Erosion budget and process selectivity of black carbon at meter scale

The fate of black carbon deposited on the soil surface after burning of harvesting residues is poorly understood. In this study we quantified horizontal as well as vertical transport of total pyrogenic carbon and its chemically most stable part (OREC) during a rainfall experiment after an experimental burn. The aim of the study was to assess the importance of splash erosion versus runoff for the export of total pyrogenic carbon and OREC from soil. Our methodological approach included the comparison of 1 m(2) plots with splash erosion to 1 m(2) plots where splash erosion was prevented by mosquito nets. On these plots, we quantified total pyrogenic carbon and OREC in the soil before and after the rainfall simulation. Additionally, we assessed the amount of total pyrogenic C and OREC exported from the plots and transported vertically into the soil. Our results showed that 7-55% of pyrogenic carbon was subject to horizontal and another 23-46% of initial deposited pyrogenic C subject to vertical transport. The export of total pyrogenic carbon and OREC at least doubled on plots where splash was allowed. OREC was less prone to vertical transport than total pyrogenic C. We explained the contrasting observation for both carbon types by the favourable floating behaviour of OREC compared to higher sedimentation rates of other pyrogenic C types, which may partly lead to redistribution of the latter. The presence or absence of splash erosion was found to determine the magnitude of horizontal versus vertical transport and thereby the fate of black C in soil. (C) 2009 Elsevier B.V. All rights reserved.