Simulation Study Of Agricultural Non-point Source Pollution In A Large Reservoir Basin Based On SWAT Model

A large reservoir is one of the most important centralized drinking water source area in Kunming.The protection of drinking water source area is an important livelihood project.The quality of drinking water is directly related to people's health.With the strengthening of point source pollution control,non-point source pollution,especially agricultural non-point source pollution,has become the main cause of water environment pollution in the large reservoir basin.Therefore,it is of great significance to quantitatively analyze the load of non-point source pollution and explore the main pollution sources to control the non-point source pollution and improve the water environment.Based on the measured data of rainfall,runoff and water quality of the large reservoir and its upstream medium-sized reservior from 2010 to 2018,this paper constructs a non-point source pollution load model of the large reservoir basin,and calibrates and verifies the model through the measured data,indicating that the model has good applicability in the research area.At the same time,the distribution characteristics of total nitrogen load in the research area were analyzed,and the key pollution sources were found out,which provided a scientific basis for the comprehensive treatment of non-point source pollution and put forward specific suggestions for improving the water quality of the large reservoir.The main research contents and conclusions are as follows.(1)In this paper,the water quality status of the large reservoir basin was comprehensively evaluated using the measured water quality data of the large reservoir section(front of the dam,middle of the dam and River 1),the medium-sized reservoir section and River 1 section from 2010 to 2018,the results show that total nitrogen is the main index of water quality.(2)Based on DEM data,land use data,soil data,meteorological data and measured hydrologic and water quality data,the SWAT model of the large reservoir basin was established to quantitatively simulate the non-point source pollution load,and the large reservoir basin was divided into 21 sub-basins and 133 hydrological response units.(3)The SUFI-2 method in SWAT-CUP software was used to calibrate parameters,and parameters sensitive to the model were selected for rate calibration and validation,of which2010-2016 is the calibration period and 2017-2018 is the validation period.The results show that both the runoff and water quality simulation results of the Station 1 can faithfully reflect the trend of development and change.Among them,in the monthly runoff simulation,the deterministic coefficient R² is 0.85 at the calibration period,and the Nash coefficient E_{N S} is 0.74.At the validation period R² is 0.91,E_NS is 0.63;The total nitrogen content was simulated in the water quality simulation,and the deterministic coefficient R² was0.70 at the calibration period,and the Nash coefficient E_NS was 0.66.At the validation periodR² is 0.72,E_NS is 0.65,the simulation results can meet the requirements,indicating that the SWAT model has a good applicability in the large reservoir basin.(4)From the spatial characteristics of pollutant distribution,the nitrogen pollution is mainly concentrated in the runoff area of the River 1,which is the largest inflow river of the large reservoir,and the runoff area accounts for 57.6%of the large reservoir.The main sources of pollutants in the River 1 were analyzed by empirical model.The main sources were farmland runoff pollution,and the contribution rate of pollution load into the river was74.8%.Based on the calculation of the water environmental capacity in the runoff area of the River 1,the quantitative estimation of the total nitrogen intake reduction should be controlled at more than 64.34 tons per year,so as to ensure the water quality of each section.