Preprints
https://doi.org/10.5194/egusphere-2022-1359
https://doi.org/10.5194/egusphere-2022-1359
 
20 Dec 2022
20 Dec 2022
Status: this preprint is open for discussion.

Validating Plutonium-239+240 as novel soil redistribution tracer – a comparison to measured sediment yield

Katrin Meusburger1, Paolo Porto2, Judith Kobler Waldis3, and Christine Alewell3 Katrin Meusburger et al.
  • 1Swiss Federal Institute for Forest, Snow and Landscape Research WSL, CH-8903, Birmensdorf, Switzerland
  • 2Dipartimento di Agraria, Università degli Studi Mediterranea di Reggio Calabria, Reggio Calabria, Italy
  • 3Environmental Geosciences, University of Basel, Switzerland

Abstract. Quantifying soil redistribution rates is a global challenge addressed with direct sediment measurements (e.g., traps), models and isotopic, geochemical and radiogenic tracers. The isotope of Plutonium, namely Pu-239+240, is a relatively new soil redistribution tracer in this challenge. Direct validation of Pu-239+240 as soil redistribution is, however, still missing. We used a unique sediment yield time series in Southern Italy, reaching back to the initial fallout of Pu-239+240 to verify Pu-239+240 as a soil redistribution tracer. Distributed soil samples (n=55) were collected in the catchment, and at potential undisturbed reference sites (n=22), Pu-239+240 was extracted, measured with ICP-MS and converted to soil redistribution rates. Finally, we used a Generalized Additive model (GAM) to regionalize soil redistribution estimates for the catchment. For the catchment sites, mean Pu-239+240 inventories were significantly reduced (16.8 ± 10.2 Bq m-2) compared to the reference inventory (40.5 ± 3.5 Bq m-2,) indicating the dominance of erosion. Converting these inventory losses into soil erosion rates resulted in an average soil loss of 22.2 ± SD 7.2 t ha-1 yr-1. The uncertainties of the approach stemmed mainly from the high measurement uncertainties of low-activity samples where samples have been bulked over depth. Therefore, we recommend taking incremental soil samples and extracting ~20 g of soil. The geographic coordinates and the flow accumulation best described the spatial pattern of erosion rates in the GAM model. Using those predictors to upscale Pu-derived soil redistribution rates for the entire catchment resulted in an average on-site loss of 20.7 t ha-1 yr-1, which corresponds very well to the long-term average sediment yield of 18.7 t ha-1 yr-1 measured at the catchment outlet and to Cs-137 derived soil redistribution rates. Overall, this comparison of Pu-derived soil redistribution rates with measured sediment yield data validates Pu-239+240 as a suitable retrospective soil redistribution tracer.

Katrin Meusburger et al.

Status: open (until 27 Feb 2023)

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Katrin Meusburger et al.

Katrin Meusburger et al.

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Short summary
Quantifying soil redistribution rates is a global challenge. Radiogenic tracers such as Plutonium, namely Pu-239+240, released to the atmosphere by atmospheric bomb testing in the 60ties are promising tools to quantify soil redistribution. Direct validation of Pu-239+240 as soil redistribution is, however, still missing. Here we used a unique sediment yield time series in Southern Italy, reaching back to the initial fallout of Pu-239+240 to verify Pu-239+240 as a soil redistribution tracer.