Study On Non-point Source Phosphorus Pollution Based On Land Use Change In Chaohu Watershed(Hefei)

Since the point source pollution had been effectively controlled, non-point source (NPS) pollution has become the main factor that affects water quality, which is closely related to land use. Land use change may affect the climate, hydrology, migration of soil nutrient and soil erosion, lead to nutrition loss with surface runoff and then produce large areas of NPS pollution.As an important city in the upper reach of Chaohu watershed, NPS pollution level of Hefei affects the water quality of Chaohu watershed directly. Therefore, studying on NPS pollution under different land use is important to the water conservation and NPS pollution control in Chaohu watershed. Taking Hefei in the upper reach of Chaohu as a case study, by establishing the non-point source phosphorus pollution estimating model, this study analyzes the NPS phosphorus pollution load of each year from different perspectives, and discusses the relationship between land use change and the NPS phosphorus pollution. The best land use development and management pattern were built and land use types were optimized. Based on the analysis of land use change trends, we proposed corresponding measures of NPS pollution control and future land management.The main contents and conclusions of this study are as follows:(1)According to the results of Soranno model, NPS phosphorus pollution load in Hefei caused by land use shows an ascending trend with an increase of20%from1639.3t in2001to1968.4t in2010.(2)NPS phosphorus pollution of Crop production land contributes highest to the total NPS phosphorus pollution load in Hefei, about56%on average. Researches show that there is a positive correlation between NPS phosphorus pollution load and annual P fertilizer application rate. The latter increased from the54.9t in2001to78.9t in2010by about45%, which showed a good consistency with the change rate of NPS phosphorus pollution load.(3)The three methods used in this paper reflects the annual NPS phosphorus pollution load from different perspectives. Using the NPS phosphorus pollution load calculated by Rainfall deduction method as the standard, applicability tests of the three models are carried out. Through the analysis and comparison of the results, we find USLE and the improved Soranno model was reasonable.(4)Based on the analysis of the land use change trends and economic condition of Hefei, the best development and management pattern of land use is established using the linear programming method. The results indicate that the best land use situation is that the area of crop production land will be545720hm2and that of urban land be176450hm2, when the NPS phosphorus pollution load will be1759t/a and the income be5,867,200RMB.(5)According to the land use management and NPS pollution control, measure of controlling and preventing NPS pollution separately from rural NPS pollution and urban NPS pollution were proposed finally.