A comparison of 210Pbxs, 137Cs, and Pu isotopes as proxies of soil redistribution in South Spain under severe erosion conditions

Abstract

Purpose The use of fallout radionuclides as proxies for the study of soil redistribution processes in semiarid environments of Southern Spain has been restricted to 137Cs. The potential and limitations of alternative proxies such as 239+240Pu and 210Pbxs should be explored given the expected constrains imposed by the features of the study area. Materials and methods Four soil and one sediment cores were collected in a highly eroded area to test the feasibility of these proxies under demanding conditions. The use of gamma spectrometry and ICP-MS did allow exploring the potential of 210Pbxs and Pu isotopes against the well-established tracer, 137Cs. The activity ratios 239+240Pu/137Cs were explored to evaluate the previous evolution of the sampling sites. Soil redistribution rates were estimated using the model MODERN. Results and discussion Despite all the profiles showed intense perturbation, Pu isotopes showed the highest potential thanks to higher sensitivity and sample throughput. The deviations of 239+240Pu/137Cs inventory ratios (0.012–0.158) from the global fallout average (0.026 ± 0.003) suggest that the sediment core was a deposition site involving alternate episodes of topsoil removal and incorporation from different sources. The calculated erosion rates ranged 34–43 t ha−1 year−1, being in good agreement for 137Cs and 239+240Pu. 210Pbxs was not used due to low-quality data. Conclusions The use of Pu as a tracer of soil redistribution processes in semiarid areas seems to be promising even under severe erosion conditions. The use of 210Pbxs is not recommended in this area due to its low concentration. Graphical Abstract

Translating deposition rates into erosion rates with landscape evolution modelling

“…It is inherently challenging to resolve temporally dynamic erosion rates over agricultural time scales, especially in systems where erosion types and rates have changed over time (Loba et al, 2022). Geochronometers such as radionuclides can provide erosion rates that are averaged over timescales that depend on their half-lives, such as cosmogenic nuclides (Granger and Schaller, 2014), or on the moment of introduction in the landscape, such as fallout radionuclides (Mabit et al, 2008;Peñuela et al, 2023). Other geochronometers, such as radiocarbon dating or optically stimulated luminescence (OSL) dating do have the ability to provide temporally resolved rates by dating layers from different depths.…”