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Journal Articles

Spatial variations in radiocesium deposition and litter-soil distribution in a mountainous forest catchment affected by the Fukushima nuclear accident

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

To understand the spatial variation in soil $$^{137}$$Cs inventory in complex mountainous topography, a whole-area investigation of $$^{137}$$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. $$^{137}$$Cs deposition on the forest floor exhibited high spatial heterogeneity and altitude-dependent distribution over the catchment. The $$^{137}$$Cs retention ratio in the organic layer ranged from 6% to 82% in 2013. The $$^{137}$$Cs retention ratios had positive correlations with the material inventory in the organic layer and the elevation. The $$^{137}$$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, $$^{137}$$Cs migration from the organic layer to mineral soil was almost completed within 4 y of the deposition.

JAEA Reports

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2019

Nakano, Masanao; Fujii, Tomoko; Nemoto, Masashi; Tobita, Keiji; Seya, Natsumi; Nishimura, Shusaku; Hosomi, Kenji; Nagaoka, Mika; Yokoyama, Hiroya; Matsubara, Natsumi; et al.

JAEA-Review 2020-069, 163 Pages, 2021/02

JAEA-Review-2020-069.pdf:4.78MB

Environmental radiation monitoring around the Tokai Reprocessing Plant has been performed by the Nuclear Fuel Cycle Engineering Laboratories, based on "Safety Regulations for the Reprocessing Plant of Japan Atomic Energy Agency, Chapter IV - Environmental Monitoring". This annual report presents the results of the environmental monitoring and the dose estimation to the hypothetical inhabitant due to the radioactivity discharged from the plant to the atmosphere and the sea during April 2019 to March 2020. In this report, some data include the influence of the accidental release from the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Co., Inc. (the trade name was changed to Tokyo Electric Power Company Holdings, Inc. on April 1, 2016) in March 2011. Appendices present comprehensive information, such as monitoring programs, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes. In addition, the data which were influenced by the accidental release and exceeded the normal range of fluctuation in the monitoring, were evaluated.

Journal Articles

A Knowledge-sharing activity on the environmental radiation monitoring results affected by the Fukushima-Daiichi Nuclear Power Plant Accident at Tokai-Oarai area in Ibaraki Prefecture

Nakano, Masanao; Hosomi, Kenji; Nishimura, Shusaku; Matsubara, Natsumi; Okura, Takehisa; Kuramochi, Akihiko; Kawasaki, Masatsugu; Takeuchi, Erina; Fujii, Yutaka*; Jinno, Tsukasa*; et al.

Hoken Butsuri (Internet), 55(2), p.102 - 109, 2020/06

After the Fukushima-Daiichi Nuclear Power Station (1F) Accident in March 2011, the increase was significantly observed in a part of the result of the environmental radiation monitoring in Ibaraki prefecture. "The review meeting of the environmental effect from 1F accident" was established to discuss technically the fluctuation of monitoring data. The review meeting collected the monitoring data from the four nuclear operators, and discussed a fluctuating trend, $$^{134}$$Cs/$$^{137}$$Cs activity ratio, and so on. In this report, the results of the dose rate and $$^{137}$$Cs in fallout, surface soil, flatfish and seabed sediment are introduced. Also the problem solving in the review meeting is introduced.

Journal Articles

Effectiveness of decontamination by litter removal in Japanese forest ecosystems affected by the Fukushima nuclear accident

Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*

Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04

 Times Cited Count:5 Percentile:62.5(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 $$^{137}$$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 $$^{137}$$Cs in the decontaminated areas were observed only in the first year after decontamination. Generally, no decontamination effects were observed on the $$^{137}$$Cs transfer in tree leaves. The primary reason for this was the rapid shift in the main reservoir of $$^{137}$$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.

JAEA Reports

Annual report on the environmental radiation monitoring around the Tokai Reprocessing Plant FY2018

Nakano, Masanao; Fujii, Tomoko; Nemoto, Masashi; Tobita, Keiji; Kono, Takahiko; Hosomi, Kenji; Nishimura, Shusaku; Matsubara, Natsumi; Maehara, Yushi; Narita, Ryosuke; et al.

