| The main ecological problem in the Loess Plateau is serious soil and water loss.Due to its special topography and complex soil erosion process,the ecological management in the region is difficult.In this study,Wangdonggou watershed in loess plateau gully region and Miaogou watershed in loess hilly gully region were selected as the research areas.Based on meteorological data,digital elevation model（DEM）,high-resolution remote sensing images,field in-situ sampling,laboratory experimental analysis and other research methods,GIS and RUSLE technologies were used to quantitatively evaluate the spatial distribution characteristics of soil erosion in the two watersheds in 2015.The effects of land use,vegetation coverage and slope on soil erosion were studied,and the differences in soil erosion inducing factors under different environmental factors were explored.In order to provide reference for the selection of land use patterns to alleviate soil erosion in typical loess gully regions.The main results are as follows:（1）The higher soil erosion intensity in Wangdonggou Valley is mainly concentrated in gully slope in the south of the basin and construction land in the north,while the lower soil erosion intensity is in agricultural land in the north of the basin and the gully bottom in the south with relatively gentle topography.Terrain is a key factor affecting soil erosion.The topography changes obviously in the north and south of the whole basin,and the soil erosion modulus increases significantly,and the erosion amount increases first and then decreases with the increase of slope.The grassland and forest land in the south affected by terrain are more seriously soil and water loss,and the soil and water loss situation is different with different vegetation coverage.Under the combined action of various factors,the soil erosion modulus of forest land with high vegetation coverage increased,and the erosion amount increased first and then decreased with the increase of slope.When the slope was 0°～8°,it belonged to no obvious erosion,and when the slope was≥8°,it belonged to slight erosion,and the overall erosion intensity was not high.The soil erosion trend of medium-high coverage woodland was consistent with that of high coverage woodland,but the erosion intensity increased significantly.There was no obvious erosion at 0°～3°,slight erosion at 3°～15°,light erosion at15°～35°,and close to moderate erosion at≥35°.Soil erosion intensity and erosion amount of grassland with high coverage increased first and then decreased with the increase of slope gradient.0°～5°belonged to no obvious erosion,5°～35°belonged to slight erosion,35°～45°belonged to light erosion,and≥45°belonged to slight erosion.The soil erosion intensity of grassland with medium-high coverage increased significantly with the increase of slope,and the erosion amount increased first and then decreased with the increase of slope.The soil erosion intensity was no obvious erosion at 0°～5°,slight erosion at 5°～15°,moderate erosion at 15°～45°,and the erosion modulus was 3037.46 t·km-2·a-1.Therefore,it is suggested that the improvement of soil and water loss in this area should give priority to the development of woodland in the range of slope 5°～35°when the vegetation coverage is≥70%.When the vegetation coverage is less than 70%and in the range of slope≥25°,should be strengthened woodland and grassland.（2）In Miaogou small watershed of hilly and gully region,the areas with high erosion intensity are mainly affected by land use in construction land,and the soil erosion is weak in the areas where cultivated land is gathered.Mountain with high altitude is the main gathering area of forest land and grassland in the basin,and its vegetation coverage is high.However,due to the influence of topography,the erosion is still strong,and the soil erosion of cultivated land and garden land with gentle slope at the bottom of mountain and gully is weak.Moreover,with the increase of slope,the soil erosion modulus and erosion amount of the watershed increased significantly,and the erosion amount decreased when the critical slope was 25°.Under the combined effects of various factors,the soil erosion modulus of high coverage,medium-high coverage woodland and grassland increased significantly with the increase of slope gradient,and the erosion amount increased first and then decreased.The range of 15°～25°still needs to be strengthened.The erosion intensity of cultivated land with medium,high-medium and high vegetation coverage increases with the increase of slope gradient.When the slope gradient is≥35°,it is light erosion and can continue to strengthen the management of cultivated land with slope gradient≥35°.The vegetation cover of watershed garden land is mainly midium-high and high vegetation cover,which changes significantly with the erosion intensity of slope.The slope range of 8°～25°is the main source of soil erosion,and it is also the key area of Miaogou governance.In view of the follow-up ecological environment management in hilly and gully areas,steep slope farmland is the focus,and the management of steep slope forest grassland and garden land still needs to be strengthened when the vegetation coverage is less than 70%.（3）The distribution of organic matter content in Wangdonggou watershed was similar to that of total nitrogen.The high contents of soil nutrients and organic matter in Wangdonggou watershed were concentrated in the north of the watershed and the southwest of the southern channel,while the contents of soil nutrients and organic matter were lower in the south and west-central areas.The distribution of soil nutrient loss was consistent with the spatial distribution of soil erosion.The annual average loss of soil organic matter,total nitrogen,available phosphorus and available potassium in the watershed was 6.763,0.418,0.103 and0.003 t·km-2·a-1.There were significant differences in nutrient loss among different land-use types.The average nutrient loss was the lowest in the garden field and the highest in the grassland.Soil organic matter and nutrient contents in the Miaogou watershed were higher in the central and southeastern regions,and lower in the northwestern region.Nutrient loss areas like soil erosion gathered at the bottom of the gully with a zonal distribution of construction land,organic matter and total nitrogen loss is more serious on the slope.The annual average loss of organic matter,total nitrogen,available phosphorus and available potassium was 4.807,0.323,0.002 and 0.064 t·km-2·a-1,and the annual loss was 24.201,1.638,0.009 and 0.323 t,respectively.Based on different land types,the loss of soil nutrients showed construction land>grassland>garden land>cultivated land>woodland.In summary,the nutrient loss difference between the plateau gully region and the hilly gully region was significant.The annual average nutrient loss of organic matter,total nitrogen and available phosphorus on the slope surface in the plateau gully region was higher than that in the hilly gully region,while the available potassium was lower than that in the hilly gully region.（4）There are significant differences in soil erosion between the plateau gully region and the hilly gully region.The soil erosion in Wangdong gully is stronger than that in Miao gully under medium-low and medium-high vegetation coverage,while the soil erosion in Miaogou gully is stronger than that in Wangdonggou gully under medium vegetation coverage.When the vegetation coverage is high,the intensity of the two basins is basically consistent.There were significant differences in soil erosion between tableland gully region and hilly gully region with different slopes.There was no obvious erosion in the two watersheds of 0°～3°.There was no obvious erosion in Wangdonggou gully region of 3°～5°and slight erosion in Miaogou gully region.When the slope was 5°～35°,the soil erosion in Wangdonggou gully region and Miaogou gully region were both slight erosion,but when the slope was≥35°,Wangdonggou gully region changed into light erosion and Miaogou gully region remained unchanged.When the slope was>25°,the soil erosion in Wangdonggou gully region was significantly stronger than that in Miaogou gully region.Therefore,the subsequent soil and water loss control in the plateau gully region should focus on the place with slope>25°to improve the coverage of forest and grassland,while the hilly gully region should focus on the utilization of slope farmland and provide coverage for steep slopes. |
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