Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 11 2009 10.5194/bg-6-2541-2009 http://www.biogeosciences.net/6/2541/2009/ http://www.biogeosciences.net/6/2541/2009/bg-6-2541-2009.html http://www.biogeosciences.net/6/2541/2009/bg-6-2541-2009.pdf 2541 2547 2009-11-10 A method to detect soil carbon degradation during soil erosion C. Alewell christine.alewell@unibas.ch M. Schaub F. Conen Institute of Environmental Geosciences, University of Basel, Bernoullistr. 30, 4055 Basel, Switzerland Soil erosion has been discussed intensively but controversial both as a significant source or a significant sink of atmospheric carbon possibly explaining the gap in the global carbon budget. One of the major points of discussion has been whether or not carbon is degraded and mineralized to CO₂ during detachment, transport and deposition of soil material. By combining the caesium-137 (¹³⁷Cs) approach (quantification of erosion rates) with stable carbon isotope signatures (process indicator of mixing versus degradation of carbon pools) we were able to show that degradation of carbon occurs during soil erosion processes at the investigated mountain grasslands in the central Swiss Alps (Urseren Valley, Canton Uri). Transects from upland (erosion source) to wetland soils (erosion sinks) of sites affected by sheet and land slide erosion were sampled. Analysis of ¹³⁷Cs yielded an input of 2 and 4.6 tha^−1 yr^−1 of soil material into the wetlands sites. Assuming no degradation of soil organic carbon during detachment and transport, carbon isotope signature of soil organic carbon in the wetlands could only be explained with an assumed 500–600 and 350–400 years of erosion input into the wetlands Laui and Spissen, respectively. 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