Temporal And Spatial Changes Of Nitrogen And Phosphorus Non-point Source Pollution In Farmland Based On SWAT Model

Water environment pollution can be divided into the form of point source pollution and non-point source pollution,when people for effective management and control of point source pollution,water quality has not been much improved,gradually realize the non-point source pollution is the main factor of water pollution of the environment,control of watershed non-point source pollutant load on the output water quality environmental protection plays a very important role.In recent years,the application amount of fertilizer driven by agricultural production increase is increasing,and the water body in China is generally polluted by non-point agricultural sources,the eutrophication of water body and the continuous decline of river water quality,and the water environment pollution is increasingly serious,which has become one of the hot issues concerned by the academia and production departments.In response to national policies,it is urgent to analyze the impact of reducing the amount of irrigation and fertilizer applied to agricultural crops on the output load of non-point source pollutants in different regions.In this paper,the shaying river basin was selected as the research area,and the SWAT model was used to simulate the non-point source pollution load,and the sensitivity analysis,parameter calibration and verification of the model were carried out to simulate the regional evolution analysis of farmland water,nitrogen and phosphorus.The main research contents and conclusions are as follows:(1)The SWAT model of shaying river was constructed,and the shaying river basin was divided into 23 sub-basins and 46 hydrological response units.Using LH-OAT sensitivity analysis method,sensitivity analysis was carried out on the parameters in the model,and 10parameters that had great influence on the model simulation process were selected.They are ESCO,CN2,EPCO,CANMX,SOL_K,SOL_AWC,GWQMN,SOL_Z,GW_REVAP,ALPHA_BF.The model is determined and verified by focusing on these 10 parameters.Calibration,verification,and simulation calculations of the SWAT model.The model was determined by using the measured runoff data from Zhoukou Hydrological Station from 1960to 1980.The measured runoff data from 2000 to 2016 was used to verify the model.After analysis,the calibration coefficient(R~2)and the efficiency coefficient Nash-Sutcliffe(ENS)of the model are 0.75 and 0.66,respectively;the verification period R~2 and the efficiency coefficient Ens are 0.77 and 0.74,respectively.It shows that SWAT model has good applicability in the Shaying River Basin.(2)The time and space distribution characteristics of agricultural non-point source load outputs are simulated and analyzed.In terms of time,agricultural non-point source pollution mainly occurs in July and August when rainfall is relatively concentrated.From the perspective of space,both the total nitrogen and total phosphorus loads in 2018 present a situation of high output of pollution loads in the central and eastern regions.In 2010,the pollution load was the highest in western China.In 2012,the pollutant load was the highest in central China.In 2015,the distribution of pollutants in the west and east was relatively high,and the distribution pattern of pollutants was consistent with the distribution pattern of rainfall and water yield.(3)According to the water-saving irrigation policy proposed by China in recent years,three possible scenarios are set.Scenario 1:the amount of nitrogen and phosphorus applied in irrigation water remains unchanged while the amount of nitrogen and phosphorus applied in fertilizer decreases by 20%;Scenario 2:irrigation water decreases by 20%with constant amount of fertilizer applied;Scenario 3:20%less irrigation water and 20%less nitrogen and phosphorus fertilizer.Application model of Shaying River Basin,the regional distribution of agricultural non-point source pollution,and different irrigation fertilization scenario simulation analysis was carried out on the influence of nonpoint source pollution load,the results showed that:in interannual variability,the situation about the amount of total phosphorus load to reduce the scene two,under scenario three times of the total nitrogen and total phosphorus load are higher than the other two scenarios.In the regional change,the total phosphorus load of northern and southern regions in scenario 1 was higher than that in scenario 2,and the reduction rate of total nitrogen and phosphorus load in central and eastern regions in scenario 1 was higher than that in scenario 2.The application of fertilizer is the main cause of agricultural non-point source pollution,and is positively correlated with the pollution load of total nitrogen,total phosphorus and nitrate nitrogen.