Estimation Of Non-point N And P Pollution Load Model And Countermeasures For Prevention And Control In Xiangxi River Basin

Since the completion and operation of the Three Gorges Reservoir,there have been many occurrences of branchwater blooms and eutrophication due to the loss of nitrogen?N?and phosphorus?P?nutrients,and the water quality of the reservoir area and tributaries has begun to deteriorate.This paper takes the Xiangxi River Basin in the head of the Three Gorges Reservoir area as the research object.Based on the full collection of existing research results at home and abroad,it uses the theories of Environmental science,Soil science,Geography,Soil and water conservation,and ArcSWAT2012,GIS software and computer technology,through the field and literature research methods to collect basic data such as the underlying surface in the basin,and carried out field monitoring.The paper mainly analyzes the effects of non-point source pollution sources,N and P spatial and temporal changes and reservoir scheduling on N and P,and analyzes the impact on non-point source N and P pollution in Xiangxi River Basin.By constructing SWAT distributed model,The non-point source N and P pollution in the Xiangxi River Basin was simulated during 2012-2017,and the amount of sediment,runoff,and total nitrogen and phosphorus pollution loads were quantitatively estimated.The time-space distribution characteristics of the key areas of loss were analyzed.According to the scenario simulation module of the model,the simulations were carried out for three scenarios of land use change,returning farmland to forest and controlling fertilizer application.Finally,the non-point source N and P pollution prevention and control measures were proposed in Xiangxi River Basin.After many years of water storage operation in the Three Gorges Reservoir,the SWAT model was used to simulate and estimate the contribution of the Xiangxi River Basin to the reservoir runoff and sediment in the period from 2012 to 2017,which were 1.26×10⁹m³/a and4×10⁵t/a,respectively.The contribution of total nitrogen?TN?and total phosphorus?TP?pollution load were 1512t/a and 326t/a,respectively,and the contribution to ammonia nitrogen?NH₄-N?was 204.78t/a.The average soil erosion modulus of Xiangxi River Basin is1247.4t/km².a.Soil erosion is a lightly lost area as a whole.Xiakou Town and Gaochun Town,which are close to the river and relatively concentrated in cultivated land,are sensitive areas of soil erosion,and the degree of soil erosion is close to moderate level.From April to September each year is the peak period of non-point source pollution in Xiangxi River Basin.The runoff accounts for 81%of the total annual runoff,the sediment volume accounts for 90%of the whole year,and the TN and TP output respectively account for 73%and 84%of the year.The loss of TN in Xiangxi River Basin is the most serious,and the maximum loss is more than 20kg/hm².The spatial distribution of TP loss is obvious.It is the most serious in the coastal areas of Xiangxi River and Nanyang River,and the loss is more than 10kg/hm².Through scenario simulation analysis,the use of returning farmland to forest or controlling the application of chemical fertilizers can effectively reduce the loss of non-point source N and P pollution;the conversion of cultivated land to forests can reduce the N and P pollution load by more than 25%,and the reduction of chemical fertilizer application can be reduced by half.The N and P pollution load is more than 15%.The control measures of non-point source N and P pollution in Xiangxi River Basin can be carried out from three aspects:water and soil conservation technology,pollution source control and management regulation,so as to reduce soil erosion and rainfall runoff intensity in Xiangxi River Basin.The results show that the SWAT model has a good simulation and estimation effect on the sediment,runoff and N and P pollution loads in the Xiangxi River Basin.The model verification coefficients R² and E_NS are both above 0.8,which meets the requirements of research accuracy.