Temporal and Spatial Simulation of Adsorbed Nitrogen and Phosphorus Nonpoint Source Pollution Load in Xiaojiang Watershed of Three Gorges Reservoir Area, China

Abstract

The presence of nonpoint source (NPS) pollution due to agricultural activities at the Three Gorges Reservoir Area in China has been of concern to the public in recent years. Due to the extent of the polluted area and seasonal dispersion mode, sediments have greatly impacted the water quality in the area. Generation and formation of adsorbed NPS pollution involves great uncertainty, which makes monitoring and controlling pollution very difficult. Rainfall erosivity factors, which are calculated by surface rainfall data from watershed hydrological simulation, and sediment delivery ratios were both selected and determined as the dynamic factors, whereas blind number theory was introduced and used to describe and deal with the factors' uncertainty of the Revised Universal Soil Loss Equation (RUSLE). Through the integration among blind number theory, dynamic factors, and pollution load model, parameter uncertainty and model dynamics could be better understood in the new and comprehensive pollution load model using GIS technology. Results indicated that rainfall runoff and sediment delivery ratio had significantly affected the uncertainty of final adsorbed NPS pollution load simulation results; the magnitude of adsorbed nitrogen and phosphorus loads from different land use types in descending order in turn was glebe, grassland, paddy fields, forestland, and urban land. This work provides a theoretical basis for control and management of soil loss and NPS pollution in the Three Gorges Reservoir Area, and these data are also useful in evaluating potential soil loss and NPS pollution loads in the watershed.