| Urban lakes are small lakes located in urban area or the outskirts of a city, which play a very important role in the national economy because of their unique geographical location. With the rapid development of the society and the improvement of living standards, ecological waterscape residence has become a tendency for people to improve their living environment and their living standards, with the outskirts of urban lakes as their preference. However, urban lakes mostly have suffered from eutrophication or hyper eutrophication as a result of the intrusion and destruction of human beings. As an outstanding problem that has threatened the balance of the ecological system and the existence of mankind, water pollution has attracted a lot of attention.A certain lake, a part of some ecological residential district, functions as a tank, a traveling resort, and a entertainment place. However, the lake is relatively shallow, with only a depth of 4.31 meters, so its ecological system is very weak, with Eutrophication of different degrees and a small competence of clearing up pollution. Therefore, it is necessary to make a research and an analysis of its pollution, and formulate efficient and scientific methods to comprehensively control and prevent the pollution in order to improve the water quality.In this thesis, based on the inspection and measurement of the water quality in a hydrological year, the author makes an analysis of the relationship of chlorophylla in the water with other water indexes, meanwhile, makes an assessment of the eutrophication in various water seasons with tropic state indexes, which shows that the general tendency of eutrophication is that flood season is bigger than usual flow season, which is bigger than low flow season. The water quality generally ranges between mesotropher and hyper eutrophication. Most of the waters are light eutrophication and mesotropher, and part of them are hyper eutrophication and middle eutrophication, with a poorer water quality in inlets of waters and dead corners, and a better water quality in open waters. Besides, according to the examination results, the ratio of nitrogen to phosphorus is approximately 20.34:1. In line with the minimum law of liebig, a primary confirmation is made that phosphorus might be the restrictive molecules, and through a recognition of several mixed model, the author finally choose the Vollenweider model as the water quality model of total phosphorus, and besides, in accordance with the requirements of water quality standard for scencry and recreation area(GB12941-91) and the water quality model, the author makes an estimate of the water environmental capability and the reductions of total phosphorus in the lake.Meanwhile, based on the analysis of the water quality of the lake, maintenance technology methods are put forward, which, for the first place, put an emphasis on pollutions with inputs, and on reducing its pollution load, for example the use of pretank and polluted water cut, and secondly, reinforce the pollution management of dead corners and reduce the pollution of lakes without inlets. Such methods includ dredging up sullage, dragging for litters and wastes in the water in due time, and placing in the water some hydrophytes and some filter-feeding fishes, to build up the ecological system to maintain the ecological balance in the water. Anyhow, through a comprehensive programming and the adoption of several methods which combin engineering methods and ecological restoration, and through a combination of control and management, the ecological environment and water function of the lake can be restored, the eutrophication can be reduced and controlled.
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