Changes of water quality in Lake Dongting before and after Three Gorges Project operation

Abstract

为了解三峡工程运行前后洞庭湖水质变化,基于19962013年洞庭湖水质监测数据,采用内梅罗污染指数(I_P)法对三峡工程运行前后洞庭湖水质进行评价,并对洞庭湖水质与主要污染物的时空变化特征进行分析. 结果表明, 19962013年洞庭湖I_P值在1.10~2.20之间,平均值为1.63,水质属轻污染～污染,总体变化平稳,但从2010年起,洞庭湖I_P值连续低于其多年平均值,总体水质趋好;主要污染物为总磷和总氮,总磷浓度变化平稳,总氮浓度则呈显著上升趋势. 与三峡工程运行前相比,三峡工程运行后洞庭湖全年和汛期总氮浓度以及南洞庭湖I_P值和总氮浓度显著升高,南洞庭湖水质显著恶化. 洞庭湖I_P值和总磷浓度的水期分布格局均由三峡工程运行前的汛期> 非汛期变化为三峡工程运行后的非汛期> 汛期,其空间分布格局均由三峡工程运行前的西洞庭湖> 东洞庭湖> 南洞庭湖变化为三峡工程运行后的西洞庭湖> 南洞庭湖> 东洞庭湖;从2010年起,洞庭湖I_P值的空间分布格局发生新的变化,其大小顺序变化为东洞庭湖> 南洞庭湖> 西洞庭湖. 三峡工程运行前后洞庭湖I_P值与总磷浓度的时空变化与其水沙条件变化有关,总氮浓度受三峡工程运行影响较小,主要受湘江、资水、沅江和澧水“四水”流域氮污染的影响.;To understand the changes of water quality in Lake Dongting before and after Three Gorges Project operation, the water quality in Lake Dongting was evaluated based on the water quality monitoring data of Lake Dongting from 1996 to 2013 by using Nemerow pollution index method, and the spatial and temporal variation characteristics of water quality and main pollutants in Lake Dongting were analyzed. The results showed that the I_P values of Lake Dongting ranged from 1.10 to 2.20, with an average of 1.63 from 1996 to 2013, the water pollution level was between light pollution and pollution, the water quality did not change significantly generally, but since 2010, the I_P values of Lake Dongting had been continuously under the average for many years, and water quality became better. Total phosphorus and total nitrogen were the major pollutants in the lake, the concentration of total phosphorus did not change significantly, but the concentration of total nitrogen showed a significant upward trend. Comparing with the period before Three Gorges Project operation, the concentration of total nitrogen in Lake Dongting and the I_P values and the concentration of total nitrogen in southern Lake Dongting increased significantly after Three Gorges Project operation, the water quality in southern Lake Dongting deteriorated significantly. The order of I_P values and the concentration of total phosphorus in different water phases changed from flood season> non-flood season to non-flood season> flood season, and in spatial distribution changed from western Lake Dongting> eastern Lake Dongting> southern Lake Dongting to western Lake Dongting> southern Lake Dongting> eastern Lake Dongting, respectively before and after the Three Gorges Project operation. Since 2010, the ranking order of I_P values had changed in spatial as eastern Lake Dongting> southern Lake Dongting> western Lake Dongting. The spatial and temporal changes of I_P value and the concentration of total phosphorus associated with changes of flow and sediment conditions in Lake Dongting before and after Three Gorges Project operation, the concentration of total nitrogen was less affected by the Three Gorges Project operation, mainly by nitrogen pollution of Xiangjiang River, Zishui River and so on in the four river basin.