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Atarashi-Andoh, Mariko; Koarashi, Jun; Tsuzuki, Katsunori; Takeuchi, Erina; Nishimura, Shusaku; Muto, Kotomi*; Matsunaga, Takeshi*
Journal of Environmental Radioactivity, 238-239, p.106725_1 - 106725_8, 2021/11
Times Cited Count：1 Percentile：6.09(Environmental Sciences)To understand the spatial variation in soil 
Cs inventory in complex mountainous topography, a whole-area investigation of Cs deposition in a broad-leaved forest catchment of a mountain stream was conducted using grid sampling. Across the catchment, organic and surface mineral soil layers were collected at 42 locations in 2013 and 6 locations in 2015. Cs deposition on the forest floor exhibited high spatial heterogeneity and altitude-dependent distribution over the catchment. The Cs retention ratio in the organic layer ranged from 6% to 82% in 2013. The Cs retention ratios had positive correlations with the material inventory in the organic layer and the elevation. The Cs retention ratios in the organic layer were less than 20% in 2015, even at the locations where the retention ratio was higher than 55% in 2013. Although there was spatial variation in the migration speed, Cs migration from the organic layer to mineral soil was almost completed within 4 y of the deposition.
Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.
JAEA-Research 2020-007, 249 Pages, 2020/10
JAEA-Research-2020-007.pdf:15.83MB
The accident of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, Japan Atomic Energy Agency (JAEA) has been conducting "Long-term Assessment of Transport of Radioactive Contaminants in the Environment of Fukushima" concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.
Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*
Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04
Times Cited Count：9 Percentile：34.78(Multidisciplinary Sciences)We conducted a pilot-scale decontamination study in a deciduous broadleaved forest in Fukushima. The entire forest, other than two untreated areas, was decontaminated by removing the litter layer approximately 3.3 years after the accident. For three years after decontamination, we quantified Cs contamination levels in the litter and topsoil layers and in the tree leaves, in the untreated and decontaminated areas. The decreased inventories of litter-associated Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of Cs from litter layers to the underlying mineral soil, which differs from the observations in post-Chernobyl studies of European forest ecosystems. The results suggest that litter-removal decontamination can only be successful if it is implemented more quickly for Japanese forest ecosystems.
Cs in organic layer and mineral soil in Japanese forests; Four-year observation and model analysisMuto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun
Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11
Times Cited Count：13 Percentile：49.32(Environmental Sciences)Vertical distributions of Cs in the soil profile were observed at five forest sites with different vegetation types for 4.4 years after the Fukushima Dai-ichi Nuclear Power Plant accident, and Cs migration in the organic layer and mineral soil was analyzed based on a comparison of models and observations. Cesium-137 migration from the organic layer was faster than that observed in European forests, suggesting that the mobility and bioavailability of Cs could be suppressed rapidly in Japanese forests. The diffusion coefficients of Cs in the mineral soil were estimated to be 0.042-0.55 cm
y
, which were roughly comparable with those of European forest soils affected by the Chernobyl Nuclear Power Plant accident. Model predictions indicated Cs mainly distributed in the surface mineral soil at 10 years after the accident. It suggest that the Cs deposited onto Japanese forest ecosystems will be retained in the surface layers of mineral soil for a long time.
Dohi, Terumi; Muto, Kotomi; Yoshimura, Kazuya; Kanaizuka, Seiichi*; Iijima, Kazuki
KEK Proceedings 2019-2, p.14 - 19, 2019/11
In order to investigate the effect of topography, meteorological condition, etc., on the spatial distribution of air dose rate on the main plume path, we evaluated walking survey data of air dose rates on Mt. Koutaishi and Mt. Juman, directed in northwest of and approximately 33 km and 11 km from the FDNPP. Measurements were performed on two orbital routs with different constant altitudes and general mountain trails in each mountain. The measurement data were compared with airborne monitoring results to investigate the relation between the dose rate distribution and elevation and orientation. At Mt. Koutaishi, the air dose rate was particularly high on the east side of the mountain, and the significant dependence of direction on the dose rate distribution was observed. Furthermore, high dose rate near the mountain foot indicates possibility of large deposition of Cs due to the plume passage from the FDNPP. At Mt. Juman, uniformly distribution of air dose rate was observed, and effect of wet deposition was considered. These results suggest the possibility of different deposition mechanisms in mountain range unit.
Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.
JAEA-Research 2019-002, 235 Pages, 2019/08
JAEA-Research-2019-002.pdf:21.04MB
The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.
Cs retention mechanism in surface soils during the early stage after the Fukushima nuclear accidentKoarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Muto, Kotomi; Matsunaga, Takeshi*
Scientific Reports (Internet), 9, p.7034_1 - 7034_10, 2019/05
Times Cited Count：32 Percentile：79.74(Multidisciplinary Sciences)The aim of the present study is to explore the retention mechanisms of Cs in the surface soil layers of terrestrial ecosystems affected by the Fukushima NPP accident, with a specific focus on the interactions between Cs, soil minerals, and organic matter. Soil samples were collected from field, orchard, and forest sites in July 2011, separated into three soil fractions with different mineral-organic interaction characteristics. The results show that 20-71% of the Cs was retained in association with relatively mineral-free, particulate organic matter-dominant fractions in the orchard and forest surface soil layers. Given the physicochemical and mineralogical properties and the Cs extractability of the soils, Cs incorporation into the complex structure of particulate organic matter is likely the main mechanism for Cs retention in the surface soil layers.
