The Study Of Eco-environmental Water Requirement And Constructed Wetlands' Benefit Of Chuanhu Lake In The Western Changchun

In our country, the serious water crisis not only restricts the development of a city, but also obsesses the citizens. In recent years, gross output value of industry and agriculture,the scale of the city and the population of Changchun have developed rapidly, which lead to an increased demand of water resources. So it is of great significance to enhance the treatment and control of the water pollution in Changchun, where the problems of water shortage are very serious. Chuanhu water system is the main framework of the water system in northwestern Changchun and its function includes flood control and drainage, irrigation, fish farming and city view, etc. With the continuous enlargement of the city and the acceleration of the process of urbanization in China, the condition of Chuanhu Lake is becoming worse in recent years. The environmental problems, including severe water pollution, the shrink of the lake's surface, the random stack of the garbage and insufficiency of the waterfront plant cover, have gravely affected the people's living and limited the construction of Chuanhu water system and land development of the riverfront. By establishing constructed wetland, the water purification and ecological restoration engineering of Chuanhu Lake will drive the restoration of natural ecosystem in the Chuanhu lake basin to promote the realization of the general objectives in Chuanhu Lake restoration.Firstly, the environmental problems in Chuanhu water system are summarized in this paper by the investigation and analysis of the present situation of the environment of Chuanhu in the western Changchun. The main problems are as follows: the natural water is so insufficient that the natural inflow is only 8200 m3 per day which is only 10.5% of the total, but the sewage discharge reaches up to 88700 m3 per day; the water pollution is so serious that the evaluation results of Chuanhu waters by the equivalent pollution load method and the pollution index method indicate that indexes of pollutants such as BOD5,CODcr,N,P exceed environmental quality standards for surface water of type three, and that the Yanming lake and Xinyue reservoir are severely polluted, whose pollution indexes are both over 5.0; the random sewage discharge and garbage dumping are common in the river course; the lack of the vegetation on lakeside as the effective slope protection and the lack of aquatic plants buffer zones impact the ecological functions of the Chuanhu Lake.Secondly, the thesis discusses eco-environment water requirement of the Chuanhu Lake. Through function method, the minimum annual eco-environmental water demand of Chuanhu lake is determined,which is 30,790.4×104 m3. It means that water resources of 30,733×104 m3 need to be recharged from surface runoff to ensure the existence of the Chuanhu lake. It can be clearly seen that current situation of water environment of Chuanhu Lake is serious as for a sewage discharge trench with insufficient natural inflow .So it is imperative to reconstruct the Chuanhu Lake.Thirdly,the feasibility of the application of the constructed wetland in Chuanhu lake in Changchun in the urban sewage treatment is analyzed and discussed by studying the building and successful operating experience in winter of other constructed wetland in northeast China. It is discussed in the aspects of the treatment effect and protection strategy in winter. The results indicate that the effect of the treatment by the built constructed wetlands in northeast China is satisfactory and the treated water can reach the local standard of landscape water except for winter. The operation results in winter show that effective heat preservation measures should be taken. For example, the harvested greening plant can be put on the packed bed, on which plastic film is covered. In this way, the temperature of the sewage in the packed bed can be increased and the effect of the heat preservation is good.Then ecosystem services and environmental-economic values of the Chuanhu Lake are discussed in detail. Based on the principals of ecology and ecosystem services, according to local investigation and research, there are following main ecosystem services functions in Chuanhu Lake: material production function, water supply function, constituent of atmosphere regulating function, water regulating function, cleaning pollutants function, biodiversity function, leisure tourism function, scientific research and culture function. The ecosystem services results show that the functions in leisure tourism and cleaning pollutants are the major ecosystem services of the Chuanhu Lake, which are respectively 58.038% and 41.587% of the total values, followed by the function in water regulating, which accounts for 0.174%. Other function in biodiversity, constituent of atmosphere regulating and material production are 0.104%,0.061%,0.021%, respectively. The function in scientific research and culture is the smallest, 0.016%. The result indicates that the function in cleaning pollutants is powerful. Meanwhile, the construction of the constructed wetland can bring the other functions of the Chuanhu ecosystem into full play and it will play an important role in the improvement of the whole image of city and surrounding environment.At last, an environmental-economic value evaluation system and model are established in this paper. The value of constructed wetlands consists of environmental-economic value and cost value. And the environmental-economic value is composed of environmental capacity value, resources value and social value while the cost value is composed of maintenance value and artificial conversion value. In the calculation of the various values, Contingent Valuation Method is applied in the study on the environmental capacity value and resources value. Then, an integrated modulus is introduced to assess the environmental-economic value of constructed wetlands. Calculating results show that its total value of the constructed wetlands of Chuanhu lake is about RMB 379.88 million yuan and the total economic benefit is about RMB 235.83 million yuan, with the cost-benefit ratio of 1:5.9,and its environmental and economic benefit is greatly prominent.The main content in this paper has important reference value in widespread use of constructed wetlands technique in northern China. In order to bring the function of the Chuanhu Lake in water purification and ecological restoration into full play, rational utilization of wetland resources is the most important. Effective measures should be taken such as enhancing scientific research work, strengthening the publicity, improving the consciousness of environmental protection and so on.