Characteristics And Simulation Of Agricultural Non-point Source Pollution In ZhuZhaoXin River Basin Of Heze City

Agricultural non-point source pollution has become the main pollution source of water environment in China,and it is also a prominent problem of agricultural sustainable development in China.As an important upstream water system of Nansihu Basin,the water quality of Zhaoxin River is closely related to the water resources security of Nansihu Lake and its downstream basin.This study took The Zhuzhaoxin River Basin in Heze City as the research area,taking COD（chemical oxygen demand）,TN（total nitrogen）,TP（total phosphorus）and NH₃-N（ammonia nitrogen）as the main evaluation factors.On the basis of analyzing the current situation of watershed non-point source pollution and estimating the load of non-point source pollution,SWAT model was constructed to simulate the runoff,TN and TP in the study area.The spatial and temporal distribution characteristics of non-point source pollution were analyzed,the key source areas of non-point source pollution were identified,and the reduction effects of different scenarios on non-point source pollution were simulated.As the theoretical basis for the prevention and control of agricultural non-point source pollution in the Zhaoxin River Basin.The main achievements are as follows:（1）Evaluation and analysis of current situation of watershed non-point source pollution:The main pollutants in the basin is TN,TP,COD and NH₃-N are slightly lighter than TN;the period of non-point source pollution was the most serious in the wet season,followed by the dry season,and the water quality was the best in the normal season;Zhu Zhao Xin River non-point source pollution is serious in the middle and lower reaches of the river basin and yun Zhu And Yun River,mainly involving Yuncheng county,Juye County,Mudan district and Juancheng County（2）Estimation of watershed non-point source pollution load:The largest amount of pollutants into the river is COD,followed by TN,TP and NH₃-N.Livestock and poultry breeding is the main source of non-point source pollution,followed by rural life pollution,and agricultural fertilizer pollution is the least.（3）Construction of SWAT model for watershed:Establish spatial database and attribute database of watershed;the model was ultimately divided into 31 subbasins with a total of 129HRUs.TN and TP were selected as the main pollutants for analysis,the model is calibrated and validated using the relevant water quality and quantity data of floor gate section from 2013 to2019.The results showed that runoff,the deterministic coefficients R² and E_ns of nutrients in calibration and validation period could meet the accuracy requirements of the model,which proves that the model has good applicability in the Zhuzhaoxin River basin（4）Simulation and analysis of watershed non-point source pollution based on SWAT model:The load of non-point source pollution in the basin has little change from year to year,the change trend of runoff and pollutants is roughly the same,and the discharge of non-point source pollution has a decreasing trend year by year;the non-point source pollutants mainly concentrated in wet season,but showed a significant decreasing trend in dry season and normal season;the non-point source pollution in the middle and lower reaches of the basin is more serious than that in the upper reaches;key sources of non-point source pollution are concentrated in the middle and lower reaches of the river basin and in the south of the river basin,mainly involving Mudan district,Yuncheng and Juye counties（5）Simulation and analysis of watershed non-point source pollution reduction effects under different scenarios:The buffer works best,and the longer the buffer the better;reducing fertilizer use also had a significant impact on pollution,the reduction in pollution was most pronounced when fertilizer inputs were reduced by 50%,but in the actual production and life should be based on the actual situation,to reduce the amount of fertilizer used.