| Soil erosion is one of the most serious soil degradation problems in the world.Its abnormally occurrence,development and change process directly affect the development and utilization of water and soil resources.Meanwhile,it threatens human survival,social and economic development.The Ten Turbutries located in northern of Ordos,Inner Mongolia Autonomous Region is a typical ecologically fragile area of ecotone in China,it has become one of the most serious soil erosion areas of sandstone loess areas in China because of the influence of topographic,geomorphological characteristics and human activities on this region,which was mainly distributed by severe erosion and covered by sandstone loess.Previous studies on soil erosion in this area are limited to the whole area or a certain watershed,but they do not pay more attention to the spatial and temporal variation of the watershed.Remote sensing techique has the characteristics of multi-source,multi-temporal image and multi-resolution,which can meet the needs of different spatial ranges.Soil erosion data can be quickly obtained by remote sensing.In our study,the soil erosion modulus was calculated using Universal Soil Loss Equation(USLE)based on ANUSPLIN,remote sensing technique,rainfall,DEM and land use/cover data.Then,we analyzed the tempo-spatial distribution and change trend of soil erosion modulus during 2000-2017.The results showed that:(1)the R factor showed not significant increased trend from 2000 to 2017(P>0.05),the average was 841.29 MJ·mm/(hm~2·h·a)and the slope was 23.94 MJ·mm/(hm~2·h·a).The spatial distribution of R factor had obvious regional differences,and the overall distribution showed an increased trend from the west to the east.The R factors of Husitai River and Dongliugou in east of study area were bigger than other basins were 1018.09 MJ·mm/(hm~2·h·a)and 983.21 MJ·mm/(hm~2·h·a),respectively,while those of Maobulakongdi and Burigasetaigou in west were smaller than others were 666.91 MJ·mm/(hm~2·h·a)and 709.78 MJ·mm/(hm~2·h·a),respectively.During the study period,the C factor showed a significant decreased trend(P<0.001),the average was 85.33%and the slope was 0.52%.The spatial distribution had obvious regional differences,and the overall distribution showed a decreased trend from northwest to southeast.From the basin point of view,the C factor of Husitai River and Dongliugou in east was the smallest among the ten basins,which were 78.05%and 81.74%respectively,while ones of Maobulakongdi and Burigasetaigou in west was the largest,which were 89.52%and 90.18%respectively.(2)The soil erosion modulus was not significant increased trend(P>0.05)from2000 to 2017.The average annual soil erosion modulus was 29.31t/(hm~2·a),which was the largest in 2016 and the smallest in 2011 were 65.6 t/(hm~2·a)and 10.95t/(hm~2·a),respectively.The soil erosion modulus of Husitai River showed an unsignificant decreased trend from 2000 to 2017,while others showed an unsignificant increased trend(P>0.05).The area of soil erosion was not significant decreased trend(P>0.05)from 2000 to 2017.Yearly average area of all kinds of soil erosion intensity type was 391985.07 hm~2,which was the largest in 2003 and the smallest in 2011 during study period that they were 468156.25 hm~2 or 277700 hm~2,respectively.The area of mild erosion,intense erosion and extremely intense erosion showed no significant decreasing trend(P>0.05),the area of moderate erosion showed a significant decreasing trend(P<0.05),and the area of slight erosion and severe erosion showed no significant increasing trend(P>0.05).The area of soil erosion in ten basins showed no significant downward trend(P>0.05).All these indicated that the scope of soil erosion was decreasing,the soil condition was improving,and the improvement condition of each watershed was relatively balanced,which means that the runoff and sediment into the Yellow River may be reduced.(3)There was a spatial distribution that the soil erosion modulus was smaller in east than in west,and the average of soil erosion modulus was between 0-487.601 t/(hm~2·a).From the basin point of view,the modulus of soil erosion in Hashilachuan and Moharigou in east of study area were bigger than other basins which were 35.62 t/(hm~2·a)and 41.49 t/(hm~2·a),respectively.The modulus of soil erosion in Maobulakongdi and Burigasetaigou in west of study area were smaller than other basins,which were 18.69 t/(hm~2·a)and 24.16 t/(hm~2·a),respectively.From the average distribution of soil erosion area,there had obvious regional differences that spatial distribution of soil erosion intensities increased from west to east,the study area was mainly dominated by moderate and intense erosion with an area of 118718.8 hm~2 and 102693.8 hm~2 that accounting for 24.94%and 21.55%of the total area,respectively.The proportion of soil erosion area of Haoqinghe,Hashilachuan and Moharigou were the largest that accounting for 87.7%?84.55%and87.14%of their basin,respectively.The soil erosion area of Maobulakongdi and Burigasetaigou in west of study area were the lightest that accounting for 70.33%and76.31%of their basin,respectively.The spatial distribution of erosion was corresponding to the spatial distribution of precipitation and vegetation in this area.It was proved that the spatial difference of precipitation and vegetation affected the spatial heterogeneity of erosion.At the same time,the terrain also intensified the heterogeneity.(4)From 2000 to 2017,the trend of soil erosion in the study area was mainly dominated by increasing area which accounted for 80.61%of the total area.Among them,the area with no significant increase was the largest with 38850 hm~2 which accounted for 79.93%of the total area.The area of constant soil erosion intensity was28043.25 hm~2 which accounting for 57.82%of the total area,and the area of conversion of soil erosion intensity was 204568.75 hm~2 which accounted for 42.18%of the total area.In 2000,there were three levels of mild,moderate and intense erosion were bigger than other intensities,which were 62868.75 hm~2,61456.25 hm~2and 40343.75 hm~2 that accounted for 30.73%,30.04%and 19.72%of the total conversional area,respectively.In 2017,the transfer area of slight,mild and moderate were smaller than other intensities,which were 57775 hm~2,56212.5 hm~2 and 41468.75 hm~2 that accounted for 28.24%,27.48%and 20.27%of the total conversional area,respectively.The change of erosion level indicated that the region was developing in a good direction,but any small factor change may reverse the direction of erosion.In the future development,more attention should be paid to the rational allocation and utilization of resources and the protection of vegetation.All in all,the spatial and temporal heterogeneity of soil erosion was the result of comprehensive action of many factor,especially precipitation and vegetation were larger than others. |
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