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論文

Impacts of freeze-thaw processes and subsequent runoff on $$^{137}$$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:2 パーセンタイル:14.14(Environmental Sciences)

The impact of freeze-thaw processes and subsequent runoff affecting the Cs-137 ($$^{137}$$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 $$^{137}$$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.

論文

Land use types control solid wash-off rate and entrainment coefficient of Fukushima-derived $$^{137}$$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:20 パーセンタイル:66.01(Environmental Sciences)

This study provides the results of observations of plot-scale $$^{137}$$Cs wash-off from various land uses (two uncultivated farmlands, two cultivated farmlands, three grasslands and one forest) from 2011 to 2014. Annual $$^{137}$$Cs wash-off rate ranged from 0.0026 to 7.5% per year, and more vegetation cover resulted in lower sediment discharge. $$^{137}$$Cs concentration observed in uncultivated farmland plot decreased with time and the rate was lower than those of riverine, suggesting that contributions of $$^{137}$$Cs from the upslope area may be insignificant to that in riverine. A negative relationship between $$^{137}$$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 $$^{137}$$Cs concentration. A contribution of coarse organic matter to $$^{137}$$Cs wash-off was suggested in the forest, which had relatively high $$^{137}$$Cs concentration and low sediment discharge.

口頭

Distributed modeling of radionuclide washing out from the watersheds in solute and with suspended sediments; Case studies Abukuma River, Fukushima Prefecture and Pripyat-Dnieper river system, Ukraine

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$$^{137}$$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$$^{137}$$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。

口頭

Impacts of freeze-thaw processes and subsequent runoff on $$^{137}$$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 $$^{137}$$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 $$^{137}$$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 $$^{137}$$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 $$^{137}$$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.

口頭

Behavior of radionuclides in rivers in Fukushima

中西 貴宏; 五十嵐 康記*

no journal, , 

福島第一原子力発電所事故により、森林など陸上に沈着した放射性物質は、水の流動に伴って斜面から河川へ、最終的には海へ輸送される。すなわち、河川は放射性物質の再移動の場として重要な役割を担っている。このため、福島の様々な河川を対象として、河川中の溶存態あるいは懸濁態の放射性セシウム観測が行われてきた。事故直後からの観測的な研究は、阿武隈川の$$^{137}$$Cs濃度が2012年から2021年までの間で約8割低下した事を明らかにした。高瀬川や請戸川における観測結果は、大規模な出水による河川の水と土砂移動が$$^{137}$$Csの輸送に大きく関与していることを明らかにしている。特に、河川敷土砂の洗い出しあるいは汚染が少ない土砂の堆積により、河川敷の空間線量率は低下した。また、河川から海洋へ流出した$$^{137}$$Csは、沿岸域における一時的な$$^{137}$$Cs濃度上昇に寄与している事も明らかとなった。近年では、河川における溶存態$$^{137}$$Cs濃度を決定する要因が、森林を流れる渓流部と平地を流れる中下流では異なる可能性も指摘されている。事故から10年間で明らかになった知見を紹介し、チェルノブイリを例に取り今後の河川中放射性物質動態研究に関する展望を議論する。

口頭

Dissolved-form Cs-137 leaching associated with DOC leaching in headwater streams

恩田 裕一*; 川野 泰地*; 永田 祐太郎*; 高橋 純子*; 榊原 孝一*; 加藤 弘亮*; 五十嵐 康記*; 新里 忠史

no journal, , 

The Fukushima Daiichi Nuclear Power Plant accident occurred on March 11, 2011, and a large amount of Cs-137 was released into the environment. When Cs-137 is discharged downstream through rivers, its concentration is important because dissolved cesium is easily transferred to aquatic organisms such as fish. The purpose of this study is to investigate how biogeochemical activities are involved in the formation of dissolved Cs-137 concentrations in the headwaters of the watershed of Fukushima Prefecture. The results indicate that the concentration of dissolved Cs-137 is formed by the decomposition of coarse organic matters in the watershed. Thus, investigating the formation mechanism of dissolved Cs-137 concentration can be an important tracer for elucidating water and material cycles and biogeochemical activities in the terrestrial environment.

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