关键词: 生态环境问题, 形成机制, 洞庭湖湿地

Abstract: In this paper the main ecological and environmental problems and their causing mechanisms in the Dongting Lake wetland are analyzed according to new investigations and observations. There are four main ecological and environmental problems. Firstly, water pollution becomes more serious and eutrophication is going to be considerable; Secondly, the infectious range of schistosoma japonicum disease has expanded and its harmful affection has recovered; Thirdly, flood and waterlogged disaster is frequent and serious, drought disaster occurs occasionally and meteorological disaster is diversified; Finally, wetland resources have degraded and ecological balance has been destroyed.There are consecutive features in the water pollution and eutrophication, such as nitrogen and phosphorus are the main pollution factors and living pollution is predominant; water pollution and eutrophication are slight as a whole and less changes in a year, but their regional difference is large; the water pollution is gradually aggravated and the eutrophication becomes obvious.Flood and waterlogged disaster in the Dongting Lake wetland is due to the synthetic influence of artificial and natural factors, such as regional link mechanism, abnormal atmospheric circulation, responding mechanism to El Nino and influence of land use change.The causing mechanism of harmful schistosoma japonicum disease contains micro-mechanism and macro-mechanism. The former is that the oncomelania-breeding region is expanding in accordance with the beach expansion and has expanded greatly to the polders due to the frequent flood disaster, increasing drainage culvert and offtake. The later is that the density of oncomelania closely relates to altitude and coverage of the beach vegetation, and is controlled by the beach environmental factors, such as groundwater table and soil water content.Water pollution and entrophication result from the synthetic effect of sewage discharged from point sources and area sources, hydrological and climatic conditions. The paper mills and fertilizer industries are the main pollution sources. The most serious pollution region is the western Dongting Lake. Generally speaking, the eutrophication in the Dongting Lake is not so obvious. The reason is the special water environment of the lake.The causing mechanisms of biodiversity reducing and ecological balance destroyed is the ecological succession from sand deposit to beach vegetation; over-fishing, over cultivation of beach and water area, water pollution and the return course of fishes broken by hydraulic structures.

Key words: ecological and environmental problems, causing mechanism, Dongting Lake wetland