北洛河上游流域土壤侵蚀变化及影响因素分析

Analysis of soil erosion changes and its influencing factors in the upper reaches of Beiluo River watershed

为探究退耕背景下北洛河上游流域土壤侵蚀变化规律,采用修正的通用土壤流失方程并结合GIS空间分析,对比研究退耕还林前后北洛河上游流域2个时段(1991—2000年及2001—2010年)土壤侵蚀及降雨侵蚀力和植被覆盖度的变化,定量分析植被覆盖及降雨侵蚀力变化对土壤侵蚀的影响。研究表明:流域多年平均年降雨侵蚀力由退耕还林前的1390.2 MJ·mm/(hm^(2)·h·a)下降到退耕还林后的1260.7 MJ·mm/(hm^(2)·h·a),降雨侵蚀力的下降导致流域土壤侵蚀强度降低;在退耕还林工程的作用下,流域植被覆盖度大幅增加,由退耕还林前的30.8%增加到退耕还林后的47.6%,植被恢复也大大削弱流域土壤侵蚀强度;在退耕还林工程和降雨变化的共同作用下,流域年均土壤侵蚀模数由退耕还林前的8078.9 t/(km^(2)·a)下降到退耕还林后的3060.7 t/(km^(2)·a),减幅为62.1%;退耕还林工程和降雨变化对减轻流域土壤侵蚀的贡献率分别为85%和15%,表明退耕还林工程对控制流域土壤侵蚀起到关键作用。研究结果为评价黄土高原生态恢复的水土保持效益提供有价值的数据资料。

[Background]The upper reaches of Beiluo River watershed,located in the hinterland of the Loess Plateau,is one of the main source districts of coarse sediment of the middle Yellow River,and is also the key area for soil erosion control and ecological construction in China.The Grain for Green(GFG)project implemented in 1999,resulting in soil erosion process in the upper reaches of Beiluo River watershed changing greatly.Clarifying soil erosion changes and driving factors in the upper reaches of Beiluo River watershed before and after the GFG project is of great significance for promoting green development and health management of the Yellow River watershed.[Methods]The revised universal soil loss equation was combined with GIS spatial analysis to study the spatial and temporal characteristics of soil erosion,rainfall erosivity and vegetation coverage before and after the GFG project(1991—2000 and 2001—2010)in the upper reaches of Beiluo River watershed.And the contribution rates of the GFG project and precipitation change on soil erosion change in the watershed were analyzed.[Results]1)The results showed that the mean annual rainfall erosivity decreased from 1390.2 MJ·mm/(hm^(2)·h·a)before the GFG project to 1260.7 MJ·mm/(hm^(2)·h·a)after the GFG project,a decrease of 9.3%.Rainfall erosivity decreased in 99.3%of the whole watershed.The decrease of rainfall erosivity reduced the intensity of soil erosion in the watershed.2)The vegetation coverage of the watershed increased from 30.8%before the GFG project to 47.6%after the GFG project,with an increase of 54.5%.About 88.3%of the area showed an increasing trend of vegetation coverage.The vegetation coverage in Wuqi county of the southeast was significantly higher than that in Dingbian county of the northwest.The increase of vegetation coverage greatly weakened the intensity of soil erosion in the watershed.The combined effect of the GFG project and the change in precipitation resulted in soil loss decreased from 8078.9 t/(km^(2)·a)before the GFG project to 3060.7 t/(km^(2)·a)after the GFG project,with a decrease of 62.1%.3)The contribution rate of the GFG project and precipitation change to reducing soil erosion in the watershed was 85%and 15%respectively.The contribution rate of the GFG project to reducing soil erosion in Wuqi county and Dingbian county was 86%and 82%respectively.[Conclusions]The degree of soil erosion reduction in the watershed is dominated by the GFG project characterized by vegetation coverage change.The results provide valuable data for evaluating the benefits of soil and water conservation of ecological restoration on the Loess Plateau.