Simulation of agricultural non-point pollution based on AnnAGNPS model

GIS(Geographic Information System) was integrated with AnnAGNPS(Annualized Agricultural non-Point Source Model), which was used to input, analyze, and visualize spatial data that agricultural non-point source pollution concerned. On this basis, the performance of AnnAGNPS, used in typical sub-watersheds of Dagu catchment was evaluated. The model was calibrated and validated using observed stream flow, sediment load and total nitrogen data during 2000 and 2001 in sub-watersheds outlet. The annually relative error of surface runoff was separately 12.7% and 7%, the difference during the wet months were in range of ±30%, and R² of 0.98 and 0.91 was separately for event-based runoff, which showed the model performed well for runoff simulation. Moderate accuracy of prediction for sediment was obtained with annually relative error of 19.1% and 15%, and R² of 0.78 and 0.73 during calibration and validation. As the annually relative error of 50% for annual output of total nitrogen, however, AnnAGNPS failed to calculate the total nitrogen with R² separately down to 0.7 and 0.6 for monthly simulation and number of rainfall. It is observed that there is a need to modify or improve the estimation methods of the total nitrogen to increase the performance of the model which can aid watershed management in local conditions. The results in this paper make a good demonstration for applying AnnAGNPS model in China, and lay a good foundation for establishment of whole Dagu basin distributed hydrological model.