JAEA-Review 2019-048, 165 Pages, 2020/03

JAEA-Review-2019-048.pdf:2.69MB

Environmental radiation monitoring around the Tokai Reprocessing Plant has been performed by the Nuclear Fuel Cycle Engineering Laboratories, based on "Safety Regulations for the Reprocessing Plant of Japan Atomic Energy Agency, Chapter IV - Environmental Monitoring". This annual report presents the results of the environmental monitoring and the dose estimation to the hypothetical inhabitant due to the radioactivity discharged from the plant to the atmosphere and the sea during April 2018 to March 2019. In this report, some data include the influence of the accidental release from the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Co., Inc. (the trade name was changed to Tokyo Electric Power Company Holdings, Inc. on April 1, 2016) in March 2011. Appendices present comprehensive information, such as monitoring programs, monitoring methods, monitoring results and their trends, meteorological data and discharged radioactive wastes. In addition, the data which were influenced by the accidental release and exceeded the normal range of fluctuation in the monitoring, were evaluated.

Journal Articles

A New perspective on the $$^{137}$$Cs retention mechanism in surface soils during the early stage after the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Muto, Kotomi; Matsunaga, Takeshi*

Scientific Reports (Internet), 9, p.7034_1 - 7034_10, 2019/05

 Times Cited Count:19 Percentile:84.46(Multidisciplinary Sciences)

The aim of the present study is to explore the retention mechanisms of $$^{137}$$Cs in the surface soil layers of terrestrial ecosystems affected by the Fukushima NPP accident, with a specific focus on the interactions between $$^{137}$$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 $$^{137}$$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 $$^{137}$$Cs extractability of the soils, $$^{137}$$Cs incorporation into the complex structure of particulate organic matter is likely the main mechanism for $$^{137}$$Cs retention in the surface soil layers.

Journal Articles

Radiocesium distribution in aggregate-size fractions of cropland and forest soils affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Sato, Tsutomu*; Nagao, Seiya*

Chemosphere, 205, p.147 - 155, 2018/08

 Times Cited Count:14 Percentile:65.6(Environmental Sciences)

There is little understanding of how soil aggregation can affect the mobility and bioavailability of $$^{137}$$Cs in soils. To explore this, soil samples were collected at seven sites under different land-use conditions in Fukushima and were separated into four aggregate-size fractions. The fractions were then analyzed for $$^{137}$$Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and $$^{137}$$Cs was largely associated with large-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and most of $$^{137}$$Cs was in the clay- and silt-sized fractions. Across all sites, the $$^{137}$$Cs extractability was higher in the large-sized aggregate fractions than in the clay-sized fractions. The results demonstrate that large-sized aggregates are a significant reservoir of potentially mobile and bioavailable $$^{137}$$Cs in organic-rich (forest and orchard) soils.

Journal Articles

Sources of $$^{137}$$Cs fluvial export from a forest catchment evaluated by stable carbon and nitrogen isotopic characterization of organic matter

Muto, 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:12 Percentile:86.92(Chemistry, Analytical)

Fluvial export of particulate and dissolved $$^{137}$$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$$mu$$m), consisting of decomposed litter and surface mineral soil, was the dominant fraction in the particulate $$^{137}$$Cs load, although the contribution of coarser size fractions increased during high water discharge in 2014. The dissolved $$^{137}$$Cs originated from the decomposition of $$^{137}$$Cs-contaminated litter. Temporal changes in $$^{137}$$Cs distribution in the litter-mineral soil system indicated that the dissolved $$^{137}$$Cs load will be moderated in several years, while particulate $$^{137}$$Cs load has the potential to continue for a long time.

Journal Articles

Post-deposition early-phase migration and retention behavior of radiocesium in a litter-mineral soil system in a Japanese deciduous forest affected by the Fukushima nuclear accident

Koarashi, Jun; Nishimura, Shusaku; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi

Chemosphere, 165, p.335 - 341, 2016/12

 Times Cited Count:25 Percentile:75.78(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 $$^{137}$$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 $$^{137}$$Cs downward fluxes for both sites. The $$^{137}$$Cs downward fluxes generally decreased year by year at all depths, indicating that $$^{137}$$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) $$^{137}$$Cs observed during early stages after deposition indicates that the litter-soil system in the Japanese deciduous forest provides only a temporary source for $$^{137}$$Cs recycling in plants.

