Redistribution of the soil <sup>137</sup>Cs inventory through litter and sediment transport on a hillslope covered by deciduous forest in Fukushima, Japan

Oda, Takayuki; Hotta, Norifumi; Miura, Satoru; Endo, Izuki; Tanoi, Keitaro; Renschler, Chris S.; Ohte, Nobuhito

doi:10.1002/esp.5393

Cited by 4 publications

(2 citation statements)

References 52 publications

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“…Despite these considerations related to 137 Cs fluxes, the form of 137 Cs is also important, as the litter exported from forests may supply radioactive materials that are more bioavailable than those transported with mineral particles to downstream rivers and lakes ( 43 – 46 ). This was not incorporated in the current model version and could be included in future work.…”

Section: Discussionmentioning

confidence: 99%

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Vandromme,

Hayashi,

Tsuji

et al. 2023

Proc. Natl. Acad. Sci. U.S.A.

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In the context of elevated concerns related to nuclear accidents and warfare, the lessons learnt from the Fukushima Daiichi Nuclear Power Plant accident in 2011 are important. In particular, Japanese authorities implemented an ambitious decontamination program to reduce the air dose rate in order to facilitate the return of the local inhabitants to previously evacuated areas. This approach contrasts the strategy adopted in Chernobyl, where the most contaminated areas remain off limits. Nonetheless, the effectiveness of the Japanese decontamination strategy on the dispersion of radioactive contaminant fluxes across mountainous landscapes exposed to typhoons has not been quantified. Based on the unique combination of river monitoring and modeling in a catchment representative of the most impacted area in Japan, we demonstrate that decontamination of 16% of the catchment area resulted in a decrease of 17% of sediment-bound radioactive fluxes in rivers. Decontamination operations were therefore relatively effective, although they could only be conducted in a small part of the area due to the dominance of steep forested slopes. In fact, 67% of the initial radiocesium contamination was calculated to remain stored in forested landscapes, which may contribute to future downstream radiocesium dispersion during erosive events. Given that only a limited proportion of the initial population had returned in 2019 (~30%), it raises the question as to whether decontaminating a small percentage of the contaminated area was worth the effort, the price, and the amount of waste generated?

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Section: Discussionmentioning

confidence: 99%

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Vandromme,

Hayashi,

Tsuji

et al. 2023

Proc. Natl. Acad. Sci. U.S.A.

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“…Another approach relied on the use of a mass balance model to map the spatial distribution of 137 Cs inventories and quantify 137 Cs transport via sediment and litter in 2016-2017 along a deciduous forested hillslope of Date, in 480 the Fukushima Prefecture (Oda et al, 2022). They showed that 137 Cs inventories were significantly higher in downslope riparian areas (455 kBq m -2 ) than in the upslope ridge area (179 kBq m -2 ).…”

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confidence: 99%

Research and management challenges following soil and landscape decontamination at the onset of the reopening of the Difficult-To-Return Zone, Fukushima (Japan)

Evrard

Clergue

Chaboche

et al. 2023

Preprint

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Abstract. Twelve years after the nuclear accident that occurred at the Fukushima Dai-ichi Nuclear Power Plant in March 2011, radiocesium contamination (with a large dominance of 137Cs, with a 30-years half-life) remains a major concern in various municipalities of Northeastern Japan. The Japanese authorities completed an unprecedented decontamination programme in residential and cultivated areas affected by the main radioactive plume (8953 km²). They implemented a complex remediation programme scheme relying on different decision rules depending on the waste type, its contamination level and its region of origin, after delineating different zones exposed to contrasted radiation rates. The central objective was not to expose local inhabitants to radioactive doses exceeding 1 mSv yr-1 in addition to the natural levels. At the onset of the full reopening of the Difficult-to-Return Zone in Spring 2023, the current review provides an update of a previous synthesis published in 2019 (Evrard et al., 2019). Although this ambitious remediation and reconstruction programme is almost completed, in the 12 municipalities of Fukushima Prefecture in which an evacuation order was imposed in at least one neighbourhood in 2011, from the 147,443 inhabitants who lived there before the accident, only 29.9 % of them had returned by 2020. Waste generated by decontamination and tsunami cleaning/demolition work is planned to have been fully transported to (interim) storage facilities by the end of 2023. The cost of the operations conducted between 2011–2020 for the so-called ‘nuclear recovery’ operations (including decontamination) was estimated by the Audit Board of Japan in 2023 to 6122.3 billion yen (~44 billion euro). Decontamination of cropland was shown to have impacted soil fertility, and potassium fertilization is recommended to limit the transfer of residual radiocesium to new crops. In forests that cover 71 % of the surface area of the Fukushima Prefecture and that were not targeted by remediation, radiocesium is now found in the upper mineral layer of the soil in a quasi-equilibrium state. Nevertheless, 137Cs concentrations in forest products (including wood for heating and construction, wild plants, wildlife game, mushrooms) often keep exceeding the threshold values authorized in Japan, which prohibits their exploitation in the area affected by the main plume. Radionuclides from forest were shown to be exported in dissolved and particle-bound forms to downstream river systems and floodplains, although multiple monitoring records showed the continuous decrease in radiocesium concentrations in both river water and sediment across the main plume between 2011–2021. Fish contamination is now generally found below the threshold limits although reputational damage remains a major concern for local fishing communities. The remobilisation of radiocesium from sediment accumulated in reservoirs of the region is also of potential concern as it may lead to secondary contamination of fish or irrigation waters supplied to decontaminated fields. Overall, this synthesis demonstrates the need to continue monitoring post-accidental radiocesium transfers in these environments and to keep sharing data in order to refine our predictive understanding of radiocesium mobility and consolidate the tools available to model contaminant transfers in ecosystems. In forests in particular, novel countermeasures and wood uses remain to be developed and tested. Furthermore, the hydrologic connectivity between ecosystems is of great influence on long term radiocesium transport. The consequences of extreme phenomena (e.g., typhoons, forest fires) that may become more frequent in the future as a result of global change in these contaminated environments should be further anticipated.

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Estimation of spatio-temporal distribution of 137Cs concentrations in litter layer of forest ecosystems in Fukushima using FoRothCs model

Nishina

Hayashi

Hirano

et al. 2023

Environmental Pollution

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Redistribution of the soil ¹³⁷Cs inventory through litter and sediment transport on a hillslope covered by deciduous forest in Fukushima, Japan

Cited by 4 publications

References 52 publications

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Research and management challenges following soil and landscape decontamination at the onset of the reopening of the Difficult-To-Return Zone, Fukushima (Japan)

Estimation of spatio-temporal distribution of 137Cs concentrations in litter layer of forest ecosystems in Fukushima using FoRothCs model

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Redistribution of the soil 137Cs inventory through litter and sediment transport on a hillslope covered by deciduous forest in Fukushima, Japan

Cited by 4 publications

References 52 publications

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Lessons learnt on the impact of an unprecedented soil decontamination program in Fukushima on contaminant fluxes

Research and management challenges following soil and landscape decontamination at the onset of the reopening of the Difficult-To-Return Zone, Fukushima (Japan)

Estimation of spatio-temporal distribution of 137Cs concentrations in litter layer of forest ecosystems in Fukushima using FoRothCs model

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Redistribution of the soil ¹³⁷Cs inventory through litter and sediment transport on a hillslope covered by deciduous forest in Fukushima, Japan