A multi-radionuclide approach to evaluate the suitability of 239+240Pu as soil erosion tracer

Abstract

Fallout radionuclides have been used successfully worldwide as tracers for soil erosion, but relatively few studies exploit the full potential of plutonium (Pu) isotopes. Hence, this study aims to explore the suitability of the plutonium isotopes (239)Pu and (240)Pu as a method to assess soil erosion magnitude by comparison to more established fallout radionuclides such as (137)Cs and (210)Pbex. As test area an erosion affected headwater catchment of the Lake Soyang (South Korea) was selected. All three fallout radionuclides confirmed high erosion rates for agricultural sites (>25tha(-1)yr(-1)). Pu isotopes further allowed determining the origin of the fallout. Both (240)Pu/(239)Pu atomic ratios and (239+240)Pu/(137)Cs activity ratios were close to the global fallout ratio. However, the depth profile of the (239+240)Pu/(137)Cs activity ratios in undisturbed sites showed lower ratios in the top soil increments, which might be due to higher migration rates of (239+240)Pu. The activity ratios further indicated preferential transport of (137)Cs from eroded sites (higher ratio compared to the global fallout) to the depositional sites (smaller ratio). As such the (239+240)Pu/(137)Cs activity ratio offered a new approach to parameterize a particle size correction factor that can be applied when both (137)Cs and (239+240)Pu have the same fallout source. Implementing this particle size correction factor in the conversion of (137)Cs inventories resulted in comparable estimates of soil loss for (137)Cs and (239+240)Pu. The comparison among the different fallout radionuclides highlights the suitability of (239+240)Pu through less preferential transport compared to (137)Cs and the possibility to gain information regarding the origin of the fallout. In conclusion, (239+240)Pu is a promising soil erosion tracer, however, since the behaviour i.e. vertical migration in the soil and lateral transport during water erosion was shown to differ from that of (137)Cs, there is a clear need for a wider agro-environmental testing.

Denudation variability of the Sila Massif upland (Italy) from decades to millennia using 10Be and 239+240Pu

“…The 240 2014; Portes et al, 2018;Lal et al, 2013, Meusburger et al, 2016Zollinger et al, 2015). In contrast, Location 1 has an unusual Pu depth trend, although similar activity trends were reported by Ketterer et al (2004) and Frielinghaus and Vahrson (1998).…”

“…In most cases, however, only samples at the top of tors/boulders were analysed (e.g., Bierman & Caffee, 2001;Darmody et al, 2008;Gunnell et al, 2013). A more detailed sampling design has very rarely been applied ( rates can be determined with nuclear fallout radionuclides (Lal, Tims, Fifield, Wasson, & Howe, 2013;Meusburger et al, 2016). Isotopes of plutonium ( 239+240 Pu) are an efficient tool in tracing soil erosion and accumulation (Alewell, Pitois, Meusburger, Ketterer, & Mabit, 2017).…”

Understanding the role of water and tillage erosion from <sup>239+240</sup>Pu tracer measurements using inverse modelling

“…Enrichment processes, due to selective transport of soil constituents that fallout radionuclides are preferentially associated with, are a critical issue for the use of most (e.g., 239+240 Pu, 137 Cs, 210 Pb) radionuclide tracers (Parsons and Foster, 2011;Mabit et al, 2014;Alewell et al, 2017). While 137 Cs is mainly associated with clay particles, 239+240 Pu binds to soil organic matter and oxides (Alewell et al, 2017) that are less affected by selective water transport and corresponding 239+240 Pu enrichment (Meusburger et al, 2016;Xu et al, 2017). Nevertheless, the 239+240 Pu activity at depositional sites, that are redistributed by water (transport by tillage is typically assumed to be non-grain size selective; Fiener et al, 2018), can be higher in relation to the activity of the https://doi.org/10.5194/soil-2020-22 Preprint.…”

Land use and land cover changes in the Haean Basin of Korea: Impacts on soil erosion

“…In addition to the forests (50%-60%), almost all land is used for crop production (35%-40%; Yun et al, 2015). Because of these intensive agricultural activities, this basin experiences high rates of soil erosion (Ruidisch et al, 2013;Arnhold et al, 2014;Meusburger et al, 2016). To supply agricultural irrigation water, ~600 groundwater wells have been developed in this basin; the number is continuously increasing.…”