Simulation Of Non-Point Source Pollution In Si He River Basin Based On SWAT Model

With the perfect ending of the 13th Five-Year Plan,the ecological protection and high-quality development of river basin under the new situation have become the focus of water conservancy work.In recent years,urban point source pollution has been effectively controlled,pollution enterprises have moved to towns,and non-point source pollution has become the main factor of river basin water pollution.The water environmental problems of Nansihu Lake Basin are very representative in Shandong Province.Sihe river is one of the main rivers into the lake.Taking Sihe River Basin as a typical basin,the analysis of pollutant load in the basin is carried out,which provides basic data support for water quality supervision,reduction of pollutants into the lake and comprehensive treatment of the river section between Nansihu Lake and Sihe river To provide technical support for the treatment of water pollution in small and medium-sized basins.In this paper,based on the collection of basic data such as elevation,land use,soil types and farmland management measures in Sihe River Basin,a distributed hydrological model SWAT model is constructed,which is calibrated and verified by swat-cup software,and a suitable pollutant simulation and optimal management and control evaluation measures model is obtained.Based on the model,the spatial and temporal characteristics of non-point source pollution in Sihe River Basin were analyzed,and the distribution law was obtained.Meanwhile,the main influencing factors of non-point source pollution load distribution were analyzed,and the correlation degree was obtained.Finally,the sub basins with high loss intensity of pollution logistics in Sihe River Basin were identified,and the control situation of five control measures on pollutant loss was evaluated.Finally,the results were summarized The results are as follows(1)Based on the output coefficient model,the output and inflow of nitrogen and phosphorus in Sihe River Basin were estimated.The main source of nitrogen and phosphorus pollution in the basin is farmland fertilization pollution,followed by livestock and poultry breeding,which is consistent with the industrial structure of Sihe River Basin.(2)The spatial and attribute databases of DEM,land use and soil type in Sihe River Basin were established by using ArcGIS,SPAW and SWAT software,and the assessment model of non-point source pollution in Sihe River Basin was established by using SWAT model.Swat-cup software was used to calibrate the monthly runoff,total nitrogen and total phosphorus of the main channel,and some parameters of SWAT model were adjusted to make the simulation results more accurate.(3)SWAT model simulation results show that the output of non-point source pollution load has obvious temporal and spatial distribution:the monthly average load output of non-point source pollution presents the characteristics of fluctuation,the peak load of nitrogen and phosphorus output in the basin is basically consistent with the rainfall period,and the annual average load output of nitrogen and phosphorus in the main flood season(June to September)accounts for more than 70%According to the response relationship between rainfall and nitrogen and phosphorus output load,the determination coefficients of the regression equation between rainfall and nitrogen and phosphorus output load are all above 0.55,which indicates that there is an obvious positive correlation between them;from the perspective of space,nitrogen and phosphorus pollution output load is mainly concentrated in the Northeast and south of the basin.(4)The natural split point method was used to classify the intensity of nitrogen and phosphorus loss,and six key sub basins of nitrogen and phosphorus output load were identified.The scenario analysis method was used to arrange five kinds of BMPs in the key source area.The results showed that the two interception measures of vegetation filter belt and grass channel had the best control effect on pollution load,and the reduction effect on nitrogen and phosphorus output could reach 35%,2%,39.2%,46.2%;two tillage measures,no tillage and contour planting,reduced total nitrogen by 19.6%,12.4%,total phosphorus by 13%,and 9.1%on average;chemical fertilizer reduction measures also had good effect in Sihe River Basin,and reduced nitrogen and phosphorus output by 9.9%and 21.9%.Soil testing and fertilization can accurately meet the demand of plant growth for fertility,and also reduce farmers’ cost,It is worth popularizing in the basin.