137Cs transfer from canopies onto forest floors at Mount Tsukuba in the four years following the Fukushima nuclear accident

This study investigated the transport of Cs-137 within a forest ecosystem by examining temporal changes in the inventory and determining the major pathways of transfer following significant atmospheric deposition. A forested area of eastern Japan was monitored for four years immediately after the Fukushima nuclear power plant accident in March 2011 that released a large amount of radionuclides. The long physical half-life of Cs-137 means that contamination can persist for decades, so it is vital to understand the mechanisms underlying the Cs-137 dynamics in ecosystems. We sampled litterfall, throughfall, and soil, mainly from a cedar stand, over a four-year period, and analyzed the Cs-137 concentrations of each sample to determine the transfer rate and total inventory. After validating our methodology through a comparison with results from an earlier study, we determined the temporal changes in the Cs-137 distribution and in the major transfer pathway. Results showed that most Cs-137 intercepted by canopies was transferred rapidly over the first nine months, and that the major pathway was not litterfall but throughfall. The ecological half-life of the Cs-137 stocked in the canopy was calculated for both the early and later stages of contamination. Although the former is consistent with previous results, the latter ecological half-life is somewhat longer, probably because of dependence on the meteorological and tree physiological conditions at the site. This study presents valuable new data on the post-Fukushima Cs-137 contamination, enhancing our understanding of the associated dynamics in forest ecosystems. (c) 2018 Elsevier B.V. All rights reserved.