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

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 Cs-137. The potential and limitations of alternative proxies such as Pu239+240 and Pb-210(xs) 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 Pb-210(xs) and Pu isotopes against the well-established tracer, Cs-137. The activity ratios Pu239+240/Cs-137 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 Pu239+240/Cs-137 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 Cs-137 and Pu239+240. Pb-210(xs) 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 Pb-210(xs) is not recommended in this area due to its low concentration.

Automated summary

The use of fallout radionuclides as proxies for studying soil redistribution in semiarid Southern Spain is mostly limited to Cs-137. Considering the constraints posed by the study area, the potential and limitations of alternative proxies such as Pu239+240 and Pb-210(xs) should be explored.