Abstract:The impact of the "four colliding" typhoons has become the focus of attention in the disaster prevention and reduction system in the Taihu basin. However, the risk impact of wind, storm, tide, and flood brought by it on the safety of flood prevention is still unclear. It is considerable to carry out the analysis of rainstorm, flood and its movement caused by the typical typhoon of "four colliding".It takes the two typical typhoons "Fitow" and "In-Fa" since 1990 as samples, and other typhoons with two or three colliding as references. Based on hydrological and engineering data, the impact of "four colliding" typhoons is compared. The results showed that: (1) The "four colliding" typhoons all caused extreme rainfall, with a large total amount and wide range, resulting in the rainfall that was more than 70% higher than the average of the two and three colliding typhoons. The higher part was basically the same as the rainfall caused by typhoon Morakot in 2009. (2) The water levels of the Taihu Lake has risen by the second and third place respectively since 1949. In particular, "In-Fa" caused numbered floods, and the maximum tilt of the Taihu Lake was more than 1.00 m. The highest water (tide) level of 33 sites in the river network broke the historical records, and the high water levels lasted for a long time, which seriously threatened the safety of regional flood prevention. (3) It was dominated by storage during "Fitow", and then the drainage capacity of backbone projects was significantly enhanced. During "In-Fa", the flood movement pattern changed to both storage and drainage, with the storage and drainage ratio changing from 1:0.6 to 1:1.1, and the proportion of drainage increased. (4) During the rainstorm of the two typhoons, the drainage was obviously restricted by the astronomical spring tide jacking. After the rainfall stopped and the astronomical spring tide passed, the drainage of the backbone projects increased significantly, especially the Yangtze river to the north and the Huangpu river to the east. (5) Although the drainage capacity of the backbone projects has been significantly strengthened, it still needs to be further improved in the face of the "four colliding" typhoon and the transfer of regional flood disaster risks. The research results could provide a reference for the scientific defense of the "four colliding" typhoon in the Taihu basin in the future.

Abstract:In agricultural watersheds across China, small water bodies serve as important phosphorus retention and storage sites, acting as protective barriers for rivers and lakes. However, under conditions of long-term phosphorus accumulation and specific environmental factors, there is a risk of phosphorus release. Currently, there is a lack of research on the phosphorus release risk of small water bodies and on the dynamic changes in phosphorus retention and release, as well as the influencing factors, through long-term experiments. This study focuses on a typical agricultural watershed and conducts sediment sampling from 4 types of ponds, along with a 6-month static incubation experiment. The study analyzes the phosphorus forms in sediments and the phosphorus exchange dynamics at the sediment-water interface, assessing the phosphorus release risk of the ponds and its influencing factors. The results showed that: (1) The total phosphorus (TP) content in pond sediments ranged from 0.55 to 3.02 g/kg, higher than that of other types of wetlands. The highest phosphorus content was found in village ponds, while the lowest was observed in paddy ponds. (2) In agricultural watersheds of the middle and lower reaches of the Yangtze River, and under the condition of long-term existence of ponds, the phosphorus exchange at the sediment-overlying water interface exhibits significant seasonal variations: sediments release phosphorus to the overlying water in summer and autumn, while phosphorus settles from the overlying water to the sediments in autumn and winter. Given similar years of existence, the phosphorus sink capacity of ponds decreases in the following order: forest pond > paddy pond = dryland pond > village pond. This study revealed the large phosphorus accumulation in agricultural ponds in China, highlighting their long-term function as phosphorus sinks that transform into phosphorus sources during the summer and autumn. The findings also clarified the influence of surrounding land use types and provided scientific guidance for improving management strategies for different pond types. These insights are widely applicable to non-point source pollution control and the protection of aquatic environments in rivers and lakes.

Abstract:Poyang Lake, China’s largest freshwater lake, serves as a crucial wintering ground for geese of East Asian. This study employed satellite tracking data from 2019 to 2024 to analyze the migratory phenology and spatial distribution patterns of Greater White-fronted Goose Anser albifrons, Swan Goose Anser cygnoides, and Bean Goose Anser fabalis. By integrating duration and home range data, we quantified the importance of Poyang Lake’s sub-lakes to these species. Our results demonstrate phenological differences in arrival and departure timing among the goose species. Greater White-fronted Geese arrived earliest (October 16th to October 28th), followed by Swan Geese (October 9th to November 30th), with Bean Geese arriving latest (November 1st to November 17th). The average overwintering duration in Poyang Lake was approximately 149±8 days for Greater White-fronted Geese, 123±7 days for Bean Geese, and 128±26 days for Swan Geese. Analysis of migratory timing dynamics revealed relative stability and low interannual variation for Greater White-fronted and Bean Geese, while Swan Geese exhibited greater interannual variability. Spatially, protected areas remained the most important distribution areas for geese. However, increasing duration and home range expansion outside of protected areas were observed, particularly for Bean and Swan Geese. This study quantified the duration and spatial utilization of geese in sub-lakes, highlighting their ecological role in supporting migratory goose populations. It also identified important conservation areas for geese and determined protection gaps. We recommend expanding protected area boundaries to cover existing protection gaps and strengthening habitat management measures both inside and outside protected areas to ensure the long-term sustainability of these important wintering habitats. This research provides scientific support for identifying critical habitats and developing targeted conservation strategies for geese and their habitats.

