Dynamics of Radiocesium in Forest Ecosystems Affected by the Fukushima Daiichi Nuclear Power Plant Accident:

Species-related Transfer Processes of Radiocesium from Tree Crowns to Ground Floor during the First Two Years

Abstract

We examined the dynamics of radiocesium in the forest ecosystems which were contaminated by the Fukushima Daiichi Nuclear Power Plant Accident. Field measurement and sampling were conducted in eight stands; plantations of Japanese cedar (Cryptomeria japonica, n = 4), Hinoki cypress (Chamaecyparis obtusa, n = 2), Japanese red pine (Pinus densiflora, n =1), and deciduous broad-leaved forest dominated by oak (Quercus serrata, n = 1). In each stand, ¹³⁷Cs deposition in trees was estimated separately for each aboveground component (leaves, branches, and stems) using the data of specific ¹³⁷Cs activities and biomass of these components obtained during 2011-2013. We found that tree-¹³⁷Cs decreased substantially during the period for all forest types. In 2013, however, the ¹³⁷Cs ratio of trees to stand total (i.e., trees plus litter and soil) differed by forest type: Japanese cedar (6-24%) and Hinoki cypress (10-12%) were higher than pine (2%) and deciduous broad-leaved (3%) forests. The results suggested that the early 2-year transfer process of radiocesium from the tree crown to the ground differed depending on the amount of initial ¹³⁷Cs deposition and differences in leaf longevity and biomass of dominant species.