Effect of soil redistribution on various organic carbons in a water- and tillage-eroded soil

• Soil erosion depleted POC and LFOC.
• The movement of eroded POC and LFOC induced the higher C pool in depositional sites.
• LFOC was preferentially transported in the process of water erosion.
• Water erosion may induce greater depletion of POC and DOC than tillage erosion.
• More SOC may be assimilated into MBC under tillage erosion than water erosion.

The information gap concerning the effect of soil redistribution on various carbon (C) pools will limit our understanding regarding the fate of eroded C. In this study, we selected a water- and tillage-eroded hillslope with a horizontal length of 45 m from the Sichuan Basin, China, to determine the impact of soil redistribution on particulate organic C from 0.0053 to 2 mm soil particles (POC), light fraction organic C (LFOC), dissolved organic C (DOC) and microbial biomass C (MBC). Soil erosion was evaluated at 5-m intervals from the summit to lower parts and soil deposition at the bottom of the hillslope. Within the erosional sites, tillage erosion- and water erosion-dominated subsites were identified. The POC content firstly decrease and then increased downslope, while the DOC exhibited an opposite pattern to the POC. The MBC content decreased downslope, while the LFOC increased. Overall, the erosional sites had lower POC and LFOC contents than depositional sites, demonstrating the depletion of POC and LFOC induced by soil erosion and the enrichment of POC and LFOC by soil deposition. Conversely, the contents of DOC and MBC were greater in the erosional sites than depositional sites. It was also observed that the LFOC distribution was strongly linked to fine (<0.05 mm) soil particles, indicating a preferentially transport of the light fraction C downslope in the process of water erosion. In addition, tillage erosion-dominated subsites had higher values of POC/SOC and DOC/SOC than water erosion-dominated subsites, suggesting lower depletion of POC and DOC by tillage erosion than water erosion. Likewise, the higher MBC/SOC values were found in tillage erosion-dominated subsites, thus implying that more SOC may be assimilated into microbial C under tillage erosion than water erosion. Our study confirms the need to consider microbial response to the dynamic replacement of erosion depleted SOC.