Simulation And Analysis Of Agricultural Non-point Source Pollution In Typical Small Watersheds In South China

Point source pollution and non-point source pollution are the two forms of water pollution.Due to the simpler mechanism,concentrated emissions and easier control of point source pollution,its pollution control in China has achieved significant results.Non-point source pollution is the focus of prevention and control of water pollution in China because of its complicated mechanism,large randomness and difficult control.The development of hydrological and water quality model has become an important technical means for the prevention and control of non-point source pollution,and HSPF model is an excellent non-point source pollution model because it combines the advantages of distributed hydrological model and other hydrological models.Taiping River Basin is an upstream tributary of the GanJiang,and its hydrological and water quality conditions affect the water quality of downstream residents.This article takes the Taiping River Basin as the research object,build a database based on spatial data such as DEM,land use types,soil types,and attribute data such as climate,hydrology,and water qualityand.Data collection,remote sensing image extraction,field investigation,site monitoring,and scenario simulation were coupled to construct HSPF,so as to simulate hydrological and non-point source pollution in the basin,analyze the load status of non-point source pollution,set climate scenarios and predict non-point scenarios Point source pollution load conditions.Its enriched the understanding of the water environment of the basin and provided a reference for the water environment management and control of the basin.Conclusions are as follows:?1?Hydrological simulation shows that after calibrating LZSN,UZSN,INFILT and other parameters,the daily,monthly,seasonal and annual runoff simulations basically meet the model accuracy requirements,but the simulated runoff is generally lower than the measured runoff.The runoff in the watershed is concentrated at 5-40 m³/s,and the largest total runoff in 2016was 53065×10⁴m³.In the simulation period after calibration,correlation coefficient of daily runoff is 0.871;the correlation coefficient of monthly runoff simulation is 0.91,and the Nash coefficient?NSE?is 0.67;deviation percentage in winter and summer runoff simulation are 4.5%and-19.1%respectively;the annual runoff simulation deviation percentage is-19.0%.During the verification period,correlation coefficient of the daily runoff simulation is 0.91;correlation coefficient of the monthly runoff simulation is 0.985,and the Nash coefficient?NSE?is 0.71;the deviation percentages in winter and summer are-13.3%and-18.8%,respectively;and the annual runoff simulation deviation percentage is-17.9%.?2?Non-point source pollution simulations shows that the sediment concentration and precipitation change are synchronous and he sediment concentration is mostly 10-40mg/L.The water temperature in the basin is in the range of 4.5-31?,simulated values of water temperature and nutrients are more compatible with the measured values,which basically meet the accuracy requirements of the simulation.The correlation coefficient,deviation percentage and Nash coefficient?NSE?of water temperature simulation during the calibration period are 0.83,12.7%and 0.43,respectively;The correlation coefficient,percentage deviation,and Nash coefficient?NSE?of the verification period were 0.87,7.85%,and 0.51,respectively.The correlation coefficients of simulated concentrations of BOD₅,NH₄-N and TP were 0.8,0.8,0.87,the deviations percentage were 10.4%,16.4%,32.6%,and the Nash coefficients?NSE?were 0.4,0.53,and 0.7,respectively.The simulation results show that the concentrations of BOD₅,NH₄-N and TP are concentrated at 1.8-2.5 mg/L,0.12-0.2 mg/L and 0.02-0.07mg/L,respectively.?3?Non-point source pollutant load and runoff load have a certain correlation in time.Sub-watershed 1 has the largest runoff and nutrient loads,and sub-watershed 3 has a large sediment load.In 2015,the load of BOD₅,NH₄-N and TP in the river basin were 2896 t/a,151t/a and 54t/a,respectively.According to the climate change trend,the scenario is set to reduce precipitation by 2.0%,solar radiation by 2.0%,average temperature by 5.0%,and wind speed by 5.0%.In this scenario,runoff load is reduced by 3.0%,TP load is reduced by 2.6%,and NH₄-N load The volume was reduced by 2.0%,and the BOD₅ load was reduced by 1.0%.