Study On Constructed Wetland Design Based On Agricultural Non-point Source Pollution

The problem of agricultural non-point source pollution (ANPSP) has become one of the main problems of rural ecological environment in China with the acceleration of China’s agricultural modernization in recent years,, The ANPSP characterized by its widely distributed and various sources and its uncertainty of export to water body is much more difficult to control than point source pollution. It has become a hot research topic around the world. Constructed wetland system considered as one of the ecofriendly water pollution control technology, is increasingly used in ANPSP’s treatment.Chaohu Lake, the largest lake in Anhui Province, is now facing serious eutrophication problem with the rapid development in the whole watershed area, especially the area around lake. Agricultural activities contribute a lot to water pollution in the lake. There are many polders, the low lying land reclamations surrounded and protected by dike, around Chaohu Lake. Agricultural activities dominate in these polders. It has been thought very import to control water pollution in and from the polders because of their location and important ecological and economical values. Wangnan polder is one of them, which is located in the northeast of Chaohu Lake, adjacent to Chaohu City. The application of constructed wetland system to the polder area will be an important measure in water pollution control for related water bodies.Based on general principles of constructed wetland design and the detailed field survey and investigation of studied polder area, specific design principles and methods of ANPSP control and the application of the design are presented in this thesis. The main points are as following:(1) The design of the constructed wetland system should considered the use of existing water,communicated them into a compound constructed wetland system with surface flow type and subsurface flow type.It can purify the agricultural surface source water generated within the polder, At the same time small processing unit will be set up in the farmland and living areas,to intercept the pollutants and pure the sewage further.(2) According to the characteristics of the polder,which is relatively closed, the entire wetland system will be designed into a new pattern of each unit are connected end to end to increase the residence time of pollutants in the wetland,and the sewage come from different ways to adapt to the actual regional situation.(3) In the selection of wetland plants, according to the principle of local existing and better adaptability,combined with the actual local situation,the plants which have strong decontamination ability of nitrogen, phosphorus nutrition and certain economic value will be selected.Acorus calamus,lotus, reed, Canna, water hyacinth and Hydrilla verticillata were chosen and distributed in different functional units.(4) According to the local terrain and economic development,landscape design area is arranged in the two-stage subsurface flow wetland through different ways, such as increasing the hydrophilic space,Selection of landscape plants to increase unit landscape effect. It can create the ecological landscape system to increase the area of wetland ecological benefit and economic benefit.