The stability and fate of Soil Organic Carbon during the transport phase of soil erosion

Soil organic carbon (SOC) is the largest pool of non-sedimentary terrestrial carbon (C) and small changes in vertical SOC fluxes in the erosion-transport-deposition system could have a significant effect on atmospheric C levels. The ongoing sink/source discussion related to SOC seems to depend on which mechanisms are dominant during each of the three stages of soil erosion: detachment, transportation and deposition. Understanding C dynamics during each phase of soil erosion is essential to accurately assess the net effect of erosion. Currently, there is a knowledge gap when it comes to the movement of mobilized SOC from the site of detachment to the depositional site. This review provides an overview on the current understanding of the fate of eroded SOC during the transport phase of soil erosion. The stability of SOC appears to be a logistic interplay between SOC accessibility, presence of decomposers and suitable abiotic conditions. The main protection mechanisms of SOC are physical and/or chemical protection, which both make SOC inaccessible to decomposers and hence prevent mineralization. Transport subjects the SOC to disturbances and changing environmental conditions which interfere with the effectiveness of the protection mechanisms. The vulnerability of these mechanisms to erosive transport are not yet known. Increased physical impact is associated with disaggregation which releases previously protected SOC. Changes in geochemical composition of soil potentially changes the extent of organo-mineral bindings and hence either strengthen or weaken chemical protection. Complex chemical structures might result in more resistant C called biochemical stable SOC and is vulnerable to destabilization during transport due to changes in (a)biotic conditions along the trajectory. A complete understanding of the fate of mobilized SOC during transportation is essential to assess the net effect of soil erosion under different conditions. Standardization of both methodology and terminology in the field of soil erosion will further contribute to resolving the controversy on the net effect of erosion. The focus for future research should be on documenting the different interacting processes active during erosive transport and their effect on SOC fluxes.