Simulation of nonpoint source nitrogen transport in two separated catchments in the hilly area of purple soil

In this study,a hydrology-biogeochemistry-based(enhanced DNDC model) model was employed to simulate the water quantity and water quality in two separate but similar watersheds in the hilly area of purple soil.The enhanced DNDC model was calibrated with data in a period of 36 months(2007-2009)and validated with data of 24 months period(2010-2011) in Jieliuyan watershed,and extended validated with data of 12 months period(2011)in Daxing watershed.The primary objective of this study was to compare hydrology,sediment and nitrogen simulation results in two separate,but similar,watersheds.The simulation results of monthly discharge,sediment and nitrogen show that the enhanced DNDC model performed satisfactorily in the study area(Ens=0.90,0.92,0.89,and 0.88 in calibration period and Ens=0.83,0.87,0.74,and 0.52 in validation period for discharge,sediment yield,total nitrogen and particulate nitrogen,respectively).The results indicate that the enhanced DNDC model is an appropriate model for the non-point source nitrogen pollution simulations in purple soil area.The possibility of extended validation has been proved due to the encouraging results during the extended validation period.However,lower Ensand larger Re for sediment yield and particulate nitrogen were observed in the extended validation period in a larger watershed due to the model weakness of channel process.