Evolution characteristics and driving factors of water quality and eutrophication of typical lakes in the middle reaches of the Yangtze River from 2016 to 2020

“十三五”时期，长江流域水环境质量改善明显，但湖泊水质和富营养化状况改善滞后. 长江中游作为我国淡水湖泊集中分布区域之一，部分湖泊存在水环境质量恶化和富营养化加重问题. 本文以长江中游区域国家开展监测的洪湖、斧头湖、梁子湖、大通湖、洞庭湖和鄱阳湖这6个典型湖泊为研究对象，科学评价其2016—2020年水质和富营养化时空变化特征及关键驱动因素，探讨其成因及治理对策. 结果表明，“十三五”时期长江中游湖泊水质和富营养化程度存在较大差异，与2016年相比，2020年大通湖水质改善最为明显，梁子湖水质变差，总磷是影响长江中游湖泊水质类别的主要因子; 洪湖富营养程度恶化最为严重，斧头湖次之，TLI(SD)对长江中游湖泊富营养化评价贡献最大. 目前长江中游湖泊呈有机污染加重和叶绿素a浓度升高现象，洪湖、斧头湖和梁子湖主要与氮、磷营养盐浓度升高有关，而大通湖、洞庭湖和鄱阳湖受水文过程、流域纳污量和湖泊管理等非营养盐因素影响较大. 总氮和总磷仍然是影响“十三五”时期长江中游湖泊水质和富营养化的最主要驱动力，且各湖泊总氮和总磷浓度变化均具有较强正相关性，建议开展河湖氮、磷标准衔接工作，提出河湖氮、磷标准限值或考核目标，以完善河湖水环境质量标准和生态健康影响评价技术规范. 同时，建议长江中游湖泊在开展截污控源、内源控制和生态修复的同时，进一步深化流域管理，特别是对洞庭湖、鄱阳湖、梁子湖和斧头湖等跨行政区湖泊，以提高湖泊治理与修复的系统性和整体性.;During the 13th Five-Year Plan period, the water ecological environment quality of the Yangtze River Basin has improved significantly, but the improvement of lake water quality and eutrophication has lagged behind. As one of the concentrated distribution regions of freshwater lakes in China, the middle reaches of the Yangtze River have the problems of deterioration of water quality and aggravation of eutrophication. This article chosed six typical lakes monitored by national agencies, including Lake Honghu, Lake Futou, Lake Liangzi, Lake Datong, Lake Dongting and Lake Poyang, to scientifically evaluate their spatiotemporal changes, key drivers of water quality and eutrophication from 2016 to 2020, and to discuss the degradation causes and governance countermeasures. The results revealed significant spatiotemporal changes in water quality and eutrophication of those lakes. From 2016 to 2020, the water quality of Datong Lake improved mostly, while Lake Liangzi became worse. TP is the main factor affecting the lake water quality and TLI(SD) is most important in the lake eutrophication evaluation. The eutrophication in Lake Honghu is the most serious, followed by Lake Futou. The lakes in the middle reaches of the Yangtze River widely experienced increasing organic pollution and chlorophyll-a concentration. Such degradation in Lake Honghu, Lake Futou and Lake Liangzi is mainly related to the increase of nitrogen and phosphorus nutrients, while Lake Datong, Lake Dongting and Lake Poyang are greatly affected by non-nutrient factors such as hydrological processes, pollution holding capacity and Lake management. TN and TP are still the main drivers on the water quality and eutrophication of these lakes during the 13th Five-Year Plan period, and change synergistically in each lake. We propose to put forward the standard limits or assessment targets of nitrogen and phosphorus in rivers and lakes, to improve their environmental quality standards of rivers and lakes and the technical specifications for ecological health impact assessment. At the same time, it is recommended that the lakes in the middle reaches of the Yangtze River should carry out pollution control, endogenous control and ecological restoration. It is important to strengthen watershed management, especially the lakes across administrative regions such as Lake Dongting, Lake Poyang, Lake Liangzi, and Lake Futou to improve the system and integrity of lake governance and restoration.