Stability of soil organic carbon and potential carbon sequestration at eroding and deposition sites

This study aims to explore the dynamics of the factors influencing soil organic carbon (SOC) sequestration and stability at erosion and deposition sites. Thermal properties and dissolved aromatic carbon concentration along with Al, Fe concentration and soil specific surface area (SSA) were studied to 1 meter depth at two contrasting sites. Fe, Al concentrations and SSA size increased with depth and were negatively correlated with SOC concentration at the erosion site (P < 0.05), while at the deposition site, these values decreased with increasing depth and were positively correlated with SOC concentration (P < 0.05). TG mass loss showed that SOC components in the two contrasting sites were similar, but the soils in deposition site contained a larger proportion of labile organic carbon and smaller quantities of stable organic carbon compared to the erosion site. SOC stability increased with soil depth at the erosion site. However, it was slightly variable in the depositional zone. Changes in SUVA(254) spectroscopy values indicated that aromatic moieties of DOC at the erosion site were more concentrated in the superficial soil layer (0-20 cm), but at the deposition site they changed little with depth and the SUVA(254) values less than those at the erosion site. Though large amounts of SOC accumulated in the deposition site, SOC may be vulnerable to severe losses if environmental conditions become more favorable for mineralization in the future due to accretion of more labile carbon. Deep soil layers at the erosion site (> 30 cm deep) had a large carbon sink potential.