B13A-0586
Investigation of radioactive cesium transportation from forest canopy to floor by litterfall, stemflow and throughfall in northern Fukushima

Monday, 14 December 2015
Poster Hall (Moscone South)
Izuki Endo1, Nobuhito Ohte2, Kohei Iseda3, Keitaro Tanoi1, Atsushi Hirose1, Natsuko I Kobayashi1, Masashi Murakami4, Naoko Tokuchi5 and Mizue Ohashi6, (1)University of Tokyo, Bunkyo-ku, Japan, (2)Kyoto University, Kyoto, Japan, (3)Ehime Prefectural Government, Matsuyama, Japan, (4)Chiba University, Chiba, Japan, (5)Kyoto University, Field Science Education Research Center, Kyoto, Japan, (6)University of Hyogo, Himeji, Japan
Abstract:
After the Fukushima Daiichi nuclear power plant accident due to Great East Japan Earthquake in March 11th 2011, large areas of forest have been highly contaminated by the radioactive nuclides. Most of the deposited radioactive material to the canopy is then washed out with rainfall or leaf fall due to the tree phenology. There have been studies showing that the amount of 137Cs transportation differs among litter components and water pathways, and was affected by seasonal variations. Thus, to evaluate the amount of 137Cs flux from canopy to forest floor, continuous monitoring of each component (litterfall, throughfall and stemflow) is required.

We investigated the annual transfer of 137Cs from the forest canopy to the floor by litterfall, throughfall and stemflow at two different forest types in northern Fukushima after two years from the accident. Seasonal variations in 137Cs transportation and differences between forests types were also determined.

Forest sites were set in the upstream part of Kami-Oguni River catchment at Date city, which locates approximately 50km northwest from the Fukushima Dai-ichi Nuclear Power Plant. The study sites consisted of two deciduous (Mixed deciduous-1, Mixed deciduous-2) and one cedar (Cedar plantation) stands.

The cumulative 137Cs transportation from the forest canopy to the floor was 6.6 kBq m−2 year−1 for the Mixed deciduous-1, 3.9 kBq m−2 year−1 for the Mixed deciduous-2 and 11.0 kBq m−2 year−1 for the Cedar plantation. 137Cs transportation with litterfall increased in the defoliation period which correlated with the increased amount of litterfall. 137Cs transportation with throughfall and stemflow increased in the rainy season. 137Cs flux by litterfall was higher in Cedar plantation compared with that of mixed deciduous forests, while the opposite result was obtained for stemflow.

The ratio of annual 137Cs flux and the estimated 137Cs amount deposited in the forests will be discussed.

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