The Study Of Nonpoint Pollution In Xu Shui River Watershed Based On RS And GIS

China is one of the serious water shortage countries in the world, and its fresh water resources per capita is only one-fourth of the world’s average. With the past three decades of high-speed economic growth, water pollution has become increasingly prominent in our country, seriously affects the living standards and restricts the social development. In recent years, some technological projects such as water pollution prevention and control, river network renovation are adopted by local governments to response to the pollution problem and play a certain effect in the local water pollution prevention and control. But thus methods are difficult to solve this problem from the root. To find out its cause, these methods, which are only the matters of expediency, can’t relieve the water environment pressure and change the fragile environment. The ultimate reason of environment problems is usually the unreasonable land use structure of the local government. Land is the carrier of all human’s economic activities. Achieve all human’s economic and social goals are finally through the change of land use. In the process of pursuing the economic and social goals, if the way of land use is unreasonable and exceeded the bearing capacity of the local environment, environment problems will be caused and water pollution is usually the first.In allusion to Zigong city, Sichuan province, the pollution load of Asahi river section was estimated by selecting land use as the ‘source’ of river pollution, which means land use change as the main effect index model of non-point source pollution.The main research results and innovation of this paper are as follows:1)3S technology is applied to speculate recent year’s land use and changes in the research area. the technology of satellite remote sensing images is used in the study, to get the maps of land use types of Gong Jin river basin along Xu Shui River in 2009 and 2013 respectively; according to the changing speed of land use, the strength and the pattern index of ecology landscape and other indicators in the study area, it is analyzed the changes of land use in the study area from 2009 to 2013. The study shows that land use in Xushui watershed changed dramatically in the last four years: farm land has been decreasing and construction field and garden field have been increasing(mainly in urban area); while LPI, AREAMN, and LPSI studies suggest that land patches have been becoming sophisticated and of diversity, in which landscape diversity and fragmentation decrease albeit land use aggregation degree increase.2)The geographic information of river network, slope and aspect of Gongjing section of Xushui River is extracted. Watershed borderline is designated and optimized drainage area threshold of research area is calculated to 2200 hm2. The sub-watershed and river network are also designated and extracted. Farmland, woodland, garden field, construction field and unused land are synthetized as classification and main variables of non-point source pollution model in estimating discharging load and river load.3)On the occasion that we don’t have any measured data, in order to estimate the pollution load in the study area, we decide to use a rapid coefficients model with efficient output. According to the present situation of land use in the study area and its topography and other factors, we select the most suitable output coefficient method for the local situation to estimate the non-point source pollution load in the study area; with a full consideration to the different slope in the study area, such as spatial difference, we set the non-point source pollution output coefficient in the typical basins in the study area, and estimate the indicators of pollution load of CODcr、TN and TP. Based on the field investigation, this model is more suitable for the local geographical and social conditions.