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Cs in a river-sea system boundary area after the Fukushima Dai-ichi Nuclear Power Plant accident高田 兵衛*; 脇山 義史*; 和田 敏裕*; 平尾 茂一*; 青野 辰雄*; 中西 貴宏; 御園生 敏治; 尻引 武彦; 青山 道夫*
Marine Chemistry, 262, p.104384_1 - 104384_6, 2024/05
被引用回数：0 パーセンタイル：0.00(Chemistry, Multidisciplinary)The radiocesium (Cs) distribution between dissolved and particulate phases was examined in river water and coastal seawater as a function of the Cs sorption behavior on suspended particles. Dissolved Cs activity concentrations in the Tomioka River (salinity 
0.1) and in coastal seawater at Tomioka fishery port (salinity 
30), Fukushima Prefecture, from June 2019 to October 2021 were 3.6-20 Bq/m
(geometric mean 11 Bq/m) and 2.4-86 Bq/m (13 Bq/m), respectively. Although the suspended particle concentration was lower in the river (0.2-44 mg/L; geometric mean 2 mg/L) than in seawater (0.8-24 mg/L; 6.4 mg/L), the mean Cs activity on suspended particles was 11,000 Bq/kg-dry in the river versus 3,200 Bq/kg-dry in seawater. Proportions of ion-exchangeable, organically bound, and refractory fractions of Cs on suspended particles were determined by sequential extraction. The ion-exchangeable fraction accounted for 0.3-2.0% (mean 1.2%) and 0.4-1.3% (0.8%) at the river and port sites, respectively. The organically bound fraction accounted for 0.3-4.8% (1.8%) and 0.1-5.5% (2.1%) at the river and port sites, respectively. In both areas, the refractory fraction accounted for 90% of Cs. Unexpectedly, the ion-exchangeable fraction did not differ between the river and port sites, and the percentage at the river site did not vary during the sampling period. Therefore, the ion-exchangeable fraction in the river's lower reach was originally low or had decreased before the particles arrived there. The small labile Cs fraction on suspended particles indicates that the mobility of radiocesium to marine biota in this coastal region is low.
Cs washoff from bare land in Fukushima五十嵐 康記*; 恩田 裕一*; 脇山 義史*; 吉村 和也; 加藤 弘亮*; 小塚 翔平*; 馬目 凌*
Science of the Total Environment, 769, p.144706_1 - 144706_9, 2021/05
被引用回数：4 パーセンタイル：20.23(Environmental Sciences)The impact of freeze-thaw processes and subsequent runoff affecting the Cs-137 (Cs) flux and concentration in sediment discharge were revealed in bareland erosion plot following the Fukushima Nuclear Power Plant accident by detailed monitoring and laser scanner measurement on the soil surface. We found that surface topographic changes due to the frost-heaving during the winter- spring period, and rill formation during the summer. We also found the evident seasonal changes in Cs concentration; high during the early spring and gradually decreased thereafter, then surface runoff from the plot frequently occurred during spring and autumn when rainfall was high and reached a maximum in summer.
恩田 裕一*; 谷口 圭輔*; 吉村 和也; 加藤 弘亮*; 高橋 純子*; 脇山 義史*; Coppin, F.*; Smith, H.*
Nature Reviews Earth & Environment (Internet), 1(12), P. 694_1, 2020/12
被引用回数：0 パーセンタイル：0.00(Environmental Sciences)The values along the mass depth axes in Figure 4a and 4b were slightly misaligned, and the relaxation mass depth markers shown in Figure 4b and 4c incorrectly located.
恩田 裕一*; 谷口 圭輔*; 吉村 和也; 加藤 弘亮*; 高橋 純子*; 脇山 義史*; Coppin, F.*; Smith, H.*
Nature Reviews Earth & Environment (Internet), 1(12), p.644 - 660, 2020/12
被引用回数：114 パーセンタイル：89.30(Environmental Sciences)This review, concerning on findings obtained by detailed field monitoring after the Fukushima Daiichi Nuclear Power Plant accident, covers the initial fallout and vertical movement of radionuclide in the land and forest, and subsequent transport and redistribution through hydrological and geomorphological processes in cropland, urban area, paddy field, and forested area. We discuss the finding of the transport of radionuclides through rivers and new discoveries for hydrological and sediment transport environmental impact in monsoonal regions.