Abstract:The Songzi River is one of the primary channels through which the Jingjiang River diverts water into Dongting Lake, and changes in its water diversion have significant implications for flood control in the river-lake system, water resource utilization, and water environmental ecology. Based on analysis of measured data and physical model experiments, this study investigates the relationships among water-sediment evolution, riverbed scouring, and diversion changes in the Yangtze main channel and Songzi Mouth reach following the operation of the Three Gorges Project.The results show that compared with the period from 1990 to 2002, the annual average sediment transport at Zhicheng Station decreased by approximately 90.6% during 2003–2022, with a synchronous reduction of about 87.1% in sediment diversion at Songzi Mouth. From 2003 to 2022, the bankfull channel between Zhicheng and Yangjiaonao experienced a total scouring volume of 239 million m3, with an average scouring depth of 2.3 m, leading to significant riverbed coarsening. In contrast, the bankfull channel at the Songzi Mouth reach was scoured by 43.25 million m3, with an average scouring depth of 3.0 m, forming a differential scouring rate compared to the pebble-sand mixed bed in the main channel.Physical model predictions indicate that long-term action of subsaturated flow will cause continuous downcutting of the sandy riverbed downstream of Yangjiaonao in the Yangtze main channel, leading to progressive declines in water levels at Yangjiaonao and corresponding reductions in diversion at Songzi Mouth. For a discharge of 7000 m3/s at Zhicheng Station, water levels at Yangjiaonao are projected to decrease by 1.58 m and 2.57 m in 2035 and 2050, respectively, resulting in diversion reductions of 8.3% and 16.7%. However, asymmetric scouring between the inner and outer parts of the mouth (with higher scouring rates in the sandy mouth reach, expanding the cross-sectional flow area) leads to increased diversion at Songzi Mouth by the end of 2035, even considering the water level decline at Yangjiaonao. During low-flow periods (with a discharge of 7000 m3/s at Zhicheng Station), diversion actually increases by 20.8%, with contribution rates of -33% from the Yangjiaonao water level drop and 133% from asymmetric mouth scouring. As the discharge increases, the absolute values of both contribution rates rise significantly, but their combined effect results in minimal net change in diversion volume, suggesting that these influences are primarily concentrated during medium- to low-flow periods.The differential riverbed composition regulates the scouring process and maintains stable diversion at Songzi Mouth. Increased low-flow diversion is beneficial for water resource allocation in Dongting Lake, but it may moderately lower main channel water levels and affect navigation during medium- to low-flow periods.

Abstract:Surface water-heat-carbon fluxes are critical indicators reflecting the water-carbon cycles in lake ecosystems under changing climates, yet the impact of extreme environmental conditions such as drought on these processes remains to be further clarified. Poyang Lake is the largest freshwater lake in China and an internationally important wetland. It is not only a key node for the regulation of water resources in the Yangtze River Basin, but also plays an important role in the global carbon cycle and water cycle. In 2022, a rare consecutive meteorological drought event occurred in the Poyang Lake Basin during the summer and autumn seasons, and the most severe drought since 1949 hit the lake area. In this study, the multi-year monitoring data from the eddy covariance instrument at the Poyang Lake Wetland Observation and Research Station were adopted. The station is located on the beach of Poyang Lake (29°27" N, 116°03" E), and it has been continuously monitoring the variation processes of the water-heat-carbon fluxes in the lake since 2015. This study analyzed the variation patterns of water-heat-carbon fluxes and their response characteristics to the extreme drought event in Poyang Lake, in 2022. The results showed that: (1) On an annual scale, the latent heat flux was relatively high from July to September, with the peak value occurring in August, and the annual average value was 49.5 W/m2. The sensible heat flux was relatively high from September to November, with the peak value occurring in October, and the annual average value was 10.6 W/m2. The CO? flux exhibited obvious seasonal variations, and the carbon source and carbon sink shifted with hydrometeorological factors such as water level and net radiation. The annual CO? flux average value was 15.0 μmol·m?2·s?1. (2) On a daily scale, the sensible heat and latent heat fluxes were basically synchronous, showing a single peak at noon, while the CO? flux had a single peak at night. (3) The extreme drought event significantly intensified the carbon source effect of the wetland ecosystem by changing the energy allocation pattern. During the drought period, the latent heat flux, sensible heat flux, and CO? flux increased to 1.23 times, 1.78 times, and 5.44 times of the average values in the same historical period, respectively. (4) The correlation analysis showed that air temperature, wind speed, net radiation, precipitation, relative humidity, NDVI, and water level were the main factors affecting the water-heat-carbon fluxes. The stepwise regression analysis further revealed the influence mechanisms of various factors on the fluxes under different periods and underlying surface conditions. During the extreme drought period, when the underlying surface was water body, the importance ranking of the influencing factors for the latent heat flux, sensible heat flux, and CO? flux was: wind speed, air temperature > relative humidity > net radiation, water level. When the underlying surface was the beach, the importance ranking of the influencing factors for the latent heat flux, sensible heat flux, and CO? flux was: air temperature > wind speed, wind speed > NDVI, air temperature > VPD > precipitation. The extreme drought event mainly promoted the energy allocation to the sensible heat flux through the increase of air temperature, wind speed, and net radiation, and significantly stimulated the CO? release. This study revealed the response mechanisms of water-heat-carbon fluxes in lakes to extreme climate events and provided a scientific basis for predicting the responses of lake ecosystems under future climate change scenarios.

