中文摘要：

根据19862015年30年的水质监测数据，利用湖泊水质单因子评价和综合营养状态指数（7L/)对洞庭湖水质营养状况变化趋势进行评价分析.19862015年全湖1.类水质百分比呈现极显著下降趋势，近5年来稳定在汉类水平，影响水质的污染物为总氮（TW)和总磷（TP),全湖TW浓度、TP浓度和7L/在过去30年里呈显著或极显著上升趋势，TW和TP等是洞庭湖水质类别的主要影响因子.在空间分布上,7L/、TW浓度、TP浓度和Chl.a浓度高低顺序均表现为东洞庭湖>南洞庭湖>西洞庭湖，且东洞庭湖TW浓度和Chl.a浓度与其它湖区差异显著.19862002年洞庭湖水质营养状态呈现波动上升趋势，主要与面源污染有关;20032007年富营养化趋势有所减缓,可能与期间工业污染下降和水环境容量扩大有关;但20082015年又开始明显加剧,可能是流域内工业与农业污染增加、内源污染释放与水环境容量减小造成的.30年来洞庭湖各湖区基本均处于中营养状态,但接近轻度富营养且20082010年和2015年东洞庭湖等部分湖区达到轻度富营养水平.洞庭湖近年来蓝藻门所占比例明显上升，部分湖区已经暴发蓝藻水华.

英文摘要：

Based on the 30 years5 monitoring data in Lake Dongting from 1986 to 2015,we evaluated the changing pattern of water quality and nutrient condition using single factor,s evaluation and water trophic level index ( T L/ ). The water quality of Lake Dongting remained at R’ level in the last five years and the percentages o f l IE level declined significantly from 1986 to 2005. Total nitrogen ( TN) and total phosphorus( T P ) were the major influential factors on the water quality. Over the long-term preriod, the concentration of TN , TP and TL/ increased significantly from 1986 to 2015.It showed that TN and TP were major factors which affected the water quality and TL/ in Lake Dongting. The ranking order of TN ,TP and Chl.a in different part of Lake Dongting was East>South>West. TN and Chl.a of the East part were the significantly highest.The water quality was significantly influenced by the flood during 1986 2002, while it tended to improve during 2003 2007 , because of the decrease of industiy pollution and water capacity expansion. However, it tended to eutrophic again during 2008 2015 which might be caused by the increase of the pollution from local industry and agriculture, endogenous pollution release and water capacity decrease. In the last 30 years, the whole lake was at the mesotrophic level, but sufferred to light eutrophication especially in the eastern lake, which arrived at light eutrophication during 2008 2010 and 2015. The abundance of blue algae in Lake Dongting increased quickly in last 5 years, while somep art of the lake had outbreak blue algae bloom.