Abstract
To elucidate the temporal changes in the radiocesium distribution in forests contaminated by the Fukushima Daiichi Nuclear Power Plant accident, we monitored the 137Cs concentration and inventory within forests from 2011 to 2015 across nine plots containing variable tree species and different contamination levels. The 137Cs concentrations in needles and branches decreased exponentially at all coniferous plots, with effective ecological half-lives of 0.45–1.55 yr for needles and 0.83–1.69 yr for branches. By contrast, the 137Cs concentration in deciduous konara oak leaves did not change over the five years. The concentration of 137Cs in oak wood increased by 37–75%, whereas that in Japanese red pine decreased by 63% over the five years. In Japanese cedar and hinoki cypress, the 137Cs concentration in wood showed an increasing trend in half of the plots. The changes in 137Cs in the organic and mineral soil layers were not strongly related to the tree species or contamination level. Our multi-site, multi-species monitoring results revealed that the pattern of temporal changes in radiocesium in the 9 forest plots was similar overall; however, changes in 137Cs in needles/leaves and wood differed among tree species.
Highlights
After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a large volume of radionuclides was released into the atmosphere
The 137Cs concentrations in each component were positively correlated with the total level of deposition; 137Cs concentrations were highest at KU1-S (630 kBq m−2 in 137Cs deposition based on aerial survey) and lowest at TD-S (10 kBq m−2 in 137Cs deposition) (Figs 2 and 3 and Table 1)
We reported temporal radiocesium changes after the FDNPP accident based on annual monitoring data of the radiocesium distributions in Fukushima forests of various types and with varying contamination levels from 2011 to 2015
Summary
After the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, a large volume of radionuclides was released into the atmosphere. The monitoring plots included three Japanese cedar plantations in Kawauchi Village (26 km from the FDNPP), Otama Village (66 km), and Tadami Town (134 km) (referred to as KU1-S, OT-S, and TD-S, respectively) and two mixed forest plots adjacent to OT-S that were dominated by broad-leaved trees (OT-Q) or Japanese red pine (OT-P). In these plots, we monitored the concentrations and inventories of radiocesium in needles/leaves, branches, bark, wood, soil surface organic layer, and mineral soil layers. We established four new plots in 2011 or 2012, with continued monitoring: a hinoki cypress forest (KU1-H) and a broad-leaved forest (KU1-Q) located close to KU1-S, a Japanese cedar forest (KU2-S) located in the same village as KU1-S but possessing a smaller contamination level from that at KU1-S, and a hinoki cypress forest in Ishioka City (TB-H) located 160 km away from the FDNPP and possessing a similar contamination level as that at TD-S
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