Abstract:Water quality is a key factor in safeguarding ecosystem functions, protecting human health, and achieving sustainable development. Land use characteristics (including type, intensity, and landscape configuration) serve as important indicators of human activity and have significant impacts on river water quality, which vary across different spatial and temporal scales. This study focuses on the source region of the Chishui River and integrates two spatial scales: riparian buffer and sub-watershed. By applying variation partitioning analysis (VPA) and random forest modeling, we comprehensively quantify the independent and combined contributions of land use type, intensity, and landscape pattern to water quality, while identifying key influencing factors and their corresponding spatial scales. The results show that:① Landscape pattern is the dominant factor affecting water quality (explaining 33–58% of the variation), followed by land use type (11–22%) and intensity (4–16%);② Riparian landscape configuration exerts a more significant influence on water quality, while land use intensity at the sub-watershed scale provides stronger explanatory power;③ The proportion of built-up land, construction intensity (LUI_Con), and agricultural intensity (LUI_Cul) are key predictors of water quality, while forest cover and landscape connectivity play important roles in reducing TN and COD concentrations. These findings suggest that watershed water quality management should consider land use characteristics at multiple scales to identify optimal combinations of riparian and sub-watershed interventions. Specifically, we recommend prioritizing the control of industrial and domestic point-source pollution at the riparian scale, while enhancing agricultural non-point source management at the sub-watershed scale—thus forming an integrated "point-source and non-point source" control system. This study offers new empirical evidence on the multidimensional interactions and scale effects of land use–water quality relationships, providing important theoretical and practical insights for watershed resource protection and spatial planning optimization.

Abstract:The sediment peak regulation (SPR) in the Three Gorges Reservoir (TGR) during flood season can significantly improve the sediment discharge effect. Studying the control indicators of SPR is of great importance for ensuring the safety of reservoir storage capacity and improving the comprehensive benefits of reservoir. On the basis of data recorded at hydrological stations in the TGR between 2003 and 2023, the characteristics of sediment transport during flood season in the reservoir were identified. After the impoundment of cascade reservoirs in the lower reaches of Jinsha River, the start-up control and process regulation indicators of the SPR in the TGR were discussed. The results indicate that the amount of sediment entering the TGR was greatly reduced since the cascade reservoirs in the lower reaches of Jinsha River were impounded. Sediment transport in the TGR occurred mainly during flood events. The main consideration is to start the SPR for the floods with forecasted peak discharge at Cuntan station not less than 50,000 m3/s or forecasted peak sediment concentration at Cuntan station not less than 1.5 kg/m3, and forecasted 7-day average sediment concentration at Cuntan station not less than 0.5kg/m3. With flood control safety as the premise, and taking into account the multi-objective benefit of the reservoir and the measured flow and sediment conditions during the SPR, dynamic scheduling can be implemented according to the dispatching strategies of the three periods: water discharge peak blocking, sediment transport in the reservoir, and sediment discharge in front of the dam. In addition, real-time monitoring and forecasting of sediment during flood season is the basis of SPR. It is necessary to continuously optimize the sediment monitoring and forecasting technologies, so as to accurately control the start time and regulation process of SPR, and improve the comprehensive benefits of the TGR. This study can provide technical support for the optimization and refinement of SPR in the TGR during flood season.

