三峡工程对洞庭湖水环境质量的影响

Water Environmental Quality of Dongting Lake Caused By Impoundment of the Three Gorges Project

通过实地调查与水样检测,运用BP神经网络模型、湖泊富营养化评价法以及Shannon-Weaver指数分别评价了三峡工程蓄水前后典型年(1986、1991、1998、2004、2006和2010年)洞庭湖水环境质量、营养化水平和水生生物状况。结果表明:三峡水库蓄水后,典型年洞庭湖水质总体变差,各断面水质超标率有明显上升,呈现以氮、磷污染为主并伴有有机污染的特征;营养化指数有上升趋势,东洞庭湖2008~2010年综合营养指数超过50,出现轻度富营养;隐藻门代替硅藻门成为洞庭湖浮游植物优势种,其生物多样性下降;东洞庭湖底栖动物优势种为梨形环棱螺,而苏氏尾鳃蚓成为西、南洞庭湖的优势种,其种类和密度呈波动下降的趋势。影响洞庭湖水质的因素除了"三口"、"四水"污染物聚集和湖区生活污染、面源污染外,三峡水库运行后入湖水沙量大幅减少以及土地利用格局变化也是其关键。

Through fieldwork and water sample monitoring, the application of BP neural network model,evaluation method of lake eutrophication and Shannon-Weaver index,the study separately evaluated the water environment quality,nutrient level and aquatic life status of Dongting lake before and after the impounding of The Three Gorges Project in typical years（ 1986,1991,1998,2004,2006 and 2010）. The results indicate that after the impounding of the Three Gorges Reservoir,the water environmental quality get worse as a whole,the over-limit ratio of the water quality of all its sections has a significant increase and it presents mainly to N, P accompanied with organic pollution. The Nutrient index has risen. The comprehensive nutrition index of east Dongting Lake from 2008 to 2010 exceeded 50 and became Mild eutrophication. Cryptophyta has replaced bacillariophyta and becomes the dominant species of phytoplankton in Dongting Lake,where its biodiversity index has descended. The dominant species of zoobenthos is bellamya purificata in east Dongting Lake while branchiura sowerbyi in the west and south Dongting,whose species and density tend to fluctuate downward. The factors affecting the water quality of Dongting lake are not only the ＂three ports＂,＂four waters＂pollutants,but also the pollution of the lake area and non-point source pollution,the crucial reasons are the great reduction of the amount of sediment in the lake and the change of land use pattern.