Abstract: Agricultural nonpoint source (NPS) pollution induces serious and extensive environmental and water quality problems that are characterized by the emissions being either difficult or too expensive to observe. The NPS pollution is potentially affected by any type of land use, and relates to the geographical location of pollution sources diffusion and controlling measures implementation, involving in complex ecological processes and landscape patterns. Spatial simulation modeling is commonly accepted in dealing with the NPS pollution problems, but associated with spatial uncertainty. The annualized agricultural nonpoint source (AnnAGNPS) model designed by U.S. Department of Agriculture (USDA-ARS and NRCS) is a continuous and distributed simulation model widely used for watershed assessment, which expands the capabilities of its predecessor AGNPS, a single eventmodel. In this paper, the features, spatial and temporal scales, and limitations of AnnAGNPS 4.0 Model were introduced, with its uncertainty and the factors affecting its prediction deviation analyzed. It was thought that the parameters in USDA-ARS and NRCS handbook and agricultural handbook (Number 703) fall short of in most cases in China, and there were obvious errors in the results of simulation when the parameters were used. According to the action mechanisms of AnnAGNPS, the principles and methods of applying the parameters were advanced, which could be helpful for the valid application of AnnAGNPS 4.0 in China.

Key words: Chromium, Daphnia carinata, Phototactic behavior, Biomonitor