Impacts of Fukushima Nuclear Accident on Freshwater Environments 9811636702, 9789811636707

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Seiya Nagao   Editor

Impacts of Fukushima Nuclear Accident on Freshwater Environments

Impacts of Fukushima Nuclear Accident on Freshwater Environments

Seiya Nagao Editor

Impacts of Fukushima Nuclear Accident on Freshwater Environments

Editor Seiya Nagao Institute of Nature and Environmental Technology Kanazawa University Kanazawa, Ishikawa, Japan

ISBN 978-981-16-3670-7 ISBN 978-981-16-3671-4 https://doi.org/10.1007/978-981-16-3671-4

(eBook)

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

Preface

The 84th annual meeting of the Japanese Society of Limnology was held in Kanazawa on 27–30 September 2019. A special session on the dynamics and fate of radiocesium in terrestrial environments was organized and successfully completed with fruitful discussion. This was the fourth special session on the FDNPP accident issues presented at the annual meeting. Close to 10 years after the FDNPP accident, the organizer planned to summarize the knowledge and dataset on the dynamics of radiocesium in the terrestrial environment. This book consists of three parts: migration behavior of radiocesium in river and lake environments, accumulation of radiocesium into organisms in freshwater, and integrated environmental analysis in a lake system and a forest-freshwater system. The book is suitable for learning the actual dispersion behavior of radionuclides released from the Fukushima accident, from the accident to the present time in the freshwater environment. It provides valuable and available scientific knowledge which is the basic information to assess the impacts of the FDNPP accident on the ecosystem and human health and to develop countermeasures for similar accidents. Kanazawa, Ishikawa, Japan

Seiya Nagao

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Contents

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Introduction: Overview of Research with Dynamics of Radiocesium in Freshwater Environment . . . . . . . . . . . . . . . . . . Seiya Nagao, Shinji Ueda, and Seiichi Nohara

Part I 2

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Rivers and Lake Environment

Differences in Radiocesium Export in River Systems 1 and 5 Years After the Fukushima Daiichi Nuclear Power Plant Accident . . . . . . Seiya Nagao, Masaki Kanamori, Hiroki Uemura, Shu Tado, Akie Shimamura, Toshiki Morokado, Seiichi Tomihara, Shun Watanabe, Kyuma Suzuki, and Shinya Ochiai Spatial and Temporal Fluctuations of Nuclear Accident-Derived Tritium Concentrations in the River Waters of Eastern Fukushima, Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shinji Ueda, Hidenao Hasegawa, Hideki Kakiuchi, and Shinya Ochiai

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Spatial and Temporal Changes of 137Cs Concentrations in River Waters and Correlation with the Radiocesium Inventory in Fukushima and Adjacent Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . Shinya Ochiai, Shinji Ueda, Seiya Nagao, Hideki Tsuji, Seiichi Tomihara, Shun Watanabe, and Kyuma Suzuki

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Inflow/Outflow of Radiocesium in a Dam Lake and Its Accumulation in Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hideki Tsuji, Ayato Kohzu, Takayuki Satou, and Seiji Hayashi

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Concentrations and Fluxes of Radiocesium Activity in Lake Chūzenji, Japan, During 2014–2016 . . . . . . . . . . . . . . . . . . . . . . . . Seiichi Nohara, Tetsuya Yokozuka, and Isao Kobori

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Contents

Part II

Ecosystem

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Relationship Between Air Dose Rate and Radiocesium Concentrations in Mountain Stream Fish in Fukushima Prefecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Wataru Teramoto, Yuto Funaki, Hiroki Nakakubo, and Tadahiro Sohtome

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Annual Changes in 137Cs Concentrations in Freshwater Fishes . . . . 123 Nobuyoshi Ishii

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Source of Variation of 137Cs Concentrations in Brown Trout in Lake Chuzenji After the Fukushima Daiichi Nuclear Power Plant Accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Tetsuya Yokozuka, Isao Kobori, Korenori Takeda, Takatoshi Tsunagawa, Masahiro Akutsu, and Seiichi Nohara

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Body Size Effect of Radiocesium Concentrations in Wakasagi (Hypomesus nipponensis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Kyuma Suzuki, Shun Watanabe, Kin-ichi Tsunoda, Masanobu Mori, Seiichi Nohara, and Yukiko Okada

