| Nansihu Lack is the largest freshwater lack of North China, which is animportant pivot of East Route Project of South-to-North Water Diversion. NasihuBasin, located in the southwest of Shangdong province(34°27′N~35°20′N,116°34′E~117°21′E), and it is an important part of Huaihe basin. Nasihu Lake is thecentre of the basin, where 53 rivers flowed into the Lake. In the 1980s, with the rapiddevelopment, a great deal of wastewater was discharged directly without treatment,which can bring about a serious pollution to the water environment of Nasihu basin.Along with the advance of East Route Project of South-to-North Water DiversionSouth to North Water Diversion and the increase of water consumption formanufacture and resident life, the problem of water pollution was not to be neglectedin Nasihu basin.Numerous studies showed that Non-Point Source Pollution (NPS) has become amainly primary cause of Nansihu basin pollution now, after the Point Source Pollutionhas been controlled. For this reason, an all-round understanding of distribution andimpact of NPS pollution in Nansihu basin were based on the research of NPS. Theresearch method can also be used as a source of reference for researching the NPS inanother basin.With the methods of field investigation, lab analysis and numerical simulation,the paper studied the simulation of NPS in Nansihu basin with SWAT model. Thecharacteristic of temporal and spatial distribution of NPS pollution in Nansihu basinwas analyzed, and the response of lacustrine deposit to NPS pollution in NansihuLake.This study included 7 chapters, which had been separated into five parts. The fistpart was the first chapter, as the opening badge, which gave a general overview of thebackground and significance of this topic, the review of NPS pollution at home andabroad. The second part included the chapter 2 and 3, which introduced the generalsituation of the research district, data preparations for SWAT model. The third partconsisted of chapter 4 and 5, which discoursed the SWAT model building , calibrationand confirmation of typical watersheds, simulation and evaluation of NPS in Nasihubasin. The fourth part was chapter 6, which analyzed the response of lacustrine deposit to NPS pollution of Nansihu Lake in chronology and spatial distribution. Thelast part was chapter 7, which elaborated on the research conclusion and outlook ofthe future research.Conclusions of this research were followed as such:1. The SWAT model was more rational to simulate the NPS pollution in Nansihu basin,and the result in the east was better than in the west.Because of the differences between the east and the west of Nansihu Lake andthe data demand of SWAT model, the typical watersheds, Sihe watershed andDongyuhe watershed, were selected to be simulated firstly. Then the models of Sihewatershed and Dongyuhe watershed were used to simulate the whole Nasihu basin,and good simulation results were got. The simulation result in the east was better thanin the west from the contrastive analysis, which showed that SWAT model was moresuited to simulate the rugged region to a certian extent.2. The NPS pollution of nitrogen and phosphorus was very serious in Nansihu basin,and the pollution in the east was more serous than it in the west.The result of simulation indicated that soil erosion in large part of Nansihu basinis not serious. The nitrogen load in this region far exceed quota, and the density ofnitrogen was more than 2mg/L, which was the key area of nitrogen pollution. Thedensity of phosphorus in about 40 percent of this region was more than 0.4 mg/L,where NPS pollution of phosphorus was serious. On the whole, NPS pollution ofnitrogen and phosphorus in the east was more serious than in the west, and theprimary contributor was Guangfuhe watershed.3. The primary pollution sources were livestock and poultry breeding andchemical fertilizer loss.The investigation, statistics and analysis of the source of NPS pollution ofnitrogen and phosphorus showed the contribution rates of all the factors, such asenvironment background value (climate, soil, topography, landuse and so on),chemical fertilizer loss, domestic sewage of village and breeding of livestock andpoultry. The research indicted that except the effect of environment background value,breeding of livestock and poultry was the primary source of NPS pollution in the eastof the basin, and chemical fertilizer loss was the mainly source of NPS pollution inthe west.4. The total nitrogen load in Nansihu watershed was mainly solution, and the totalphosphorus load in Nansihu watershed was mainly adsorption. The simulation with SWAT model and the map making with ArcGIS received thespatial distribution maps of runoff, silt, gradient, rainfall, NPS nitrogen load and NPSphosphorus load. In order to know the relation among these factors, the correlation ofthem was analyzed. The result showed that: (1) The sequence of the factor, whicheffected the stream flow, was slope > rain fall. (2) The stream flow impact on silt wasgreater than rain fall and slope. (3) The total nitrogen load and the stream flow werepositively correlation with the correlation coefficient 0.733, so the nitrogen wasmainly solution. (4) The total phosphorus load and the sediment flow were positivelycorrelation with the correlation coefficient 0.97, so the phosphorus was mainlyadsorption.5. Some responses of sediment to the NPS pollution in the lake existed in both spaceand time.In space, the phosphorus in sediment had relation to the NPS of phosphorus inthe lake, because the phosphorus was adsorption both in sediment and lack. In time,the nitrogen and phosphorus in lack impact on them in sediment, but the change ofsediment was latter than lake.The contributions and achievements of this research were as follow.①It was the first time to simulate the runoff, silt, NPS nitrogen and phosphorus loadwith SWAT model. This can provide data for mastering the hydrologic process andNPS pollution of Nansihu basin.②The spatial distribution of NPS pollution in Nansihu basin of recent ten years wasresearched, and the key areas of soil erosion and nutriment loss were confirmed.This work was the basis of making pollution regulation and water protectionmeasures.③It was an efficient method to select typical watersheds to simulate firstly, and tosimulate the entire Nansihu basin with calibrated models of typical watersheds,which can be used to simulation similar watershed.④The responses of nitrogen and phosphorus in sediment to them in the lake wereanalyzed. The result showed the origin of the nitrogen and phosphorus in sediment,which was scientific basis of sediment pollution improvement.⑤The data base, which contained hydrology information, pollution data, and so on,was built, and it was the basis of the other research of Nansihu basin.
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