The Influence Of Biological Soil Crust Covering Slope On The Process Of Runoff And Sediment Production

Biological soil crusts are widely distributed in the Loess Plateau,and their coverage can reach more than 70%.Covering the surface with biological soil crusts can significantly affect the process of runoff and sand production on slopes.Affected by the types and growth characteristics of biological soil crusts,there are also significant differences in their effects on the process of soil invasion.In this study,moss crusts and algae crusts widely distributed in loess hilly and gully regions were selected as the research objects.Through artificial cultivation,the influence of water and fertilizer coupling conditions on the growth characteristics of biological crusts was clarified.At the same time,by setting different rainfall gradients(60,90,120,150 and 200mm/h)and crust coverage(15,30,40,50,60 and 80%),the impact of rainfall intensity and crust coverage on slopes was studied.The influence of surface hydrodynamic parameters,runoff and sedimentation processes and their mechanism of action,respectively quantified the relationship between rainfall intensity and bio-crust coverage and runoff and sediment yield on slopes,and clarified the runoff under bio-crust coverage.The interaction of sediment and sediment provides theoretical support for evaluating the benefits of soil and water conservation of vegetation in the Loess Plateau.The following main conclusions are reached:(1)It is determined that the best combination of water and fertilizer for biological crust cultivation is:2 L/2 days+1 L/2 days Hoagland nutrient solution.After 60 days of artificial cultivation of moss crust and algae crust through the coupling of water and fertilizer,the coverage,biomass and thickness of moss crust were 53.52～73.48%,24.88～52.29 g/m~2 and 2.29～4.09 mm,respectively.The chlorophyll of the algae crust was 0.24～1.07 mg/g.In the treatment with the same amount of water and Hoagland nutrient solution,the water stability of moss crust and the kinetic energy of raindrops were higher than that of algae crust treatment.Under natural conditions,the moss crust biomass,thickness,sediment loss rate and raindrop kinetic energy range from 21 to 169.33 g/m~2,7.95 to 11.25 mm,42.51 to23.68%and 0.057 to 0.13 J.The algal crust chlorophyll,The range of shock damage time and raindrop kinetic energy is between 2.76～14.72 mg/g,10～75″and0.0011～0.0015 J.(2)The influence of moss crust on the hydrodynamic parameters of slope is stronger than that of algae crust.With the increase of rainfall intensity,the runoff rate increased by 1.43～60.12%.The flow patterns of algal crust and moss crust are laminar,the Flow regime of algal crust is jet flow,and moss crust is jet flow under200 mm/h rain intensity.Moss crust slope surface flow resistance coefficient,Manning coefficient,runoff shear force and water flow power are all higher than algal crust,which are 2.14～10.44,1.61～3.70,1.44～2.21 and 1.01～1.60 times of algal crust,respectively;The unit water flow power and section unit energy of moss crust are lower than that of algae crust,and they are reduced by 10.53～54.19%and12.04～64.09%respectively compared with algae crust.With the increase of rain intensity,the yield of algal crust and moss crust on the slope gradually increased.Under the rain intensity of 60～200 mm/h,the runoff rate and total runoff on the moss crust slope increased by 37.55～6.86%compared with the algae crust slope.Compared with the bare soil treatment,the average runoff rate of moss crust slope increased by 2.32%,while the algal crust decreased by 5.87%.In general,the total runoff covered by biological crusts increased with rainfall intensity,and the two showed a very significant linear functional relationship(R~2>0.90;P<0.01).(3)The sand yield of the moss crust covered slope was significantly lower than that of the algal crust and the control bare land.With the increase of rain intensity,the ability of the algal crust and moss crust to inhibit the sand production of the slope decreased.The sand yield rate and sand yield of the moss crust covered slope were 14.31 g/min and 867.72 g,respectively,which were reduced by 88.43%compared with the algae crust.With the increase of rain intensity,the ability of algae crust and moss crust to inhibit sand production on slopes decreased;compared with bare land slopes,the sand production of moss crusts on slopes decreased by15.10～92.30%.The sediment yield on the algae crust slope surface decreased by26.47～93.52%under the rain intensity of 60,90 and 150 mm/h,while the sand yield increased under the rain intensity of 120 and 200 mm/h.86.75 and 85.88%.With the increase of rainfall intensity or flow rate,both the algal crust and moss crust covered slope surface sediment yield increased exponentially(R~2≥0.81;P<0.05).Regarding the erodibility index between moss crusts,the slope covered by moss crusts is significantly lower than that of algal crusts.Under the rain intensity of 60～200mm/h,the erodibility index between moss crusts and rills is 25.77～88.84%lower than that of algal crusts..(4)With the increase of crust coverage,the hydrodynamic parameters of algal crust and moss crust covered slopes showed significant differences,and both the runoff rate and runoff showed a decreasing trend.The flow pattern on the slope covered by biological crust is laminar flow,and the flow pattern on the slope covered by algae crust is rapid flow,and the flow pattern of moss crust is slow flow.Moss crust slope surface flow resistance coefficient,Manning coefficient,runoff shear force and water flow power are overall higher than algal crust,which are 21.63～451.76,3.15～11.42,5.71～30.78 and 1.07～2.44 times of algae crust respectively;The unit current power and section unit energy are lower than the algal crust,which is 59.56～89.99% and 29.72～71.82% less than the algal crust,respectively.When the crust coverage increased from 15% to 80%,the runoff rate of moss crust slope decreased significantly,and it was 1.07～1.30 times that of algae crust.Compared with bare land slopes,the runoff of algal crust and moss crust increased by 42.61 and 69.50% on average.As the degree of crust coverage increases,the runoff of moss crusts increases linearly(R~2=0.82;P<0.01).Algal crusts only show a decreasing trend,and there is no significant functional relationship.(5)With the increase of crust coverage,the influence of moss crust on the sand production process of slope is greater than that of algae crust.Compared with bare land slope,the sand production of algae crust and moss crust decreased respectively.63.61～78.26% and 9.63～89.55%.When the crust coverage is < 40%,the algal crust sand production rate is lower,which is 52.25～66.51% less than that of the moss crust;and when the crust coverage is ≥40%,the sand production rate of moss crust is lower,which is 32.52～51.92% less than that of algae crust.The algal crust was reduced by 32.52～51.92%.Both the algal crust and moss crust slope surface sediment yield decreases linearly with the increase of coverage(R~2≥0.30;P<0.01),When moss crust coverage reaches 40% and algae crust coverage reaches 50%,its ability to inhibit soil erosion tends to be relatively stable.For moss crusts,the sediment yield can be characterized as the power function relationship of coverage,remaining crust thickness and runoff;while for algal crusts,there is no significant correlation between sand yield,crust characteristics and runoff.When the crust coverage is < 40%,the erodibility index between the algal crust rills is lower,which is 37.77～58.35% less than that of the moss crust;When the crust coverage is ≥40%,the moss crust is lower,which is 36.93～58.73% less than the algal crust.