Effects of shrub-grass patterns on soil detachment and hydraulic parameters of slope in the Pisha sandstone area of Inner Mongolia,China

The characteristics of soil holding capacity for different shrub-grass patterns are important to research the mechanisms regulating vegetation on slopes.The objective of this study was to describe the characteristics and mecha-nisms of soil erosion and hydraulic parameters under differ-ent vegetation patterns in the Pisha sandstone area of Inner Mongolia on lands of 8°slope gradient.We carried out field scouring experiments on five different shrub-grass patterns as treatments,viz no shrubs(GL),shrubs on the upper part of the slope(SU),middle part of the slope(SM)and lower part of the slope(SL).We designated bare slope(BL)as the control.We employed three different water flow rates(15,20,30 L·min^(−1)).Our results showed that the contribution of plant root systems to slope sediment reduction ranged from 64 to 84%.The root systems proved to be the main contributing factor to reduction of erosion by vegetation.The relationship between soil detachment rate,stream flow power,and flow unit stream power under different scouring discharge rates showed that soil detachment declined in rank order as:BL>GL>SU>SM>SL.The SL pat-tern had the lowest soil detachment rate(0.098 g·m^(−2)·s^(−1)),flow stream power(2.371 W·m^(−2)),flow unit stream power(0.165 m·s^(−1))and flow shear stress(16.986 Pa),and proved to be the best erosion combating pattern.The results of decision coefficient and path analysis showed that stream power was the most important hydraulic parameter for describing soil detachment rate.The combination of stream power and shear stress,namely Dr=0.1ω−0.03τ−0.56(R^(2)=0.924),most accurately simulated the soil detachment characteristics on slopes.Our study suggests that the risk of soil ero-sion can be reduced by planting shrub-grass mixes on these slopes.Under the conditions of limited water resources and economy,the benefit of sediment reduction can be maxi-mized by planting shrubbery on the lower parts of slopes.

Impacts of different surface features on soil detachment in the subtropical region

Near-surface features have a great influence on runoff and detachment processes by overland flow,but the contributions are still unclear on steep slopes with yellow soil in subtropical humid regions.Field scouring experiments were conducted to investigate how near-surface features affect hydraulic parameters and detachment rate by overland flow.Five treatments and a baseline(disturbed rootless bare cropland)were designed to identify the contributions from stem-leaves,litter,biological soil crusts(BSCs),root systems and non-disturbance,respectively.The results showed that(1)the values of velocity,Reynolds number and Froude number for vegetated slopes were significantly lower than that of baseline,and stem-leaves made a greater contribution(average of 47.30%)to reducing kinetic energy than the other features;(2)the total contribution rate of grassland was 99.38%,and of this total,1.19,1.44,2.49,49.79 and 44.47%reductions were attributed to the stem-leaves,litter,BSCs,root systems and non-disturbance,respectively.Root system and non-disturbance dominated the detachment rate reduction;(3)with increasing flow rate or slope gradient,the total contribution rate remained between 98%and 100%;and(4)for each treatment,the relationship between detachment rate and hydraulic parameters remained constant,and the stream power was the best predictor to detachment rate.The study results are helpful in evaluating the effects of near-surface features on erosion control and providing reference for government decision-makers to choose appropriate soil conservation and management practices.