Decision support for the selection of reference sites using <sup>137</sup>Cs as soil erosion tracer

Abstract

Abstract. The classical approach to use 137Cs as soil erosion tracer is based on the comparison between stable reference sites and sites affected by soil redistribution processes, and enables to derive soil erosion and deposition rates. The method is associated with potentially large sources of uncertainty with major parts of this uncertainty being associated with the selection of the reference sites. We propose a decision support tool to Check the Suitability of reference Sites (CheSS) for systematic validation or rejection of reference sites. The method is based on a repeated sampling approach, where the reference sites are resampled after a certain time period. Suitable reference sites are expected to present no significant temporal variation in their decay corrected 137Cs depth profiles. Possible causes of temporal variation are narrowed down by a decision tree. More specifically, the decision tree tests for (i) uncertainty connected to small scale variability of 137Cs due to its heterogeneous initial fallout (such as in areas affected by the Chernobyl fallout), (ii) signs of erosion/deposition processes, (iii) artefacts due to the collection, preparation and measurement of the samples and (iv) finally, if none of the above can be assigned, this variation might be attributed to "turbation" processes (e.g. bioturbation, cryoturbation and mechanical turbation such as avalanches or rock falls). CheSS has been tested in one Swiss alpine valley, where the suitability of six reference sites was tested.