Study Of The Prevention Of Biological Soil Crust On Soil Wind And Water Combined Erosion

The wind erosion and water erosion in the water-wind erosion crisscross region of the Loess Plateau occur alternately throughout the year,causing serious soil erosion problems.Since the implementation of the“grain for green”project,biological soil crust was widely developed in the Loess Plateau region,which significantly influences physical and chemical properties of soil and enhances its erosion resistance.Thus,bio-logical soil cruts was considered to be a non-negligible factor in soil erosion research in this area.At present,few studies were focused on the effects of biological soil crust on wind-water combined erosion.The relationship between the prevention of biological soil crust on wind-water combined erosion and its coverage is still unclear,which greatly limits the application of biological soil crust in the prevention and control of soil erosion in the water-wind erosion crisscross region.Therefore,in this study,the effects of different coverages of biological soil crust on the sediment yield of wind-water combined erosion and its relationship with the order of wind erosion and water erosion were studied by means of indoor wind tunnel and simulated rainfall test,in order to provide a new biological measure for soil erosion prevention and control in the water-wind erosion crisscross area.The main conclusions are as follows:（1）Biological soil crust significantly affected the sediment yield of wind-water combined erosion,and the degree of such influence was related to the order of occurrence of wind erosion and water erosion.Compared with single water erosion,water erosion after wind erosion led to a greater amount of sediments yield on the slope with biological soil crust,and the water erosionrate after wind erosion was 29.26%higher than that of single water erosion.Compared with single wind erosion,wind erosion after water erosion led to a lower amount of sediments yield,and the wind erosion rate of after water erosion was 90.52%lower than that of single wind erosion.The average soil erosion rates of the slope from the bare soil and biological soil crust of water erosion after wind erosion were 23.47 g·m^-2·min^-1 and 6.06 g·m^-2·min^-1,respectively.The soil erosion rate of biological soil crust slope was 74.18%lower than that of bare soil.Under the erosion mode of water erosion first and then wind erosion,the erosion amount of slope of bare soil and biological soil crust was significantly lower than that of single wind erosion.（2）Biological soil crust significantly reduced the sediment yield of wind-water combined erosion,and the degree of reduction was related to the coverage of biological soil crust.Under two different orders of erosion mode,one of that was water erosion first and then wind erosion,and the other was wind erosion first and then water erosion,the sediment yield amount decreased with the increase of biological soil crust coverage.When the coverage of biological soil crust was less than 55%,the amount of sediment,caused by water erosion after the first wind erosion,of the slope would significantly increase.When the coverage of biological soil crust was more than 55%,the promotion effect on the amount of sediment,which caused by water erosion after the first wind erosion,was not significant.The biological soil crust under this coverage had a good prevention and control effect on wind-water combined erosion.（3）In the erosion mode of wind erosion first and then water erosion,wind erosion significantly promoted the sediment yield of water erosion by affecting the micro-topography and the hydrodynamic parameters of runoff of biological soil crust slope.The effect of wind erosion significantly reduced the coverage of biological soil crust,increased the surface roughness and soil hardness,and the influence ranges were11.57%,217.5%and 7.47%,respectively.Wind erosion significantly affected the hy-drodynamic parameters of slope runoff in subsequent water erosion.Compared with single water erosion,the slope flow velocity,Reynolds number,Froude number and flow power increased by 20.60%,25.49%,17.22%and 20.62%,respectively,and the resistance coefficient decreased by 37.57%.It can be seen that the wind erosion pro-vided the erosion dynamic basis for the sediment production of water erosion on the biological soil crust slope.（4）In the erosion mode of water erosion first and then wind erosion,water erosion significantly inhibited the sediment production of wind erosion by affect-ing the surface morphology and stability of biological soil crust.The effect of water erosion significantly reduced the coverage of biological soil crust and soil hardness,and increased the surface roughness.The influence ranges were9.34%,44.76%and 182.13%,respectively,which significantly reduced the erosion rate of wind erosion.In this study,aiming at the serious soil erosion problem in the water-wind erosion crisscross area,the effects of biological soil crust on the sediment yield of wind-water combined erosion and its relationship with the coverage of biological soil crust were clarified.It was found that when the coverage of biological soil crust was higher than55%,the biological soil crust effectively reduced the promotion effect of wind erosion on the sediment yield of water erosion.This result provides a scientific basis for the new biological prevention and control measures in this area.