Simulation Of Non-Point Source Pollution And Best Management Measures In The Guanzhong Section Of The Weihe River Basin

The Weihe River basin is the first major tributary of the Yellow River,the mother river of the people of Shaanxi Province,and is vital to the economic development of Shaanxi Province.With the implementation of relevant treatment projects by Shaanxi provincial government,point source pollution in the Weihe River basin has been basically controlled,while nonpoint source pollution has become a major factor affecting the water environmental quality of the Weihe River basin due to its wide range of sources,high randomness,and difficulty in monitoring.Therefore,it is important to analyze the distribution pattern of nonpoint source pollution and identify the driving factors affecting nonpoint source pollution to improve the water environmental quality in the Weihe River basin.In this study,the SWAT model was used to simulate the nonpoint source pollution load in the Guanzhong section of the Weihe River basin,analyze the spatial and temporal distribution characteristics of nonpoint source pollution in a typical hydrological year,identify and determine the key source areas of nonpoint source pollution in the basin,evaluate the reduction effect of best management practices(BMPs)on the nonpoint source pollution load,assess the cost-effectiveness of BMPs,and screen out the suitable BMPs for the study area.Best management practices(BMPs)were screened for the study area in order to provide a reasonable reference for the prevention and control of nonpoint source pollution in the Weihe River basin.The main research findings are as follows:(1)A SWAT model of the Guanzhong section of the Weihe River basin was constructed.Based on the spatial and attribute databases,the SWAT model divided the Guanzhong section of the Weihe River basin into 27 sub-basins and 516 hydrological response units(HRUs).The SWAT-CUP software was used to rate and validate the model parameters based on measured runoff data and water quality data,and the rate and validation results met Ens≥0.50 and R~2≥0.60,indicating that the SWAT model is applicable in the study area.(2)The spatial and temporal distribution characteristics of nonpoint source pollution in the Guanzhong section of the Weihe River basin during a typical hydrological year were analyzed.The Pearson type III curve fitting algorithm identified the study area as the typical hydrological years of abundance,flatness,and depletion in 2010,2018,and 2013.The interannual variation pattern of nitrogen and phosphorus loads from nonpoint sources of pollution in the Guanzhong section of the Weihe River basin was highest in abundant water years and the seasonal variation pattern was highest in summer(June-September).The spatial distribution of precipitation and runoff in the Guanzhong section of the Weihe River basin is characterized by higher sediment load on the south bank of the basin than on the north bank,and similar sediment load and precipitation.(3)Key source areas of nonpoint source pollution in the Guanzhong section of the Weihe River basin were identified.The key source areas in the watershed were identified using the unit area load index method,and the key source areas in the Guanzhong section of the Weihe River basin were identified as sub-basins 1,12,13,14,23,24,and 26 located in Xi’an and Xianyang counties.The key source areas accounted for 25.69%of the area of the entire study area,and the nonpoint source pollution nitrogen and phosphorus loads accounted for about half of the nonpoint source pollution loads in the entire study area.(4)The reduction effects of best management practices(BMPs)on nonpoint source pollution loads were evaluated.The reduction efficiency of individual BMPs on nonpoint source nitrogen and phosphorus loads was ranked from highest to lowest as follows:Scenario3(planting vegetation filter strips and grassed waterways)>Scenario 5(contour plant hedges)>Scenario 4(contour tillage)>Scenario 1(fertilizer reduction)>Scenario 2(installation of biogas digesters in rural areas).Scenario 8(20%reduction in fertilizer application+installation of biogas digesters in rural areas+planting of vegetated filter strips and grassed waterways+contour tillage)among the combined BMPs had the highest reduction rates of 57.68%and 58.56%of nitrogen and phosphorus loads from nonpoint source pollution,respectively.(5)The cost-effectiveness of best management practices(BMPs)was assessed.The cost-effectiveness calculations revealed that the cost-effectiveness values of engineering measures were higher than those of non-engineering measures.In the Guanzhong section of the Weihe River basin,a combination of BMPs is recommended on a large scale,with the best reduction effect of scenario 7(20%reduction in fertilizer application+planting of vegetation filter strips and grassed waterways+contour tillage);on a small scale,scenario 3(planting of vegetation filter strips and grassed waterways)is recommended,along with a reduction in fertilizer application.