Simulation Of Non-point Source Pollution Load In Jialing River Basin

After water storage of the Three Gorges Reservoir, the hydrological situation of rivers in reservoir area has been a fundamental change.It meets the hydrological factors demand to eutrophicate for water bodies. In recent years, "water bloom" occurred from time to time in the sub-rivers, which has had a serious impact on the ecological environment security of the reservoir area. Studies showed that nitrogen and phosphorus's nutrient level of water body is the key limiting factor, and the non-point source nitrogen and phosphorus loads with rainfall runoff is an important source of nitrogen and phosphorus for water bodies. Therefore, the study on non-point source nitrogen and phosphorus loads of sub-rivers has an important meaning for revealing the relevant change laws of water quality and non-point source pollution. And also it is of great significance for protection of the water environment safety in the Three Gorges reservoir and promoting the ecological harmony of reservoir area.Because of the non-point source pollution's characteristics of random, widespread, and latent, it's difficult to research and control. So the important means is to simulate its process of generation and transport with model for non-point source pollution study. This paper based on the United States Universal Soil Loss Equation, considering the two main factors of hydrology condition and land management practice which can influence the soil loss change yearly, put forward a new sediment load evaluation method which can reflect the yearly change process of soil loss, then established a yearly load evaluation model of the adsorbed nitrogen and phosphorus pollution; Based on Distributed hydrological model SLURP, established a model of dissolved non-point source pollution load outputted from various types of land and rural life; Then, on GIS platform, a dynamic model of non-point source pollution load applicable to the large-scale basin was built up by Organically coupling each sub-model,and was certificated.By the established model, the yearly load and spatial distribution of non-point source nitrogen and phosphorus pollution from various types of land and rural life in the Jialing River Basin from 1990 to 2005 have been studied. The main conclusions are as follows:â‘ The loads of non-point source nitrogen and phosphorus gradually decreased at basin outlet from 1990 to 2005, which rebounded or fell due to the impact of hydrological factors during the time. Average annual loss loads of non-point source nitrogen, phosphorus respectively are 86039 t/a and 4875 t/a from 2001 to 2005. Compared to 1990 they declined 40.7% and 48.2%. In 2005, non-point source nitrogen and phosphorus loads respectively are 130924 t and 7308 t, which was a strong rebound.â‘¡The loads of dissolved non-point source nitrogen and phosphorus are Very relevant to runoff at basin outlet, and the same situation occurred between the adsorbed non-point source nitrogen and phosphorus a load and sediment load. Load mix has changed from 1990 to 2005. The ratio of dissolved non-point source nitrogen load has increased from 38% to 64%, while adsorpted non-point source phosphorus load ratio has decreased from 74% to 50%.â‘¢The Serious region of non-point source nitrogen and phosphorus loss are mainly in the downstream of Jialing River's mainstream, the downstream of Qujiang River, the middle and lower reaches of Fujiang River,and Some areas of Xihanshui River and Bailongjiang River in upper reaches. The pollution loads from most counties of Gansu Province and Shanxi Province are relatively lower, while the Sichuan Province, Chongqing Municipality is the opposite situation. The highest losses Moduluses of TN, TP respectively are 4.489 t/km2 and 0.4325 t/km2 in Jialing River Basin.â‘£Viewied from the contribution to the total load of basin outlet, the Fujiang River Basin is an important pollution source, whose contribution rate of nitrogen, phosphorus loads almost close to 30%. And the second is Qujiang River Basin which also accounted for more than 20%. These two sub-basins'pollution loads occupy 50 % of the entire basin. The contribution rates of the other three sub-basins are relatively averious, between 13% and 18%.