黄土高原六道沟小流域近30年来土壤侵蚀变化评价

Soil erosion evaluation of Liudaogou catchment in the Loess Plateau during the past 30 years

为了探讨退耕还林(草)工程对黄土高原六道沟小流域土壤侵蚀的影响,为黄土高原小流域土地利用规划与水土流失防治提供参考依据。结合航片、遥感影像与实地调查,采用土地利用转移矩阵与中国土壤流失方程(CSLE)分析黄土高原六道沟小流域1990—2017年近30年来的土地利用与土壤侵蚀时空变化。结果表明:1)1990—2017年间,小流域旱地持续减少,灌木林地、农村居民点和独立工矿用地持续增加,且2002年实施退耕还林(草)后,土地利用变化速率明显加快;2)近30年来小流域土壤侵蚀总体呈减弱趋势,年均土壤侵蚀模数从1990年的27.8 t/(hm^2·a)减少至2017年的7.2 t/(hm^2·a);微度侵蚀面积占比不断增加,强烈及以上强度面积比例不断减小;3)各土地利用类型中,独立工矿用地侵蚀强度最大,旱地次之,草地和灌木林地最小。研究结果证实,退耕还林(草)工程对六道沟小流域的土壤侵蚀起到了显著的遏制作用。

[Background]The Grain for Green Project has been implemented for approximately 20 years,aiming to alleviate flooding and soil erosion across China.It is required to systematically evaluate its impact on soil erosion of the small catchments in the Loess Plateau of China,which has long been characterized by severe water scarcity and serious soil erosion.[Methods]Field investigation was combined with aerial photographs and remote sensing images to acquire the distributions of various land uses as well as diverse soil and water conservation practices in the Liudaogou catchment in 1990,1995,2002,2010 and 2017.Land use transition matrices were employed to evaluate the spatio-temporal variations of land use during the nearly 30 years from 1990 to 2017,and soil erosion of the small catchment was assessed using the Chinese Soil Loss Equation(CSLE)integrating rainfall erosivity factor(R),soil erodibility factor(K),slope length factor(L),slope steepness factor(S),biological control factor(B),engineering control factor(E)and tillage factor(T).The value of R was acquired using the daily rainfall data of Shenmu,Shaanxi province during 1957-2014,K was obtained from the First National Water Conservancy Census and further calibrated using the runoff plot data,L and S were extracted from the 1∶10000 topographic map,B was estimated by vegetation coverage that derived from remote sensing products,and the values of E and T were assigned according to the related outcome of the First National Water Conservancy Census.[Results]1)The land use pattern substantially changed during 1990-2017,with the area of dryland persistently decreasing,and the areas of shrubland,rural residential land as well as industrial and mining land continuously increasing.Besides,the land use change apparently accelerated since the local implementation of the Grain for Green Project in 2002.2)In accordance with land use change,soil erosion generally weakened in the past 30 years,with the annual soil erosion rate decreasing by 74.1%,i.e.,from 27.8 t/(hm^2·a)in 1990 to 7.2 t/(hm^2·a)in 2017.Considering soil erosion intensity classes,the proportion of slight erosion was persistently increasing,whereas,the severe,extremely severe and most severe erosion occupied less and less areas.The area percentages of the latter three classes were only 2.6%in total in 2017.3)Among the land use types investigated,the industrial and mining land suffered from the most serious erosion,followed by dryland,and the grassland and shrubland possessed the least soil erosion rates.[Conclusions]The results demonstrate the critical role of the Grain for Green Project in inhibiting soil erosion in the Liudaogou catchment,which holds important implications for land use planning and soil and water conservation in the small catchments of the Loess Plateau,and perhaps other arid and semiarid regions.