Effects Of The Biological Soil Crusts Growth On Soil Detachment Process

As a widely developed surface cover in arid and semi-arid areas,biological crusts（biocrusts）significantly affect the soil erosion process.Biocrusts protect soil from rainfall impact and runoff scouring,increase surface roughness and enhance soil erosion resistance.Affected by different growth stages and types of biocrusts,their effects on soil erosion are different.At present,the research on soil erosion is mostly focused on the effect of anti-scour and growth characteristics of biocrusts on soil detachment process,whereas the research on the effect of biocrusts type and their growth on the soil detachment process is less reported.In view of this,the algae crust and moss crust widely developed in the Loess Plateau were taken as the research objects in this study.The biological characteristics of algae crust,moss crust,and natural succession crust at different development stages were systematically studied by the methods of inoculation cultivation and variable slope flume erosion.The influence of the growth of biocrusts on the soil detachment process was clarified,and the relationship between soil detachment capacity,gully erodibility index and critical shear force,and the characteristic factors of the biocrusts were quantified.The fitting equation of soil detachment capacity based on the characteristics of the biocrusts was constructed.The results of this study are helpful to further understanding the mechanism of biocrusts affecting soil detachment.The main results are as follows:（1）The growth of biocrusts significantly increased biomass,thickness,cover,and roughness,and enhanced soil erosion resistance.After 176 days of growth,the biomass,thickness,coverage,and roughness of the algal crust treatment were168.4mg/g,3.31mm,80.04%,and 0.138,respectively,and the moss crust treatment were 147.5mg/g,2.96 mm,86.64%and 0.126,respectively,and the natural succession treatment was175.2mg/g,2.97mm,87.19%,and 0.131,respectively.Besides,the cohesive force,quality loss rate,and thickness loss rate of the algal crust treatment were 6.78,54.43%,and 32.19%,respectively,the moss crust treatment was 6.90,42.68%,and 22.08%,respectively,and the natural succession treatment was 6.90,40.92%,16.54%.The effect of enhancing soil erosion resistance in the early stage of growth and development of the three treatments was weak,and complete loss of soil after 29 days of growth.With the growth of biocrusts,their role in enhancing soil erosion resistance gradually increased.（2）The growth of biocrusts significantly reduced the soil detachment capacity,but there were differences among different biocrusts types.With the growth of biocrusts,the soil detachment capacity of algal crusts,moss crusts,and natural succession biocrusts was 0.16kg/m²·s,0.118kg/m²·s,0.236kg/m²·s,respectively.and decreased by92.56%,94.50%,and 89%than bare land.In general,the algal crusts and natural succession biocrusts were dominated by algae in the initial growth stage,and the soil detachment capacity was 2.01-4.07 times higher than that of the moss crusts treatment;after 176 days of growth,the soil detachment capacity of the natural succession biocrust treatment was 2.79 and 1.5 times lower than that of the algal crust and the moss crust treatment,respectively,which indicated that the biocrusts had a stronger ability to inhibit soil detachment during the natural succession process.（3）The growth of biocrusts significantly reduced the rill erodibility index and increased the critical shear force.With the growth of biocrusts,the erodibility indices of the rills for algal crusts,moss crusts,and natural succession crusts were 0.0252s/m,0.0139s/m,and 0.0583s/m,respectively,and decreased by 86.14%,92.35%,and 67.93%than bare land;the critical shear forces were 6.97Pa,4.98Pa,and 5.82Pa,which were4.99 times,3.66 times,and 4.27 times that of bare ground.Similar to the soil detachment capacity,algal crusts and natural succession biocrusts were mainly algae in the initial growth stage,and the erodibility index of the rill was larger,which was 2.87-5.13 times that of the moss crusts.Due to the rapid development of algal crusts in the early growth stage,the critical shear force of algal crusts was relatively large,which was 1.81-1.15times than that of moss crusts and natural succession biocrusts,respectively.In the later stage of growth,the critical shear force of the algal crusts and natural succession biocrust treatment was 1.39 and 1.33 times that of the moss crust treatment,respectively.（4）Biocrusts characteristic factors and soil properties significantly affected the soil detachment process.Biocrust biomass,thickness,coverage,roughness,and cohesion significantly reduced soil detachment capacity and rill erodibility index,and there was a significant negative correlation（p<0.01）,quality loss rate,thickness loss rate significantly increased the soil detachment capacity,and there is a significant positive correlation（p<0.01）;the thickness,roughness,and cohesion of the biological crust significantly increased the critical shear force,and there was a significant positive correlation between them（p<0.01 or p<0.05）.In general,the water flow shear force（τ）,biocrust thickness(C_TH),and cohesion force（Coh）were the main parameters that affect the soil detachment process on the slope covered by biocrust,which could better fit the soil detachment capacity.The function is Dc=10^-1.43·τ^2.071·C_TH^-0.507·Coh^-2.536（R²=0.54NSE=0.61 n=90）.