ZOOM Meeting ID: 215-314-2974

要旨

The Fukushima Dai-ichi Nuclear Power Plant accident occurred in March 2011 caused extensive radiocesium (¹³⁷Cs) contamination in eastern Japan. In particular, forests are the most contaminated part on the land and will be the largest reservoir of ¹³⁷Cs for decades or more because of their high land coverage rate (ca. 70 %), high ¹³⁷Cs interception efficiency by branches and leaves, and high ¹³⁷Cs adsorption ability of soils. Transfer of ¹³⁷Cs into stem woods is also a matter of great concern. While the ¹³⁷Cs transfer from foliage and bark surfaces can be a main source of the initial ¹³⁷Cs contamination in woods, the amount of ¹³⁷Cs transfer via root is the decisive factor for the long-term contamination. Thus, understanding the ¹³⁷Cs dynamics in the forests and woods is critically important for both human activities in the forests and usage of forest products including woods in the future.

To assess the actual situation of the ¹³⁷Cs contamination and understand the ¹³⁷Cs dynamics in forest ecosystems, a monitoring survey have been conducted by FFPRI since 2011. It showed that the ¹³⁷Cs distribution in the forests changed drastically in the first several years but afterward it was relatively steady and more than 90 % of the ¹³⁷Cs in the forest has come to exist in forest floor (organic and mineral soil layers). Although the percentage of ¹³⁷Cs distribution in woods is quite small, ¹³⁷Cs concentration in woods of some tree species showed increasing trends at some study sites. Further monitoring surveys and detailed researches are necessary to predict the ¹³⁷Cs contamination in woods accurately.

Fig. 1 Temporal trends of ¹³⁷Cs concentration in cedar woods sampled at four sites (Ohashi et al. 2017).
Ohashi, S., Kuroda, K., Takano, T., Suzuki, Y., Kubojima, Y., Zhang, C., Yamamoto, K., 2017. Temporal trends in ¹³⁷Cs concentrations in the bark, sapwood, heartwood, and whole wood of four tree species in Japanese forests from 2011 to 2016. J. Environ. Radioact. 178–179, 335–342.

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2018年12月7日作成

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