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Home > Research > Research Results > Radiocesium dynamics within forest ecosystems following the Fukushima Daiichi Nuclear Power Plant accident

Update:December 15, 2017

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Radiocesium dynamics within forest ecosystems following the Fukushima Daiichi Nuclear Power Plant accident: migration of radiocesium from upper tree parts to the soil surface over 5 years

 

Article title

Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident

Author (affiliation)

Naohiro Imamura (a), Masabumi Komatsu (b), Shinta Ohashi (c), Shoji Hashimoto (d), Takuya Kajimoto (e), Shinji Kaneko (a), Tsutomu Takano (f)

 (a) Center for Forest Restoration and Radioecology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan
 (b) Department of Myshroom Science and Forest Microbiology, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan
 (c) Department of Wood Properties and Processing, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan

 (d) Department of Forest Soils, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan

 (e) Tohoku Research Center, Forestry and Forest Products Research Institute, Morioka, Iwate, Japan

 (f) Research Planning and Coordination Department, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan

Publication Journal

Scientific Reports, 7:8179, August 2017、DOI: 10.1038/s41598-017-08261-x( External link )

Content introduction

After the accident at the TEPCO’s Fukushima Daiichi Nuclear Power Plant, we conducted a 5-year investigation to reveal the dynamics of radiocesium within forest ecosystems.

In August 2011, we established investigation sites in nine forests (sugi cedar, hinoki cypress, konara oak, and akamatsu pine forests located in the villages of Kawauchi and Ohtama and the town of Tadami in the Fukushima Prefecture and Mount Tsukuba in the Ibaraki Prefecture). At these sites, we monitored changes in the concentration and inventory of radiocesium present in the needles of leaves, branches, bark, and stem wood of trees, as well as in the organic and mineral soil layers (Figure 1). Changes in the distribution of radiocesium in these forests over the 5 years after the accident are described below.
1) Radiocesium concentrations in the needles and branches of coniferous trees sharply decreased over time (Figure 2).
2) Radiocesium concentrations in the stem wood decreased in akamatsu pine trees and slightly increased in sugi cedar and konara oak trees, but the concentrations remained lower in the stem wood than in the other parts of the trees (Figure 2).
3) The radiocesium inventory in the upper tree parts sharply declined over time in these forests. In contrast, the radiocesium inventory in the organic and mineral soil layers increased. Consequently, >90% of the entire radiocesium inventory in the forests migrated into the organic and mineral soil layers by 2014 (3 years after the accident) and mostly into the surface soil up to the depth of 0-5cm (Figure 3).

The above results demonstrated that radiocesium from the Fukushima nuclear disaster migrated down from the trees into the soil and mostly remained present in the surface soil.

This study is the first comprehensive assessment of the long-term dynamics of radiocesium within forest ecosystems in the wake of the Fukushima nuclear disaster. The data will be invaluable on a world scale. We hope that these findings will be applied in the forestry management of affected areas and will assist in developing long-term prediction models for radionuclides in the future.

 

Figure 1. (a) Locations of the investigation sites. 

Figure 1. (a) Locations of the investigation sites. (b) and (c) Sampling of stem wood and soil specimens.

 

Figure 2. Chronological changes in radiocesium concentrations in

Figure 2. Chronological changes in radiocesium concentrations in each tree part.The graphs show results obtained from sugi cedar, konara oak, and akamatsu pine forests in Ohtama village. The lines are drawn to signify statistically significant changes.

 

 

Figure 3. Chronological changes of the distribution of radiocesi

 

 

Figure 3. Chronological changes of the distribution of radiocesium inventories in cedar forests. The left and right graphs show results from a sugi cedar forest in Kawauchi Village and a konara oak forest in Ohtama Village, respectively.