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Monitoring of Seasonal Variations in Radiocesium from the Fukushima Accident in Litterfall of Four Broad-Leaf Tree

Toshihiro Yoshihara, Hideyuki Matsumura and Shin-Nosuke Hashida

The concentration of radiocesium (¹³⁷Cs) primarily derived from the Fukushima accident in March 2011 was measured in litterfall of four broad leaf trees (Prunus x Yedoensis cv. Somei-Yoshino, Cinnamomum camphora, Acer buergerianum, and Aesculus hippocastanum) to see whether a typical reduction would occur during defoliation as with its biologically essential analogue, potassium (K). The sampling was performed every two to four weeks between 2011 and 2014, using a trap to prevent contact with the ground. Results indicated that the concentrations of ¹³⁷Cs basically decreased over time in each defoliation season, although a small derangement could be seen. On the other hand, the concentrations of K in litterfall (except for Somei-Yoshino) once increased at the mid-season and then decreased. As a result, although the K concentrations in litterfall collected last were less than that collected earlier in the season, the seasonal changes in K and ¹³⁷Cs were not synchronized except for Somei-Yoshino. It is possible that an unknown species-specific K regulationbased time-lag and/or irregularity could influence the synchrony between ¹³⁷Cs and K transportation, although the seasonal reduction in ¹³⁷Cs concentration would typically occurred as part of the physiological demand for K.