The Simulation Study of Agricultural Non-Point Source Pollution of Nitrogen and Phosphorus Based LUCC in GuangFu River Basin

Rivers eutrophication may cause algae and plankton blooms, water-oxygen reducing and the high number of deaths which may cause water pollution. On a global scale, about 30%similar to 50% surface water eutrophication. The nitrogen and phosphorus loads of rivers is the main cause of water eutrophication, and the majority of nitrogen and phosphorus comes from agricultural non-point sources. LUCC (Land-Use and Land-Cover Change) of the river basin had direct effect to agricultural non-point source nitrogen and phosphorus loads. For example, LUCC can influence the climate, hydrology, volume of runoff and erosion amount of the river basin that may lead to soil erosion and Nitrogen and phosphorus nutrition elements run off with the direct surface runoff. That may cause a large area of agricultural non-point source pollution. GuangFu River locates in the southwest of Shandong province, and pours into Nansi Lake from north to south. But Guangfu River was the most seriously polluted in all the rivers which immit Nansi Lake. According to the sample survey data analysis for years, the content of NH3-N in Guangfu River was the top in all rivers. The agricultural non-point sources pollution of nitrogen and phosphorus were too heavy for agricultural irrigation. The land use type in Guangfu River was mainly composed of cultivated land, so under the flushing action of rainfall, there were a lot of pesticides and fertilizers flowing into Guangfu River following the surface runoff and sediment. That was the mainly reason of the pollution of Guangfu River. Therefore, to simulate the nitrogen and phosphorus loads of Guangfu River and to discuss how to reduce the pollution through optimizing the local land use had the important realistic significance. In this paper, SWAT model was used to simulate the nitrogen and phosphorus pollution loads of GuangFu River basin under different land use scenarios, then the contribution rates of nitrogen and phosphorus pollution loads were analyzed based different land use types, and the best ways of land use in the watershed were discussed. The research results showed that: (1) Through the calibration and verification of the model, SWAT model was suitable for simulating the nitrogen and phosphorus pollution loads of GuangFu River. (2) From the result of annual average nitrogen and phosphorus loads under the land use types of 2010 and 1987, it showed that the contribution to the nitrogen and phosphorus loads of cultivated land is the biggest, followed by the grassland, and the forest. (3) And then, the land use scenarios of the returning cultivated land to forest and closing the land for reforestation were simulated. Through comparing the simulation results, the scenarios of closing the land for reforestation was the more effective method to controlling the agricultural non-point source pollution of nitrogen and phosphorus.