Influences Ofthe Runoff Generation And Confluenceon Nutritions Export And Transport In The Watershed

The “2013 Report on the State of the Environment in China” indicates the worrying water environment of the Haihe River, Yellow River, Huaihe River, Liao River, etc. The deterioration of water quality exacerb ated the situation of water shortages. Non-point source pollution has been the major threat to the water environment, and nitrogen and phosphorus are the key causes of water eutrophication. Nutritions export and transport of the watershed is closely associated with the process of the rainfall and runoff generation and confluence. Only by research on the interaction process, we can understand the mechanism of nutritions export and transport along with the variational process of rainfall and runoff.This research focuses on the experimental watershed called “Xitaizi” of the Liuli River basin located in Huairou District of Beijing. We tried water yield and quality experiments based on the scale of the hillside and all the watershed, and using the experimental data of the basins from the United States Department of Agriculture and the SWAT model. We do research on the influences of the runoff generation and confluence on nutritions export and transport of the watershed by means of making experiments, analyzing ex perimental data and using model simulation.First of all, we collected water samples of the hillside under the process of the rainfall and runoff. The result of analyzing the data indicates that the surface flow had greater flow-weighted mean total nitrogen concentration than the rainwater by the erosive forces of raindrops and surface flow of water, and also had greater flow-weighted mean NO3-N concentration than the rainwater. The nitrogen and phosphorus losses from the surface flow is greater than from the lateral subsurface flow on the scale of the hillside, while flow-weighted mean total nitrogen and total phosphorus concentration of the surface flow are both also greater than those of the lateral subsurface flow. The flow-weighted mean NO3-N and total phosphorus concentration of the soil water are obviously higher than those of the rainwater, while the flow-weighted mean NH4-N concentrationof the soil water is lower than that of the rainwater. This result indicates that NO3-N and total phosphorus of the soil water transport with the infiltration water by the way of leaching, while NH4-N is adsorbed by the soil colloid. And total nitrogen is accumulated in the groundwater over time.Secondly, we collected water samples and observed volume from the river water in the output of the watershed along with comparing the data from the experimental basins of the USDA. The result indicates that the raininess is the important element of the variation of the NO 3-N concentration in the process of the rainfall and the runoff. We use M(V) curves to evaluate the first flush of the rainfall events of the experimental watershed, and the result indicates that the first flush of NH4-N and total phosphorus appeared obviously. By comparison with the results from different wat ersheds, NH4-N and total phosphorus have the same first flush.In the end, SWAT model simulated nitrogen and phosphorus losses from the Liulihe River watershed over thirty years. The result shows that NO3-N losses from thelateral subsurface flow >the surfa ce flow >the groundwater flow, and mean NO3-N concentration of the surface flow >the lateral subsurface flow > the groundwater flow. The flood period(from June to September) is the main season of the total nitrogen and phosphorus losses.And NO3-N losses from thelateral subsurface flow and thegroundwater flow are less affected by the flood period than thethe surface flow, while the flood period has more effect onthe total phosphorus than the total nitrogen.