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).Ito, Satomi; Sasaki, Yoshito; Niizato, Tadafumi; Watanabe, Takayoshi; Mitachi, Katsuaki*
KEK Proceedings 2019-2, p.132 - 137, 2019/11
no abstracts in English
Watanabe, Takayoshi; Sasaki, Yoshito; Niizato, Tadafumi; Mitachi, Katsuaki*; Ito, Satomi
KEK Proceedings 2019-2, p.114 - 119, 2019/11
no abstracts in English
Watanabe, Takayoshi; Oyama, Takuya; Ishii, Yasuo; Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito
KEK Proceedings 2017-6, p.122 - 126, 2017/11
no abstracts in English
Sasaki, Yoshito; Ishii, Yasuo; Abe, Hironobu; Mitachi, Katsuaki; Watanabe, Takayoshi; Niizato, Tadafumi
The Horticulture Journal, 86(2), p.139 - 144, 2017/04
To examine the translocation of radiocesium (Cs) scattered by the Fukushima Daiichi Nuclear Power Plant accident that occurred in March 2011 to the Japanese chestnut, we investigated the autoradiography and radiocesium concentration in each part of the Japanese chestnut. The Japanese chestnut fruit has a thin skin between the kernel (cotyledons) and shell; the kernel of the fruit is edible. 
Cs concentration in each part of the fruit was found to be almost the same at about 1.0
10
Bq
kg
. Radiocesium concentration in chestnut weevil larvae found on the fruit was approximately one-seventh of that in the kernel.
Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito; Ishii, Yasuo; Watanabe, Takayoshi
Journal of Environmental Radioactivity, 161, p.11 - 21, 2016/09
Times Cited Count：29 Percentile：67.15(Environmental Sciences)Estimations of radiocesium input and output budgets concerning the forest floor in a mountain forest region have been conducted in the north and central part of the Abukuma Mountains of Fukushima, after 2 to 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 the experimental plots have been monitored on a forest floor of evergreen Japanese cedar and deciduous Konara oak forests. The results at both monitoring locations show the radiocesium input to be 4-50 times higher than the output during the rainy season in Fukushima. These results indicate that the radiocesium tend to be preserved in the forest ecosystem due to extremely low output ratios. Thus, the associated fluxes throughout the circulation process are key issues for the projecting the environmental fate of the radiocesium levels.
) contaminated by radionuclides from the Fukushima Dai-ichi Nuclear Power Plant accidentSasaki, Yoshito; Abe, Hironobu; Mitachi, Katsuaki; Watanabe, Takayoshi; Ishii, Yasuo; Niizato, Tadafumi
Journal of Environmental Radioactivity, 161, p.58 - 65, 2016/09
Times Cited Count：16 Percentile：45.60(Environmental Sciences)We report the behavior of radiocesium on the tree bark and its transfer into the stemflow of chestnut in a forest in Fukushima. The radiocesium concentration is greatest in 
2-cm stem, less in 
5-mm stem, and least in the leaves. In the 2-cm stem, the radiocesium concentration of the bark was approximately 10 times that of wood. The average Cs-137 concentration of the dissolved fraction of stem flow was about 10 Bq/L; the pH was nearly constant at 5.8. A strong positive correlation was observed between the radiocesium concentration and the electrical conductivity of the dissolved fraction of stemflow; this result suggests that radiocesium and electrolytes have the same elution mechanism from the tree. Some of the particles in the particulate fraction of the stem flow was strongly adsorbed radiocesium.
Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Ishii, Yasuo; Sasaki, Yoshito; Watanabe, Takayoshi; Kitamura, Akihiro; Yamaguchi, Masaaki
no journal, ,
This paper presents outflow characteristics of Cs-137 in mountainous forest of the Abukuma Mountains, Fukushima, during 2013-2014. Cs-137 deposition via throughfall, stemflow, and litterfall processes was estimated to be on the order of 10
Bq m
, and the outflow of Cs-137 via surface washoff was estimated to be on the order of 10
Bq m from April 2013 to December 2014 in the experimental plots installed in deciduous broad-leaved and cedar forests in the Abukuma Mountains. Cs-137 inventories of forest soil down to a level of 1 cm were decreasing in ridge and valley-bottom soil during the period from December 2012 to October 2014. The inventories in mountain slope showed both decreasing and increasing tendencies because of the heterogeneous transportation of Cs-137 via surface washoff on the slope. The results of outflow rate simulations using the SACT model developed in the Japan Atomic Energy Agency indicate decreasing tendency accompanied with a deeper penetration of Cs-137 into soil profile. Thus, the forest floor in the mountainous forest seems to be a sink of radiocesium contamination rather than a source for the contamination of the other ecosystems.
Ishii, Yasuo; Mitachi, Katsuaki; Abe, Hironobu; Niizato, Tadafumi
no journal, ,
Mountainous forest is currently one of the most important sources of radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant Accident in Fukushima. This study reports the changes in amounts and concentrations of radioactive cesium of the surface run-off substances and dose rate at forest observation plots in Ogi district of Kawauchi-mura and Yamakiya district of Kawamata-machi, and Ogaki soil saving dam, Fukushima during 2013 - 2015.
Ishii, Yasuo; Watanabe, Takayoshi; Oyama, Takuya; Sasaki, Yoshito; Abe, Hironobu; Mitachi, Katsuaki; Niizato, Tadafumi
no journal, ,
Mountainous forest is currently one of the most important sources of radioactive cesium released from the Fukushima Daiichi Nuclear Power Plant accident in Fukushima prefecture, which was covered approximately 70% of the land area by the forest. This study reports the changes in concentrations of radioactive cesium in sediments outflowed from the steep mountainous forest of the Abukuma Mountains, Fukushima, during September - December 2015.
