退耕驱动的近地表特性变化对土壤侵蚀的潜在影响

Potential effects of changes in near soil surface characteristics driven by farmland abandonment on soil erosion

黄土高原是我国、乃至全球土壤侵蚀最严重的区域之一,侵蚀强度及时空分布特征受近地表特性的显著影响。退耕还林(草)工程大面积的有效实施,势必会引起近地表特性(土壤理化性质、植被茎秆、枯落物、生物结皮、根系系统)的显著变化,进而对坡面径流的水动力学特性及侵蚀过程产生影响。本文从退耕驱动的近地表特性变化、近地表特性变化对坡面径流水动力学特性的影响、近地表特性变化对土壤侵蚀过程(土壤分离、泥沙输移、泥沙沉积)的影响及其机制、区域土壤侵蚀对退耕的响应4个方面较为系统地总结近几十年国内外的研究成果,并提出了目前亟待强化的研究领域。这对理解退耕坡面土壤侵蚀过程及其动力机制、建立植被覆盖坡面的土壤侵蚀过程模型、评价退耕坡面的水土保持效益,具有重要的理论意义。

[Background] The Loess Plateau is one of the most erodible regions in China,even over the world.The erosion intensity and properties of spatial and temporal distribution are significantly affected by near soil surface characteristics.The effective implementation of the ＂Grain-for-Green＂ project certainly causes the great changes in near soil surface characteristics,i.e.soil physiochemical properties,vegetation stem,litter,biological soil crust,and root system,which will lead to great influences on hydraulics of overland flow and soil erosion processes.[Methods] We collected 74 references from relevant studies in the past several decades,and comprehensively analyzed them.We presented the review results by 1） the changes in near soil surface characteristics driven by ＂Grain-forGreen＂;2） the effects of changes in near soil surface characteristics on hydraulics of overland flow;3）the potential effects of changes in near soil surface characteristics on soil erosion processes（soil detachment,sediment transport,and sediment deposition） and their mechanisms;4） the responses of regional soil erosion to ＂Grain-for-Green＂;and 5） research prospects in this field.[Results]1） Therewere great changes in near soil surface characteristics,i.e.soil physiochemical properties,vegetation stem,litter,biological soil crust,and root system.2） The effects of changes in near soil surface characteristics on hydraulics of overland flow after ＂Grain-for-Green＂ project were related to plant flexibility,density and arrangement,types of litter,coverage and thickness,type of biological crusts,a variety of factors,community structure and coverage etc.3） Soil detachment was decreasing with the years of ＂Grain-for-Green＂increasing,also fluctuating due to many factor,and finally reached stable.Vegetation from ＂Grain-for-Green＂ decreased the sediment transport in the runoff duo to the existence of vegetation stems and bio-crust though the mechanisms were extremely complex.Moreover,grass after ＂Grain-for-Green＂ significantly retained sediment.4） In general,the changes in near soil surface characteristics enhanced the soil resistance to both of overland flow and soil erosion,though the mechanisms have not been fully understood yet.5） Thus more studies are needed in the future a） the effects of changes of near surface characteristics driven by ＂Grain-for-Green＂ on the hydraulic characteristics of runoff on slope and its mechanism;b） the separation capacity model on farmland under the condition of ＂Grain-for-Green＂,especially the functional relationship between rill erodibility,critical shear stress and near surface characteristics;c） the overland flow sediment transport capacity equation under the condition of vegetation restoration;d） and sediment deposition process and simulation on vegetation covered hillslopes.[Conclusions] This review is conducive to understand soil erosion processes and their dynamic mechanism,to develop process-based soil erosion models,and to evaluate soil and water conservation benefits for vegetation covered hill-slopes.