Effects of rock fragments on soil erosion by water at different spatial scales: a review

Abstract

This paper reviews the various effects of rock fragments on soil erosion by water. Since these effects are scale dependent, they are investigated at three different nested spatial scales: the microplot (4 × 10 −6–10 0 m 2), the mesoplot (10 −2–10 2 m 2) and the macroplot (10 1–10 4 m 2). For each scale the corresponding process mechanisms are discussed. Particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes. At the mesoplot scale, i.e. on interrill areas, rock fragments at the soil surface can have negative as well as positive effects on sediment yield. These ambivalent effects are conditioned by the type of fine earth porosity, soil surface slope, vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion. At the microplot scale, i.e. the soil surface area which is covered by a single rock fragment, and at the macroplot scale, i.e. upland areas where both interrill and rill erosion takes place, rock fragments at the soil surface have a negative effect on sediment yield. In these two scales rock fragments can thus be considered as natural soil surface stabilizers. At the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function. The scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses. These findings have implications for erosion modelling and soil conservation.