Study On Estimation And Control Technology Of Agricultural Non-point Source Pollution In Bahe Samll Watershed

Agricultural non-point source pollution has seriously affected the ecological environment of the river basin and the healthy and sustainable development of agriculture,and the comprehensive improvement of small watersheds plays an important role in the process of non-point source pollution control of the river basin.The Bahe small watershed includes an important agricultural product planting base in Xi’an,and the water quality of the Bahe River directly affects the water quality of the Mother River-Weihe River in Shaanxi Province.This paper takes the Bahe small watershed as the research object,analyzes the water environment status of the watershed,estimates the agricultural non-point source pollution load of the river basin,and analyzes the temporal and spatial variation laws and influencing factors of the agricultural non-point source pollution in the basin in combination with the non-point source model.Control measures for non-point source pollution provide scientific basis for reducing non-point source pollution in the Bahe River Basin and improving water environment in the basin,and provide technical support for the healthy and sustainable development of agriculture in the Bahe River Basin.The paper mainly draws the following conclusions:1.Through the analysis of the present situation of water environment of Bahe river basin,the water quality of middle and upper reaches of Bahe river was in good condition,all testing indexes could reach the surface Ⅳ class water quality index(GB3 83 8-2002).After flowing through Lantian county,the water quality becomes worse,especially total nitrogen(TN).During 2015 to 2019,the TN concentration(2.85-9.19 mg/L)in Bahe mouth was more than the surface Ⅳ class water quality index(1.5 mg/L).However,the standard-reaching rates of total phosphorus(TP),Chemical oxygen demand(COD),Ammonia nitrogen(NH3-N)were reached 99%.That showed that the main pollutant of Bahe river basin was TN.2.According to the estimated results of agricultural non-point source pollution load in Bahe river basin,Lantian county had the largest impact on agricultural non-point source pollution,and its contribution rate to the non-point source pollution of the whole basin was 61.67%.In addition,the proportion of pollution from rural domestic sewage and crop farming was also relatively large,accounting for 38.85%and 33.35%,respectively.3.The simulation results of the SWAT non-point source model in the Bahe River Basin show that rainfall has a great influence on the non-point source pollution in the basin.Rainfall,TN and TP pollution load in high water year,normal water year and low water year decrease sequentially;nitrogen and phosphorus pollution are more serious in flood season,and the output of various non-point source pollutants increases with the increase of rainfall From the perspective of the spatial distribution of non-point source pollution load output in the watershed,the output intensity of TN in the Bahe River Basin is about 12.93-208.84 kg/ha;the output intensity of TP is about 0.09-2.08 kg/ha;areas with high pollution loads such as nitrogen and phosphorus Mainly concentrated in Lantian County,Baqiao District and Chang’an District.Compared with the current year,the annual output load of TN and TP in the Bahe River Basin planning year has decreased slightly,down by 14%and 11%respectively.4.In terms of the contribution load of total nitrogen and total phosphorus loss pollution,cultivated land,orchards,and commercial land had the greatest impact on nitrogen and phosphorus influx loads.Among them,cultivated land had the largest contribution to the total output of organic nitrogen,organic phosphorus,and nitrate nitrogen,accounting for 41.75%,43.36%and 40.42%,respectively.From the contribution rate of different pollution sources to non-point source pollution,rural life pollution and agricultural cultivation had the more contribution rate to the pollution in the whole basin.The contribution rate of TN was 39.10%and 34.89%respectively,and that of TP was 38.67%and 37.01%respectively.5.Block from the source reduction and process the related Ba river watershed non-point source pollution control measures would be put forward.The reduction effects of pollutants:vegetation buffer zone>grass planting channel>fertilizer reduction.The combination of source reduction and process control can effectively control the non-point source pollution.The reduction of fertilizer application amount(20%)combined with the vegetation buffer zone(area ratio of 30)has the most appropriate on the control of the non-point source pollution in the ba river basin,which could cut 30.03%percent of TN and 75.04%percent of TP.