Distribution of Biological Soil Crust and Its Significance to Aeolian Environment in Shapotou Section Protective System of Baotou-Lanzhou Railway

Abstract

This study analyzed the spatial distribution of the type and thickness of biological soil crust,ground surface compaction and grain-size composition of surface sediments through a cross-section parallel to the prevailing wind direction in Shapotou section of Baotou-Lanzhou railway protective system,and discussed the significance of the biological soil crust to the changes of the aeolian environment in the protective system.Results showed that the biological soil crust was developed gradually from lichen-algae crust to crossly exist of moss crust and lichen-algae crust along the prevailing wind direction in the protective system.The crust distribution was developed from no crust,patch style to continuous crust formation with gradually increasing on surface compaction along the prevailing wind direction in the vegetation area of the protective system.The ground surface compaction was much higher in the vegetation area than the mobile dune area no matter with developed crust or not.The grain size of the surface sediments became fine,and the sorting got worse with the increasing of the protective distance.Suspended components(grain size0.1 mm) increased along the protective distance.The suspended component was much higher in the vegetation area than in the mobile dune area along the cross-section direction,and much higher in the crust layer than the 5 cm layer under curst in the depth direction.The content of silt and clay in the biological soil crust layer was much higher than its below layers in the vertical direction,and they increased with undulation which caused by the terrain change of the fixed dunes along the cross-section.These results implied that the aeolian environments tended to be stable along the cross-section.It changed gradually from intense erosion and deposition aeolian activity in the upwind mobile dune area to deposition dominated aeolian environment in the downwind vegetation area of the protective system.The upwind area of the vegetation area that without crust developed was a transition area from erosion and deposition to deposition dominated aeolian environments.There was still erosion and deposition activity at this area but the intensity was much less than the mobile sand area.Relative stable aeolian environment produced advantageous conditions for the development of the biological soil crust,which inversely enhanced surface stability and its wind erosion resistance ability remarkably in the vegetation area of the protective system.The better-developed moss crust was distributed in the gentle terrain area of the fixed and semi-fixed dunes while the lichen-algae crust was widely distributed in the vegetation area of the protective system.This spatial distribution variation of difference type crust implied the spatial difference on surface stability of the aeolian environments in the protective system.Spatial distribution of the attributes of the biological soil crust vibrated with the terrain of fixed dunes showed that dune terrain influenced local aeolian environment in the protective system.