| In recent years,with the im plementation of comprehensive control project in Weihe River Basin,Point source pollution in river basins has been basically controlled,non-point pollution has become the main cause of water environmental pollution in Weihe River Basin.Therefore,quantitative analysis of the non-point pollution in the basin and exploring the influencing factors of non-point source pollution are of great significance to control non-point source pollution and imp rove the water environment of the basin.In this study,Xianyang-Xi’an section of Weihe River basin with poor water quality is taken as the research area.In 2016 as the current year,the non-point source pollution load model of Weihe River basin is established to estimate the non-point N and P inflow load,analyze the temporal and spatial distribution characteristics of’ non-point pollution in the basin,identify the main pollution in the basin,and analyze the impact of various influencing factors on the discharge of non-point pollution in order to serve as the Weihe River.Non-point pollution control and river water environmental protection provide scientific theoretical support.The main results are as follows:(1)The water quality of Xianyang-Xi’an section of Weihe River in 2016 was evaluated.The comprehensive pollution index of Xianyang outbound section was 3.73 and the single factor pollution index was 5.03.The comprehensive pollution index of Xi’an outbound section was 5.68 and the single factor pollution index was 5.41.The water quality of both sections was seriously polluted.The main pollution indexes of Xianyang and Xi’an exit sections are total nitrogen and total phosphorus.(2)A non-point pollution load model for Xianyang-Xi’an section of Weihe River Basin is established.The model was calibrated and validated by synthesizing factors such as soil type,land use,CMADS meteorological data and hydrological and water quality data.The simulation results were evaluated by the resolvable coefficient R2,Nash coefficient(Ens)and relative error r.The results show that the simulated and measured values of flow,total nitrogen and total phosphorus,R2,Ens and r,can meet the accuracy requirements of the model,which indicates that the non-point pollution load model has good applicability to Xianyang-Xi an section of Weihe River Basin.(3)Through simulation calculation,the inflow loads of non-point TN and TP in Xianyang-Xi an section of Weihe River Basin in 2016 were 7654.0t and 626.5t.From the spatial distribution,the high nitrogen and phosphorus pollution areas in the basin are concentrated in Lantian County,Chang an District,northern Huyi District,Binxian County and Xunyi County.The TN output intensity per unit area is 1.82-28.52kg/ha,and TP is 0.56-5.72kg/ha.In terms of land use types,the contribution rate of cultivated land to TN and TP inflow load in 2016 was the largest,61.65%and 57.06%respectively.From the point of view of pollution,the amount of soil background N and P and the application of agricultural chemical fertilizer are the main non-point pollution in the basin.Among them,the contribution rate of soil background to total nitrogen and total phosphorus inflow load is 31.7%and 39.3%,and the contribution rate of agricultural chemical fertilizer application is 32.4%and 34.2%.The contribution rate of rural domestic sewage is also higher,20.3%and 16.9%respectively.(4)The influencing factors of non-point pollution load in Xianyang-Xi an section of Weihe River Basin are analyzed.Land use and rainfall have great influence on the output of non-point pollution load.Based on the land use data of four different years in the study area,the representative land use scenarios of 1995 and 2015 were set up to simulate and analyze the non-point pollution in the study area.The TN load and TP load in the land use scenario in 2015 decreased by 2.48%and 3.56%,compared with the land use scenario in 1995.This is mainly due to the reduction of cultivated land area.Through the simulation calculation of non-point TN and TP inflow loads in plain water year(2010),bigh water year(2011)and low water year(2013),it is concluded that non-point pollution loads inflow into the river in high water year>plain water year>low water year.(5)According to the General Plan for the Construction of Weihe Ecological Zone in Shaanxi Province and the Plan for the Promotion of Agricultural Modernization in Shaanxi Province,four scenarios for river basin management were set up to simulate and analyze the non-point pollution in the study area.The results show that the order of reducing the non-point pollution load is comprehensive management measures>improving fertilization methods and quantity>improving soil and water conservation measures>setting biogas digesters. |
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