Temporal variation of SOC enrichment from interrill erosion over prolonged rainfall simulations

Sediment generated by interrill erosion is commonly assumed to be enriched insoil organic carbon (SOC) compared to the source soil. However, the reported SOCenrichment ratios (ERSOC) vary widely. It is also noteworthy that most studies reported thatthe ERSOC is greater than unity, while conservation of mass dictates that the ERSOC ofsediment must be balanced over time by a decline of SOC in the source area material.Although the effects of crusting on SOC erosion have been recognized, a systematic study oncomplete crust formation and interrill SOC erosion has not been conducted so far. The aim ofthis study was to analyze the effect of prolonged crust formation and its variability on theERSOC of sediment. Two silty loams were simultaneously exposed to a rainfall simulation for6 h. The ERSOC in sediment from both soils increased at first, peaked around the point whensteady-state runoff was achieved and declined afterwards. The results show that crustingplays a crucial role in the ERSOC development over time and, in particular, that theconservation of mass applies to the ERSOC of sediment as a consequence of crusting. A“constant” ERSOC of sediment is therefore possibly biased, leading to an overestimation ofSOC erosion. The results illustrate that the potential off-site effects of selective interrillerosion require considering the crusting effects on sediment properties in the specificcontext of the interaction between soil management, rainfall and erosion.