Yoshifumi Wakiyama

Fukushima University · Institute of Environmental Radioactivity

Radionuclide depth distribution in bottom sediments in deep-water zones of dam reservoirs, where no sediment mixing occurs, can be used to reconstruct time changes in particulate activity concentrations of radionuclides strongly bound to bottom sediments. This approach was used to analyze the ¹³⁷Cs concentration profile in a bottom sediment core co...

This study presents the temporal variations in riverine ¹³⁷Cs concentrations and fluxes to the ocean during high-flow events in three coastal river catchments contaminated by the Fukushima Daiichi Nuclear Power Plant accident. River water samples were collected at points downstream in the Niida, Ukedo, and Takase Rivers during three high-flow event...

The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident released large amounts of radioactive materials into the environment. River systems play an important role in the terrestrial redistribution of FDNPP‐derived ¹³⁷Cs in association with water and sediment movement. We examined the seasonal fluctuations in dissolved and particulate ¹³⁷Cs...

Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi nuclear power plant accident in March 2011. These particle-bound substances deposited on soils of north-eastern Japan, located predominantly within a ∼3000 km2 radioactive fallout plume and dr...

Since the 1986 Chornobyl accident transport of radionuclides by Pripyat River shares more than 90% of the annual total flux of radioactivity coming out the Chornobyl Exclusion Zone (ChEZ). 90Sr was the main contributor to this flux. In course of time destruction of the accidentally dispersed "fuel particles" leads to increase of mobile, e.g. water-...

Desorption of radiocesium (¹³⁷Cs) from riverine particles into seawater strongly influences ¹³⁷Cs concentrations in coastal seawater. This process is important for quantifying the input of radionuclides to marine environments. Here we quantify the particulate ¹³⁷Cs flux from the Abukuma River, Japan, during typhoon Hagibis and following typhoons in...

The paper is concerned with the results of 137Cs monitoring in the irrigation ponds of the Okuma town in the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) exclusion zone. The 137Cs activity concentrations in the ponds appeared to be higher than those in the rivers and dam reservoirs in the region. The study has revealed a trend for a decline in 13...

Artificial radionuclides including radiocesium (134Cs and 137Cs) and radiosilver (110mAg) were released into the environment following the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. These particle-bound substances deposited on soils of Northeastern Japan located predominantly within a ~3000 km2 radioactive fallout plume and drai...

This study analyzes the 137Cs behavior in the ponds of Okuma Town from 2015 to 2019 in the Fukushima Dai-ichi nuclear power plant (FDNPP) exclusion zone. A decline in both particulate and dissolved 137Cs activity concentrations was revealed. The decline rate constants for the particulate 137Cs activity concentration were found to be higher than for...

На основе использования комплекса полевых методов и расчетов по эрозионным моделям выпол-нена оценка перераспределения наносов и транспортируемого совместно с ними 137 Сs на водосборе Щекинского водохранилища (Тульская область) и определено изменение содержания 137 Сs в почвах различных типов, произошедшее за период 1986-2018 гг. Темпы смыва почв н...

The deposited ¹³⁷Cs is one of the long-lived radionuclides, that was released following the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, has been hydrologically transported as particulates in the terrestrial environment of the Fukushima region. The impact of freeze-thaw processes and subsequent runoff affecting the ¹³⁷Cs flux and concen...

The Fukushima nuclear accident in March 2011 generated a 3000 km 2 plume of soils heavily contaminated with 137 Cs. Decontamination was completed early in 2019. Typhoon Hagibis was the first extreme event that occurred in the region after decontamination. Its impact on sediment sources and sediment 137 Cs contamination was investigated through the...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, Japan, released the largest quantity of radionuclides into the terrestrial environment since the 1986 accident at Chernobyl. This accident resulted in 2.7 PBq of radiocaesium (¹³⁷Cs) contaminated forests, agricultural lands, grasslands and urban areas, which subsequently migrated thro...

