| Eutrophication in the water body is one of the problems of global water pollution control and environmental management. As a kind of terrestrial ecosystems, lakes and/or reservoirs' role in the geochemistrical and nutrient cycles becomes more and more significant. From the global perspective, about 30%~40% of the lakes in the world are under the impacts of eutrophication at different levels. At present, the eutrophication impacts on water quality of lakes are prominent in China. And it becomes one of the environmental problems that block the economic development. With economic development and population growth, the pollutants containing N and P discharged into lakes and/or reservoirs will degrade water quality and make the eutrophication more serious than ever.After the Three Gorges Dam built up, the water environment of Yangtze River in the Three Gorges Area will be transformed from a typical stream body to a kind of lake body, and the water ecosystem will be also changed radically. The water quality development trend after the Three Gorges Dam built up has become one of the global attentions. Therefore, it is urgent and significant to study the water quality development trend. Many attentions has already been paid to the enforcement of management and predication of the water quality This research is conducted from following aspects:(1) The author analyzed the relationships between nitrogen cycle, phosphorus cycle and the eutrophication based on the analysis of nitrogen and phosphorus cycle, physical characteristics such as irradiation and water temperature.(2) Based on continuous water quality monitor data of ecological and environmental monitoring system of Three Gorges Reservoir from 1996 to 2000, the author considerably and systemically evaluated the present water pollution situation of main stream and tributaries of Yangtz River using methods such as single-factor evaluation and aggregative index evaluation.(3) Quantitatively analyzed the contribution of different water pollution sources including industrial wastewater, urban sewage, urban solid waste, runoff of farmland and marine vehicle pollution.(4) After the complet of Three Gorges Dam, the land submerged will release organic pollutants, N, P, and trace heavy metals such as Cu, Cr. Cumulated into water body through dissolving, exchanging, diffusing, and this will increase the concentration of those pollutants in the water body. The release of pollutants in the submerged land of Three Gorges Reservoir area is analyzed through related experiments.(5) Based on the analysis of the present situation of water quality in the tributaries, several typical tributaries are taken as examples. Both the rules and ranges of water quality variation and the trend of eutrophication in the tributaries are paid particular attention. Changshou Lake, which is located in the downstream of Longxi River (a tributary of Yangtze River), is carefully evaluated; and the eutrophication situation of Wujiang River, a tributary of Yangtze River, is modeled and simulated under the water body eutrophication model. Main innovations of this dissertation are:(1) By creatively applying multivariate statistical method firstly used and the SPSS10.0 adopted, the author analyzes the main pollutants of the monitor sectors of Yangtze River to study the relations between the water quality indicators of the Three Gorges Reservoir,(2) After the Three Gorges Dam built up, the arable land submerged under the water will become another pollution source of the Reservoir., Experiments and simulations under solid-liquid phase balanced stateless the law of the variation of the pollutants from the submerged arable land in the dam area are studied in the dissertation to deal with this problem.(3) Based on the one dimensional water quality ecological model with zooplankton function, and the hydrological and hydraulic variations of Wujiang River after the Three Gorges Dam built up, the QUAL-â…¡E model is first adopted to simulate the eutrophication of the secondary stream of Yangtze Ri... |
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