Input and output budgets of radiocesium concerning the forest floor in the mountain forest of Fukushima released from the TEPCO's Fukushima Dai-ichi nuclear power plant accident

Estimations of radiocesium input and output concerning the forest floor within a mountain forest region have been conducted in the north and central part of the Abukuma Mountains of Fukushima, northeast Japan, after a 2–3 year period following the TEPCO Fukushima Dai-ichi nuclear power plant accident. The radiocesium input and output associated with surface washoff, throughfall, stemflow, and litterfall processes at experimental plots installed on the forest floor of evergreen Japanese cedars and deciduous Konara oaks have been monitored. Despite the high output potential in the mountainous forest of Fukushima, the results at both monitoring locations show the radiocesium input to be 4–50 times higher than the output during the summer monsoon in Fukushima. These results indicate that the radiocesium tends to be preserved in the forest ecosystem due to extremely low output ratios (0.05%–0.19%). Thus, the associated fluxes throughout the circulation process are key issues for the projecting the environmental fate of the radiocesium levels, along with the subsequent reconstruction of life emphasized within the setting. •Input and output budgets of radiocesium in the mountainous forest of Fukushima were investigated in 2013 and 2014.•137Cs outputs were 4–50 times higher than the 137Cs outputs during the monsoons.•The proportion of 137Cs output to radiocesium inventories was in the range of 0.05%–0.19% during the monsoons.•Radiocesium tends to be preserved in the forest ecosystem due to extremely low output ratios.•The forest floor seems to be a sink of radiocesium contamination than a source for the other ecosystems.