Assessment of the AnnAGNPS model in simulating runoff and nutrients in a typical small watershed in the Taihu Lake basin, China

The Annualized Agricultural Non-Point Source Pollution (AnnAGNPS) model is a distributed-parameter continuous-simulation watershed-scale model used to simulate runoff, sediment, nutrient, and pesticide loads exiting from agricultural areas through drainage streams. The aim of this study was to evaluate the performance and suitability of the AnnAGNPS model in predicting runoff and nitrogen and phosphorus loading in a typical small drinking water source watershed located in the region of Taihu Lake (China) using estimated yearly runoff data and monthly observed nutrient data. The estimated runoff data for the years 2005-2009 and 2010-2013 were used to calibrate and validate the annual runoff. The data for the monthly observed nutrients from July 2008 to September 2009 and December 2012 to December 2013 were used to calibrate and validate the monthly nutrient load. The results showed that the model provided satisfactory simulations of annual surface runoff, and for the calibration and validation, the coefficient of determination (R-2) values were 0.96 and 0.97, respectively, and Nash-Sutcliffe efficiency coefficient (Ens) values were 0.96 and 0.97, respectively. The model was also capable of simulating the monthly nitrogen and phosphorus load, with the nitrogen load simulation yielding moderate calibration and validation results of R-2 = 0.86 and 0.88, respectively, and Ens = 0.82 and 0.87, respectively, and the phosphorus load yielding slightly poorer calibration and validation results of R-2 = 0.60 and 0.83, respectively, and Ens = 0.61 and -3.86, respectively. The results obtained from applying the AnnAGNPS to this typical small watershed in the Taihu Lake basin demonstrate that the model has considerable potential as a research and management tool for comparative assessments and runoff and nutrient yield estimations in similar watersheds. (C) 2015 Elsevier B.V. All rights reserved.