SWAT Model-based Non-point Source Pollution In Zhou River Basin

As one of the main sources of drinking water in Dazhou City,the Zhou River Basin,water safety problems caused by NPS pollution not only seriously affect the health of residents,but also hinder the economic development of the basin.Therefore,this paper builds a spatial and attribute database based on the SWAT(Soil and Water Assessment Tool)model and combines measured hydrological data to simulate and verify the evolution characteristics,temporal and spatial distribution,morphological composition,and risk factors of runoff,sediment and nitrogen and phosphorus pollutants in the Zhou river basin;Based on climate change and land use scenarios,the evolution of NPS load was explored.The results are as follows:(1)A digital elevation,land use,soil,and meteorological database of the SWAT model of the Zhou river basin was constructed,and the watershed was divided into 21 sub-basins and 686 hydrological research units(HRUs)through data discretization;Model calibration and verification,parameter sensitivity analysis,correlation coefficients(R~2)of runoff,sediment and water quality are all greater than 0.6,and Nash coefficients(NSE)are all greater than 0.5,which proves that the SWAT model in the Zhou river basin applicability.(2)The model after the utilization is determined simulates the output change and spatial distribution of NPS pollution load in 34 years.The results show that the NPS pollution load is unevenly distributed in time and has a positive correlation with rainfall,and the output in summer and autumn is stronger than in spring and winter,and the yield in the high water period is large.In space,NPS pollution load is mainly concentrated in the 3,5,6 sub-watersheds upstream of the watershed and the 13,17,18,19,sub-watersheds downstream of the watershed,which are closely related to slope,soil type,rainfall,and human activities;the contribution of different forms of nitrogen and phosphorus pollution load to the total nitrogen and phosphorus load was analyzed.(3)Based on GIS grid technology,process data through raster transformation and layer assignment technology,analyze watershed risk factors;weight and superimpose 7risk factors to find the hazardous risk area of NPS pollution.The types of water safety risks in the river basin are mainly mild and moderate,accounting for 83.53%and 16.47%,respectively.The areas with higher risks are mainly located in Puguang,Qingxi and other towns in Xuanhan County,and suggestions are made according to local conditions.(4)Exploring the impact of NPS pollutants under climate change,it is found that the output of NPS pollutants is positively correlated with temperature and the temperature increase has a greater impact on sediment and TN.The effects of land use change on NPS pollutant load were explored by setting up five types of returning farmland scenarios.The conclusion is that returning farmland to forests is more effective in reducing pollutants than returning farmland to grassland;high water period is the key period for pollutant treatment;sediment Reduction situation:flat water period>high water period>low water period,while TN,TP reduction situation:low water period>flat water period>high water period.The change of NPS pollution load under climatic conditions and land-use changes is explored.It is shown that compared with land-use changes,climate change has a greater impact on the change of NPS pollutants.