Cs, and their time dependence脇山 義史*; 恩田 裕一*; 吉村 和也; 五十嵐 康記*; 加藤 弘亮*
Journal of Environmental Radioactivity, 210, p.105990_1 - 105990_12, 2019/12
被引用回数：21 パーセンタイル：61.47(Environmental Sciences)This study provides the results of observations of plot-scale Cs wash-off from various land uses (two uncultivated farmlands, two cultivated farmlands, three grasslands and one forest) from 2011 to 2014. Annual Cs wash-off rate ranged from 0.0026 to 7.5% per year, and more vegetation cover resulted in lower sediment discharge. Cs concentration observed in uncultivated farmland plot decreased with time and the rate was lower than those of riverine, suggesting that contributions of Cs from the upslope area may be insignificant to that in riverine. A negative relationship between Cs concentration normalized by initial deposition amount and sediment concentration in runoff water was found. Cultivation appeared to cause enhanced soil erosion and resulted in constant relatively low Cs concentration. A contribution of coarse organic matter to Cs wash-off was suggested in the forest, which had relatively high Cs concentration and low sediment discharge.
Yang, B.*; 恩田 裕一*; 大森 良弘*; 関本 均*; 藤原 徹*; 脇山 義史*; 吉村 和也; 高橋 純子*; Sun, X.*
Science of the Total Environment, 603-604, p.49 - 56, 2017/12
被引用回数：2 パーセンタイル：6.32(Environmental Sciences)In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was investigated over a four-year period. The results indicate that the effect of topsoil removal measure on the accumulation of radiocesium in rice plants was effective. We summarized four year's data to further confirm that potassium and nitrogen fertilizers had an opposite effect on the accumulation of radiocesium in rice plants. Increasing potassium and reducing nitrogen fertilizer conditions tended to inhibit the radiocesium uptake by rice plants.
Yang, B.*; 恩田 裕一*; 脇山 義史*; 吉村 和也; 関本 均*; Ha, Y.*
Environmental Pollution, 208(Part B), p.562 - 570, 2016/01
被引用回数：18 パーセンタイル：47.53(Environmental Sciences)In this study, we investigated the temporal changes of radiocesium in soil, irrigation water, and rice plant in two adjacent rice paddies, with and without surface-soil-removal practice, in Fukushima Prefecture for over three years (2012 to 2014). Our results showed that radiocesium migrated into 24-28 cm soil layers and that the concentration and inventory of radiocesium in paddy soils generally decreased. The newly added radiocesium to paddies through irrigation water contributed only the maximum values of 0.15% and 0.75% of the total amount present in normal and decontaminated paddies, respectively, throughout the study period. The change trend of radiocesium concentration in suspended sediment in irrigation water exponentially decreased. Radiocesium accumulation in rice plant also decreased with time in both paddies. However, the transfer factor of radiocesium for rice plant in the decontaminated paddy increased compared with normal paddy.
Konoplev, A.*; Golosov, V.*; Laptev, G.*; 難波 謙二*; 恩田 裕一*; 高瀬 つぎ子*; 脇山 義史*; 吉村 和也
Journal of Environmental Radioactivity, 151(Part 3), p.568 - 578, 2016/01
被引用回数：83 パーセンタイル：91.69(Environmental Sciences)Comparative analysis is provided for radiocesium wash-off parameters and Kd between suspended matter and water in rivers and surface runoff on Fukushima and Chernobyl contaminated areas for the first years after the accidents. It was found that radiocesium distribution coefficient in Fukushima rivers is essentially higher than those in Chernobyl. This can be associated with two factors: a higher RIP of samples in Fukushima and the presence of water insoluble glassy particles. It was found also that dissolved wash-off coefficients for Fukushima catchments are lower than those in Chernobyl. Particulate wash-off coefficients are comparable for Fukushima and Chernobyl. The radiocesium migration in undisturbed forest and grassland soils at Fukushima has been shown to be faster than those in Chernobyl. Investigation and analysis of radiocesium distribution in soils of Niida river catchment revealed accumulation of contaminated sediments on its floodplain.
脇山 義史*; 馬目 凌*; 恩田 裕一*; 吉村 和也
no journal, ,
本研究では、斜面スケールでの土砂移動に伴う放射性セシウムの移動プロセスを明らかにすることを目的として、福島原発により放射性セシウムが沈着した地点に土壌侵食プロットを設置して土砂およびCs-137流出量の観測を行うとともにレーザープロファイラによる地表面の地形変化を追跡し、土砂移動に伴うCs-137流出の時間変化および季節性について考察を行った。本研究結果は、放射性セシウムの移行には季節性があることを示しており、将来予測の精度向上のためには斜面スケールにおけるCs-137移動プロセスについての複数年の観測が有用であることが示唆された。
Chaboche, P.-A.*; 脇山 義史*; 高田 兵衛*; 和田 敏裕*; Evrard, O.*; 御園生 敏治; 尻引 武彦; 舟木 泰智
no journal, ,
Following the Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident in March 2011, large quantities of radionuclides in general, and radiocaesium (
Cs) in particular, were emitted in terrestrial and marine environments of Fukushima Prefecture. Although Cs activity in these environments has decreased since the accident, the secondary inputs via the rivers draining and eroding the main terrestrial radioactive plume were shown to sustain high level of Cs in riverine and coastal sediments, which are likely deposited off the coasts of the Prefecture. Accordingly, quantifying the riverine sources of sediment deposited along the coast and characterizing its spatial and depth distribution, as well as its physico-chemical properties, is of the utmost importance to ensure the safety of fishery products and anticipate the environmental fate of radiocaesium. To conduct this project, coastal sediment cores (n=6) from 26 to 60cm depth were collected during cruise campaigns between July and September 2022 at the Ota, Niida and Ukedo river mouths. In this presentation, we report preliminary results regarding the spatial and depth distribution of radiocaesium activities in these sediment cores. Finally, we will discuss the main challenges identified so far to design and implement a sediment tracing method along the coast of the Fukushima Prefecture.
