| Soil and water loss is the main ecological and environmental problem in loess hilly region.Rainfall is the driving factor of soil and water loss.Since the end of the 20 th century,biological crust has been widely developed in the converted farmland in loess hilly area,which has a significant impact on the yield of slope sand.It is of great scientific and practical significance to pay attention to the response rule of sediment yield and runoff on biological crust slope in loess hilly region to rainfall intensity.Therefore,this paper studies the response of soil erosion from biocrust slope in different coverage and different types to rainfall intensity through indoor and field simulated rainfall experiments.The influence of rainfall intensity and biocrust in soil erosion were compared,and finally the mechanisms the effect of the biocrusts on runoff and sediment yield were further analyzed.In order to clarify the changes and mechanism of the biological soil crust anti-soil erosion with the rainfall intensity,to lay the foundation for the establishment of the soil erosion prediction model considering the biological soil crust factor,the research has achieved the following main results:(1)Rainfall is the driving factor of soil and water loss on biological soil crust slope,and rainfall intensity has a significant impact on the yield of runoff and soil erosion.Rainfall intensity significantly affected runoff and sediment yield from the intact biological crust slopes.When rainfall intensity was 0.83,1.17,1.50,2.00,2.50 mm min-1,biological soil crusts reduced by 78.44 %,69.01 %,66.78 %,49.93 %,20.71 % of runoff yield and 89.99 %,95.20 %,94.94 %,77.13 %,77.03 % of sediment yield compared with bare soil slopes,respectively,indicating that the role of biological soil crusts in decreasing the slope runoff and sediment yield decreased with the increase of rainfall intensity,and the role of biocrusts in decreasing runoff yield was less than decreasing sediment yield.The biocrust slopes can significantly improve the erosion erosive rainstorm standard on the Loess Plateau to 1.50 mm min-1 or above.The threshold value of runoff generation from the complete biological soil crust slopes was 0.71 mm min-1,and the inflection point value was 1.74 mm min-1.Rainfall intensity significantly affected the runoff and sediment yield from biocrust slopes in different coverage and types,and the runoff and sediment yield on the slope were related to the coverage and type of biocrust.The biocrust coverage was about 60 %.When the rain intensity increased from 1.50 mm min-1 to 2 mm min-1,the runoff intensity increased significantly from 0.342 mm min-1 to 0.835 mm min-1 firstly,and the sediment yield rate increased significantly from 4.409 g m-2min-1 to 30.106 g m-2 min-1firstly.The inflection point values of rainfall intensity on the 60 % coverage biocrust slopes about runoff intensity and sediment yield rate were equal or greater than 1.50 mm min-1.The inflection point values of rainfall intensity corresponding to the 20 % coverage biocrust slopes runoff intensity were less than or equal to 1.17 mm mm-1.Therefore,the inflection point values of rainfall intensity corresponding to the runoff and sediment yield of the biological crust slope increased with the increase of the coverage.The effects of biocrust coverage on the runoff and sediment yield on the slopes were phased and not strictly linear.The variation of runoff intensity from cyanobacterial soil crust slopes with rainfall intensity was similar to that of bare soil slopes.The role of moss soil crusts in prolonging the significant influence of rainfall intensity in runoff and sediment yield was greater than cyanobacterial soil crusts.(2)The effects of rainfall intensity on sediment yield on slope were mainly caused by runoff,and the effects of rainfall intensity on slope runoff were greater than that of biological soil crust.The effects of biocrusts on the runoff of slope was mainly due to the difference of soil surface roughness,but the response of the biological soil crust slope runoff to rainfall intensity was mainly caused by the moss crust.And the effects of biocrusts on the sediment yield of slope were mainly affected by the coverage and type of biological crust.Under different rainfall intensity,the anti-soil erosion effects of moss soil crusts were significantly greater than that of cyanobacterial soil crusts,and the anti-soil erosion effects of biocrusts was mainly covered by moss.When the rainfall intensity was less than or equal to 1.50 mm min-1,the effect of biological soil crust on the sediment yield on the slope was greater than the rainfall intensity,and conversely,less than the rain intensity.Under different rainfall intensity,the effect of biological crust on the sediment concentration of runoff on slope was greater than that of rainfall,which was mainly affected by the moss soil crust.In the event of extreme rainfall intensity(rainfall intensity between 2.00 and 2.50 mm min-1),biological soil crust significantly inhibited sediment yield from the slopes.(3)In the linear relationship between sediment yield and runoff intensity on biological soil crust slopes in different coverage,the smaller the slope,there was the greater the erosion resistance.In the linear relationship between sediment yield and runoff intensity on biological soil crust slopes in different types,the smaller the intercept,there was the greater the erosion resistance the greater the erosion resistance. |
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