Journal Articles

Year-round variations in the fluvial transport load of particulate $$^{137}$$Cs in a forested catchment affected by the Fukushima Daiichi Nuclear Power Plant accident

Matsunaga, 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

AA2015-0821.pdf:3.78MB

 Times Cited Count:5 Percentile:54.39(Chemistry, Analytical)

Particulate $$^{137}$$Cs in stream water was collected continuously for two years in order to assess the long-term trend of the $$^{137}$$Cs discharge from the forest environment. Sampling was conducted from December 2011 to December 2013 in a mountainous stream, which received the $$^{137}$$Cs from the Fukushima Daiichi Nuclear Power Plant accident. A seasonal increase in fluvial transport load of particulate $$^{137}$$Cs associated with suspended solids (SS) was observed in August and September when rainfall was abundant. The particulate $$^{137}$$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 $$^{137}$$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 $$^{137}$$Cs concentration in SS.

Journal Articles

Fluvial discharges of particulate and dissolved radiocesium from a forest and its monthly trend

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 $$mu$$m, 500-2000 $$mu$$m, 75-500 $$mu$$m, and $$<$$75 $$mu$$m fractions. The $$^{137}$$Cs concentrations in the samples were measured using $$gamma$$-ray spectrometry with Ge semiconductor detectors. The $$^{137}$$Cs discharge increased with the river water discharge. The particulate $$^{137}$$Cs discharge was dominant in both 2013 and 2014. The $$^{137}$$Cs discharge rate of the dissolved component increased in winter, when the river water discharge decreased.

Journal Articles

Catchment-scale distribution of radiocesium air dose rate in a mountainous deciduous forest and its relation to topography

Atarashi-Andoh, Mariko; Koarashi, Jun; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Matsunaga, Takeshi

Journal of Environmental Radioactivity, 147, p.1 - 7, 2015/09

AA2014-0585.pdf:2.18MB

 Times Cited Count:19 Percentile:61.83(Environmental Sciences)

We collected a large amount of radiocesium air dose rate data by mountain-walking with a small $$gamma$$-ray survey system, KURAMA-II, to create an air dose rate map of a mountainous deciduous forest that received radiocesium from the Fukushima Dai-ichi Nuclear Power Plant accident. Measurements were conducted in a small stream catchment 0.6 km$$^{2}$$ in size in August and September 2013, and the relationship between air dose rates and the mountainous topography was examined. Air dose rates increased with elevation, suggesting that more radiocesium was deposited on ridges, and that it had remained there for 2.5 years with no significant migration due to soil erosion or water drainage. Slope aspect also strongly affected air dose rates. By the continuous measurement using KURAMA-II, we describe the variation in air dose rates in a mountainous area and suggest that it is important to consider topography when selecting sampling points to estimating dose rates or contaminant deposition.

Journal Articles

A Passive collection system for whole size fractions in river suspended solids

Matsunaga, Takeshi; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Tsuzuki, Katsunori; Nishimura, Shusaku; Koarashi, Jun; Otosaka, Shigeyoshi; Sato, Tsutomu*; Nagao, Seiya*

Journal of Radioanalytical and Nuclear Chemistry, 303(2), p.1291 - 1295, 2015/02

 Times Cited Count:3 Percentile:32.14(Chemistry, Analytical)

An innovative, yet simple method for the passive collection of radioactive materials in river water has been developed and validated. The method employes large filter vessels, containing multiple cartridge filters. River water is led to the system naturally using a drop of the riverbed by hose from upstream. This method makes long-term, unmanned monitoring possible. In addition to regular radioactivity analyses, this method provides an opportunity for the characterization of suspended materials based on its ample collection quantities (more than several tens of grams). This method may also be applicable to sediment-bound chemicals.

