Effects Of Soil Crusts On Runoff And Erosion In The Serious Erosion Degradation Region Of Red Soil

In the serious erosion degradation region of red soil,there is a scene of"green mountains in the distance,soil and water flow in the near future",and the soil and water loss under the forest is more serious.With the implementation of the ecological restoration project,the erosion environment has changed,and some biological crusts have been widely developed under the forest(grass)gaps in some degraded lands in the area.biological crusts covering the surface can significantly affect the process of soil and water loss on the slope.however,due to the influence of regionality and crust coverage,there are obvious differences in the process of soil and water loss.In this paper,biological crusts of severely eroded degraded land in Hetian Town,Changting County,Fujian Province,were studied by using a portable simulated rainfall system to conduct rainfall experiments with four rain intensities(0.5,1.0,1.5 and 2.0 mm/min)and four crust cover degrees(20%,40%,60%and 80%).By studying the effects of different rainfall intensities and crust cover on the physical properties,process of runoff and sediment yield,and hydrodynamic process of granite red soil,and quantitatively analyzing the correlation between rainfall intensity,crust cover and slope erosion process.It can reveal the effect of soil and water conservation under the influence of different factors,and also provide theoretical support for the effective prevention and control of soil erosion.The main conclusions are as follows:(1)Different rainfall intensities can significantly affect the soil erosion process on the slope.Under the rainfall intensity of 0.5-2.0 mm/min,the runoff rate and cumulative runoff of crusted slopes increased with the increase of rainfall intensity.The initial runoff time of the crusted slope was significantly higher than that of the control slope.The results showed that the crust covered significantly delayed the runoff on the slope and reduced the runoff,but with the increase of the rainfall intensity,the delaying effect gradually decreased.There was a very significant power function relationship between the rainfall intensity and the cumulative runoff in each treatment(R~2>0.99;P<0.01).The soil erosion rate and accumulated sediment amount on the slope surface increased with the increase of rainfall intensity.Under the four rainfall intensities,the order of the total amount of accumulated sediment was:rainfall intensity 2.0 mm/min>1.5 mm/min>1.0 mm/min>0.5 mm/min,indicating that the greater the rainfall intensity,the greater the impact on the slope erosion process.The rainfall intensity also has an effect on the content of water-stable aggregates lost during the process of sediment production.By fitting the relationship between the rainfall intensity and the cumulative amount of the slope,the results showed that the rainfall intensity and the cumulative sediment amount on the slope in each treatment showed a very significant power function relationship(R~2>0.99;P<0.01).(2)Different rainfall intensitties can significantly affect the hydrodynamic process of the slope.Under different rainfall intensities,the slope Reynolds number of each treatment is less than 500,and the slope flow is laminar;The degree of surface disorder increased,and under the rain intensity of 2.0 mm/min,only≥60%of the slope surface with crust coverage showed a slow flow state.Compared with the control slope,the water flow Manning coefficient of the crust-covered slope increased by 63.03%on average,and the slope flow resistance coefficient,runoff shear force,water flow power and section unit energy decreased by 70.64%,22.12%,59.25%and 60.07%compared with the control treatment on average.(3)Biological soil crust with different coverages can significantly affect the process of soil erosion on the slope.With the increase of biological crust coverage,the slope soil bulk density and penetration resistance showed a significant downward trend,decreased by19.85%and 52.29%respectively compared with the control,while soil adhesion showed an upward trend,with a maximum of 80%coverage and 9.38 kg/cm~2.When the crust coverage increased from 0%to 80%,the initial runoff time on the crust slope was significantly delayed compared with the control slope,and the infiltration intensity during rainfall increased with the increase in crust coverage.With the increase of coverage,the overall slope runoff rate also showed a decreasing trend.Compared with the control slope,the runoff rate and cumulative runoff of the crusted slope were smaller,and the order of their size was as follows:coverage 0%>20%>40%>60%>80%.There was a very significant relationship between the change of crust coverage and the slope runoff rate(P<0.01).Slope runoff and sediment volume decreased with the increase of crust coverage,but the sediment reduction effect of crust was more obvious.The order of the proportion of total erode-d sediment in each treatment slope was as follows:coverage0%>20%>40%>60%>80%.The results showed that when the crust coverage was greater than or equal to 40%,its inhibitory effect on slope sediment production was more obvious.There was a very significant relationship between the sediment production rate and the coverage of crusted slopes(P<0.01).(4)Biological soil crust with different coverages had a significant effect on the hydrodynamic parameters of the slope.The water flow pattern of the crust slope was laminar flow.Under different rainfall intensities,the water flow velocity increased,resulting in different flow patterns on the slope.The Froude number of the slope with crust≥60%coverage was less than 1,and the water flow pattern was slow flow;under heavy rainfall conditions,the Froude number of the crusted slope with coverage≤40%was greater than 0%,and the water flow pattern was rapids.The average resistance coefficient and Manning coefficient of the crust covered slope were 2.84 times and 2.66 times that of the control treatment.In general,compared with the control treatment,the reductions in the slope runoff shear force,water flow power and energy per unit of the section in the crusting treatments with different coverages were as follows:coverage 80%>60%>40%>20%.(5)Under different rainfall intensities,crust covering had obvious benefits of reducing flow and sediment.Under different rainfall intensities,the runoff depths on the slopes of each treatment ranged from 0.58 to 4.47 m,and the runoff depths on the slopes in the control were the maximum values.The benefits of flow reduction were as follows:coverage80%>60%>40%>20%;soil loss on slopes with different crust coverage ranges from 0.45to 7.5 g,and soil loss from control plots ranged from 5.27 to 9.38 g.In between,the performance of sediment reduction benefits was:coverage 80%>60%>40%>20%.The sediment reduction benefits of crusted slopes with different coverage degrees were significantly higher than the flow reduction benefits.