Cs fluvial export from a forest catchment evaluated by stable carbon and nitrogen isotopic characterization of organic matterMuto, Kotomi; Atarashi-Andoh, Mariko; Koarashi, Jun; Takeuchi, Erina; Nishimura, Shusaku; Tsuzuki, Katsunori; Matsunaga, Takeshi*
Journal of Radioanalytical and Nuclear Chemistry, 314(1), p.403 - 411, 2017/10
Times Cited Count：16 Percentile：83.87(Chemistry, Analytical)Fluvial export of particulate and dissolved Cs was investigated to reveal its sources and transfer mechanisms in a broadleaved forest catchment using a continuous collection system. The finest size fraction (
75
m), consisting of decomposed litter and surface mineral soil, was the dominant fraction in the particulate Cs load, although the contribution of coarser size fractions increased during high water discharge in 2014. The dissolved Cs originated from the decomposition of Cs-contaminated litter. Temporal changes in Cs distribution in the litter-mineral soil system indicated that the dissolved Cs load will be moderated in several years, while particulate Cs load has the potential to continue for a long time.
Koarashi, Jun; Nishimura, Shusaku; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi
Chemosphere, 165, p.335 - 341, 2016/12
Times Cited Count：40 Percentile：77.33(Environmental Sciences)We established field lysimeters in a Japanese deciduous broad-leaved forest soon after the Fukushima nuclear accident to continuously monitor the downward transfer of Cs at three depths: the litter-mineral soil boundary and depths of 5 cm and 10 cm in the mineral soil. Observations were conducted at two sites within the forest from May 2011 to May 2015. Results revealed similar temporal and depth-wise variations in Cs downward fluxes for both sites. The Cs downward fluxes generally decreased year by year at all depths, indicating that Cs was rapidly leached from the forest-floor litter layer and was then immobilized in the upper (0-5 cm) mineral soil layer through its interaction with clay minerals. The decreased inventory of mobile (or bioavailable) Cs observed during early stages after deposition indicates that the litter-soil system in the Japanese deciduous forest provides only a temporary source for Cs recycling in plants.
Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accidentMatsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; et al.
Journal of Radioanalytical and Nuclear Chemistry, 310(2), p.679 - 693, 2016/11
Times Cited Count：6 Percentile：49.29(Chemistry, Analytical)Particulate Cs in stream water was collected continuously for two years in order to assess the long-term trend of the Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate Cs concentration decreased at a faster rate than the rate due to radioactive decay. This decrease might be resulted from redistribution of the easily eroded and polluted soil surface due to heavy rain events such as typhoons. These findings indicate that the particulate Cs load was subject to the inter-annual variations in rainfalls, and decreased gradually over a long period of time due to a decrease in Cs concentration in SS.
Muto, Kotomi; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku; Koarashi, Jun; Tsuzuki, Katsunori; Nakanishi, Takahiro; Matsunaga, Takeshi
KEK Proceedings 2015-4, p.252 - 257, 2015/11
As a result of the Fukushima Daiichi Nuclear Power Plant accident, a large amount of radiocesium released into the atmosphere was deposited in forests. This study estimated the monthly trend in the fluvial discharges of radiocesium from a forest. The study site was a forested catchment in Kitaibaraki City. Radiocesium in river water was collected with a filtration system as both particulate and dissolved components. Filters and columns including dissolved Cs absorbent were replaced every month. The collected suspended solids were sieved into 2000-3000 m, 500-2000 m, 75-500 m, and 75 m fractions. The Cs concentrations in the samples were measured using 
-ray spectrometry with Ge semiconductor detectors. The Cs discharge increased with the river water discharge. The particulate Cs discharge was dominant in both 2013 and 2014. The Cs discharge rate of the dissolved component increased in winter, when the river water discharge decreased.
Cs in forest soil profiles after the Fukushima nuclear accidentMuto, Kotomi; Atarashi-Andoh, Mariko; Koarashi, Jun; Matsunaga, Takeshi
no journal, ,
no abstracts in English
Takeuchi, Erina; Atarashi-Andoh, Mariko; Koarashi, Jun; Nishimura, Shusaku; Muto, Kotomi; Tsuzuki, Katsunori; Nakanishi, Takahiro; Matsunaga, Takeshi
no journal, ,
no abstracts in English
Cs) in forest soils after the Fukushima Dai-ichi Nuclear Power Plant accident; Observations and model analysisMuto, Kotomi; Atarashi-Andoh, Mariko; Koarashi, Jun; Matsunaga, Takeshi
no journal, ,
no abstracts in English
Ishii, Yasuo; Muto, Kotomi; Hagiwara, Hiroki; Ito, Shoichi*; Takahashi, Makoto*; Tagomori, Hisaya; Dohi, Terumi; Kitamura, Akihiro
no journal, ,
A forest fire broke out on 29 April, 2017 in the Mount-Juman that straddles the Namie-city and Futaba-city in Fukushima Prefecture. The fire was extinguished on 10 May, 2017. In this period, atmospheric particle matters have been collected by Radiation Monitoring Unit Fukushima Prefectural Government in neighboring region. In this study we performed chemical analysis of the atmospheric particle matters and investigated the origination.
Muto, Kotomi; Dohi, Terumi; Yoshimura, Kazuya; Kanaizuka, Seiichi*; Iijima, Kazuki
no journal, ,
no abstracts in English