Journal Articles

Topographic heterogeneity effect on the accumulation of Fukushima-derived radiocesium on forest floor driven by biologically mediated processes

Koarashi, Jun; Atarashi-Andoh, Mariko; Takeuchi, Erina; Nishimura, Shusaku

Scientific Reports (Internet), 4, p.6853_1 - 6853_7, 2014/10

 Times Cited Count:39 Percentile:80.12(Multidisciplinary Sciences)

The accident at the Fukushima Daiichi Nuclear Power Plant caused serious radiocesium ($$^{137}$$Cs) contamination of forest ecosystems located in mountainous and hilly regions with steep terrain. To understand topographic effects on the redistribution and accumulation of $$^{137}$$Cs on forest floor, we investigated the distribution of Fukushima-derived $$^{137}$$Cs in forest-floor litter layers on a steep hillslope in a Japanese deciduous forest in August 2013. Both leaf-litter materials and litter-associated $$^{137}$$Cs were accumulated in large amounts at the bottom of the hillslope. At the bottom, a significant fraction (65%) of the $$^{137}$$Cs inventory was observed to be associated with newly shed and less degraded leaf-litter materials, with estimated mean ages of 0.5-1.5 years, added via litterfall after the accident. Newly emerged leaves at the site were contaminated with Fukushima-derived $$^{137}$$Cs in May 2011 (two months after the accident) and $$^{137}$$Cs concentration in them decreased with time. However, the concentrations were still two orders of magnitude higher than the pre-accident level in 2013 and 2014. These observations are the first to show that $$^{137}$$Cs redistribution on a forested hillslope is strongly controlled by biologically mediated processes and continues to supply $$^{137}$$Cs to the bottom via litterfall at a reduced rate.

Oral presentation

Shifts in microbial sulfate reduction to CO$$_{2}$$ reduction depending on groundwater flow characteristics in deep granitic aquifers

Konno, Yuta*; Komatsu, Daisuke*; Nishimura, Shusaku*; Fukuda, Akari; Aosai, Daisuke; Mizuno, Takashi; Nagao, Seiya*; Tsunogai, Urumu*; Suzuki, Yohei*

no journal, , 

no abstracts in English

Oral presentation

Characterization of dissolved organic matter in groundwater during laboratory incubation

Nishimura, Shusaku*; Suzuki, Yohei*; Fukuda, Akari; Konno, Yuta*; Shuin, Kuniko*; Nagao, Seiya*

no journal, , 

no abstracts in English

Oral presentation

Production of charred plants and subsequent their distribution, behavior and function in soils

Yanagi, Yukiko*; Shindo, Haruo*; Nishimura, Shusaku

no journal, , 

Biochar, consisting of charred biomass products involving plants, is a stable form of C. The findings obtained in our studies, in which the production and the distribution, behavior, and function of charred plant fragments (CPFs) in soils have been investigated, may get a better understanding of the role of biochar. (1) The dehydrative polycondensation reactions occurred during the burning. (2) The CPFs were hardly mineralized by soil microorganisms. (3) The silt-sized fraction was an important reservoir of CPFs. (4) The CPFs are subjected to weathering and biological degradation in soil after burning, and are transformed to black humic acids. (5) In conclusion, after burning, the CPFs produce the black humic acids with the progression of abiotic and biotic degradation in soils. The parts of these CPFs are more stabilized by forming the complexes with inorganic components in the silt-sized fraction. Thus, their complexes are preserved in the fraction for a long period of time.

Oral presentation

Distribution of Cs-137 in soil aggregate fractions

Nishimura, Shusaku; Koarashi, Jun; Atarashi-Andoh, Mariko

no journal, , 

no abstracts in English

Oral presentation

Measurement of air dose rate distribution in a forest catchment using KURAMA-II

Takeuchi, Erina; Atarashi-Andoh, Mariko; Koarashi, Jun; Nishimura, Shusaku; Tsuzuki, Katsunori; Matsunaga, Takeshi

no journal, , 

no abstracts in English

Oral presentation

Fluvial discharges of particulate and dissolved radiocesium from a forest catchment

Takeuchi, Erina; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Nakanishi, Takahiro; Tsuzuki, Katsunori; Koarashi, Jun; Matsunaga, Takeshi

no journal, , 

no abstracts in English

29 (Records 1-20 displayed on this page)