Simulation Of Non-point Source Pollution Based On Swat In Heihe Reservoir

With the rapid development of economy and society,the contraction between supply and demand of water resources is increasing,and the problem“all the water polluted”becomes one of the strategic issues of the world.In recent years,with point source controlled,non-point source pollution has become an important reason for our country water environment pollution,to solve the problem,the fundamental way is to control pollution source and ways.Therefore,the study of non-point source pollution has great significance to the improvement in water quality.In this paper,combining with the upstream basin of Heihe reservoir in Shaanxi province,the SWAT model is used to study on non-point source pollution of the reservoir’s upstream,analyzing time and space distribution characteristics,identifying the contribution of pollution load of different land use types,exploring the different agricultural management practices for non-point source pollution control effect,providing scientific support for reservoir water environment quality improvement.The main research contents and conclusions are as follows:(1)Building spatial and attribute database on research area,spatial data including DEM,land use map,soil type map,weather site map,etc.,using unified projection coordinate system,extracting water system diagram by Arc GIS;using SPAW,1stopt software to build soil database and SWAT weather.exe to establish the weather generator.The study area is divided into 31 subbasins,633 HRUs.(2)In this study,there are measured data of runoff、sediment、total nitrogen and total phosphorus of Hei Yukou hydrology site from 2001 to 2008,using LH-OAT(Latin Hypercube One-Factor-the At-a-Time)for sensitivity analysis.2001 as the warming period,from2002 to2005 as the Calibration period,from 2006 to 2008 as validation period,using three indexes relative error,correlation coefficient,Nash-suttcliffe to evaluate model,the relative errors are below 30%,correlation coefficients are above 0.6,Nash-suttcliffes are above0.5,showing that model has good applicability to Heihe reservoir upstream basin.(3)Analyzing non-point source pollution load of time and space distribution characteristics of Heihe reservoir upstream watershed.On time scales,it shows that average annual sediment yield is 64.07 x 10~3 t,36753 kg of total nitrogen,34282 kg of total phosphorus from 2002 to 2008;Non-point source pollution output has significant relationship with rainfall,mainly concentrated in the flood season from June to October,sediment output accounted for74.23%,total nitrogen accounted for 72.58%,total phosphorus accounted for 70.27%.On spatial scale,there is a certain relationship between sediment output and rainfall distribution,and nitrogen and phosphorus output have high space consistency with sediment output,non-point source pollution output mainly concentrated around downstream of Heihe river and both sides,because of residents and also the highest concentration of the cultivated land,corresponding administrative regions are Shuang Miaozi town and Chen He town.(4)Different land use types’contribution to the pollution load quantity is different.Arable land’s organic nitrogen and organic phosphorus contribute most,mainly attribute to human fertilization activity;though forestland area accounted for 51.66%of total land use area,but the contribution rate is in the second,mainly because vegetation in the basin is quite good;high covered grassland,medium covered grassland,shrubbery pollution load output are little difference,in the middle level;Rural residential area is small,pollution load is minimum.Different land use type per unit area has different pollution load,cultivated land is the largest,the rural residential is second,forestland is the smallest.(5)Set up different scenarios,in scenario 1 cultivated land respectively increases and decreases by 20%,setting to forestland;in scenario 2 cultivated land respectively increases and decreases by 20%,setting to shrubbery.Cultivated land decrease,can significantly reduce the output of sediment and organic nitrogen and phosphorus,cultivated land increasing,the output adverse.