Japan Geoscience Union Meeting 2016

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-AG Applied Geosciences

[M-AG24] Dynamics of radionuclides emitted from Fukuchima Dai-ichi Nuclear Power Plant in the environment

Mon. May 23, 2016 9:00 AM - 10:30 AM A03 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Kazuyuki Kita(Faculty of Science, Ibaraki University), Yuichi Onda(Center for Research on Isotopes and Environmental Dynamics, University of Tsukuba), Teruyuki Nakajima(Japan Aerospace Exploration Agency), Yasuhito Igarashi(Atmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute), Masatoshi Yamada(Institute of Radiation Emergency Medicine, Hirosaki University), Chisato Takenaka(Graduate School of Bioagricultural Sciences, Nagoya University), masayoshi yamamoto(Low Level Radioactivity Laboratory, Kanazawa University), Jota Kanda(Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology), Atsushi Shinohara(Osaka university), Chair:Yukihiko Satou(Graduate School of Pure and Applied Sciences, University of Tsukuba)

10:00 AM - 10:15 AM

[MAG24-05] Effects of radiocesium transfer from the canopy to forest floor on its accumulation in litter and soil layers.

*Hiroaki Kato1, Yuichi Onda1, Ayumi Kawamori1, Keigo Hisadome2 (1.Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 2.Asia Air Survey Co. LTD.)

Keywords:Radiocesium, Forest, Transfer, Litter layer

Radiocesium deposited on forest area is initially intercepted by forest canopy and subsequently deposits on forest floor in association with rainwater and litter-fall. The intercepted radiocesium by the canopy acts as a source of secondary radioactive contamination of forest floor, however those effects on the accumulation of radiocesium to litter and soil layers have not been assessed quantitatively.
We investigated the transfer of canopy-intercepted radiocesium to the forest floor during 4 years following the Fukushima Daiichi Nuclear Power Plant accident. The cesium-137 (137Cs) contents in throughfall, stemflow, and litterfall were monitored in two coniferous stands (plantation of Japanese cedar) and a mixed deciduous broad-leaved forest stand (Japanese oak with red pine). We also measured the gamma count rate of radiocesium at the forest floor using a portable Ge gamma-ray detector.
Total Cs-137 deposition flux from the canopy to forest floor for the mature cedar, young cedar, and the mixed broad-leaved stands were 166 kBq/m2, 174 kBq/m2, and 60 kBq/m2, respectively. These values correspond to 38%, 40% and 13% of total atmospheric input after the accident. The spatial pattern of radiocesium at the forest floor have not changed during monitoring period, suggesting that radiocesium partitioning and leaching by the forest canopy is rather constant over time. We investigated temporal change of radiocesium inventory in litter and soil layer in the study site (Takahashi et al., 2015; NRA, 2015), which was later compared with the radiocesium depositional flux onto forest floor. The radiocesium inventory in litter layer decreased with time in all the forest sites, although the radiocesium continuously deposited on the forest floor (~ 400 Bq/m2/day). The radiocesium migration rate from the litter layer to the underlain mineral soil layer was estimated based on the analysis of the measured temporal changes of depositional flux to forest floor and inventory in litter and soil layers.