喀斯特地区土壤侵蚀风险评价——以贵州省关岭布依族苗族自治县为例

Soil Erosion Risk Assessment in Karst Area ——Case Study in Guanling County of Guizhou Province

我国西南喀斯特地区土壤侵蚀的严重后果除了土壤肥力损失、质地恶化、淤塞河渠水道等外 ,还有一个特殊的石漠化问题 ,因此喀斯特地区的土壤侵蚀风险评价研究必须综合考虑石漠化问题。土壤侵蚀风险评价首先需要确定土壤侵蚀级别 ,按照年均土壤侵蚀模数确定土壤侵蚀级别的方法在喀斯特地区存在很大的争议。提出一种新方法 ,通过求取石漠化扩展速度 ,也就是土壤面积损失速度 ,从而得到土壤抗蚀年限 ,对土壤侵蚀风险进行评价。具体过程以贵州省关岭县为例 ,在对两期 TM影像 (1987～ 1999年 )进行线性光谱分离的基础上 ,得出研究区两个时段植被、裸土和裸岩的比例 ,根据裸岩比例变化求取研究区 13年间石漠化发展速度 ,通过裸土、植被比例和石漠化速度计算研究区裸露土壤和全部土壤的抗蚀年限 ,从而对研究区土壤侵蚀风险有一个比较可信的把握。计算结果是研究区 13年间石漠化扩展速度是每年增长 0 .37% ,裸露土壤抗蚀年限为 4 9.3年 ,全部土壤抗蚀年限为 93.7年 ,土壤侵蚀危险级别都属于“危险型”。

The serious effects of soil erosion include the fertilities loss of soil, soil quality deterioration, the blockade of ditches and so on in the Karst area sitting in the southwest of China. Besides that, there is another special problem, i.e., rocky desertification. Therefore, the risk assessments of soil erosion in that area have to take rocky desertification into account. During the process of the assessments, there are so many disputations about the method of showing the soil erosion grade according to the modulus of soil erosion per year. The authors put forward a new method from a new perspective. Based on the expending speed of rocky desertification that means the loss speed of soil area, the duration time of soil erosion can be calculated from which the assessments will be executed. Guanling County is selected as the case study area. Based on the linear spectral unmixing of TM image of 2 time stage, the ratios of the vegetation, bare soil and naked rock between the two stages was calculated. The expending speed of rocky desertification made clear because of the ratio change of naked rock during 13 years. With the speed of rocky desertification and the ratios of naked soil and vegetation, the duration time of soil erosion of bare soil and total soil in the research area are achieved. Thus the risk assessments of the soil erosion in that area are convincible. The calculation results include the rocky desertification speed is 0.37% per year, the duration time of soil erosion of bare soil and total soil are 49.3 years and 97.3 years respectively. The risk grade of the soil erosion is 'danger' told by the assessments.