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| 城市河流缺氧现象驱动因素识别及机制解析——以南京秦淮河为例 |
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郑婉婷1, 李一平1, 潘泓哲1, 刘军2, 柏松2, 赵明明2, 胡静2, 谢鑫苗2, 王亚宁1, 金巧依1, 余晨1
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1.河海大学环境学院;2.江苏省南京环境监测中心
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| 摘要: |
| 人为干扰和气候变化导致城市河流缺氧现象频发，研究缺氧成因对于水生态保护至关重要。基于2021年丰水年与2022年枯水年秦淮河流域4个典型水质监测站实测数据，分析了年际、汛期-非汛期和典型降雨事件3个时间尺度下溶解氧的时空变化规律。采用Spearman秩相关法识别了溶解氧变化的主要影响因素及驱动机制，并构建了包含以上因素的决策树模型，揭示了流域轻度、重度缺氧现象的控制因素阈值及其联合诱发过程。结果表明，空间上，秦淮河流域溶解氧浓度从上游到下游逐渐降低，低值区位于外秦淮河入江口处的三汊河口站，年均值为5.37 mg/L。不同时间尺度上，2022年秦淮河流域溶解氧水平优于2021年，4站点溶解氧年均值上升0.54 mg/L~1.25 mg/L，轻度及重度缺氧发生次数减少0.1~3.7倍；4站点汛期溶解氧均值比非汛期低3.38 mg/L~4.57 mg/L；随着雨强增大，河流雨后亏氧现象减少，中雨下的亏氧频率和程度最高。各河段的缺氧特征和机制不同，周边汇水区域以林地和耕地为主且轻度缺氧发生居多的河段，其轻度及重度缺氧现象由水温、pH和高锰酸盐指数诱发。而在汇水区域以建成区为主且重度缺氧发生居多的河段，汛期溶解氧变化多由总磷、氨氮和高锰酸盐指数驱动，其轻度及重度缺氧现象的关键诱发因素包括水温、pH和总磷。基于此，对不同河段提出了针对性的防控措施，有助于减缓城市河流缺氧现象。 |
| 关键词: 城市河流 溶解氧 时空变化 驱动因素 决策树模型 缺氧机制 |
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| 基金项目:国家重点研发计划项目（2023YFC3208900，2023YFC3208904）、国家自然科学基金项目（52039003）、江苏省环境监测科研基金项目（2101）、南京市环保科研课题资助项目（202214）、江苏省南京环境监测中心自主立项科研项目。 |
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| Driving Factors Identification and Mechanism Analysis of Hypoxia in Urban Rivers—Considering the Qinhuai River in Nanjing |
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ZHENG Wanting1, LI Yiping1, PAN Hongzhe1, LIU Jun2, BAI Song2, ZHAO Mingming2, HU Jing2, XIE Xinmiao2, WANG Yaning1, JIN Qiaoyi1, YU Chen1
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1.College of Environment,Hohai University;2.Nanjing Environmental Monitoring Center of Jiangsu Province
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| Abstract: |
| Abstract: Human interference and climate change have led to frequent hypoxia events in urban rivers. Studying the causes of hypoxia is crucial for aquatic ecological protection. Based on the measured data collected from four typical water quality monitoring stations in Qinhuai River Basin from the wet year of 2021 to the dry year of 2022, this study analyzed the spatiotemporal variation patterns of dissolved oxygen on three-time scales: annual, flood season to non-flood season, and typical rainfall events. The Spearman rank correlation method was used to identify the main influencing factors and driving mechanism of dissolved oxygen changes and a decision tree model including these factors was constructed to reveal the threshold of controlling factors and their joint induction process of mild and severe hypoxia in the basin.The results show that the dissolved oxygen concentration in the Qinhuai River Basin gradually decreases from upstream to downstream, with the low-value area located at the Sancha estuary station at the entrance of the Qinhuai River, having an annual average of 5.37 mg/L and only 3.23 mg/L during the flood season. On different time scales, the dissolved oxygen level in Qinhuai River Basin in 2022 was better than that in 2021, with the annual average at four stations increasing by 0.54 mg/L~1.25 mg/L, and the number of mild and severe hypoxia events decreasing by 0.1~3.7 times. The average dissolved oxygen in flood season is 3.38 mg/L~4.57 mg/L lower than that in non-flood season. With the increase in rainfall intensity, the phenomenon of oxygen deficiency in rivers after rain decreases, with the frequency and degree of oxygen deficiency under moderate rain being the highest, at 98.0% and 1.13 mg/L respectively. The characteristics and mechanisms of hypoxia differ in each river reach. In the reaches where the surrounding catchment area is mainly forestland and cultivated land, mild anoxic events occur mostly, and mild and severe hypoxia events are mostly induced by water temperature, pH, and permanganate index. However, in the river sections where the catchment area is mainly built-up areas and severe anoxic events occur mostly, the change of dissolved oxygen during flood season is mostly driven by total phosphorus, ammonia nitrogen, and permanganate index. The key inducing factors of mild and severe anoxic events include water temperature, pH, and total phosphorus. Based on this, targeted prevention and control measures were proposed for different river sections to help mitigate hypoxia in urban rivers. |
| Key words: urban rivers dissolved oxygen spatiotemporal variation driving factors decision tree hypoxia mechanism |
