皇甫川流域土地利用变化与土壤侵蚀评价

Land use change and soil erosion evaluation in Huangfuchuan Watershed

基于“3S”技术,揭示了皇甫川流域近十多年来的土地利用变化情况,并采用通用土壤侵蚀方程(Universal Soil Loss Equation,USLE)定量研究了不同土地利用背景下的土壤侵蚀分布规律。结果表明,近十几年来流域土地利用变化剧烈,其总体趋势是城镇用地、林地、耕地和灌丛的面积逐渐增加(速率依次减小),水体、草地、沙地和裸砒砂岩面积逐渐减小(其中水体缩减的幅度最大),土地利用格局持续承受着来自当地快速城市化进程及社会经济发展和生态环境保护及建设两方面相互矛盾的巨大压力;与此同时,流域土壤侵蚀模数由1987年的16160.72t/km2减少到2000年的13943.32t/km2,其中6种不同土地利用类型在同一年份内土壤侵蚀模数的大小顺序为裸砒砂岩>沙地>耕地>草地>林地>灌丛,表明林、灌措施是流域植被恢复和减少土壤侵蚀的首选,草地限制土壤侵蚀的效果也较为明显,而沙地尤其是分布面积较广的裸砒砂岩则是土壤侵蚀综合治理的难题和关键;虽然十几年来水土流式综合治理效果显著,但由于裸砒砂岩和沙地的面积仍在整个流域占有相当的比例以及耕地剧增等因素,土壤侵蚀模数仍明显高于流域土壤允许侵蚀的临界值,流域生态环境仍然处于不安全状态,有必要对未来土地利用格局进行优化以确保生态安全。最后,在讨论中阐明了流域土地利用格局调整和优化的方向。

Supported by ＂3S＂ technology, this paper brought forth the land use change in Huangfuchuan Watershed from 1987 to 2000, then studied the distribution rules of soil erosion under different land use patterns quantificationally by Universal Soil Erosion Equation （USLE） during that period, and emphasized the impact of changes of land use pattern on soil erosion in the watershed. The results showed： （1） In the recent ten years, the general tendency of land use change in the study area was that the proportion of urban land, woodland, cropland and shrub increased gradually with the speed descending, and that the proportion of water, grassland, sandy land and bare rock shrunk with the highest extent of water. During this course, the watershed pattern of land use was under the tremendous pressure from the standing conflict, which burst out between the rapid urbanization, economic development and the conservation and rebuilding of ecological environment. This status would survive for a long time in the future, and moreover, the distinct decline of water area would be the bottleneck of above contradiction; （2） With the change of land use pattern, the annual modulus of soil erosion decreased rapidly from 16160.72t/km^2 in 1987 to 13943.32t/km^2 in 2000. According to the annual modulus of soil erosion in the same year, different land use types in Huangfuchuan Watershed arrayed with the order： bare rock 〉 sandy land 〉 cropland 〉 grassland 〉 woodland 〉 shrub, indicating that woodland and shrub were the preferred measures for vegetation restoration and the reduction of soil erosion. Furthermore, the alteration of sandy land and bare rock would be the key problem of comprehensive harnessment of soil erosion, which could not be overlooked; （3） The effect of soil and water conservation was significant in the recent ten years, however, due to the high proportion of sandy land and bare rock and the proliferating cropland in the watershed, the annual modulus of soil erosion were still higher than permissible soil erosion amount between 3700t/km^2 and 6900t/km^2. The ecological environment of watershed would be in the status of insecurity, thus, the watershed pattern of land use must be optimized to meet the requirement of ecological security. Generally, this paper emphasized the impacts of different land use types and patterns on soil erosion of watershed, illuminated the adjustment or optimization of land use pattern, and improved the technical system of soil erosion assessment for the simulation and forecasting of land use change, which has wide application in the future.