Experimental Investigations On The Effect From Freeze-thaw Cycle To The Anti-erosion Ability Of Soil Crust

Soil crust covers 35% of the land surface(even more than 70% in some areas).It plays an important role in the soil-water-plant system in arid and semi-arid areas and plays an important ecological role in desertification restoration.The cohesion between particles in soil crust is much greater than that in loose soil,and the content of free dust on the surface of soil crust is less,so the anti-wind erosion ability of crust covering surface is greatly enhanced.In desertification areas,soil crust is often scoured by wind-sand flow.Understanding and analyzing the impact of wind-sand flow on soil crust is of great significance for predicting dust release and soil erosion in desert areas.In the past 20 years,the anti-erosion ability of soil crust has attracted more and more people's interest,and the research on soil crust has become more and more intensive.In arid and semi-arid areas of northern China,freeze-thaw phenomenon is prevalent,especially in the period of alternating seasons of late winter,early spring and late autumn and early winter.However,there are few studies on dust release and soil erosion caused by impact damage of soil crust under freeze-thaw,so this paper focuses on the impact of freeze-thaw on soil crust resistance to wind erosion.Various soil crusts were used in the experiment.In order to control the similarity of crusts and reduce the errors in experimental measurements,the process of making soil crusts was carried out in the laboratory.Six kinds of crusts were used in the experiment,including five kinds of biological crusts and one kind of physical crusts made from microorganisms found in the crusts of arid and semi-arid areas.Because soil water is mainly supplemented by snow or rainfall,this paper simulates snowfall and snow melting events in experiments,studies their effects on soil crust in arid and semi-arid areas,and defines freeze-thaw erosion enhancement coefficient to quantify the impact of snowfall and snow melting events on different kinds of crust resistance to wind erosion.The effects of moisture content and freeze-thaw times on the freeze-thaw cycle of crust were also studied in detail.The results show that biological crusts are generally more resistant to erosion than physical crusts,but biological crusts are greatly affected by freezing and thawing.Freeze-thaw decreases the penetration strength of crust greatly.The higher the moisture content,the faster the penetration strength decreases with the increase of freeze-thaw times.The results of snow-thawing experiments show that the biological crust formedby Nostoc punctiforme(NP)is most affected by freezing and thawing at high wind speed.The maximum coefficient of freezing-thawing erosion is 4.68,and the erosion rate is increased by368%.The erosion rate increases with the increase of water content and freeze-thaw times.When the water content is 21%,the freeze-thaw coefficient is 4.08,and the erosion rate increases by308%.