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Katata, Genki*; Yamaguchi, Takashi*; Watanabe, Makoto*; Fukushima, Keitaro*; Nakayama, Masataka*; Nagano, Hirohiko*; Koarashi, Jun; Tateno, Ryunosuke*; Kubota, Tomohiro
Atmospheric Environment, 298, p.119640_1 - 119640_12, 2023/04
Ota, Masakazu; Koarashi, Jun
Isotope News, (784), p.28 - 31, 2022/12
In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with Cs. However,
Cs transfer processes determining the tree contamination (particularly for stem wood, a prominent commercial resource) remain insufficiently understood. We propose a model (SOLVEG-R) for simulating dynamic behavior of
Cs in a forest tree-litter-soil system and applied it to contaminated forests of cedar plantation and natural oak stand in Fukushima to elucidate relative impact of distinct
Cs transfer processes determining the tree contamination. The transfer of
Cs to the trees occurred mostly (
99%) through surface uptake of
Cs trapped by needles and bark during the fallout. Root uptake of soil
Cs was several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, internal contamination of the trees proceeded through an enduring recycling (translocation) of
Cs absorbed on the tree surface. A significant surface uptake of
Cs through bark was suggested, contributing to 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining uptake occurred at needles) of the total uptake by the trees. It was suggested that the activity concentration of
Cs in stem wood of the trees at these sites are currently (as of 2021) decreasing by 3% per year, mainly through radioactive decay of
Cs and partly through dilution effect from tree growth.
Abe, Yukiko*; Liang, N.*; Teramoto, Munemasa*; Koarashi, Jun; Atarashi-Andoh, Mariko; Hashimoto, Shoji*; Tange, Takeshi*
Geoderma Regional (Internet), 29, p.e00529_1 - e00529_11, 2022/06
Times Cited Count:1 Percentile:57.56(Soil Science)This study aimed to clarify the causes of spatial variation in soil respiration rate on volcanic ash soil. From January 2013 to August 2019, soil respiration rates were measured at 40 measuring points periodically at a 35-year-old plantation in Tokyo, Japan. In August 2019, the carbon content of the litter layer, total carbon content of soil organic matter (SOM), carbon content of the low-density fraction (LF-C) of SOM, fine root biomass, and bulk density of soil were measured at all measuring points. Results of the multiple regression analysis showed that the model with only the LF-C as an explanatory variable had the highest capability for predicting the respiration rate at a soil temperature of 20
C, indicating that LF-C, which is considered to be readily available to soil microorganisms, can be the main factor responsible for the spatial variation in soil respiration rate.
Ota, Masakazu; Koarashi, Jun
Science of the Total Environment, 816, p.151587_1 - 151587_21, 2022/04
Times Cited Count:1 Percentile:55.46(Environmental Sciences)In forests affected by the Fukushima Daiichi Nuclear Power Plant accident, trees became contaminated with Cs. However,
Cs transfer processes determining tree contamination (particularly for stem wood, which is a prominent commercial resource in Fukushima) remain insufficiently understood. This study proposes a model for simulating the dynamic behavior of
Cs in a forest tree-litter-soil system and applied it to two contaminated forests (cedar plantation and natural oak stand) in Fukushima. The model-calculated results and inter-comparison of the results with measurements elucidated the relative impact of distinct
Cs transfer processes determining tree contamination. The transfer of
Cs to trees occurred mostly (
99%) through surface uptake of
Cs directly trapped by leaves or needles and bark during the fallout. By contrast, root uptake of
Cs from the soil was unsubstantial and several orders of magnitude lower than the surface uptake over a 50-year period following the accident. As a result, the internal contamination of the trees proceeded through an enduring recycling (translocation) of
Cs absorbed on the tree surface at the time of the accident. A significant surface uptake of
Cs at the bark was identified, contributing 100% (leafless oak tree) and 30% (foliated cedar tree; the remaining surface uptake occurred at the needles) of the total
Cs uptake by trees. It was suggested that the trees growing at the study sites are currently (as of 2021) in a decontamination phase; the activity concentration of
Cs in the stem wood decreases by 3% per year, mainly through radioactive decay of
Cs and partly through a dilution effect from tree growth.
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:0 Percentile:0(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.
Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi; Nishina, Kazuya*; Ota, Masakazu; Ohashi, Shinta*; Calmon, P.*; et al.
Journal of Environmental Radioactivity, 238-239, p.106721_1 - 106721_10, 2021/11
Times Cited Count:3 Percentile:40.73(Environmental Sciences)This study was aimed at analysing performance of models for radiocesium migration mainly in evergreen coniferous forest in Fukushima, by inter-comparison between models of several research teams. The exercise included two scenarios of countermeasures against the contamination, namely removal of soil surface litter and forest renewal, and a specific konara oak forest scenario in addition to the evergreen forest scenario. All the models reproduced trend of time evolution of radiocesium inventories and concentrations in each of the components in forest such as leaf and organic soil layer. However, the variations between models enlarged in long-term predictions over 50 years after the fallout, meaning continuous field monitoring and model verification/validation is necessary.