脇山 義史*; 馬目 凌*; 恩田 裕一*; 吉村 和也
no journal, ,
This study presents a three years' Cs-137 wash-off observation and morphological surveys on a soil erosion in area affected by the accident of Fukushima nuclear power plant to describe detailed processes of Cs-137 wash-off. Cs-137 concentration varied enormously and it appeared to decrease gradually from spring to autumn and increased again after winter. Based on the photos and scan data of soil surface, the expansions of a rill from spring to summer and elevations of soil surface from winter to spring were found. Our analysis suggests that freezing and thawing cycles resulted in high Cs-137 concentration of sediments during winter, whereas expansion of rill makes decrease in Cs-137 concentration in warm seasons.
恩田 裕一*; 谷口 圭輔*; 脇山 義史*; 吉村 和也; Smith, H.*; Blake, W.*; 岩上 翔*; 加藤 弘亮*
no journal, ,
An intensive field monitoring campaign has been started, immediately after the Fukushima NPP accident including detailed monitoring site in upstream (Yamakiya site), and 30 monitoring sites in downstream river sites. In this presentation, I will present the summary of four years environmental transfer studies after the Fukushima NPP accident. The detailed monitoring of activity concentration of radiocesium and their flux, which can be applicable for the fate and flux of the radionuclide transfer in humid temperate environment. We also found that land use controls most of the transport and then fate of Cs-137 in terrestrial environment.
Cs wash-off from bareland in Fukushima五十嵐 康記*; 恩田 裕一*; 脇山 義史*; 吉村 和也; 加藤 弘亮*; 小塚 翔平*; 馬目 凌*
no journal, ,
The impact of freeze-thaw processes and subsequent runoff affecting the Cs flux and concentration in sediment discharge were revealed in bareland erosion plot following the Fukushima nuclear power plant accident by detailed monitoring and laser scanner measurement on the soil surface. We found that surface topographic changes due to the frost-heaving during the winter-spring period, and rill formation during the summer. We also found the evident seasonal changes in Cs concentration; high during the early spring and gradually decreased thereafter, then surface runoff from the plot frequently occurred during spring and autumn when rainfall was high and reached a maximum in summer. From these results, the higher Cs concentration in spring was caused by a mixture of unstable surface sediment following freeze- thaw processes and then transported in the early spring, but erosion amount is not significant because of the less rainfall event. The sediment with a lower Cs concentration, which was supplied from the rill erosion and its expansion, was wash-offed during the summer, contributing most of the flux from erosion in bareland in Fukushima region.
恩田 裕一*; 谷口 圭輔*; 吉村 和也; 脇山 義史*
no journal, ,
The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released the largest quantity of radiocaesium into the terrestrial environment since the Chernobyl nuclear accident. The surrounding land received 2.7 PBq of radiocaesium to forests, agricultural lands, grasslands, and urban areas, from which the radionuclides migrated through soil and waterways. In this presentation, the deposition and distribution of radionuclides, especially radiocaesium, in the terrestrial environment as a result of the FDNPP accident are discussed based on the past 10 years' intensive dataset. Anthropogenic activities such as rice and vegetable cultivation and residential activities in the upstream area have led to a rapid decline in the activity concertation of Cs of suspended sediment (SS) transport in the river network, and these declines directly control the dissolved Cs concentration in the river water. We outline the environmental and anthropogenic factors that in uenced the subsequent transport and impacts of radionuclides through the environment. The environmental aftermath of the accident at Fukushima is compared to Chernobyl, and the relatively rapid remediation of the Fukushima region relative to the region surrounding Chernobyl will be explained.
