Effects Of The Three-Gorge Project On The Ecological Environment Of Dongting Lake

Dongting Lake is one of the classic complex lakes in the world, which absorbs the water from four rivers: the Xiang River, the Zi River, the Yuan River and the Li River, and also exchanges water with the Yangtze River. It is an inland lake with the functions of adjusting and storing . Dongting Lake plays a critical role in the environment and economy of the Hunan Province and the entire Yangtze River water system. Its functions include transportation, aquatic production and environmental improvement as well as a flood barrier for the Jing River region and the middle and downstream region of the Yangtze River. Three-Gorge Project is the biggest hinge project in China as well as in the world. And it is also the key skeleton project to treat and develop the Yangtze River which is the focus in the world.Dongting Lake is immensely influenced by the ongoing Three-Gorge Project because of the extensive interaction between them. After the operation of the project, the buffering effect of the Three-Gorge reservoir will significantly change the relation between the Yangtze River and the Dongting Lake, and also change the hydrography and water quality of the Lake, which inevitably results in the change of the ecological environment of the Dongting Lake.In this article, based on the basic environmental and ecological concepts, we try to describe and briefly analyze the major environmental issues of the Dongting region, which include escalating water pollution, rising eutrophication, decrease of biological diversification, severe flood disaster, silt stagnation, shrink of the water body, escalating soil erosion and schistosomiasis, etc.We use the projection pursuit model based on the improved ant colony algorithm to analyze the status of the water quality of the Dongting Lake in 2001. The results show that the pollution is heavier in the Muping Lake, South Dongting Lake and East Dongting lake, while it is lighter in the inlets of the Yuan River and Yangtze River.Using the water quality data of the Dongting Lake from 1991 to 2000, we study the annual dynamic variation of TN, TP, COD, BOD, NO_X~- -N andNH4+-N and also the regional variation of COD, BOD and TP. The results indicate that the pollution is still mainly caused by point pollution source.To address the insufficiency of common studies on the progress and cause of severe lake water quality, which limit on the study of total amount control or environmental capacity of N and P, we propose that nutrientnitrogen deposition critical load will play an significant role due to the human intervention in the control of the pollution of N, P pollution. Our calculation of the critical loads of the years 1974, 1996, 1998 and 1999 demonstrates that this value remains steadily at the level between 1.16 and 1.20 with little annual variation.After brief introduction to the characteristics of the Three-Gorge Project, using the hydraulic gradient as the major water power factor instead of water level or water amount, we discuss the change of hydraulic gradient before and after the operation of the Three-Gorge Project.Based on the sample data of November of four representative years: 1974, 1996, 1998 and 1999, we calculate nutrientnitrogen deposition critical loads before and after the operation of Three-Gorge Project. Using the probability instead of the common used possibility, we estimate the super risk of the critical loads in the representative months and years. The results indicate the control of the Three-Gorge reservoir can reduce the super risk of the nutrientnitrogen deposition critical load of the Dongting Lake.To study the effect of the Three-Gorge Project on the biological diversification of the Dongting lake, we take xanthium and bulrush as representive wetland plants. We analyze the correlation between the growth of the plants and the hydraulic gradient to study the influence of the project on the growth of wetland plants. Then we try to briefly describe the effects of the project on the animal and other major environmental issues.We introduce the concepts of ecological safety and health after discussing the effect of the Three-Gorge Project. After introducing related content of ecological safety, ecosystem health and water environment health, we do the health risk assessment based on the water quality data of 2001 and analyze the annual health hazard risk of the carcinogen and non-carcigenic chemicals in the water of Dongting lake.At last, we introduce the related theory of ecological restoration and...