A Study On Influences Of Small Watersheds Land Use Pattern In Three Gorges Reservoir Area On Soil And Water Loss

Recent years, the degradation of environment represents as soil and water loss is primary problem of three gorges reservoir small watersheds. The irrational land use pattern (constitution, type, and allocation of land use system) is the main reason of soil and water loss. The application of optimal allocation of land use pattern to improve vegetation restoration is the only way of restraining area soil and water loss and of sustainable development ultimately. This paper investigates the influences of different land use patterns on soil and water loss in watersheds in typical soil and water loss area Kaixian county Nanshan Qiaogou, on the basis of landscape ecology, land resource science, soil and water conservation, and application of special analysis technique in GIS. The author proposes that the application of optimal allocation mode of land use pattern to prevent soil and water loss not only can mitigate soil and water loss, and improve the sustainable utilization of land resources, but also can provide a model of the development of ecological environment vulnerable area in three gorges reservoir area and in upper reaches of the Yangtze River. The investigation shows that:(1) Land use type distribution changes with the alternation of topographic factor from the perspective of the relationship within small watersheds elevation, slope, aspect, and land use type. Farmland distributes on the semi-sunny and sunny slope of low hill area, mainly sloping field in sharp sloping field. Although the land area decreased and reduced soil and water loss, the decrease extent has not reach the ideal target. Forest land changes a lot, in detail, it is inversely proportional to elevation, and is direct ratio to slope. The distribution of semi-sunny slope and sunny slope increased. Grassland mainly distributes in the middle and bottom part of hills, and increase with slope. The aspect of grassland is mainly semi-sunny slope, but it has the intention of changing to other aspects. Although partial controls have been adopted to reduce soil and water loss in watersheds, the spatial pattern of land use improved in 2006 compared with 2003, the land use structure of watersheds has turned to be irrational because of the comprehensive influences of natural factors such as elevation, slope, aspect and human disturbance.(2) Landscape pattern of farmland as chief component and forest land and orchard as complement has formed in small watersheds. As a whole, the stability of watersheds landscape has been weakened and spatial heterogeneity degree has increased. Landscape diversity has increased. The variety of landscape is influenced by topography. Landform, farmland, and grassland show a complex shape, and they are changing and developing all the time. However, human settlements, orchard, and other forestland represent a comparatively stable shape because of the great influences of human activity. Small watersheds landscape pattern represents that the environmental protection measures is efficient in the improving of ecological environment, and the regulation of land use pattern is helpful for the diversity and rationality of the ways of land uses.(3) The results of the quantitative discuss of soil and water loss shows that: the average modulus of soil erosion of small watersheds is 3048t/km~2. The degree of erosion is moderate, and is far bigger than the standard soil loss tolerance of south China which is proscribed by Ministry of Water Resources. As a result, soil and water loss control is still facing great difficulties.(4) Land use pattern in small watersheds is related to soil and water loss degree in a certain extent. The land use pattern of the whole watersheds represents a kind of pattern characteristic that is negative to soil and water loss and trend to heterogeneity. Modulus of soil erosion in 2006 is 618.90t/km~2 less than that in 2003. Heavy erosion of watersheds has been efficiently controlled. Quantity and modulus of soil erosion has markedly decreased.(5) The irrationality of land use pattern is main reason which causes soil and water loss. Consequently, it is helpful to control soil and water loss, prevent land deterioration, and improve the sustainable use of land resources and the sustainable development of ecological environment through certain methods such as optimizing land use and adjusting the mode such as land use type and structure according to different land use patterns and soil and water loss characters of small watersheds.