A method to detect soil carbon degradation during soil erosion

C Alewell,M Schaub,F Conen

doi:10.5194/bg-6-2541-2009

Abstract

Abstract. 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. The latter is highly unlikely with alpine peat growth rates indicating that the upper horizons might have an age between 7 and 200 years. While we do not conclude from our data that eroded soil organic carbon is generally degraded during detachment and transport, we propose this method to gain more information on process dynamics during soil erosion from oxic upland to anoxic wetland soils, sediments or water bodies.

Highlights

The soil organic carbon (SOC) pool contains twice the amount of the atmospheric carbon pool and is considered a potential major source to drive global climate change
By combining the caesium-137 (137Cs) approach with stable carbon isotope signatures 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)
While we do not conclude from our data that eroded soil organic carbon is generally degraded during detachment and transport, we propose this method to gain more information on process dynamics during soil erosion from oxic upland to anoxic wetland soils, sediments or water bodies

Summary

Introduction

The soil organic carbon (SOC) pool contains twice the amount of the atmospheric carbon pool and is considered a potential major source to drive global climate change. Soil erosion is the most widespread form of soil degradation and significant amounts of carbon are either relocated to lower situated soils, water bodies and sediments or degraded to CO2 during soil erosion The latter has been a point of intensive discussion over the last 5 years (Lal, 2004; Lal and Pimentel, 2008; Lal et al, 2004a, b; Harden et al, 2008; Renwick et al, 2004; Smith et al, 2001, 2007; Stallard, 1998; van Oost et al, 2004, 2007, 2008). Experimental studies to assess whether or not SOC is degraded during soil erosion are scarce and have mostly be bound to incubatory studies and CO2 flux measurements under laboratory conditions

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