Abstract:There is highly risk of odorous compounds trouble in drinking water source reservoirs in the Changjiang River catchment in later spring. However, the key drivers for the odorous compound occurrence are remain unclear. During May 2024, we investigated nine drinking water source reservoirs across the upper, middle and lower reaches of the Changjiang River, measuring four odorous compounds, included 2-methylisoborneol (2-MIB), geosmin (GSM), β-cyclocitral (CYC) and β-ionone (ION), along with associated environmental factors. Results showed that 2-MIB was the most common odorous compound, with an average concentration of 35.5 ng/L across the 32 samples from 9 reservoirs (59.4 % exceeding the detection threshold of 10.0 ng/L). In contrast, GSM posed a lower risk, with an average concentration of 2.9 ng/L and only 12.5 % exceeding the threshold value of 10 ng/L, while CYC (averaged at 18.2 ng/L) and ION (averaged at 7.2 ng/L) exhibited minimal odorous concerns. Pseudanabaena sp. was identified as a likely major producer of 2-MIB, with its cell density showing a significant positive correlation with the concentration of 2-MIB. However, the presence of 2-MIB in two reservoirs without detectable Pseudanabaena suggests more complex 2-MIB sources in some reservoirs. Furthermore, 2-MIB levels were also positively related to the trophic state index (TSI), indicating that eutrophication could promoted 2-MIB production. Rainfall amount in 7 days ahead the sampling (RF7) was negative relative to 2-MIB concentration, suggested that short-term weather condition also influence the odorous situation in reservoirs. Despite generally mesotrophic conditions, the widespread 2-MIB exceedances highlight a persistent risk in these reservoirs. To ensure drinking water quality, measures such as reducing external nutrient loads and optimizing aquatic food webs are recommended.

Abstract:The influx of a large amount of sulfate (SO42-) into water bodies can deteriorate the water environment quality. During the period from 2019 to 2023, water samples from the Pingzhai Reservoir Basin in the southwestern karst area, precipitation samples, and sewage samples were collected. The physical and chemical indicators of the water bodies, as well as the characteristics of sulfate sulfur and oxygen isotopes (δ34SSO4, δ18OSO4), hydrogen and oxygen isotopes of water (δDH2O, δ18OH2O), and dissolved inorganic carbon isotopes (δ13CDIC) were analyzed during the monitoring period. Qualitative and quantitative studies on the sources of SO42- in the water bodies were carried out. The hydrochemical types of the basin are mainly of the Ca-HCO3 type and Ca-HCO3-SO4 type, and the hydrochemical characteristics are influenced by the dissolution of carbonate rocks. Isotope characteristics reveal that the biogeochemical process of SO42- in the Pingzhai Reservoir Basin is dominated by oxidation (when sulfides are oxidized, on average, 61% of the oxygen comes from the surrounding water bodies). During the monitoring period, the sources of SO42- in the basin are mainly sulfide oxidation, soil organic sulfur, and agricultural sulfur fertilizers. The results of quantitative calculations show that sulfide oxidation has the highest average contribution rate (72.9%), followed by soil organic sulfur (14.1%) and agricultural sulfur fertilizers (12.9%). The results of uncertainty analysis indicate that the contribution rate of agricultural sulfur fertilizers is the most stable, while that of sulfide oxidation shows relatively large uncertainty. The research results can provide data reference and scientific basis for the protection of water environment quality in the Pingzhai Reservoir and similar karst areas.

Abstract:Enclosure aquaculture (EA) in lakes is one of the primary types of inland freshwater aquaculture, making significant contributions to food security, employment, and economic growth. However, with the rapid booms in EA intensity, the ecological balance of lakes is gradually being disrupted. Thus, it is crucial to profoundly understand the spatiotemporal dynamics of EA for lake ecosystem preservation and restoration. Compared to field surveys, satellite remote sensing offers advantages such as large-scale coverage, traceability, and cost-effectiveness, making it the optimal choice for monitoring lake EA. This study developed an automatic algorithm for monitoring EA based on Sentinel-1 SAR data and the U-Net model. The algorithm was validated on 10 selected typical lakes, and it achieved a classification accuracy of over 80% in all cases. Additionally, the algorithm was used for monitoring EA lakes in the Yangtze-Huaihe River Basin, providing insights into the spatiotemporal evolution of EA from 2016 to 2023. The results show that a total of 48 lakes (larger than 10 km2) in the Yangtze-Huaihe River Basin engaged in aquaculture activities. From 2016 to 2023, the area of EA in these lakes significantly decreased, with the total area shrinking from 2118.72 km2 to 462.94 km2. Among these lakes, 36 (approximately 77%) have completely removed their enclosure nets. Our findings offer crucial support for evaluating the dynamics of lake water environments and the transformation of aquatic ecosystems pre- and post-enclosure EA removal. Additionally, they offer a scientific basis for formulating measures aimed at lake ecosystem restoration, environmental protection, and sustainable development.