长江流域水体富营养化演化驱动机制及防控对策

富营养化已成为长江流域河流、湖泊与水库面临的共性问题,基于近10 a来长江流域水质状况、营养物质含量、水文泥沙过程、富营养化评价指数等数据及相关历史文献,分析了长江流域水体富营养化现状及演化趋势,以典型河流、水库与湖泊为例,剖析了长江流域水体富营养化驱动机制。结果表明:①长江流域水体富营养化程度为河流水库湖泊,上游四川盆地与中游江汉平原是长江流域富营养化湖泊与水库的主要聚集区。②近10 a来,中度富营养化湖泊比例从2009年的31.3%增加至2018年的42.7%,水库营养水平正从中营养向轻度富营养快速发展。③长江流域水体营养充足,受闸坝建设运行影响,流速减缓、流量偏枯,水体交换慢与河湖连通性差是河流、水库与湖泊富营养化的重要驱动力。为防控水体富营养化,建议监测重要控制断面氮磷浓度与通量,加强农田灌溉退水与水产养殖废水排放管理,开展流域水、沙、营养物质耦合输送调控。

Evolution,driving mechanism and control strategy for eutrophication in Changjiang River Basin

Eutrophication is a common and urgent problem for rivers, lakes and reservoirs in the Changjiang River Basin. Based on the monitoring data and related historical literature on water quality, nutrient concentration, hydrology process and sediment transportation as well as eutrophication assessment index, current trophic status and its evolution trends of the waters in the whole basin during the past decades were analyzed, and the eutrophication driving mechanism for typical rivers, lakes and reservoirs were further demonstrated. It was indicated that eutrophication ranking for different kinds of waters from low to high were rivers, reservoirs, lakes. Sichuan Basin in the upstream and Jianghan Plain in the middle stream were the key concentrate region for eutrophic lakes and reservoirs. During the past 10 years, proportions of the moderate eutrophic lakes to total assessed lakes continually increased from 31.3% in 2009 to 42.7% in 2018, and trophic level of the reservoirs dramatically changed from mesotrophic to slightly eutrophic. Due to nutrient discharge by anthropic activities and operations of massive dams, factors including sufficient nutrient sources, declined flow velocity, decreased runoff, slow water exchange and worsen connectivity for water bodies greatly induced the occurrence of the eutrophication. Therefore, countermeasures including monitoring the nutrient such as nitrogen and phosphorus concentrations and flux on controlled sections, strengthening the discharging management for agricultural irrigation recession water and aquaculture waste water, and implementing the coupled regulation for water, sediment and nutrient at the basin level have been recommended to control the development of eutrophication in the basin.