The researchers studied nitrogen and phosphorus pollution in Xiao-Jiang watershed in the Three Gorges Reservoir Area. They used a hydrological model to simulate pollution from surface runoff and land use. Results showed that pollution levels were closely linked to rainfall and land type, with farmland being a major source. Nitrogen and phosphorus pollution was highest in glebe and mixed land, followed by paddy fields, grassland, urban areas, and forests. Land use contributed 78%-85% of the pollution, while livestock and poultry contributed 13%-20%.