黄土丘陵区坡面形态和植被组合的土壤侵蚀效应研究

The Effects of Slope Configuration and Vegetation Pattern on Soil Erosion in the Loess Hilly Area

以位于陕北黄土丘陵区的羊圈沟流域为重点研究区,针对不同坡面类型(坡长、坡形、坡度)和植被组合进行野外土壤采样,利用137Cs元素示踪方法评估坡面的土壤侵蚀效应。研究发现:1坡面形态对土壤侵蚀具有重要影响。自坡顶至坡脚,"直-凹"组合的坡型一般具有相对较低的土壤侵蚀模数,整体上起到"汇"的作用;但"凹-直/凸"组合的坡型具有相对较高的土壤侵蚀模数,在土壤侵蚀方面起到"源"的作用;其他坡型,如直坡、凸坡、"直-凸"和复杂性坡型的土壤侵蚀模数介于两者之间。2坡面不同植被空间配置对土壤侵蚀的影响具有明显差异。研究发现,坡面植被组合(自坡顶至坡脚)为荒草地-果园、有林地-其他植被类型组合和荒草地-其他植被类型的坡面具有相对较低的土壤侵蚀模数,起到了一定"汇"的功能,但人为干扰较为强烈的景观坡面(无水土保持措施)具有相对较高的土壤侵蚀模数,整体上表现为土壤侵蚀的"源"区。

Land use/land cover and slope configuration are important factors affecting soil erosion in the gully and hilly area of the Loess Plateau. However, most work conducted in China against soil erosion in the loess plateau mainly focused on vegetation restoration, and few of them is concerned with the influences of slope configuration and vegetation combination along the slope transacts. The combination of the slope forms and vegetation patterns in the hill-slopes may give rise to different results to the soil erosion process, to be a source or a sink. It is, to great extent, determined by the slope configuration, the position of vegetation on the hill slope, as well as their combination. In this study, the effects of slope configuration and vegetation pattern on soil erosion in the loess hill-slope were explored by using137 Cs isotope method and extensively field sampling in Yangquangou catchment of the Northern Shaanxi Province. In total, 118 sampling sites in 25 slope profiles are selected, and these slopes are classified into 6 types according to the configuration and 8 groups based on the vegetation patterns. The results show that： 1） Slope configuration will have significant impacts on soil erosion. In general, the slope configuration with straight form in the upper hill-slope and concave form in the lower hill-slope may have the lowest soil erosion modus, which will become a sink in term of soil erosion as a whole. However, the slope configuration with concave form in the upper hill-slope and straight/convex form in the lower hill-slope has the highest soil erosion modus. This slope may function as a source in term of soil erosion. The soil erosion effects of the other slope configurations fall in between the above two slope configurations. 2） Much difference exists on soil erosion regarding to different vegetation patterns on the loess hill-slope. It was found that the loess hill-slope with wild grassland or woodland in the upper hill-slope and orchard or other vegetation types in the lower hill-slope may have the lowest erosion modus, which plays as a sink in terms of soil erosion from the whole slope. However, the slope with strong human disturbance, for example the sloping farmland, will have the highest soil erosion modus, which plays as the source of soil erosion as a whole. 3） For controlling soil erosion, planting mature forests and grasses in the upper and middle position of loess hill-slope may remarkably reduce the overall soil erosion and sediment yields in the entire watershed.The results are valuable for land-use pattern optimization in the loess hill-slope by identifying the potential risky area of soil erosion in both slope configurations and vegetation patterns. And also, it is helpful for sustainable land use planning and ecosystem management at catchment in the loess plateau.