Distribution and influencing factors of soil organic carbon in a typical karst catchment undergoing natural restoration

Understanding the distribution patterns and controlling factors of soil organic carbon (SOC) in karst areas is important for soil carbon management. However, due to the wide variety of human activities and karst habitats, the factors influencing SOC in karst areas vary. A typical catchment undergoing natural restoration in the karst region of South China was investigated to determine the distribution and variation of soil properties and SOC stocks (SOCSs) under three types of terrain: a hillslope, a depression and a sinkhole. The factors influencing SOC under the different terrain types were determined by redundancy analysis and multiple linear regression modelling. The results indicated that terrain and hydrological conditions affect the distribution of SOC on the hillslope. The spatial heterogeneity of SOC and dissolved organic carbon (DOC) on the hillslope was high. Terrain type and land use differences significantly affected the SOC and DOC concentrations at the catchment scale. SOC loss was more serious in the depression due to agricultural activities, and SOC accumulation was more obvious on the hillslope due to its relatively long natural restoration period. The average SOCSs of the hillslope were 16.5% and 54.6% larger than those of the depression and sinkhole, respectively, and the average dissolved organic carbon stocks (DOCSs) were 70.6% and 179.7% larger, respectively. In addition, the impacts of environmental factors on SOC and DOC varied among the different terrain types. Soil texture and topography were the main factors controlling the distribution of SOC and DOC on the hillslope and in the whole catchment, and soil texture was the main factor controlling SOC at the catchment scale. In addition, soil loss through sinkholes may be an important carbon sink in karst areas. The results of this study are of great significance for evaluating soil carbon storage and vegetation restoration strategies in karst areas.