Nagano, Hirohiko; Nakayama, Masataka*; Katata, Genki*; Fukushima, Keitaro*; Yamaguchi, Takashi*; Watanabe, Makoto*; Kondo, Toshiaki*; Atarashi-Andoh, Mariko; Kubota, Tomohiro*; Tateno, Ryunosuke*; et al.
Soil Science and Plant Nutrition, 67(5), p.606 - 616, 2021/10
Times Cited Count:0 Percentile:0.01(Plant Sciences)We analyzed the relationships between nitrogen deposition (deposition of nitrate and ammonium ions) and soil microbial properties in a cool temperate forest surrounded by normally fertilized pasture grasslands in northern Japan. The aim of the present study was to gain the primary information on soil microbial response to moderately elevated nitrogen deposition ( 10 kg N ha
y
). We established three experimental plots in the forest edge adjacent to grasslands and other three plots in the forest interior at least 700 m away from the grasslands. During May to November 2018, nitrogen deposition in each plot was measured. In August 2018, litter and soil (0-5 cm depth) samples were collected from all plots to measure net nitrogen mineralization and nitrification rates as indicators of microbial activity, and microbial biomass carbon and nitrogen and various gene abundances (i.e. bacterial 16S rRNA, fungal ITS, bacterial amoA, and archaeal amoA genes) as indicators of microbial abundance and structure. Nitrogen deposition in the forest edge was 1.4-fold greater than that in the forest interior, even while the maximum deposition was 3.7 kg N ha
. Nitrogen deposition was significantly correlated to the net nitrogen mineralization and nitrification rates and the 16S rRNA and bacterial amoA gene abundances. Microbial community structures were different between litter and soil samples but were similar between the forest edge and interior. Significant correlations of nitrogen deposition to the soil carbon to nitrogen ratio, and the nitrate and ammonium contents were also observed. Thus, our results show that moderately elevated nitrogen deposition in nitrogen-limited forest edges can stimulate microbial activities and abundances in soils.
Tanaka, Sota; Kakinuma, Hotaru*; Adachi, Taro*; Atarashi-Andoh, Mariko; Koarashi, Jun
Journal of Nuclear Science and Technology, 58(4), p.507 - 514, 2021/04
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)Understanding the pathways of Cs transfer to predatory spiders is useful to assess long-term behavior of
Cs in the environment, because spiders obtain food resources from both the grazing and detritus food chains in terrestrial-aquatic linking forest ecosystems. In the present study, we collected spider samples at forest interior and riverside. The sample collection was approximately 6.5 years after the FDNPP accident. Moreover, a transfer factor value (T
) for
Cs in spiders was quantified. Stable carbon and nitrogen isotope ratios (
C and
N) of the spiders were also investigated to estimate the transfer pathways of
Cs to the spiders.
Koarashi, Jun; Atarashi-Andoh, Mariko; Nagano, Hirohiko*; Sugiharto, U.*; Saengkorakot, C.*; Suzuki, Takashi; Kokubu, Yoko; Fujita, Natsuko; Kinoshita, Naoki; Nagai, Haruyasu; et al.
JAEA-Technology 2020-012, 53 Pages, 2020/10
There is growing concern that recent rapid changes in climate and environment could have a significant influence on carbon cycling in terrestrial ecosystems (especially forest ecosystems) and could consequently lead to a positive feedback for global warming. The magnitude and timing of this feedback remain highly uncertain largely due to a lack of quantitative understanding of the dynamics of organic carbon stored in soils and its responses to changes in climate and environment. The tracing of radiocarbon (natural and bomb-derived C) and stable carbon (
C) isotopes through terrestrial ecosystems can be a powerful tool for studying soil organic carbon (SOC) dynamics. The primary aim of this guide is to promote the use of isotope-based approaches to improve our understanding of the carbon cycling in soils, particularly in the Asian region. The guide covers practical methods of soil sampling; treatment and fractionation of soil samples; preparation of soil samples for
C (and stable nitrogen isotope,
N) and
C analyses; and
C,
N, and
C measurements by the use of isotope ratio mass spectrometry and accelerator mass spectrometry (AMS). The guide briefly introduces ways to report
C data, which are frequently used for soil carbon cycling studies. The guide also reports results of a case study conducted in a Japanese forest ecosystem, as a practical application of the use of isotope-based approaches. This guide is mainly intended for researchers who are interested but are not experienced in this research field. The guide will hopefully encourage readers to participate in soil carbon cycling studies, including field works, laboratory experiments, isotope analyses, and discussions with great interest.
Wijesinghe, J. N.*; Koarashi, Jun; Atarashi-Andoh, Mariko; Kokubu, Yoko; Yamaguchi, Noriko*; Sase, Takashi*; Hosono, Mamoru*; Inoue, Yuzuru*; Mori, Yuki*; Hiradate, Shuntaro*
Geoderma, 374, p.114417_1 - 114417_10, 2020/09
Times Cited Count:6 Percentile:47.76(Soil Science)Koarashi, Jun; Atarashi-Andoh, Mariko; Nishimura, Shusaku; Muto, Kotomi*
Scientific Reports (Internet), 10(1), p.6614_1 - 6614_11, 2020/04
Times Cited Count:6 Percentile:42.91(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.
