| Soil is one of basic factors which life beings in the earth rely on. Soil degradation increasingly restricts human development, and soil erosion is one of the reasons. China is one of the most serious soil erosion Country in the world, and the proportion of Chinese soil erosion area is 33.2%. Research the principle of soil erosion and the method that how to control and deal with it have been the focus of the world. Many scholars have studied the theories and mechanism of soil erosion from 1960's.With the development of computer technique, combined GIS with RS to study soil erosion has been the advanced filed in researching soil erosion quantificationally. Using nucleus tracer technique to quantificationally research soil erosion has unsubstituted advantage, such as exactness, speediness, precision, and so on. Now more and more researchers become to pay attention to them.Beijing has faced the condition that lack water seriously in this century. Miyun reservoir that located in the center of Miyun county is the biggest drinking water source of Beijing. The soil erosion and land-use pattern of mountains around the reservoir decided the water quality of Miyun reservoir. GIS RS and l37Cs tracer technique are integrated to research the soil erosion situation and establish the Ian i-use optimum pattern, in order to provide the foundation of praising the and quality of surrounding are; of Miyun reservoir In this study. Assuring the reservoir's water clear and providing the science basis of elective control method are also this study's aims.Based on the field survey advanced position and the surrounding area of Miyun reservoir, this study selected typical soil samples of 29 sampling areas and 84 sampling points in research region and measured their pH value, mechanical composition, organic content, concentrations of total P-and total N, available N and P contents and 137Cs concentrations. Using the erosion model in which 1377Cs was the important factor to calculate soil erosion rate in order to determinate the soil erosion grades of research region. According to the erosion conditions to find the natural and economical factors that induced soil erosion, and regarded these factors as the main attribute data of soil erosion database.After ascertain soil erosion correlative factors, the database system of soil erosion correlative factors has been established by Access 2000.This database classified and synthesized the data of field survey and collected graphics data, in order to make sure the erosion correlative factors and make inquire correlative data expediently.In order to estimate the soil erosion situation more effectively, this study took the GIS-RS method to classify the soil erosion condition of research region. At the same time, the erosion model based on 137Cs was combined with GIS to established soil erosion spatial database of sampling area, and erosion situation was obtained. Contrasted erosion situations that got from two methods, for the sake of exactly praising the soilerosion grades of Miyun reservoir surrounding area. The estimate result indicated that slight erosion was the primary erosion condition of Miyun reservoir surrounding area, but increasing extent of median erosion area was bigger. The total erosion area has the increasing trend, and the potential soil erosion criticality of research region is bigger. The dominating reasons that made the soil erosion are land-use structure of low mountains andhilly regions and economy activity of human.Sustaining by the erosion correlative factors database and spatial data of research region, Miyun reservoir surrounding area land-use pattern and forecast system was established by MO to statistic erosion grades and land-use condition and show the optimization measure by figure. This system can effectively organize the spatial data and attribute data, prevent soil erosion area from spreading, realize land-use rationalization, and provide the reference to protect entironment of Miyun reservoir surrounding area and water quality in Miyun reservoir.
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