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

Abstract

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 (Dc), 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 Dc decreased significantly with crust coverage under both moss and mixed crusts. The mean Dc 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 Dc 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 © 2015 John Wiley & Sons, Ltd.

Soil erodibility as impacted by vegetation restoration strategies on the Loess Plateau of China

“…The BD of the vegetationrestored lands decreased significantly compared with the slope cropland (Table II). This result agrees with the results of Liu et al (2016), who found that BD decreased significantly with vegetation restoration on the Loess Plateau. Cerdà (1996b) also found that soil bulk densities of slope positions covered by vegetations were significantly lower than those of bare positions in Spain.…”

Effects of biological crust coverage on soil hydraulic properties for the Loess Plateau of China

“…The differences in the soil hydraulic properties and soil properties between BSC‐covered soils and controls were detected using an independent sample t test. To draw a more general conclusion regarding the potential effects of BSC coverage on soil hydraulic properties, the relative soil sorptivity under a pressure of 0 cm ( RS 0 ) was calculated as the ratio of the absolute soil sorptivity at the location covered with BSCs under a pressure of 0 cm to the absolute soil sorptivity of the bare control under a pressure of 0 cm (Knapen et al, ; Liu et al, ). The relative soil sorptivity under a pressure of −3 cm ( RS 3 ), the relative saturated hydraulic conductivity ( RK s ), the relative wetting front depth ( RWFD ), and the relative mean pore radius ( Rλ m ) were calculated using the same approach as for RS 0 .…”

Quantifying the surface covering, binding and bonding effects of biological soil crusts on soil detachment by overland flow

“…It is widely accepted that the later successional BSCs composed of lichens and mosses growing above the soil surface add greater roughness than the early successional cyanobacteria crust (Belnap, ; Rodríguez‐Caballero et al ., ). Moreover, many studies have indicated that BSCs have the ability to enhance soil aggregates, resulting from the combination of physical binding effect (cyanobacteria filaments and moss rhizoids) and extruded bonding effect (polysaccharides and organic gels extruded by the cyanobacteria components) (Belnap, ; Chamizo et al ., ), thus decreasing the overland flow and soil detachment rate (Liu et al ., ). Nevertheless, some other studies reported that BSCs reduced infiltration due to extrusion of hydrophobic compounds, which swell upon wetting, clogging soil pores, and enhancing runoff rate and soil detachment capacity by flowing water (Belnap, ; Wang et al ., ).…”

“…In general, BSCs develop from the early‐successional cyanobacteria crust to the late‐successional lichen and moss crusts (Ochoa‐Hueso et al ., ). Although BSCs represent a small fraction of the soil profile, they profoundly influence many soil surface characteristics known to affect hydrological processes (Belnap, ; Chamizo et al ., ; Rodríguez‐Caballero et al ., ; Liu et al ., ). Previous studies reported that the presence of BSCs contributes cover and roughness to the soil surface, which absorb the energy of falling raindrops, modify soil surface interactions, and reduce shear effect and the velocity of overland flow, thereby minimizing the detachment of soil particles (Belnap, ; Rodríguez‐Caballero et al ., ).…”

“…Liu et al . () quantified the effects of moss crust and mixed crust on the soil detachment process by overland flow on abandoned farmlands of the Loess Plateau and demonstrated that soil detachment capacity decreases exponentially with increase in BSC cover.…”