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Characteristics of 137Cs Concentration and Radioactivity Transfer in Large Aquatic Insect Species . . . . . . . . . . . . . . . . . . . . 169 Takeshi Fujino, M. D. H. Jayasanka Senavirathna, Masaru Sakai, and Takashi Gomi

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Relationships Between Stomach Contents and Radiocesium Contamination of Fish by Fukushima Radioactive Accident in 2011, in Japan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 Mayumi Yoshimura and Akio Akama

Part III

Case Studies at Different Watershed Environments

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The Dynamics of Radiocesium in the Lake Onuma Ecosystem, Mt. Akagi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 Shun Watanabe, Kyuma Suzuki, Kin-ichi Tsunoda, Masanobu Mori, Seiichi Nohara, Yukiko Okada, and Seiya Nagao

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Radiocesium Transfer from Forest Catchment to Freshwater Fish Living in Mountain Streams Estimated from Environmental Monitoring Data in Fukushima Prefecture . . . . . . . 227 Hiroshi Kurikami

Chapter 1

Introduction: Overview of Research with Dynamics of Radiocesium in Freshwater Environment Seiya Nagao, Shinji Ueda, and Seiichi Nohara

Abstract Large quantities of radionuclides were released after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident on March 11, 2011. The e-book entitled Impacts of Fukushima Nuclear Accident on Freshwater Environments summarizes radionuclides accumulation and its effects on the ecosystem in the freshwater environment. This chapter introduces an overview of research with radiocesium in the freshwater environment presented in this book. Keywords Fukushima Nuclear Power Plant accident · Migration · Deposition and accumulation of radiocesium · Freshwater fishes and insects · River and lake watershed

1.1

Introduction

Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred on March 11, 2011 after the Tohoku Earthquake and Tsunami in Japan because of loss of all power sources (Fukushima Prefecture 2015). Large quantity of radionuclides were released into the atmosphere (Chino et al. 2011; Katata et al. 2012). The radionuclides released were diffused to the North Pacific Ocean and eastern Japan (Katata et al. 2015) and were deposited mainly in the Tohoku and Kanto regions (Kinoshita et al. 2011; Tsuruta and Nakajima 2012). The spatial distribution of 134Cs and 137Cs inventory of surface soil determined by aircraft survey in November 2011 was

S. Nagao (*) Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa, Japan e-mail: [email protected] S. Ueda Department of Radioecology, Institute for Environmental Sciences, Rokkasho, Aomori, Japan S. Nohara National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 S. Nagao (ed.), Impacts of Fukushima Nuclear Accident on Freshwater Environments, https://doi.org/10.1007/978-981-16-3671-4_1

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reported by the MEXT (2011). The higher inventory was distributed at northwest region from the FDNPP. The relatively higher accumulation of radiocesium was also observed at mountain area in Tochigi and Gunma Prefectures. The similar spatial distribution has reported for surface soil based on the radioactivity determined by Ge detector (Saito et al. 2015; Agriculture, Forestry and Fisheries Research Council 2020). After the deposition of radiocesium on the ground surface, radiocesium has been transporting from watershed to rivers and lakes due to rainfall and snow-melt (Nagao et al. 2013, 2017; Ueda et al. 2013; Taniguchi et al. 2019). The radiocesium in rivers, lakes, and coastal marine environments has been taken up by living organisms (Fisheries Agency 2020). Japanese and local governments have been monitoring the temporal and spatial distribution of radionuclides in terrestrial and marine environments from short- to long-term period after the accident. The aim of this book is to report the impacts of radionuclides released from the FDNPP accident on aquatic environment in land. There are many scientific papers and reports with dynamics of radionuclides, especially radiocesium in land and marine environment because of large release, relatively long half-life (134Cs 2.07 years, 137Cs 30.17 years) and higher contribution to external exposure to human health. Monitoring surveys have been performed for radioactivity of 134Cs and 137Cs in river and lake systems in Kanto and Tohoku region and study the transport of radiocesium from the watershed to the river waters and the impacts on human health and ecosystem (NRA 2020). These results have been published in scientific papers, reports, and books related to the FDNPP accident (e.g., Niizato et al. 2014; Nakanishi et al. 2019; Takenaka et al. 2019; Onda et al. 2020). This book focuses on the dynamics of radiocesium, which is studied in land aquatic environment and consists of three categories: transport of radiocesium in river and lakes, accumulation of radiocesium to ecosystem, and integrated environmental studies. Figure 1.1 shows a location map with research sites in this book.

