Large uncertainties still exist on both the rates of soil organic carbon (SOC) mobilization by soil erosion as well as the fate of the eroded C. Using a range of techniques we characterized soil C redistribution by water erosion in two small agricultural catchments in the Belgian Loess Belt. Results from rainfall simulations showed that C enrichment in eroded sediments was much higher than clay enrichment (average enrichment ratios of 2.47 and 1.36 on average respectively). Selectivity was also observed in depositional processes: sediments deposited within the catchments were depleted in C and finer fractions as compared to the source soil. Selectivity was much more pronounced in winter than in summer, which is related to the degree of aggregation of the transported/deposited sediment. The combined selectivity of erosion and depositional processes resulted in a significant C enrichment of the sediment exported from the catchments with the C enrichment ratio (CER) between 1.2 and 3.0. Overall, catchment-scale C enrichment was higher than clay enrichment: enrichment ratios varied both with season and event intensity. The uncertainties on catchment-wide erosion and deposition rates precluded the closure of the sediment-C budgets. However, using a simple model we were able to show that both the magnitude and variation of observed catchment-scale CER was as expected from our understanding of C mobilization and deposition within the catchment. This suggests that most of the mobilized C was not mineralized during the erosion events but either re-deposited within the catchment or exported with the runoff. This was confirmed by the comparison of the elemental and isotopic signatures between exported sediments and source soil. In order to assess the role of erosion in the C cycle, understanding how C is mobilized and re-deposited selectively by erosion appears therefore as important as improving our understanding of the impact of erosion on C mineralization.
Wang, Zhengang ; Govers, Gerard ; Steegen, An ; Clymans, Wim ; Van den Putte, An ; et. al. Catchment-scale carbon redistribution and delivery by water erosion in an intensively cultivated area. In: Geomorphology, Vol. 124, no.1-2, p. 65-74 (2010)