Distributions of 137Cs in dissolved and particulate phases of the downstream of seven rivers and adjacent nearshore and offshore waters as far as ~60 km south of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) were studied during the high-river-flow period (June–September 2019) and during the period of October 2019 after typhoon Hagibis. Dissolv...

Strontium-90 (90Sr) is the major long-lived radionuclide derived from the Chernobyl accident, and is still being detected in the heavily contaminated catchments of the Chernobyl Exclusion Zone. This study examines the long-term decrease in the dissolved-phase 90Sr concentration and the concentration–discharge (90Sr-Q) relationship in stream water s...

Processes responsible for long-term changes in environmental radioactivity after the Fukushima accident are currently high on the agenda. Dynamics of particulate and dissolved radiocesium (r-Cs) has been studied on a number of water bodies, namely Abukuma River, Niida River and Maeda River, the dam reservoirs of Yokokawa (Ota River), Sakashita (Kum...

Wildfires may play a role in redistributing radionuclides in the environment in combination with hydrological processes such as surface runoff and soil erosion. We investigated plot-scale radionuclide wash-off at forest sites affected by wildfires in the Chernobyl Exclusion Zone (CEZ). We also compared speciation of the washed-off radionuclides wit...

Closed and semi-closed water bodies, such as lakes and ponds, are important water resources in Fukushima area and they are the most sensitive environments to radioactive contamination after the Fukushima Dai-ichi nuclear power plant accident. Wakiyama et al. (2017) investigated 137Cs activity in water and bottom sediment in four ponds; Suzuuchi (SU...

Eight sites in the Fukushima contaminated area were surveyed for long-term changes in D-shuttle dose equivalent rate above the soil surface during 2015–2017. D-shuttle readings in most cases decreased faster than if due to radioactive decay only. More rapid decrease can be explained by natural attenuation processes, such as erosion of the topsoil,...

Understanding solid 137Cs wash-off in sediment sources is important for predicting radiological risks in zones contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident. Yoshimura et al. (2015) studied solid 137Cs wash-off using soil erosion plots representing different land uses in Fukushima. However, temporal trends of 137Cs activity co...

A proper understanding of radioactive contamination levels of food resources near the Fukushima Dai-ichi Nuclear Power Plant is necessary to estimate the potential effects of radionuclide contamination on human health. This study was conducted to present a direct comparison of radiocesium (134 Cs and 137 Cs) concentrations in marine and freshwater...

Processes responsible for long-term changes in environmental radioactivity after the Fukushima accident are currently high on the agenda. Detailed analysis of Chernobyl data covering an extended time period can provide a basis for long-term prediction of changes in environmental radioactive contamination in Fukushima contaminated area. Dynamics of...

17.12.2015 г. После доработки 01.03.2016 г. Приведены результаты исследований содержания и распределения радиоцезия между раствором и взвесью в прудах ближней зоны АЭС Фукусима-1 после аварии на АЭС в 2011 г. Показано, что сум-марная концентрация 137 Cs в воде прудов и ее изменчивость в значительной степени определяются содержанием взвеси, достигая...

The article presents the results of studying radiocesium concentration and distribution between dissolved and particulate forms in ponds in the near zone of Fukushima Dai-ichi NPP NPP after the 2011 accident. The total concentration of 137Cs in pond water and its variations are shown to be largely governed by the concentration of particulate matter...

Detailed study of different sections of floodplain was undertaken in the Niida River basin (Fukushima Prefecture) after an extreme flood event which occurred in the middle of September 2015. The upstream part of the basin is located in the area with very high level of radionuclide contamination after the accident at Fukushima Dai-ichi NPP. Field an...

Extreme floods can have different effects on the river bottom relief depending on several factors. The geomorphological impact of the extreme flood occurring in the Niida River basin (Fukushima prefecture, Honshu inland, Japan) on the channels and river bottom of different reaches of the river is analyzed. High-resolution satellite images and field...

