Non-point Source Nitrogen And Phosphorus Pollution In Baimaguan River Basin Of Miyun Based On AnnAGNPS Model

The Baimaguan River Basin is an important source of water in the upper reaches of the Miyun Reservoir.However,at present,the water quality of the basin is poor,and the total nitrogen content is higher than the surface class II standard.The water body has the risk of eutrophication and affects the water quality of Miyun Reservoir.Therefore,it is particularly important to study the input sources,load characteristics and optimal measures for pollutant reduction of nitrogen and phosphorus non-point source pollutants in the basin.In this study,the Baimaguan River Basin was used as the research object.The NIAN and NAPI models of human activity net nitrogen were used to estimate the nitrogen and phosphorus input of the basin.Based on the AnnAGNPS non-point source pollution model,the migration and loss process of total nitrogen and total phosphorus was simulated,based on nitrogen and phosphorus input.The output intensity identifies the key risk areas and uses the AnnAGNPS model to screen and evaluate the optimal measures for nitrogen and phosphorus reduction in the basin.The main conclusions are as follows:(1)The total nitrogen in the Baimaguan River Basin is mainly derived from the net nitrogen input of food/feed and atmospheric nitrogen deposition.The high-intensity areas of nitrogen input are former Huoshiling,Baimaguan and Nantaizi;the main influencing factors are nitrogen fertilizer application intensity,crop yield and The population density.Total phosphorus is mainly derived from food/feed,and the areas with higher phosphorus input are Xiaying and Baimaguan;the main influencing factors include crop yield,livestock and poultry farming density and population density.(2)The AnnAGNPS model has good applicability in the Baimaguan River Basin and can be used for the assessment of non-point source pollution in the study area.Among them,the annual runoff fitting results of Baimaguan River Basin are the best,the Ens and R2 of the periodic and verification period are greater than 0.72;the annual runoff rate and the Ens and R2 of the verification period are greater than 0.5,which can meet the model simulation requirements;total nitrogen total The correlation coefficient R2 between the simulated and measured values of phosphorus is above 0.4 and 0.2,respectively.There is a large uncertainty in the simulation results.(3)The total nitrogen total phosphorus output load time in the basin increased with the increase of rainfall,and it gradually decreased from upstream to downstream.The contribution rate of cultivated land to non-point source pollutants is the highest,and the contribution rates to total nitrogen and total phosphorus are 71.46%and 91.55%,respectively.Based on the intensity of nitrogen and phosphorus input and output,it is determined that the former Huoshiling,Siyingzi,Baimaguan and Huanglianggen villages are key risk areas for non-point source pollution in the Baimaguan River Basin.(4)The scenario analysis method was used to simulate and optimize the optimal nitrogen and phosphorus control measures in key risk areas.The results showed that the reduction rate of vegetation filter belt was the highest,followed by the measure of returning farmland to forest,and the reduction effect of fertilizer reduction measures and no-till measures were the worst.In general,the vegetation buffer zone should be a priority for non-point source pollution control in the Baimaguan River Basin.