Soil Erosion Patterns And Driving Mechanisms Based On The Degree Of Karst Development

Constrained by the non-homogeneous karst surface and complex erosion patterns,soil erosion in karst areas is far more complex and special than that in non-karst areas.The degree of karst development,lithology and rocky desertification are considered to be important influencing factors of soil erosion in karst areas.However,studies have focused on the influence of lithology and rock desertification on soil erosion,and studies on the influence of the degree of karst development on soil erosion have often been neglected.International studies on this subject are also rare,and there is a lack of data support and experience in technical methods.In view of this,this paper establishes a set of karst zoning criteria based on the degree of karst development,taking into account lithology,rock exposure rate,vegetation cover and soil thickness,and divides Guizhou province into pure-karst,sub-karst and non-karst zones,taking into account previous studies on the degree of karst development.On this basis,the spatial and temporal patterns of soil erosion in different karst zones in Guizhou Province from 2005 to 2020 were analyzed,and the driving factors of soil erosion in different karst zones were explored.The main results are as follows:（1）The area of karst in Guizhou is 109,100 km² and the area of non-karst is 67,000 km².During the study period,the area of non-karst areas remained the same,while the area of pure-karst areas and sub-karst areas changed somewhat.2005,the area of pure-karst areas was 100,400 km²and sub-karst areas was 8700 km²;2010,the area of pure-karst areas was105,600 km² and sub-karst areas was 3500 km²;2015,the area of pure-karst areas was 76,000 km² and sub-karst areas was 33,100 km²;2020,the area of pure-karst areas was 43,800 km² and sub-karst areas was 65,300km².In 2015,the area of pure-karst zone is 76,000 km² and the area of sub-karst zone is 33,100 km²;in 2020,the area of pure-karst zone is 43,800 km²and the area of sub-karst zone is 65,300 km².The overall performance is that the area of pure-karst zone decreases and the area of sub-karst zone increases.Spatially,pure-karst areas have obvious aggregation characteristics in 2005,2010 and 2015,and more uniform distribution in2020;sub-karst areas change from sporadic distribution to spread throughout the karst area.（2）The average rainfall erodibility（R）in Guizhou gradually increased from 2005 to 2020,with 3488.43,4249.37,5330.21,and 5858.81MJ·mm·ha^-1·h^-1,respectively;the spatial distribution pattern was high in the southwest and low in the northeast.Soil erodibility（K）ranged from0.0216-0.0479 t·hm²·h/（MJ·mm·hm²）,with a mean value of 0.03t·hm²·h/（MJ·mm·hm²）.Spatially,soil erodibility was lower in the northeast and south and higher in the east.The maximum value of slope length factor（L）is 1.77,the minimum value is 1,and the average value is 1.074.Spatially,the slope length factor is large in the east and small in the west.The maximum value of slope factor（S）is 23.806,the minimum value is 0,and the average value is 4.97.From 2005 to 2020,the vegetation cover and management measures factor（C）and soil and water conservation measures factor（P）show a decreasing trend;the average values of rock exposure rate are 26.2%,26.8%,25.91%and 28.01%,respectively.（3）The multi-year average soil erosion rates were 14.26,14.01 and20.78 t ha^-1a^-1 in pure-karst,sub-karst and non-karst zones,respectively,showing non-karst>pure-karst>sub-karst zones.In terms of area share of erosion intensity,pure-karst,sub-karst and non-karst zones all showed mild>slight>moderate>strong>very strong>intense.The average percentages of slight and mild erosion in pure-karst area were 34.39%and39.33%,moderate and intense were 12.87%and 7.02%,and very intense and intense were 5.12%and 1.29%,respectively.The average percentages of slight and mild erosion in the sub-karst zone were 31.58%and 46.39%,moderate and intensity were 10.93%and 5.63%,and extreme intensity and intensity were 4.25%and 1.21%,respectively.The average percentages of slight and mild erosion in non-karst areas were 30.38%and 47.23%,moderate and intensity were 10.62%and 5.77%,and extreme intensity and intensity were 4.64%and 1.33%,respectively.（4）Intense and very intense soil erosion in the pure-karst zone is mainly distributed in the west,south and northeast;slight and mild erosion is mainly distributed in the east and central part.The non-karst zone is mainly distributed in the southwest and northeast,and a small amount of intensity and extreme intensity soil erosion is also distributed in the southeast;the slight and mild erosion is mainly distributed in the southeast and north.The spatial distribution of soil erosion intensity in the four periods of 2005,2010,2015 and 2020 varies significantly in the sub-karst area due to the area change.（5）Soil erosion under different spatial gradients has a high degree of spatial heterogeneity.Soil erosion of cultivated land is strong,and when the slope is greater than 15°,soil erosion of cultivated land exceeds that of forest land on any slope.There is a critical value of 0.5-0.6 for the relationship between soil erosion and vegetation cover when the rainfall is≤1200 mm;and when the rainfall is>1200 mm,the effect of rainfall on soil erosion is significantly greater than that of vegetation cover.Soil erosion under different rainfall all increases with slope,and soil erosion is lower in limestone and dolomite.（6）The contributions of soil erosion factors were land use,slope,rainfall,lithology,vegetation cover,and elevation in descending order,and the interaction of multiple factors could enhance the influence of single factors on soil erosion.The interaction between land use and slope was the dominant factor in the spatial differentiation of soil erosion in all three karst zones,but the explanatory power（q value）was much higher in sub-karst and non-karst zones than in pure-karst zones.The interaction between slope and rainfall significantly exacerbated soil erosion,and the significance of the interaction between lithology and rainfall was a unique feature of karst zones.Based on the soil erosion and dominant factor data explored in three karst zones,this study can provide strong scientific support for relevant policy makers to implement soil and water conservation measures and carry out ecological restoration in the future.In addition to soil erosion,the geology,vegetation,and hydrology of karst zones are also highly spatially heterogeneous.The refined zoning of this study can accurately identify the relevant ecological process differences,which is an important guidance for implementing specific protection measures.