Radial Distribution and Transport Processes of 137 Cs from Bark to Wood of Japanese Cedar ( Cryptomeria japonica ) in a Mountainous Forest of Fukushima

Predicting radiocaesium activity concentrations in standing trees over a period of decades or more in the radioactively contaminated mountain forests of Fukushima is one of the most important topics for resuming the use of forestry products after the TEPCO Fukushima Daiichi Nuclear Power Plant accident. The transport processes of 137Cs within Japanese cedar (Cryptomeria japonica) based on the detailed distribution of 137Cs from the outermost part to the center of the tree (outer bark, inner bark, sapwood, and heartwood) are discussed. In a cedar plantation in the Abukuma Mountains of Fukushima Prefecture, located approximately 14 km south-west from the TEPCO Fukushima Daiichi Nuclear Power Plant, three standing trees were felled in September 2017, and bark and wood samples were collected at cross-section intervals of approximately 1 cm. Besides, bark and wood samples were collected from living trees using an increment borer in the same forest stand every summer from 2015 to 2019. The transport process of 137Cs within the Japanese cedar is considered to have been influenced by the chemical form of 137Cs deposited on the bark surface and by the suppressive effects of potassium within the tree. Specifically, immediately after the accident, 137Cs deposited on the outermost layer of the outer bark migrated into the tree trunk through passive diffusion, with insoluble components remaining on the outermost outer bark. Subsequently, as root uptake of 137Cs began, the transport of 137Cs progressed from the inner bark towards the outer bark, while simultaneously being transported into the heartwood. As the 137Cs activity concentration in the heartwood increased, it is assumed that it eventually competed with potassium stored in the heartwood, resulting in a suppression of the further transport of 137Cs into the heartwood, causing a plateau in its activity concentration. In order to clarify the timing of the transition in the transport process within the tree body, long-term transport experiments over more than ten years using stable caesium are required

Bark (sound) · Biology · Botany · Cryptomeria · Geography · Japonica · Forestry · Horticulture · Korean Peninsula Historical and Political Studies · Radioactive contamination and transfer