Muto, Kotomi; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Koarashi, Jun
Journal of Environmental Radioactivity, 208-209, p.106040_1 - 106040_10, 2019/11
Times Cited Count:10 Percentile:49.77(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.
Nagano, Hirohiko; Atarashi-Andoh, Mariko; Koarashi, Jun
Soil Science and Plant Nutrition, 65(5), p.525 - 533, 2019/10
Times Cited Count:2 Percentile:15.64(Plant Sciences)In the present study, two volcanic ash soils (soil A and B) from a temperate broad-leaved forest in eastern Japan were incubated under repeated dry-wet cycles and continuously constant moisture conditions. The primary aims were to quantify the potential for enhancement of carbon dioxide (CO) release owing to increased water fluctuation and to examine differences in the responses of volcanic ash soils with different physicochemical properties. Soil B, rather than soil A, was a typical Andosol. During incubation at 20
C for 120 days with five dry-wet cycles, the CO
release rate was measured periodically. Abundance of the stable carbon isotope in CO
(
C-CO
) was measured to capture changes in the origin of decomposed soil organic matter (SOM) owing to the dry-wet cycles. The CO
release rate under the dry-wet cycles was up to 49% higher than the values predicted from a parabolic relationship between CO
release and water content during incubation under the continuously constant moisture condition. The magnitude of CO
release enhancement was 2.7-fold higher in soil B relative to that in soil A. The
C-CO
value in the dry-wet cycles was enriched by 0.3-2.3%
compared to that during incubation under the continuously constant moisture conditions, suggesting that the decomposition of old and/or well-metabolized SOM was enhanced by the dry-wet cycles. Thus, the present study suggests that Andosols, which have been believed to have a strong SOM stabilization ability, are vulnerable to dry-wet cycles. Then, increased water fluctuation in a future warmer world would have significant potential to stimulate CO
release from soils.
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:26 Percentile:82.59(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.
Koarashi, Jun; Atarashi-Andoh, Mariko
Journal of Radioanalytical and Nuclear Chemistry, 320(1), p.179 - 191, 2019/04
Times Cited Count:15 Percentile:91.15(Chemistry, Analytical)To quantify the Cs retention behavior in forest-floor organic layers in relation to the litter dynamics, litter samples were collected at five forest sites in Fukushima in 2011 and 2015, and separated into eight fractions with different precursor species and degrees of degradation; afterward,
Cs inventory was determined in each litter fraction. The ecological half-lives of
Cs in the litter fractions were estimated to be from 0.7 to 4.4 years and found to depend not on the sampling site but rather on the precursor species of the litter materials. Broadleaf- and pine-needle-originated litter fractions exhibited shorter ecological half-lives of
Cs, while those of cedar-originated and finely fragmented litter fractions were longer. The results suggested that the organic layers in Japanese forest ecosystems have a low
Cs retention capability, although it differs depending on the forest type.
Koarashi, Jun; Nishimura, Shusaku; Atarashi-Andoh, Mariko; Matsunaga, Takeshi*; Sato, Tsutomu*; Nagao, Seiya*
Chemosphere, 205, p.147 - 155, 2018/08
Times Cited Count:15 Percentile:56.08(Environmental Sciences)There is little understanding of how soil aggregation can affect the mobility and bioavailability of 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
Cs content and extractability and mineral composition. In forest soils, aggregate formation was significant, and
Cs was largely associated with large-sized aggregates. In contrast, there was less aggregation in agricultural field soils, and most of
Cs was in the clay- and silt-sized fractions. Across all sites, the
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
Cs in organic-rich (forest and orchard) soils.
Fujita, Hiroki; Maehara, Yushi; Nagaoka, Mika; Koarashi, Jun
KEK Proceedings 2017-6, p.35 - 39, 2017/11
no abstracts in English
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:15 Percentile:85.97(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; Atarashi-Andoh, Mariko; Amano, Hikaru*; Matsunaga, Takeshi
Journal of Radioanalytical and Nuclear Chemistry, 311(1), p.473 - 481, 2017/01
Times Cited Count:16 Percentile:87.34(Chemistry, Analytical)Vertical distributions of global fallout Cs and
C were investigated in a Japanese forest soil in 2001. Even 38 years after the fallout,
Cs was still observed mostly in the uppermost 5 cm. A preferential accumulation of
Cs was found in a 1-cm-thick transition layer between organic-rich A and underlying B horizons. This unique observation indicated that
Cs migrated through the A horizon at a rate of 0.20% y
and the transition layer acted as a barrier for
Cs migration to deeper layers. The vertical distributions of
Cs and
C were significantly correlated, suggesting a coupled downward migration of
Cs and organic matter on a time scale of decades, along the same physical pathways.
Koarashi, Jun; Nishimura, Shusaku; Nakanishi, Takahiro; Atarashi-Andoh, Mariko; Takeuchi, Erina; Muto, Kotomi
Chemosphere, 165, p.335 - 341, 2016/12
Times Cited Count:34 Percentile:77.58(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.