基于土地利用结构变化的水土流失动态评估

Dynamic Assessment for Soil Erosion Based on Land use-Structure Change

基于土地利用结构动态变化研究水土流失的变化趋势 ,引入层次分析法确定不同土地利用类型在影响水土流失方面的权重 ,并采用相关区域的土地利用结构特征指标定量反映针对区域水土流失的土地利用结构的综合影响。在此基础上 ,类比快速生物评价方法的基本思想 ,通过参照点选择、参照组构建、参照组匹配、观测 -期望比值 ( O/E比 )计算等具体过程实现区域水土流失的动态评估。这一方法在安塞纸坊沟流域的应用表明 ,评估得到的水土流失动态变化特征与研究区域的历史开发过程较为吻合 ,说明了方法的合理性和有效性。这一方法不侧重于研究具体评估模型在不同区域和空间尺度应用时的精确性问题 ,而是关注区域水土流失相对于某参照条件的动态变化趋势及其快速评估 ,以便提高不同区域数据及结果的重用性和可比性、节省评估时间和费用。

The variation of land use structures is of significance to soil loss as well as ecological protection. Therefore, dynamic assessment of soil erosion and identification of the effect of human activities could be carried out by monitoring the land use change. Based on the analysis of characteristics of land use change and soil loss, this paper presents an approach for soil loss assessment in terms of land use structure change. The analytic hierarchy process is introduced to identify the impacts of land use on soil loss in terms of the hierarchical structure of regional landuse associated with different scales or resolutions, and weights at different levels could be determined with the pairwise comparison matrix. As a result, a characteristic index for land use structure is proposed to reflect the comprehensive impacts of various types of land use, which is defined as the sum of products between the weight assigned to each type of land use and its corresponding area percentage over the total for the concerned region. Moreover, a new dynamic assessment method for regional soil erosion is proposed based on the analogy of the rapid biological assessment method advanced for water quality in recent years. With a series of processes of selection of reference sites, classification of reference groups, determination of environmental indexes, identification of the matching groups for the concerned sites, and the comparison of the observed and expected results through an O/E ratio, the trend of the soil loss in an assessment area could be predicted very rapidly. A case study of the Zhifanggou Watershed in Ansai, Shaanxi Province was preformed and the systematic comparison of landuse characteristics from 1938 to 1999 was revealed. The characteristics from the assessment method are conformed to the major historical development processes in the study area and thus show flexibility for evaluation of regional soil erosion and ecological status. At the same time, the method retains most advantages in rapid ecological assessment method and pays more attention to dynamic variations rather than absolute status for regional soil erosion. It could also mitigate the limitations to regions and scales as encountered in other traditional methods, and is helpful to enhancing the assessment process for regional soil erosion and ecological quality in a dynamic manner. For large scale assessment, the presented method could be more flexible in data re use, and could save much time and expenses.