| The organic carbon in soil is a crucial material foundation for soil fertility and health in ecosystems.The permafrost region on the Plateau stores a large amount of soil organic carbon,but due to climate warming,the melting of permafrost over the years has had two effects.On one hand,it has caused the release of a significant amount of organic carbon that was formerly trapped in the frozen soil,which can accelerate climate warming.On the other hand,the melting permafrost is providing a large amount of melt water,which poses a high risk of triggering hydrological erosion.As a result,the lateral migration of soil organic carbon caused by hydrological erosion will have significant impacts on the carbon cycle in terrestrial,river and ocean ecosystems.Therefore,clarifying the laws of soil organic carbon migration and transformation in the process of erosion on the Qinghai-Tibet Plateau,exploring the lateral migration and spatial differentiation characteristics of soil organic carbon under erosion on the Plateau,can provide a scientific basis for the prevention and control of global climate change and soil erosion in high-altitude regions.In this study,the Qinghai-Tibet Plateau was selected as the research area,and field investigations and experimental analyses were conducted to explore the differences in soil organic carbon content under different land use types on the plateau,as well as to clarify the spatial distribution characteristics of soil organic carbon in different regions on the surface.The machine learning method was used in combination with remote sensing images and Soil Grids250m to draw a spatial distribution map of surface organic carbon on the plateau.The CSLE model was used to calculate the soil erosion modulus of the Qinghai-Tibet Plateau,and the spatial distribution of soil organic carbon in the plateau was combined to quantitatively study the lateral migration characteristics of soil organic carbon under water erosion on the Qinghai-Tibet Plateau.The main conclusions are as follows.(1)Among the four land use types on the Qinghai-Tibet Plateau,the average soil organic carbon content in the soil showed the following order from high to low:forest(30.96±22.92 g/kg),farmland(27.61±8.92 g/kg),grassland(20.64±16.79 g/kg),and sandy land(2.52±1.00 g/kg),and there was a significant difference(p<0.05).The soil organic carbon content on the Qinghai-Tibet Plateau mainly showed a trend of being high in the east and low in the west.The organic carbon content in the eastern region was generally greater than 18.06 g/kg,and the Yarlung Zangbo River Basin in the eastern and southern regions had higher soil organic carbon content.In most parts of the western region,the soil organic carbon content was lower than 7.31 g/kg.There was no correlation between soil organic carbon content and soil clay content,while there was a highly significant positive correlation with soil silt content(p<0.01),and a significant negative correlation with soil sand content(p<0.05).(2)The Random Forest(RF)model exhibits higher determination coefficient(R~2=0.82)and prediction performance-to-deviation ratio(RPD=2.54).The covariates selected based on the variable importance results of the prediction include SOC＿250m,B2,B11,Soil-Adjusted Vegetation Index(SAVI),Normalized Difference Vegetation Index(NDVI),B5,and Soil-Adjusted Total Vegetation Index(SATVI).Among them,SOC＿250m has the highest contribution rate of 41.69%,while B2(14.84%)and B11(14.74%)also have relatively high contribution rates.The predicted values of soil organic carbon range from1.465 to 69.30 g/kg,whereas the measured values of soil organic carbon range from 0.781to 84.78 g/kg.The soil organic carbon content on the Qinghai-Tibet Plateau generally shows a decreasing trend from southeast to northwest,with the organic carbon content mainly concentrated between 1-40 g/kg.Over 31.34%of the region has soil organic carbon content between 0-10 g/kg,while only 2.58%of the region has soil organic carbon content between50-60 g/kg and 60-70 g/kg.(3)The average erosion modulus of the hydro-erosion on the Qinghai-Tibet Plateau is2.40t/ha/yr,with a total eroded area of 364,000 km~2.The area affected by slight erosion is253,300 km~2,while the areas of mild and moderate erosion are 59,400 km~2 and 31,700 km~2respectively.The areas of severe,extremely severe and intense erosion are 11,600 km~2,4,100 km~2,and 3,900 km~2 respectively.The lateral migration rate of potential soil organic carbon in surface soil is 875.56 kg C/ha/yr.Overall,the lateral migration rate of soil organic carbon caused by hydro-erosion on the Qinghai-Tibet Plateau exhibits an increasing pattern from north to south.The average lateral migration rate of soil organic carbon in grasslands is 1136.27 kg C/ha/yr,with a total migration amount of 173.54 Tg.The average lateral migration rate of soil organic carbon in forests is 695.08 kg C/ha/yr,with a total migration amount of 18.94 Tg.The average migration rate of farmland is 5826.12 kg C/ha/yr,with a total migration amount of 12.50 Tg. |
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