基于土地利用变化的三峡库区小流域生态风险评价——以草堂溪为例

为揭示三峡库区小流域土地利用变化对生态风险的影响,选择草堂溪小流域作为研究区,以1990、2000、2004和2010年4期TM和CBERS影像获取草堂溪小流域土地利用信息,以500 m×500 m为基本单位,制作格网作为辅助评价单元,借助GIS技术为数据分析平台,对土地生态风险指数进行空间插值,生成1990、2000、2004和2010年4期生态风险分级图。结果表明:1990-2010年研究区土地利用相对合理指数上升0.03;研究区5种风险等级连片分布,与耕地和水域分布区域具有显著的空间相关性,5种生态风险等级主要集中在15~25°和>25°坡度带上以及500~1 000 m和1 000~1 500 m两个高程带上;研究区生态风险呈现先恶化后好转的趋势,较低风险等级面积在1990和2010年最大,分别占研究区总面积的28.23%和37.41%,2000和2004年高风险等级面积最大,分别为29.69%和35.54%。研究得出草堂溪小流域生态风险时空变化原因主要为自然条件限制和人为因素控制。针对研究区生态风险时空变化特征提出调控对策,具体有:进行最优土地利用组合类型搭配,调整不合理土地利用类型,改良林分结构;对流域近消落带部位的土地利用在统筹考虑水环境污染治理和土壤侵蚀问题的同时进行统一合理规划管理。

Ecological Risk Assessment of Small Watershed of the Three Gorges Reservoir Area Based on Land Use Change—A Case Study of Caotang River

To reveal the impact of ecological risk of land use change in the small watershed of the Three Gorges Reservoir Area, Caotang River watershed is chosen as the study area. Land use information was obtained from satellite remote sensing TM images of 1990, 2000, 2004 and CBERS data of 2010. The grid by 500 m×500 m was created as the auxiliary evaluation unit, and the GIS technology was employed as the data integration analysis platform. In order to generate the map of land ecological risk in 1990, 2000, 2004 and 2010, the system sampling method and block Kriging were used to make the index a spatial variable. The results indicated that land use reasonable index in the study area increased from 0.78 to 0.81, a rise of 0.03 from 1990 to 2010, appearing first a deteriorating trend and then improved trend, land use structure is reasonable along with contiguous distribution of five ecological risk levels of the study area. Edge of the study area is at low risk, the closer the distance, the higher the level of risk of the center of the study area. Regional ecological risk distribution patterns have obvious space correlation with arable land and water distribution area. Five types of ecological risk are mainly concentrated on the slopes of 15°-25° and >25° and at elevations of 500-1000 m and 1000-1500 m. Ecological risk appears first a deteriorating trend and then improved trend. The largest area of ecological risk is at lower level risk in 1990 and 2010 of the study area, accounting for 28.23% and 37.41% of the total area; in 2000 and 2004, the largest area of ecological risk is at high level risk, accounting for 26.29% and 35.54% respectively. The study revealed the main reason for the temporal and spatial variation of the Caotang River Small Watershed Ecological Risk is the constraint of natural conditions and control of human factors. The natural conditions are the incentives and human factors control is the main reason. Type of land use changes is the most important impact of changes on ecological risk factors. Finally we put forward some countermeasures for temporal and spatial variation of regional ecological risk. Specific measures include to find out the optimal combination of land-use types with improved unreasonable land-use types, to improve the stand structure, vigorously transformation of coniferous forest and shrub replanting made mixed coniferous forest; we should undertake unitive reasonable planning and management for land use which was closed with Hydro-Fluctuation Belt area while considering the water environmental pollution and soil erosion problems as a whole.