Simulation Of Agricultural Non-point Source Pollution And The Determination Of Best Management Practices In Yitong River Watershed

Simulation of Agricultural Non-point source pollution and the Determination of Best Management Practices in Yitong River WatershedThe increases of the Chinese population enlarge the food demand. These days, to gain the agricultural output, excessive pesticide and chemical fertilizer have been used and agricultural waste increased sharply. These pollute both surface and subsurface water, destroy the vegetation, and cause the water loss and soil erosion. Spatially, the agricultural non-point source pollution distributes depressively, and affected by geographical, climatic and hydrological condition. The polluted matters type is enormous. Most of them transport in the water and soil within complicate rules and is hard to monitory. Therefore, it is widely concerned to assess the process of nitrogen, phosphorus, sediment, which is the main polluted matter source from agriculture, transporting in the soil and water.Yitong River plays a significant role for the people living along it. According to the recent field investigation and data analysis, due to overusing pesticide and fertilizer, the water in Yitong River has been polluted seriously. This is worsening for the transformation of forest and grass land to the agricultural land.In this thesis, we used the SWAT as the model to learn the process of agricultural non-point pollution in Yitong River. First is using the MapGis6.7 and ArcGis9.2 to interpret and analyze the relative maps, including the maps of DEM. soil type and hydrographic net. And then prepare the database for climatic condition and soil type. Based on the data prepared a model that can generalize the filed character of non-point source pollution have been estimated, verified, after studied the sensibilities of parameters.Assess the process of agricultural non-point source pollution by use of the SWAT model above. It can be concluded that, in 2008. the sediment runoff in the Yitong river is 3.458.700 t. with the total nitrogen and phosphorous of 10.534.27t and 1.132.42t respectively. Affected by the climatic condition, especially the rainfall. the weight of the nitrogen and phosphorous have been reduced half when compared with them in 1985. There is more nitrogen infiltrated into groundwater than into surface water, with 2.4 times in 1985 and 5.5 times in 2008. Temporally. caused by the precipitation and characteristics of pollutants, the pollutant output of June, July, August account for about 90% of the year, and the varying rules of phosphorous is corresponding with that of sediment runoff. Spatially, the maximum output of nitrogen ad phosphorous appeared in the upper and mid-lower of the Yitong River, while that of sediment in lower reaches. More nitrogen infiltrated into groundwater on the downstream area. Researched showed that the maximum pollution output in glebe and maximum in the forest. Therefore the change in the output of pollution is determinate by the area of glebe.Finally, coupling the best management practices (BMPs) theory into the actual character of the research zone, the best methods to manage the agricultural pollution in this area have been proposed. Plant the alfalfa vegetation along the river can reduce 65% of the pollution. Converting the cultivated into forest and grass land can vanish 10～40% of the pollution. In addition, it is necessary to come up with the laws to regulate the land use along the Yitong River and extremely important is to use the fertilizer and pesticide effectively and efficiently.