Changes in the distribution of radiocesium in the wood of Japanese cedar trees from 2011 to 2013

Published Date
September 2016, Vol.161:51–57, doi:10.1016/j.jenvrad.2015.12.021

Special Issue: Radioactive contamination in forest ecosystems: From Chernobyl to Fukushima

Title

Changes in the distribution of radiocesium in the wood of Japanese cedar trees from 2011 to 2013

• Author 

• Hideki Ogawa ^a,b,,
• Yurika Hirano ^a
• Shigemitsu Igei ^a
• Kahori Yokota ^a
• Shio Arai ^a
• Hirohisa Ito^b
• Atsushi Kumata ^b
• Hirohisa Yoshida ^a

• aGraduate School of Urban Environmental Science, Tokyo Metropolitan University, Minami-Osawa, Hachioji, Tokyo 192-0397, Japan
• bFukushima Prefectural Forestry Research Centre, Nishi-Shimasaka, Asaka, Koriyama, Fukushima 963-0112, Japan

Received 17 March 2015. Revised 24 December 2015. Accepted 24 December 2015. Available online 7 January 2016.

Highlights

• •
  Profiles of ¹³⁷Cs distribution in the wood of Japanese cedar trees changed considerably from 2011 to 2013.
• •
  The radial ¹³⁷Cs distribution profiles differed depending on the vertical position on the tree in 2012.
• •
  The ¹³⁷Cs distribution in heartwood became uniform in 2013 by the vertical and radial diffusion of ¹³⁷Cs.

Abstract

The changes in the distribution of ¹³⁷Cs in the wood of Japanese cedar (Cryptomeria japonica) trunks within three years after the Fukushima Dai-ichi Nuclear Power Plant (FDNP) accident in 2011 were investigated. Thirteen trees were felled to collect samples at 6 forests in 2 regions of the Fukushima prefecture. The radial distribution of ¹³⁷Cs in the wood was measured at different heights. Profiles of ¹³⁷Cs distribution in the wood changed considerably from 2011 to 2013, and the process of ¹³⁷Cs distribution change in the wood was clarified. From 2011 to 2012, the active transportation from sapwood to heartwood and the radial diffusion in heartwood proceeded quickly, and the radial ¹³⁷Cs distribution differed according to the vertical positon of trees. From 2012 to 2013, the vertical diffusion of ¹³⁷Cs from the treetop to the ground, probably caused by the gradient of ¹³⁷Cs concentration in the trunk, was observed. Eventually, the radial ¹³⁷Cs distributions were nearly identical at any vertical positions in 2013. Our results suggested that the active transportation from sapwood to heartwood and the vertical and radial diffusion in heartwood proceeded according to the vertical position of the tree and ¹³⁷Cs distribution in the wood approached the equilibrium state within three years after the accident.

Graphical abstract

Keywords

• Fukushima Dai-ichi Nuclear Power Plant accident
• Radiocesium
• Japanese cedar tree
• Tree contamination
• Wood

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• ∗ 
  Corresponding author.

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