduct quantitative discharge estimation for the Yangtze headwaters. Results indicate that the new method achieves high esti-mation accuracy at both virtual stations, with Nash"s efficiency coefficients (NSE) exceeding 0.74. The root mean square error (RMSE) of estimated discharges was 302.13 m3/s and 316.46 m3/s, respectively, with relative root mean square errors (RRMSE) of 30.0% and 32.8%. Overall, discharge estimation accuracy at the ZMD_1 virtual station outperformed that at ZMD_2. The ZMD_2 virtual station results exhibited significant fluctuations, primarily due to the presence of mid-channel bars within the ZMD_2 buffer zone, which compromised the accuracy of flow inversion at the virtual station. This study, based on multi-source satellite remote sensing for estimating river flows in the Yangtze River source region, provides theoretical methods and technical references for flow estimation in data-scarce areas.
