水蚀流域土地覆被格局土壤保持能力空间分布式评价

Spatial distribution assessment of the soil conservation capacity of land cover pattern in catchments dominated by rainfall-triggered erosion

以丹江口水库以上的汉江流域为例,利用植被覆盖度、坡度加权的上游有效汇流面积空间分布型式和驱动-阻力耦合空间分布拟合函数2个指标,评价水蚀流域土地覆被格局土壤保持能力,并基于研究区14个子流域水文站泥沙资料进行验证。结果表明:汉江干流沿岸河谷盆地和丹江口水库周边丘陵区子流域是研究区城镇和农田的主要分布区,植被覆盖度低,距离汉江较近,当前覆被格局土壤保持能力相对较低,是河流泥沙的主要直接来源地;有效汇流面积空间分布型式和驱动-阻力耦合空间分布拟合函数能有效反映流域泥沙输出,可作为评价流域土地覆被格局土壤保持能力的指标。该评价方法基于土地覆被格局与土壤侵蚀的作用机制,简单易行,可为评价土地覆被格局土壤保持能力、土地覆被格局变化的土壤侵蚀效应提供一种简捷的途径。

Taking upper Han River basin as case region, the soil conservation capacity of land cover pattern was assessed. Two indictors integrating fraction of vegetation cover （fc） and slope （S） were developed and applied in the assessment. One indicator is the spatial distribution pattern of upper effective catchment area weighted by fe and S, and the other is the spatial distribution pattern of the coupling of driven force and resistance relevant to soil erosion. The efficiency of the two indicators was tested using the sediment delivery data of 14 gauged stations in the study area. The results imply that the adjacent sub-watersheds of the river trunk are the main direct source areas of sediment. This situation can be attributed to the low soil conservation capacity of land cover pattern resulted from the low vegetation cover and short flow path length to the river trunks. The two indicators are confirmed effective to indicate the sediment yield at watershed level, and reliable tools for evaluating soil conservation capacity of a given land cover pattern. The approach developed in this study is based on the mechanism of the interaction between land cover pattern and soil erosion, and highly feasible. It provides an easy-to-use avenue for assessing the soil conservation capacity, and the impacts of land cover pattern change on soil erosion.