Erosion, deposition and replacement of soil organic carbon in Mediterranean catchments: a geomorphological, isotopic and land use change approach

[摘要] Determination of whether soil erosion can constitute a net terrestrialcarbon dioxide (CO₂) sink continues to suffer from lack of sufficientfocused studies and field data. Two of the major gaps in our understandingof the erosion induced terrestrial carbon sink issue include rate of erodedsoil organic carbon replacement by production of new photosynthate andstability of eroded organic carbon (OC) post deposition. Here we examinedthe effect of erosion processes and land use change on the stock, type, andstability of OC in two medium-sized subcatchments (18 and 50 ha in size) inSE Spain. We analysed soil samples from drainage areas and depositionalsettings for stock and isotopic composition of OC (¹⁴C and ¹³C),and particle size distribution. In addition, we conducted land use changeanalysis for the period 1956–2008 and a geomorphological survey of thecurrent erosion processes taking place in the slope-streambed connections.Our findings demonstrate that land use change influenced the dominatingerosion processes and, thus, the source of eroding sediments. Carbonisotopes used as tracers revealed that in one of the subcatchments thedeposited sediments were derived from deep soil (average Δ¹⁴Cof −271.5 ‰) through non-selective erosion processes and channel incision. Inthe other subcatchment, topsoil material was predominantly eroded and theaverage Δ¹⁴C in sediments was −64.2 ‰. Replacement of erodedsoil OC was taking place in the analysed soil profiles in the slopessuggesting that erosion processes do not necessarily provoke a decrease insoil OC stock over time.

[学科分类] 地球化学与岩石