Spatial-temporal Variation Of Soil Erosion Intensity In Pisha Sandstone Area

Pisha sandstone area is located in the Ordos Plateau of the Yellow River Basin,which is the main source area of coarse sediment of the Yellow River.It is called"earth ecological cancer",which brings unpredictable losses to regional economic development.Pisha sandstone turns into mud when meeting water and sand when meeting wind,which forms the unique environmental characteristics of Pisha sandstone area,and also makes the area extremely prone to soil erosion.This kind of erosion occurs continuously throughout the year.Wind erosion mainly occurs in spring,water erosion mainly occurs in summer,and freeze-thaw mainly occurs in spring and winter,almost all the year round.After many years of treatment and restoration,although the environmental conditions of soil erosion have improved,due to the lack of monitoring of the spatial-temporal change characteristics of soil erosion types and their composite action characteristics,the precise control measures of soil erosion in this region have certain limitations.Therefore,based on the collection and arrangement of meteorological data(1980-2017),remote sensing image data,soil data and land use data,this study analyzed the characteristics of soil erosion environment and its time-space change regulations.Using wind erosion model,water erosion model and freeze-thaw erosion model,it monitored the spatio-temporal variability of soil water erosion,wind erosion,freeze-thaw erosion and their composite action in 1980s,1990s,2000s and 2010s.It can provide data bases for understanding the occurrence and development process of soil and water loss of Pisha sandstone,what's more,it is able to provide theoretical support for various ecological restoration measures and projects in this area.The main results are as follows:(1)The fragmentary surface characteristics are beneficial to the occurrence of soil erosion in the Pisha sandstone area.The characteristics of the general erosion environment in the Pisha sandstone area,from the aspects of topography,landform,soil,etc,more than82%of the terrain in the area is in the balanced middle-aged period,with relatively stable development environment,but low topographic wetness index.The elevation is concentrated between 1100-1400m,and obviously increased from east to west.96.86%of the surface roughness is between 1-1.1,which is high in the east and low in the west.the overall slope is less than 15°,almost covering the whole study area.In addition,the sun-ward and shaded halves areas are evenly distributed,but flat lands are relatively few.The geomorphic types here are mainly tablelands and hills with moderate cutting.There are17 soil types,and the spatial distribution is complex.(2)The warm-wet characteristics of climate and the change of land use create conditions for the reduction of soil erosion intensity.During 1980-2017,the monthly average temperature of the Pisha sandstone area increased significantly,and its distribution characteristics always maintained that in the southern and western is much more than in the northern and eastern.However,the annual rainfall and monthly average wind speed show the trend of falling-rising-falling,and the overall distribution of the two is complex.Except for the turning point of decreasing in 2000,the vegetation coverage overall kept the trend of stable increase in coverage area.The land use situation changed significantly in 1995 and 2015 respectively,and the distribution pattern of the two years was similar,while in other years,the area and distribution change of various land use types were not obvious.(3)Over the past 38 years,the erosion situation in the Pisha sandstone area has improved,and the overall erosion intensity is concentrated below mild.From the 1980s to the 2010s,the wind erosion intensity of most of the Pisha sandstone areas remained below the micro degree,the total area of the erosion areas above the intensity decreased by about900km~2,and the spatial distribution of different erosion intensities was relatively stable.In general,the areas with different water erosion extent are micro degree>mild>moderate degree>severe>extreme intensity>intensity,and the area order of erosion intensity in different ages is slightly different.The erosion above moderate degree is dispersedly distributed with patch shape.The area size of freeze-thaw erosion intensity is moderate or below degree>intensity>extreme intensity>severe,and the above intensity erosion spreads from the middle to the four sides.The composite erosion features are wind,water,freeze-thaw interactive erosion>hydraulic dominant erosion>freeze-thaw dominant erosion>wind and water interactive dominant erosion>wind dominant erosion>water,freeze-thaw interactive dominant erosion>wind,freeze-thaw interactive dominant erosion.All kinds of composite erosion types are scattered in points.