A fate of radiocesium fallout deposited on Japanese cedar between 2011 and 2015

Radiocesium (¹³⁷Cs) activity concentrations, mainly derived from the Fukushima accident of March 2011, were measured in green leaves without separation by leaf age (bulk green leaves; GL) and litterfall (LF) of Japanese cedar (Cryptomeria japonica) from 2011 to 2015. In all samples, ¹³⁷Cs concentrations decreased exponentially over time, but were always higher in LF than in GL. The difference in the fitting curve between GL and LF would reflect a difference in the dominant factor of the decrease between living and dead tissues (i.e., internal translocation and weathering, respectively). Over this same timeframe, potassium (K) concentrations in both GL and LF experienced repetitive periodical changes within a certain range, and thus, there was no specific correlation between ¹³⁷ Cs and K concentrations. However, analyses of the age classified green foliar parts (GL-S) could indicate another views. The annual changes in residual rates of both ¹³⁷Cs and K concentrations in GL-S demonstrated very similar reductions and an obvious linear correlation between each other. A complicated age configuration of the foliar parts and a difference in the translocation potential/attribute of each element would make the correlation between K and ¹³⁷Cs concentrations difficult to see in Japanese cedar. (author)