Simulation And Research Of Non-Point Source Based On AnnAGNPS Model In Bahe River Of China

Bahe River Basin is the primary tributary of Weihe River and the typical urban river in Xi'an.It is an important link connecting the two major ecological belts in Xi'an City(Qinling and Weihe Rivers),and is also a key urban ecological compensation zone in Xi'an.With the rapid development of social and economic in Xi'an City,the ecological health problems in the Bahe River Basin have been increasingly concerned by relevant departments.In recent years,with the implementation of comprehensive control projects in the Bahe River Basin,point source pollution has been well controlled,and the non-point source pollution should be solved urgently.This paper takes the Maduwang watershed in the upriver of Bahe River as the research area,discusses the applicability of the AnnAGNPS model in the Bahe River Basin,and proposes measures for the non-point source pollution in the Bahe River Basin.(1)The relative error between the measured and simulated values of annual runoff in the Bahe River Basin was controlled within±13%,Ens is 0.93,and R~2 is0.99;the monthly and daily scale simulation deviation is controlled within±12%,the monthly scale R~2 and Ens are all greater than 0.84,and the daily scale R~2 and Ens are all greater than 0.56.This model was suitable for the runoff simulation in the Bahe River Basin.(2)The model non-point source pollution data was verified using five rainfall events in July and August 2017.The relative error of simulated and measured total nitrogen was controlled within±13%(except for the rainfall of 20170813 event),the relative error between the simulated and measured values of total phosphorus with three rainfall events Re remained between-12%and 40%.The calibrated AnnAGNPS model was used to quantitatively simulate the non-point source pollution load in the basin.The annual runoff,total nitrogen and total phosphorus load in the Bahe River Basin from 2007 to 2016 showed an overall downward trend.In the simulated year 2007,2009 and 2011,the mount of annual runoff reached more than 200 million m~3,the total nitrogen load was as high as 5300 t,and the total phosphorus load was more than 1000 t.In 2016,66%of the total rainfall was mainly appeared from May to August.The runoff,total nitrogen and total phosphorus in the three months accounted for 84%,93%and91%of that in the simulated year,respectively.(3)The simulation results showed that the non-point source pollution load per unit area is mainly distributed in the middle and lower reaches of the basin.The average total nitrogen and total phosphorus load per unit area was 31.63 kg/ha and 9.31 kg/ha,respectively.The total nitrogen load per area ranged 5.79 to 115.75kg/ha,and the total phosphorus load ranged 0.65 to 27 kg/ha.Under different types of land use,the contribution of non-point source load varied greatly.Total nitrogen load was 5.7 kg/ha,and total phosphorus load was 0.65 kg/ha for the arbor.Total nitrogen load was 32.19 kg/ha,and total phosphorus load was 9.28 kg/ha for cultivated land.(4)Based on the above analysis,different scenario plans were proposed for the study basin and the typical subwatershed.The countermeasures for the prevention and control of non-point source pollution were put forward.For the study basin,adjustment factor P of soil and water conservation measures,The reduction of total nitrogen load and total phosphorus load were 35.63%and43.45%,respectively.For the typical subwatershed,the implemented measures returning farmland to forests,supposed the ration of 30%,50%and 100%,total nitrogen load decreased by 28.20%,43.01%and 78.23%,and total phosphorus decreased by 33.56%,53.94%and 66.81%,respectively.