黄土高原小流域植被恢复的土壤侵蚀效应评估

Effect of Revegetation on Soil Erosion in Small Watershed of the Loess Plateau

植被建设是治理土壤侵蚀的重要途径,特别是坡面土壤侵蚀。退耕还林还草是黄土高原乃至全国最大规模的植被建设工程,黄土高原是该工程的重点地区之一。小流域是土壤侵蚀综合治理的基本单元。通过退耕还林工程实施前后小流域土壤侵蚀的模拟和分析,可以为植被建设成效评估和调整治理策略提供参考。运用修正土壤流失方程RUSLE,在ARCGIS10.2平台下模拟了羊圈沟小流域1984年、1996年、2006年、2012年和2014年5个年份的土壤侵蚀,评估了退耕还林前后黄土高原小流域植被恢复对土壤侵蚀的影响。降雨侵蚀力R利用延安气象站30年（1984—2014年,除1999年外）的日降雨数据计算,LS因子利用将矢量化的1∶5 000地形图插值生成DEM提取;土壤可蚀性K因子利用2006年实测土壤理化数据计算,总结概括前人研究成果获取C、P因子值。研究结果表明：（1）各坡度带侵蚀都显著减弱,15°~25°,25°~35°和〉35°坡度带是中度以上侵蚀发生的主要区域。1984—2014年3种坡度带的侵蚀面积之和分别占总面积的44.93%,42.65%,35.78%,23.23%和22.98%;（2）退耕还林前后相比,土壤侵蚀强度显著降低：中度以上侵蚀面积急剧减少,土壤侵蚀转变为以微度、轻度和中度侵蚀为主,3类侵蚀面积之和在2006年、2012年和2014年分别占总侵蚀面积的26.53%,44.24%和43.47%;（3）土壤侵蚀模数呈现减小的趋势,从1984年到2014年,土壤侵蚀强度从15 327.57t/（km2·a）降至3 270.19t/（km2·a）,降低70%以上。总体上,土壤侵蚀明显降低,表明植被建设有效遏制了土壤侵蚀,退耕还林工程对水土保持和治理土壤侵蚀起到了显著的效果。

Vegetation construction was an important approach to control soil erosion,especially in the slope soil erosion.Converting cropland to forest and grassland was a largest vegetation construction project in Loess Plateau and even the whole country.In this study,the effects of revegetation on soil erosion under implementation of the Grain for Green Project were evaluated for five single years（1984,1996,2006,2012and2014）using the revised universal soil loss equation（RUSLE）supported by ARCGIS 10.2.Daily rainfall data of three decades（from 1984 to 2014,excluding 1999）of Yan＇an weather station was used to calculate the rainfall erodibility（R）.Values of topographical factor（LS）were extracted from digital elevation model,which was generated by applying interpolation based on topographic map with a scale of 1∶5 000.The K factor was obtained using physical and chemical properties of soil samples of study area,in 2006.Cand Pfactors were generally derived from previous studies on the Loess Plateau.Results showed that areas of moderate high,high and very high erosion declined sharply,and most of them transferred to very low,low and moderate.The average soil erosion rate decreased from 15 327.57t/（km2·a）in 1984 to 3 270.19t/（km2·a）in 2014.Slope belts of 15°~25°,25°~35°and 35°were the main areas of severe soil erosion.Thesethree slope belts accounted for 44.93%,42.65%,35.78%,23.23%and 22.98%of total study area from 1984 to 2014.Furthermore,the areas with very low,low and moderate erosion occupied 26.53%,44.24% and43.47% of the total area of the watershed in 2006,2012 and 2014,respectively.Generally,the soil erosion in Yangjuangou watershed reduced significantly.It was indicated that revegetation had positive effects on soil and water conservation and soil erosion,and the Grain for Green Project led to a success in soil erosion control.