Using fallout 137Cs and OSL as sediment tracers in badlands: a case study of Tepezalá volcano (Central Mexico)

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ABSTRACT Badlands are dynamic landforms that cause soil loss over extensive areas. In this study, we analyze recent sediment mobilization in a badland area by using a novel approach that integrates fallout 137Cs and optically stimulated luminescence (OSL). We assess how erosion and sediment storage operate over the Tepezalá volcano, a tephra cone located in central Mexico. We analyzed a set of sediment samples extracted from the surface of an altitudinal sequence with different land uses to explore how landscape management practices relate to erosion and, depth profiles from local sinks, to detect patterns of sediment mobilization and sedimentation. We compared 137Cs and OSL results with reference values to evaluate whether erosion or deposition is predominant and to assess how deep the erosive processes in the landscape are. Results from fallout 137Cs values indicate that in those badlands with implemented actions to mitigate erosion, sediment is retained. The high luminescence values show that the edaphic soil has been flushed away, and subsoil crops out in some of the sampled sites. For the case of depth profiles, maximum values of 137Cs coincide with high luminescence values, suggesting that in such sites, the sediment was mobilized during rapid incision episodes that caused widespread erosion of the landscape. We detected at least three episodes of rapid incision in 10 years of sediment record. We propose that using 137Cs and OSL together can provide valuable information of the sediment transport in settings dominated by fast erosion as do occur for the case of badlands.