Extreme floods can have different effects on the river bottom relief depending on several factors. The geomorphological impact of the extreme flood occurring in the Niida River basin (Fukushima prefecture, Honshu inland, Japan) on the channels and river bottom of different reaches of the river is analyzed. High-resolution satellite images and field...

A wide area of paddy fields was contaminated by radiocesium derived from the Fukushima nuclear accident. Implement of agricultural countermeasures is one of the principle methods to reduce the contamination of rice plants. In this study, the effect of topsoil removal measure and fertilizer application on radiocesium uptake by rice plants was invest...

The mobility and bioavailability of radiocesium (r-Cs) is governed by the ratio of its chemical forms during a contaminant release and the subsequent site-specific environmental characteristics in which the contaminant is dispersed. The objective of the research was to compare environmental fate and transport of r-Cs from two major technogenic sour...

The Fukushima Daiichi Nuclear Power Plant accident has released massive amount of radiocesium into the terrestrial environment, and the radiocesium (Cs-137) transfer and flux through river network is important to understand the redistribution of radiocesium in terrestrial environment, which is essential for assessing the external and internal radio...

Fallout from the Fukushima Dai-ichi nuclear power plant accident resulted in a 3000-km² radioactive contamination plume. Here, we model the progressive dilution of the radiocesium contamination in 327 sediment samples from two neighboring catchments with different timing of soil decontamination. Overall, we demonstrate that there has been a ~90% de...

Advances in precipitation isoscape studies and its basis/application were reviewed with a focus on mountainous regions. A recent study showed that precipitation isoscapes over Japanese Alps region can be mapped by a relatively simple model considering altitude and inland effects. However, accurate modelling of a steady state isoscape requires isoto...

Presented are results of the study of radiocesium vertical distribution in the soils of the irrigation pond catchments in the near field 0.25 to 8 km from the Fukushima Dai-ichi NPP, on sections of the Niida River floodplain, and in a forest ecosystem typical of the territory contaminated after the accident. It is shown that the vertical migration...

The mobility and bioavailability of radiocesium (r-Cs) of accidental origin is governed by the ratio of its chemical forms in fallout and site-specific environmental characteristics determining the rates of leaching, fixation-remobilization, as well as sorption-desorption of the mobile fraction (its solid-liquid distribution). R-Cs in the environme...

This study investigates the source and flux of particulate 129I in the downstream reaches of the Niida River system in Fukushima. The upper watershed is a relatively highly contaminated zone located 30–40 km northwest of the Fukushima Daiichi Nuclear Power Plant. Samples of total suspended substance (SS) were collected continuously at Haramachi (5....

Precipitation isotope maps over mountains are critical for water resource assessment, yet isoscape modeling has been minimally investigated for complex terrain with high relief. Here we show that multiannual (2011–2015) mean precipitation isoscapes across the Japanese Alps region can be represented by simple multiple-regression models with strong g...

About half of the total paddy field area, which is the dominant agricultural land in Fukushima Prefecture, was contaminated by radiocesium released by the Fukushima Daiichi Nuclear Power Plant accident. In this study, we investigated the temporal changes of radiocesium in soil, irrigation water, and rice plant in two adjacent rice paddies, with and...

Core soils and falling litter samples were collected in Japanese cypress forest (Chamaecyparis obtuse) to determine the litter-feed 210Pbex and organic carbon transfer from forest canopy to soil and their subsequent distribution. Of the canopy residing 210Pbex pool, litterfall annually transports 53% to the forest floor while it adds 117 g m–2 year...

Mobility and bioavailability of radiocesium of accidental origin is governed by the ratio of radiocesium chemical forms in fallout and site-specific environmental characteristics determining the rates of leaching, fixation/remobilization, as well as sorption-desorption of the mobile fraction (its solid-liquid distribution). Distinct features of th...

This study investigates the potential impacts of regional climate change on hydrological cycles using eight years of observations on snowmelt runoff from a small forested watershed (Kurahone watershed) in Nagano Prefecture, Japan. We compared discharge in winter and spring (January–May) in 1991, 1997, 1998, 2003, 2004, 2006, 2012 and 2013. Early ye...

