Analysis Of Non-point Source Pollution In Qingshui River Basin Based On SWAT Model

In the study,Qingshui river basin was taken as the research object,the SWAT non-point source pollution model at basin scale was constructed with the support of GIS technology.Then,the spatial-temporal distribution characteristics of non-point source pollution and its relationship with rainfall was analyzed according to the simulation results of the model,and the key source area of pollution was determined.Finally,based on the analyzed results,the suggestions for control and management of the pollution were put forward so as to provide scientific basis for improving the water environment quality of the basin.The main conclusions were as follows:(1)The water quality monitoring and evaluation results of Qingshui River Basin during the non freezing period from 2017 to 2018 showed that:TN concentration was seriously over standard,and the water pollution problems needed to be solved urgently.The agricultural non-point source was an important pollution source of Qingshui River Basin,and the control of non-point source nitrogen and phosphorus was one of the effective measure to improve water quality.The comparison of water quality in the wet and dry periods showed that rainfall and runoff would produce non-point source pollution Certain impact.(2)The SWAT model of Qingshui River Basin was constructed with the help of Arc GIS platform.The data of DEM,land use,soil,hydrological,meteorological and agricultural management data were collected and transformed into the format which the model required,then established the basic database of SWAT.The model was calibrated and verified by the measured runoff data of Zhangjiakou hydrological station,with 2007?2009 as the warm-up period,2010?2013 as the regular rate,2014?2016 as the verification period,and the applicability of the model was evaluated according to the results of Ens and R~2.The results showed that the regular Ens and R~2of the model rate were 0.505 and 0.660 respectively,and the Ens and R~2of the validation period were 0.674 and 0.738 respectively,which all met the accuracy requirements of SWAT model,indicated that SWAT model has good applicability in Qingshui river basin.(3)Based on the verified SWAT model,the characteristics of non-point source TN and TP pollution in the study area were analyzed.The results showed that:in time,the non-point source pollution caused by TN was more serious,and the generation of non-point source pollution load had obvious seasonality,summer and winter was the peak and low periods respectively,the pollution output load of each sub basin in flood season was significantly greater than that in non flood season.In space,non-point source pollution load intensity was closely related to land use type,fertilizer application amount,fertilizer utilization rate and rainfall,and the pollution load intensity was higher in sub basins 1,2,3,5,6,12 and 14.The rainfall,runoff and non-point source pollution load in the study area were all in the shape of high in the middle and low at both ends.The TN and TP pollution loads in flood season accounted for 75.07%and 79.56%of the total amount of the whole year respectively.The output load of sub basins 2,4,5 and 14 had a high correlation with precipitation,which was mainly distributed in Zhenggou,both sides of Xigou and the upper reaches of Donggou.Precipitation was the leading factor leading to the loss of non-point source pollution in the region.The key sources of pollution in the study area were sub basins 2,3,4,5,6,7,10,12 and 14,which were mainly distributed on both sides of Donggou and Xigou water systems,and cultivated land was the main land use type.(4)Analysis the sources of non-point source pollution in the study area.The key source areas of pollution were mainly distributed in the plain and hilly areas with small slopes on both sides of the river.These areas were mainly cultivated land and grassland.The planting of high-yield crops such as vegetables,traditional fertilization methods and soil erosion were the main causes of non-point source pollution.In this regard,we put forward reference suggestions from the perspective of soil and water conservation and source control.