Seasonal Changes in the Concentration of ¹³⁷Cs in the Coppiced Trees of Konara Oak (Quercus serrata) Regenerated after the Fukushima Dai-ichi Nuclear Power Plant Accident

Abstract

We investigated the seasonal changes in the concentrations of ¹³⁷Cs and potassium in various parts of konara oaks (Quercus serrata) that were regenerated after the Fukushima Daiichi Nuclear Power Plant accident. Samples of leaves, branches, and trunks were collected from six individuals at four times between June 2022 and February 2023. We measured ¹³⁷Cs concentrations in the leaves, branches, and trunks, as well as potassium concentrations in the leaves and trunk xylem. Seasonal changes were observed in the ¹³⁷Cs concentrations of the leaves, bark and outer xylem of the trunks. The ¹³⁷Cs concentrations in the leaves decreased from early summer (June) to autumn (November), while the concentrations in the bark and outer xylem of the trunks increased from early summer (June) to late summer (September), and then decreased from autumn (November) to winter (February). The potassium concentrations in the leaves and trunk xylem showed a similar trend with the ¹³⁷Cs concentrations. This study indicated that ¹³⁷Cs concentrations in branches and the whole trunk had only small variations throughout the year. It is suggested that¹³⁷Cs concentrations in konara oak trunks can be estimated by measuring ¹³⁷Cs concentrations in branches potentially reducing the need for seasonal corrections.