Soil erosion is the initial process which drives radiocesium into the aquatic systems and therefore the quantifi-cation of radiocesium wash-off associated with soil erosion is indispensable for mitigating the risks. This study presents two year's observation of soil erosion and radiocesium wash-off to quantify differences in radiocesium behavior in...

The relationships of erosion-induced displaced soil organic carbon (SOC) to discharged 210Pbex and 137Cs in a hillslope forested area were investigated using runoff plots in three different forest types. A significant correlation was found between the displaced SOC and the radionuclides in each examined forest type. Compared with 137Cs, however, th...

Inter-annual variations of snowmelt runoff timing in 15 basins across central Japan were analyzed across 30 years, from 1980–2009, to determine if mountain hydrology has been affected by global warming. Observed daily river discharge was utilized to calculate center time (CT) of mass of flow. CT was found to be occurring significantly earlier in th...

Although the excess of lead-210 (210Pbex) has been described as an alternative or complementary nuclide to cesium-137 (137Cs) for soil erosion assessment, the potential use of 210Pbex in forested environments has not been examined sufficiently. In this study, to investigate the potential use of 210Pbex for the assessment of soil erosion on various...

To elucidate splash erosion processes under natural rainfall conditions, temporal variations in splash detachment were observed using a piezoelectric saltation sensor (H11B; Sensit Co., Portland, ND, USA). Preliminary laboratory tests of Sensit suggested that they were suitable for field observations. Field observations were conducted between July...

Japanese cypress (Chamaecyparis obtusa) is one of the most common plantation species in Japan. In most Japanese cypress plantations, closure of the forest canopy hinders understory growth because of insufficient management practices. Thus leaf litter barely covers the soil surface. Such plantations are vulnerable to surface erosion triggered by rai...

Temporal variation in each sub-process of soil erosion during rainfall is one of causes which add the difficulty in the prediction of their extents. However, monitoring such variation in each process had caused technical difficulties especially under natural rainfall conditions. This study presents temporal variations in splash detachment under nat...

本論文は，九州大学農学部附属演習林福岡演習林内に設置された御手洗水試験流域の土壌の性質と水分特性（透水性と保水性）を報告する．管理放棄されたヒノキ人工林が分布する本流域において，粒径分布，土粒子密度，乾燥密度，間隙率，飽和透水係数を採取した土壌サンプルを用いて計測し，土壌硬度と土層厚の計測を現場で行った．また，現場において土壌の体積含水率と圧力水頭の計測を行い，土壌の保水性を水分特性曲線によって示した．その結果，本流域の土層は40－60cmと浅く，全体的には，飽和に近い段階から排水が開始され，かつ排水が持続的に生じるという団粒もしくは粒状構造の土壌が持つ土壌水分特性を示した．一方で，斜面中腹部から下部の一部の土壌は，土壌がある程度まで乾燥しないと排水が生じず，移動可能な水分が少ないという壁状...

蛇紋岩山地における地形形成と土壌の粘土鉱物組成との関係を明らかにするため，斜面傾斜角と土壌中の粘土鉱物の関係を調べた．蛇紋岩を母岩とする御手洗水流域内の13地点から土壌を採取し，X線回折による土壌中の粘土鉱物分析を行った．また，土壌採取地点においてクリノメーターを用いた簡易な方法により局所的な斜面傾斜角を測定した．X線回折の結果より，この地域の土壌に含まれる粘土鉱物は蛇紋石・緑泥石・タルク・石英であった．斜面傾斜角は最大で33.5°であり，蛇紋岩山地としては比較的急傾斜の地点が見られた．採取地点の斜面傾斜角と粘土鉱物含量との比較により，蛇紋石含量と斜面傾斜角との間に正の相関（相関係数：r = 0.48）が見られた．蛇紋石を多く含む土壌は，同じく蛇紋岩地帯に見られるタルク・緑泥石を多く含む土壌...