Simulation Study On Non-point Source Pollution Load In Xiaojiang River Watershed

After the water storage of the second phase of the Three Gorges Reservoir, the hydrological situation of rivers in the reservoir region has changed. Because of the rising of the water level and the pushing of backwater in the main stream, the flow of the backwater paragraph is slowing, the entrained sediment of the water is being a large of deposition, The phenomenon of eutrophication in the most of the sub-rivers of the reservoir area have frequently taken place. Xiaojiang River, the largest tributary of the main stream, which is located on the north shore of Three Gorges reservoir area, its backwater area has been increasing water pollution, "Water bloom" outbreaks year after year. Xiaojiang River Watershed is a typical leaf mountain, high mountains and deep valley, the more sloping land, the serious soil erosion and loss, non-point source pollution has become a major source of pollution in Xiaojiang River. As a result, the study of non-point source pollution load in Xiaojiang River Watershed, the revealing related laws of non-point source pollution in typical watershed of the reservoir area, are of great significance for social, economic and environmental sustainable development, the promotion of ecological harmony of the Three Gorges Reservoir area, as well as protecting the security of water environment in the reservoir area.Through the introduction of the SLURP distributed hydrological model which has a physical mechanism in the study, taking the land-use type as study unit, taking into the loss of dissolved nitrogen, phosphorus in the course of transport, using GIS technology, land use and rural settlement output of non-point source pollution annual load model were respectively established; at the same time, based on RULSE the United States universal soil loss equation, with the view of the basin rainfall, soil, topography, vegetation, soil and water conservation, sediment delivery ratio and other factors with the characteristics of uncertainty in the adsorbed load, using the blind number to define the uncertainty of the factors, the absorption non-point source pollution load dynamic mathematical model under the blind number theory and GIS were constructed, the model was verified with related data. According to the model, the annual output as well as the load about the non-point sources of nitrogen and phosphorus of different types of dissolved, absorption resulting from soil loss were simulated and quantitatively estimated from temporal and spatial distribution of different sources and the state in Xiaojiang River Watershed of the Three Gorges Reservoir area from 1991 to 2007.The main conclusion of the study are as follows:â‘ From the view point of time series, the non-point source pollution of nitrogen and phosphorus load of the basin export have been significantly changing year by year from 1991 to 2007, which is related to annual hydrology changes, non-point source pollution is significant changing by the impact of runoff. The non-point source nitrogen and phosphorus average annual load of basin export from 1991 to 2007 are respectively 6039.51t/a and 344.38t/a. The inter-annual change of nitrogen and phosphorus load at the export of the watershed are significantly impacted by the total size of the rainfall and runoff.â‘¡From the view point of spatial distribution, the worst areas of non-point source pollution of nitrogen and phosphorus are mainly located in the Puli River, particularly in the upper reaches of the river, the middle and lower reaches of the East River and populated areas along the coast of Nanhe River. The highest loss modulus of the total non-point source Nitrogen, phosphorus in the watershed were 2.0t/km~2, 0.12 t/km~2 from 1991 to 2007; are the lowest loss modulus of the total non-point source nitrogen and phosphorus during that period were 0.662 t/km~2,0.037 t/km~2.â‘¢Dissolved nitrogen and phosphorus pollution is closed with hydrological process. The proportion of non-point source pollution of dissolved nitrogen and phosphorus load accounting for the total load of the export of are about 50% and 20% over the years, the contribution rates of total nitrogen load of land use and rural settlements into the river in the watershed were 81.18% and 18.82%; the contribution rates of total phosphorus load into the river were 89.58% and 10.42%, land-use nitrogen and phosphorus load of the export is dominant.â‘£Adsorbed nitrogen and phosphorus pollution load of the watershed are mainly related to the amount of soil erosion and sediment discharge, and the amount of soil erosion and sediment discharge basin is closely related to the size of rainfall runoff. The proportion of adsorbed non-point source pollution of nitrogen and phosphorus load accounting for the total load of the export are about 50% and 80% over the years, while the main source of the adsorbed nitrogen and phosphorus pollution load are the dry land and mixture, and the grass, the corresponding contribution rates of nitrogen and phosphorus Load into the river are respectively 55% to 60% and 35%.