| The eight southern provinces of southern China(Yunnan,Guizhou,Sichuan,Chongqing,Hubei,Hunan,Guangxi,Guangdong)are inclined to cross geomorphic three steps from the northwest to the southeast,which are high east and low in the west,including the east of the Qinghai Tibet Plateau(Western Sichuan Plateau),Yunnan Guizhou Plateau,Hengduan Mountains,Sichuan basin,Dongting Lake plain,and two grades of geomorphic units in the hills of Guangdong and Guangxi.Soil erosion has become one of the most serious ecological and environmental problems in the region due to the complex topography and seasonal rainfall.In addition,the eight provinces of southern China are located in the core area of karst concentrated distribution area in East Asia.The ecological environment system in karst has the characteristics of poor stability,high variability sensitivity,weak ability to carry interference and low environmental ecological capacity.In addition,the traditional rainfall erosivity algorithm often accumulates annual rainfall,but not every rainfall in the actual rainfall process will produce soil erosion.Only when the rainfall reaches a certain threshold,soil erosion will occur.And the overestimation of the erosivity of rainfall causes an overestimation of soil erosion.Due to the slow rate of soil formation,the small amount of soil formed,the shallowness of the soil layer,and even the exposed characteristics of the bedrock in the karst area,the amount of erosion calculated in the karst area is often higher than its actual amount of soil.Therefore,the soil erosion in the karst area is overestimated by two times.In view of this,this paper has made repeated improvements to soil erosion in order to assess soil erosion in eight provinces in southern China in a more accurate and efficient manner.Concluded as follow:(1)In the traditional rainfall erosivity algorithm,the rainfall erosivity under different lithologic backgrounds of karsts and non-karsts is not separated.When using the effective rainfall erosion threshold method,the mean rainfall erosivity in karst regions is only 59.91% in the non-karst,and the surface runoff from erosive erosion caused by different lithologies of karst and non-karst is fully reflected.(2)Compared with the traditional rainfall erosivity algorithm,the effective rainfall erosion threshold algorithm improved the average rainfall erosivity in the non-karst region by 14.77%,improved the average rainfall erosivity of the karst region by 42.60%,and optimizes the karst region is much greater than in non-karst areas.(3)The optimization and improvement of different thresholds for rainfall erosion in karst and non-karst regions can eliminate the influence of ineffective precipitation on soil erosion estimation and successfully solve the problem of soil overestimation error transmission due to high rainfall erosivity.Compared with the unimproved algorithm,when the effective threshold algorithm for rainfall erosivity is improved,the multi-year average decrease of soil erosion in the study area is 40.15%,the multi-year average decrease of the effective erosion area is 3.89%,and the multi-year average decline of the average erosion modulus is 40.41%.(4)The second improvement of the soil loss tolerance to soil erosion can effectively eliminate the overestimation of the theoretical erosion relative to the actual soil loss,and realize the correction from the theoretical erosion amount to the true loss amount.Compared with the effective threshold erosion improvement algorithm for rainfall erosivity,the average multi-year decrease of soil erosion in the study area is 18.95%,the average multi-year decrease of the effective erosion area is 22.87%,and the average erosion modulus is 19.01% for years.(5)During the study period,the total erosion in the study area is decreasing,the effective erosion area is decreasing,the average erosion modulus of the whole area is decreasing,and soil erosion shows an improvement trend,but in the later period,the soil erosion appeared a certain fluctuation.(6)The transfer of soil erosion grade is mainly from high erosion grade to low erosion grade,and the proportion of the transfer from low erosion grade to high erosion grade is low.The proportion of the micro and mild erosion grades in the total area and total erosion is rising,and the ratio of the intensity and the above erosion level in the total area and total erosion is obviously decreasing.(7)During the study period,the average risk index of the study area and the proportion of erosion risk area in the total area showed a downward trend,and the soil erosion status in the study area was improving.For different levels of erosion risk,the proportions with extremely low and extremely high risk levels are relatively large,and the medium risk level is relatively low,exhibiting the features of the lower middle and high sides.(8)The spatial distribution of the soil erosion risk index is greatly influenced by the two factors of topography and lithology.There is a positive correlation between the size of the soil erosion risk index and the relief of the terrain.The greater the relief,the higher the erosion risk.In different lithologic backgrounds,the overall soil erosion risk grades in karst regions are dominated by medium and high grades,and low risk grades are relatively rare;the non-karst region's soil erosion risk grades are generally consistent with the spatial distribution of soil erosion intensity,the reason for this phenomenon is the difference in rates of weathering to soil in different lithologic settings. |
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