Effects of biological soil crusts on soil detachment process by overland flow in the Loess Plateau of China

Biological soil crusts (BSCs) cover up to 60 to 70% of the soil surface in grasslands after the Grain for Green' project was implemented in 1999 to rehabilitate the Loess Plateau. However, few studies exist that quantify the effects of BSCs on the soil detachment process by overland flow in the Loess Plateau. This study investigated the potential effects of BSCs on the soil detachment capacity (D-c), and soil resistance to flowing water erosion reflected by rill erodibility and critical shear stress. Two dominant BSC types that developed in the Loess Plateau (the later successional moss and the early successional cyanobacteria mixed with moss) were tested against natural soil samples collected from two abandoned farmland areas. The samples were subjected to flow scouring under six different shear stresses ranging from 7.15 to 24.08 Pa. The results showed that D-c decreased significantly with crust coverage under both moss and mixed crusts. The mean D-c of bare soil (0.823 kg m(-2) s(-1)) was 2.9 to 48.4 times greater than those of moss covered soil (0.017-0.284 kg m(-2) s(-1)), while it (3.142 kg m(-2) s(-1)) was 4.9 to 149.6 times greater than those of mixed covered soil (0.021-0.641 kg m(-2) s(-1)). The relative detachment rate of BSCs compared with bare soils decreased exponentially with increasing BSC coverage for both types of BSCs. The D-c value can be simulated by flow shear stress, cohesion, and BSC coverage using a power function (NSE 0.59). Rill erodibility also decreased with coverage of both crust types. Rill erodibility of bare soil was 3 to 74 times greater than those of moss covered soil and was 2 to 165 times greater than those of mixed covered soil. Rill erodibility could also be estimated by BSC coverage in the Loess Plateau (NSE 0.91). The effect of crust coverage on critical shear stress was not significant. Copyright (c) 2015 John Wiley & Sons, Ltd.