中文摘要：

通过对近几十年来洞庭湖水情、泥沙、污染和湿地生态等不同方面问题的回顾分析,认为在三峡工程建设、洞庭湖退田还湖和极端天气事件影响下,洞庭湖主要生态环境问题发生了一些变化。由于气候干旱化,加之三峡水库蓄水影响,导致洞庭湖入湖水量季节性减少,湖区水位下降,干旱期延长。模拟显示2006和2009年三峡秋季蓄水使洞庭湖出口水位平均下降2.03和2.11 m;由于三口来沙急剧减少,入湖泥沙打破了以淤积为主的模式,2006年洞庭湖第一次出现从拦蓄泥沙变成向长江净输出泥沙。低水位运行不仅对洲滩演进和湖泊水质带来影响,也加速了对湖滩的开发利用,外来物种的发展威胁了湖泊湿地生物多样性和动物栖息地的稳定。同时,湖区复合型水污染威胁加重,洞庭湖水质从2008年的Ⅳ类水下降为Ⅴ类水。洞庭湖在缺水与洪涝矛盾中,正从单一洪灾为主转向矛盾的两个方面共存。这些变化一方面与气候变化有关,也是流域生产由传统农业转向农、林、水、工的综合发展,以及湖泊与流域关系改变的结果。

英文摘要：

With the evolution of sediment,hydrological regime and pollution,major environmental issues have gradually changed around Dongting Lake in recent decades.Especially under the impacts from the Three Gorges Project,returning farmland to lake project and the increasing of climate extremes,Dongting Lake is undergoing low water level occurrences.The water level dropped 2.03 and 2.11 m at the outlet of the lake in 2006 and 2009 respectively,caused by the water storage of Three Gorges Reservoir.The water quality has deteriorated from grade Ⅳ to grade Ⅴsince 2008.Low water level accelerated the change in wetland structure and the degradation in wetland function.Invasive plant has threatened the biodiversity and the stability of habitat.Due to continuous decrease in sediment discharge,Dongting Lake,for the first time,changed from trapping to supplying net sediment to the Yangtze River in 2006.The environmental conflict around Dongting Lake is changing from flood dominated to flood and drought coexisted.These environmental changes have reflected the social structure transformed from traditional agriculture to a comprehensive development in agriculture,forestry and industry,as well as changes in the lake-catchment interaction.