Abstract: Xijian Lake (formerly Chengxi Reservoir) is the unique surface water source of Chuzhou City, Anhui. Its water quality deterioration is mainly caused by the nonpoint source pollution. Based on the pattern of land use/land cover (LULC), a model was established by GIS platform to simulate the quantity of nonpoint source pollution exported to the aquatic environment and retained by the different LULC on each cell on the platform of GIS. This study chose phosphorus as a pollutant surrogate and relevant data of the year 2010 were used in the model. The quantity of phosphorus exported to the lake and phosphorus retained were simulated under five different LULC scenarios. The results showed that in 2010, the total phosphorus exported to the lake was 2461.20 kg. Critical source areas of phosphorus mainly included the city’s Institute of Agricultural Science, Chengjiao resident area, the Institute of Aquaculture in the northwestern of watershed. Most of the exported phosphorus was effectively retained by the different LULC in the process of transportation, and the total phosphorus retained by LULC was 5422.36 kg, accounting for 68.8% of the total phosphorus loads. The simulated results for the amounts of phosphorus exported to the lake under five different LULC scenarios were in the order of cropland > built-up > grassland > forestland. The scenarios 4 and 5 that included vegetation buffer zones with different widths planted along the shore and on the intersection of runoff would largely improve the efficiency of phosphorus retention. However, the program of returning croplands to forests, which guided the land cover changes only based on the slope ranks, would be less efficient to prevent phosphorus from the watershed entering the aquatic environment.

Key words: landscape pattern, spatial evolution, Guizhou, basin, land use intensity