Effects and Mechanism of Biocrusts on Soil Detachment Process by Overland Flow in the Three Gorges Reservoir Area

The study quantified the effects of moss-dominated biocrusts on soil detachment capacity(Dc) and soil erosion resistance to flowing water in the Three Gorges Reservoir Area. Potential factors driving soil detachment variation and their influencing mechanism were analyzed and elucidated. Five levels of coverage treatments(1% ～ 20%, 20% ～ 40%, 40% ～ 60%, 60% ～ 80% and 80% ～ 100%) were designed and a nearby bare land was taken as control in a moss-dominated site. Undisturbed soil samples were taken and subjected to flow scouring in a hydraulic flume under six shear stresses ranging from 4.89 to 17.99 Pa. The results indicated that mean Dc of moss-crusted soil varied from 0.008 to 0.081 kg/(m~2·s), which was 1.9 to 21.0 times lower than that of bare land(0.160 kg/(m~2·s)). Rill erodibility(Kr) of moss-crusted soil ranged from 0.009 5 to 0.000 9 s/m, which was 2 to 20 times lower than that of bare land(0.018 7 s/m). Both relative soil detachment rate and Kr showed an exponential decay with increasing biocrust coverage, whereas the critical shear stress(τc) for different biocrust coverage levels did not differ significantly. Biocrust coverage, soil cohesion, and sand content were key factors affecting Dc, while biocrust coverage and soil bulk density were key factors affecting Kr. A power function of flow shear stress, soil cohesion, and biocrust coverage fitted well to estimate Dc(NSE=0.947). Our findings implied that biocrusts prevented soil detachment directly by their physical cover and indirectly by soil properties modification. Biocrusts could be rehabilitated as a promising soil conservation measure during ecological recovery to enhance soil erosion resistance in the Three Gorges Reservoir Area.