脇山 義史*; 恩田 裕一*; 吉村 和也; 中村 典子*; 馬目 凌*
no journal, ,
This study shows approximately three years observation results of plot-scale Cs-137 wash-off at various land uses in Kawamata town after the accident of FDNPP. Soil erosion rate were positively correlated with vegetation cover on undisturbed soils, whereas high erosion rate were found on cultivated farmlands even with similar vegetation cover to uncultivated farmlands. Annual Cs-137 wash-off rate ranged from 0.003 to 9.3 %/year and the largest was from uncultivated farmland followed by cultivated farmlands. Decreasing trends of Cs-137 concentration were found on uncultivated farmlands, whereas no trend was found on other plots. Our results suggest that the active soil erosion results in decrease in Cs-137 concentration of sediments on uncultivated slopes, while cultivation resulted in the no trend of temporal decrease in Cs-137 concentration due to constant vertical distribution of Cs-137.
吉村 和也; 脇山 義史*; 恩田 裕一*; 高瀬 つぎ子*
no journal, ,
This study presents Cs-137 wash-off observations on various land uses including decontaminated lands in Fukushima. We established rectangle soil erosion plots on six landscape; uncultivated farmland (UFL), cultivated farmland (CFL), grassland (GL), forest (F), uncultivated and cultivated farmlands on a decontaminated land (D-UFL and D-CFL). The D-UFL and DCFL were established after the decontamination of erosion plots. Mean Cs-137 concentrations on decontaminated lands decreased down to approx. 10 to 40 % of values observed before decontamination. No significant difference in amount of eroded sediment was found between contaminated and decontaminated lands, suggesting that decontamination works decrease total Cs-137 wash-off.
Zheleznyak, M.*; Pylypenko, O.*; Kivva, S.*; 佐久間 一幸; 五十嵐 康記*; 脇山 義史*; Konoplev, A.*; 難波 謙二*
no journal, ,
物理モデルベースの水、土砂輸送を考慮した流域モデルを開発し、福島県内の試験プロットで懸濁態Cs流出について試計算を実施した。また、GISベースで経験的な流出率を用いる流域モデルを開発した。開発したモデルを用いて福島県阿武隈川でCsについて試計算を実施し、ウクライナのPripyat川とDnieper川を対象に、放射性核種輸送について妥当性を検証した。
Chaboche, P.-A.*; 脇山 義史*; 高田 兵衛*; 和田 敏裕*; Evrard, O.*; 御園生 敏治; 尻引 武彦; 舟木 泰智
no journal, ,
The Fukushima-Daiichi Nuclear Power Plant (FDNPP) accident trigged by the Great East Japan Earthquake and subsequent tsunami in March 2011 released large quantities of radionuclides in terrestrial and marine environments of Fukushima Prefecture. Although radiocaesium activity in these environments has decreased since the accident, the secondary inputs via the rivers draining and eroding the main terrestrial radioactive plume were shown to sustain high levels of Cs in riverine and coastal sediments, which are likely deposited off the coast of the Prefecture. Accordingly, identifying the sources of sediment is required to elucidate the links between terrestrial and marine radiocaesium dynamics and to anticipate the fate of these persistent radionuclides in the environment.
Cs in a river-sea system boundary area高田 兵衛*; 和田 敏裕*; 脇山 義史*; 平尾 茂一*; 佐藤 俊*; 青野 辰雄*; 中西 貴宏; 御園生 敏治; 尻引 武彦
no journal, ,
The Cs sorption behavior on suspended particles was studied in river and coastal seawater, Fukushima Prefecture from June 2019 to October 2021. Although the suspended particle concentration was lower in the river than in seawater, the Cs activity on suspended particles in the river lager than that in seawater. Proportions of ion-exchangeable, organically bound, and refractory fractions of Cs on suspended particles were also determined by conducting sequential extraction method. The ion-exchangeable fraction was less than 1% at both areas. The organically bound fraction was a few %, resulting in that the refractory fraction accounted for 90%. Thus, it is indicated that the mobility of Cs to marine biota is low in the studied areas.
Chaboche, P.-A.*; 脇山 義史*; 高田 兵衛*; 和田 敏裕*; 御園生 敏治; 尻引 武彦; 舟木 泰智
no journal, ,
2011年3月の東日本大震災とそれに続く津波に端を発した福島第一原子力発電所(FDNPP)事故は、福島県の陸域および海域環境に大量の放射性核種を放出する結果となった。これらの環境中の放射性セシウム(すなわち
CsとCs)の放射能濃度は事故以来低下しているが、主な陸上放射性プルームを流出・浸食している河川からの継続的な流入が測定されており、福島県の沿岸沖に堆積した河川堆積物や沿岸堆積物中のCsの濃度が高いまま維持されている。したがって、陸域と海域の放射性セシウム動態の関連性を解明し、環境中の残留性放射性核種の運命を予測するためには、堆積物の発生源を特定することが必要である。
