Effect Of Biological Soil Crusts Development On Slope Water Erosion Process

The loess Plateau is one of the most serious soil erosion areas in China.With the implementation of the project of"Grain for Green"in 1999,biological soil crust has been widely developed,and its coverage rate can reach more than 70%,which plays an important role in reducing soil erosion in this region.The impact on the process of biological soil crusts on the process of abortion of the slope surface has been studied,but the differences in soil erosion caused by the type of biological soil crusts still lack systemic research.In addition,the impact of the development of biological soil crusts on the outflow of the slope surface is not clear.Based on this,this study is based on the extensive development of biological soil crusts after returning farmland of the Loess Plateau,setting three treatment of algal crust,moss crust and natural succession crust,using inoculation to cultivate biological soil crusts and simulation rainfall methods,systematically study algal crust,moss crust and natural succession crust development characteristics and its impact on soil traits.The response characteristics of the development process,the quantitative slope surface production sand and the interaction between the characteristics of biological soil crusts and the soil trait,reveal the mechanism of the biological soil crusts development process of the soil erosion of the slope surface,and provide theoretical theory for the recovery of soil and soil conservation benefits of the Loess Plateau.The main conclusions are as follows:(1)Biological soil crusts development can significantly increase the coverage,thickness and biomass.After 5 months(176 days)of growth and development,the coverage,thickness and biomass of algal crust,moss crust and natural succession biological crust were 1.90 to8.86,5.51 to 8.70 and 1.98 to 17.29 times of the initial growth(29 days),respectively.With the increase of development time,the coverage,thickness and biomass of the three treatments increased exponentially(R~2(?)0.81,P<0.01).After 58 days of growth,algal crust and natural succession biological crust gradually evolved into moss crust.The coverage,thickness and biomass of moss crusts were higher than those of algal crust and natural succession biological crust at 132 days before growth,but there were no significant differences among the three kinds of biological soil crusts.(2)The growth and development of crusts can significantly improve the surface roughness and soil cohesion.After 176 days of cultivation,the surface roughness of algal crust,moss crust and natural succession biological crust increased by 4.25,4.58 and 4.62 times,respectively,and the cohesion increased by 72.47%,75.59%and 75.59%,compared with that of bare soil.The surface roughness and cohesion of the three treatments increased exponentially with the increase of the days of crust growth(R~2(?)0.66,P<0.01).The change of crusts growth characteristics was the main factor affecting soil properties.The surface roughness and cohesion increased exponentially with the increase of crusts coverage,thickness and chlorophyll(R~2(?)0.74,P<0.01).In addition,under the same incubation time,the effect of moss crust on surface roughness and soil cohesion was stronger than that of algal crust.(3)The development of biological soil crust can significantly affect the flow pattern of overland flow and increase the runoff resistance coefficient and shear force.The runoff patterns of algal crust,moss crust and natural succession biological crust were laminar flow.In the first 58 days of crust growth,the flow pattern was rapids,and then it was slow flow.With the increase of growing days,the runoff velocity of algal crust,moss crust and natural succession biological crust decreased exponentially(R~2(?)0.82,P<0.01),and the Darcy-weisbach resistance coefficient and flow shear force of flow increased exponentially(R~2(?)0.85,P<0.01).The runoff velocity decreased exponentially(R~2(?)0.73,P<0.01)and the Darcy-weisbach resistance coefficient increased exponentially(R~2(?)0.73,P<0.01)with the increase of crust coverage,thickness and biomass.(4)The growth and development of biological crust can effectively shorten the initial runoff generation time and promote runoff generation on slope.After 176 days of cultivation,the initial flow-producing time of algal crust,moss crust and natural succession biological crust decreased by 60.90%,65.79%and 69.92%,respectively,compared with bare land,and the runoff increased by 16.19%,21.92%and 12.98%,respectively.The initial flow-producing time of algal crusts,moss crusts and natural biological crusts decreased with the increase of crusts growth days,and the natural biological crusts decreased exponentially(R~2(?)0.73,P<0.01).There was no significant difference in runoff at other growth stages except 92 days when it was relatively high.(5)The development of biological crusts can reduce the erodibility index between soil rills and sediment yield on slope.After 176 days of cultivation,the interrill erodibility of algal crusts,moss crusts and natural succession biological crusts decreased by 96.65%,97.32%and98.24%,respectively,and the sediment content decreased by 96.34%,97.03%and 98.14%,respectively,compared with bare soil.The intergully erodibility of algal and moss crust decreased exponentially with the increase of the days of crusts growth(R~2(?)0.78,P<0.05).The sediment yield of the three biological crusts showed a decreasing trend,and the sediment yield of the moss crusts treatment was lower than that of the algae crusts and the natural succession biological crusts in different degrees in 132 days before growth,but there was no significant difference in the latter three treatments.(6)The change of biological crust development and its effect on soil properties and slope hydrodynamics can significantly affect the sediment yield process on the slope.With the increase of crust coverage and chlorophyll,sediment yield decreased exponentially(R~2=0.71,P<0.05).The sediment yield also decreased exponentially with the increase of surface roughness and soil cohesive force(R~2(?)0.73,P<0.05).With the decrease of runoff velocity,sediment yield decreased exponentially(R~2(?)0.71,P<0.05).By further regression analysis,soil adhesion,crust coverage and slope runoff can better simulate sediment yield(R~2=0.69,NSE=0.56).