Tudy On Non-point Source Nitrogen Pollution Load Nder The Influence Of Cascade Development In Middle And Lower Reaches Of Lancang River

The middle and lower reaches of lancang river is rich in water resources,which is one of the major hydropower development bases in southwest China,and also an important ecologically fragile and sensitive area.The cascade hydropower development in the basin not only brings great economic benefits,but also changes the regional economic and social development mode and the ecological environmental characteristics of the river,which leads to the change of land use around the reservoir area.Nitrogen is one of the most important nutrients in the ecosystem,and the high concentration of nitrogen in the river will damage the stability of the river ecosystem,while many factors such as soil structure characteristics,land use changes and agricultural management measures are the main sources of non-point source nitrogen pollution in the river.At present,there are many researches on land use change and non-point source caused by single hydropower project construction,but few researches on non-point source nitrogen pollution load change caused by cascade hydropower development.Based on this,the SWAT model,output coefficient model and USLE model were constructed to estimate the non-point source nitrogen pollution load in the basin before and after the construction of cascade hydropower project,and the internal causes of the change were compared and analyzed.Based on Arcgis,this paper studied the spatial differentiation characteristics of non-point source nitrogen pollution load,identified the key source area and main source of high nitrogen load transported to water body in the basin,and provided theoretical basis for exploring the impact of cascade development on non-point source nitrogen pollution load in the middle and lower reaches of lancang river basin,as well as the control and reduction of nitrogen pollution.The main conclusions of this study are as follows:(1)The non-point source nitrogen pollution load before cascade development of middle and lower lancang river was estimated by constructing SWAT model.In 1980,as a representative of the cascade development of the time before the output through the model simulation of runoff and sediment value,estimate 1980 study OuDeFei point total nitrogen pollution load is 22855.74 tons,including land use dissolved nitrogen non-point source pollution load is 14230.18 tons,rural residential areas of dissolved nitrogen pollution load is 2064.15 tons,total dissolved nitrogen pollution load is 16294.33 tons,absorption nitrogen non-point source pollution load is 6561.41 tons.(2)The output coefficient model and soil erosion model were used to estimate the non-point source nitrogen pollution load after cascade development in the middle and lower reaches of lancang river.In 2015,as a representative of the cascade development time by empirical model to estimate the 2015 study OuDeFei point total nitrogen pollution load is 29009.16 tons,including land use dissolved nitrogen non-point source pollution load is 14535.82 tons,rural residential areas of dissolved nitrogen pollution load of 7126.99 tons,total dissolved nitrogen non-point source pollution load is 21662.81 tons,adsorption state nitrogen non-point source pollution load is 7346.35 tons.(3)The results of non-point source nitrogen pollution load before and after the cascade development of middle and lower lancang river were analyzed and the main pollution sources and pollution areas were determined.After the cascade development,the total load of non-point source nitrogen pollution increased by 26.9% compared with that before the development,in which the load of dissolved non-point source nitrogen pollution increased by 32.9%,and the load of adsorbed nonpoint source nitrogen pollution increased by 12%.Ladder development has an impact on the change of land use type,but on the whole,the land use composition changes little,and the annual change of dissolved non-point source nitrogen pollution load is mainly affected by the life of rural settlements.From the spatial distribution characteristics of nitrogen non-point source pollution load,is located in lancang river middle reaches area of dissolved nitrogen non-point source pollution load,on the whole,the pollution load is less than the downstream region,located in lancang river middle reaches area of the adsorption state nitrogen non-point source pollution load is greater than the lancang river downstream pollution load of non-point source nitrogen pollution total load in the spatial distribution of river basin as a whole change trend is not obvious,but on the whole,the lancang river downstream of nitrogen pollution total load is greater than the middle region.Lancang and fengqing counties contribute the most to the total load of non-point source nitrogen pollution in the study area,and the main pollution sources are agricultural fertilization pollution,livestock and poultry breeding pollution and soil erosion pollution.