Niizato, Tadafumi; Sasaki, Yoshito; Mitachi, Katsuaki*
no journal, ,
The outflow of Cs from the mountainous forest floor was estimated in the Abukuma Mountains, Fukushima. The outflow rates are decreased with a cover rate of the forest floor by a litter layer. The result shows the important role of the litter layer and undergrowth on a migration control of the radiocesium outflow from the forest floor.
Niizato, Tadafumi; Sasaki, Yoshito; Watanabe, Takayoshi; Mitachi, Katsuaki*; Ito, Satomi; Kuramoto, Takayuki*; Arai, Hirotsugu*; Nomura, Naoki*; Hayashi, Seiji*; Tamaoki, Masanori*
no journal, ,
Cs released from the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident has a long half-life of about 30 years, it is necessary to monitor the distribution and its radioecological impact over the long term. Mountainous forests, which accounts for about 70% of Fukushima prefecture, tend to be a sink of radiocesium contamination rather than a source for the contamination of other ecosystems. An understanding of the environmental dynamics of radiocesium in the forest floor of various conditions is important issue, while progressing to the resident return. In this paper, we report on the results of the field investigation into the Cs distribution and the Cs outflow in the mountainous forest of Fukushima, where the wildfire broke out in the spring of 2017.
Watanabe, Takayoshi; Ishii, Yasuo; Niizato, Tadafumi; Sasaki, Yoshito; Mitachi, Katsuaki*
no journal, ,
no abstracts in English
Watanabe, Takayoshi; Oyama, Takuya; Ishii, Yasuo; Niizato, Tadafumi; Abe, Hironobu; Mitachi, Katsuaki; Sasaki, Yoshito
no journal, ,
no abstracts in English
Sasaki, Yoshito; Niizato, Tadafumi; Mitachi, Katsuaki*
no journal, ,
We collected the tree sap in the Japanese cedar, and clarified the concentration of the dissolved radiocesium contained in the sap. It was shown that the amount of dissolved radiocesium in sap in each part was about 30 to 50% of the total amount of radiocesium at each part.
Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Mitachi, Katsuaki*; Watanabe, Takayoshi
no journal, ,
Sasaki, Yoshito; Niizato, Tadafumi; Mitachi, Katsuaki*; Ito, Satomi; Watanabe, Takayoshi
no journal, ,
no abstracts in English
Niizato, Tadafumi; Watanabe, Takayoshi; Mitachi, Katsuaki*; Sasaki, Yoshito; Ito, Satomi; Abe, Hironobu
no journal, ,
An understanding of long-term environmental dynamics of radiocesium, which is released by the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident, is a key issue for predicting the future radiocesium distribution and forest products radioactivity in a forested environment, especially Cs with half-life of 30 years. We compiled the five-years monitoring results of radiocesium input-output budgets in broad-leaved deciduous forests and Japanese cedar evergreen forests of the Abukuma Mountains, Fukushima, Japan. The input-output rates were a few percent of the radiocesium inventory of the monitoring site. In addition, both rates have been decreasing with time. Belowground radiocesium occupied 90% of the total inventory in the Japanese cedar forest on October 2015. The belowground radiocesium was distributed mainly in the topsoil of 0-6 cm depth, approximately 70-80% of the underground inventory on August 2016. These results indicate that the distribution of radiocesium in the forest is similar to the distribution of tree rootlet responsible for absorption of inorganic elements, nutrients, and water. This means long residence time of radiocesium in rooting zone. In the condition of the limited amount of radiocesium input-output rates in the forest, estimation of the migration flux of radiocesium from forest floor to the forest products are considered to be most important issues in the present.
Osawa, Kota*; Niizato, Tadafumi; Mitachi, Katsuaki*; Kawamura, Makoto*; Okawa, Masahiro*
no journal, ,
Primary outflow process of radiocesium, which is released by the TEPCO's Fukushima Dai-ichi Nuclear Power Plant accident, from a forest slope to a mountain stream is a particulate-bond state transport. A detailed estimation of riverbed form and sediment volume changing with time is a key issue to assess the radiocesium distribution in the forested environment. We attempt to restore the three-dimensional structure of underwater riverbed form in the mountain stream from the captured digital images by applying the SfM (Structure from Motion) and MVS (Multi View Stereo) technologies. Discrepancy between measured and analytical results increase with depth, the estimation errors are 73% and 93% in the depth of 20-25 cm and 10-15 cm, respectively. Next step is an improvement of the correction and image-capturing methods to reduce the estimation errors by elimination of the light refraction on the stream water surface.
Ito, Satomi; Sasaki, Yoshito; Niizato, Tadafumi; Watanabe, Takayoshi; Mitachi, Katsuaki*
no journal, ,
no abstracts in English
Watanabe, Takayoshi; Mitachi, Katsuaki; Abe, Hironobu; Niizato, Tadafumi
no journal, ,
Radionuclides such as radioactive cesium, now the main radiological contributor, were released in the environment by the Fukushima Dai-ichi Nuclear Power Plant accident. Japan Atomic Energy Agency initiated a project entitled "Long-Term Assessment of Transport of Radioactive Contaminant in the Environment of Fukushima" (F-TRACE project) in November 2012. To understand radioactive cesium transport in forest, we have conducted forest investigation at Ogi district, Kawauchi Village and Yamakiya district, Kawamata Town, Fukushima Prefecture since December 2012. As a part of the investigation, we carried out geophysical exploration of soil structure with ground penetrating radar (GPR) with 100 MHz and 500 MHz radio wave. In this presentation, we report correlation between imaging of soil structure obtained by GPR survey and depth profile of radioactive cesium in soil.