1.2 1.2.1

Migration Behavior of Radionuclides in Freshwater River Systems

To estimate the impacts of radiation dose to human health, it is important to understand dynamics of radionuclides, especially 134Cs and 137Cs, in river and lake watershed environments. Nagao et al. (Chap. 2) reported the temporal variation of radiocesium concentration in waters from the lakes and river systems Fukushima, Miyagi, Gunma, Ibaraki, and Chiba prefectures in Japan and discuss with factors controlling spatial and temporal variations. Ueda et al. (Chap. 3) have shown that the measured 3H concentrations were higher than the background level in 2012 and decreased with time. They found good correlations between 3H concentrations in the

1 Introduction: Overview of Research with Dynamics of Radiocesium in. . .

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Fig. 1.1 Locations of rivers and lakes used for the studies of radionuclides dynamics. Results of distribution survey of radioactive substances by aircraft monitoring are cited from the MEXT (2013) and JAEA (2020). The map was obtained from Global Map Japan (GIAJ 2020b), Fundamental Geospatial Data (GIAJ 2020a) and MLIT (2020)

water samples and 137Cs inventories in the catchment areas. The effective half-life of 3 H in forest-type river waters was longer than that in paddy-type waters, depending upon the different water retention capacities of the watersheds. Ochiai et al. (Chap. 4) compiled previously reported data of dissolved and particulate 137Cs in rivers of Fukushima and adjacent areas during 2011–2019 to investigate the controls of 137Cs inventory on the spatial and temporal changes of 137Cs concentrations in river waters. Additionally, they also examine the contributions of 137Cs sources which have different distances to the sampling points based on the geomorphological analyses to clarify the difference in behavior of particulate and dissolved 137Cs (Fig. 1.1).

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Lakes

In lake environmental researches, Tsuji et al. (Chap. 5) investigated the concentration of particulate and dissolved radiocesium in the inflow and outflow water of a dam lake and its bottom sediment. They discussed with the dynamics of radiocesium in the dam lake environment from the time-series data of its concentration and inventory distribution. Nohara et al. (Chap. 6) have shown the research results at Lake Chuzenji in Tochigi Prefecture in eastern Japan. The inventory of bottom sediment was 15,100 Bq m 2 the radiocesium deposits after the FDNPP accident. Total outflow of radioactivity from Lake Chuzenji was about 1% of cumulative dose of the lake at the decreased rate of 0.66 Bq year 1. About 40% of radioactivity was still in lake water of Lake Chuzenji in 2014.

1.3

Effects of Radiocesium on Ecosystem

The effects of radiocesium on ecosystem have been reported in Chaps. 7–11. Radiocesium deposited on the ground surface transports into rivers and lakes after the FDNPP accident in 2011 and has been taken by living organisms. A wide variety of species including fishes were contaminated in aquatic environment after the accident in 2011(Fisheries Agency 2020).

1.3.1

Fishes

Ten years have passed since the accident, freshwater fish contamination with radiocesium is still serious issue in some area because shipping restrictions and restraint have continued. It is important to monitor the contamination level and temporal variation in freshwater fishes because of estimation of internal radiation exposure. Teramoto et al. (Chap. 7) investigated radioactivity of river fishes in Fukushima Prefecture. Ishi reported freshwater fishes in Lake Inba in Chiba Prefecture (Chap. 8). Activity concentrations of 137Cs in the muscle of crucian carp remained constant after November 2016. The similar trends were found for catfish, snakehead, largemouth bass, bluegill. Yokozuka et al. (Chap. 9) elucidate radioactive contamination of brown trout Salmo trutta in Lake Chuzenji. They investigated correlation with the radioactivity of 137Cs and brown trout body weight and sources of radiocesium on the basis of stomach contents weight and prey’s 137Cs concentrations. Suzuki et al. (Chap. 10) reported the effects of body size of wakasagi (Hypomesus nipponensis) on radiocesium level in the Lake Onuma ecosystem.

1 Introduction: Overview of Research with Dynamics of Radiocesium in. . .

1.3.2

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Insects and Another Species

Variations in the 137Cs radioactivity level caused by flashing, resuspension, and retention of suspended particulate matter in streams influence the concentration factors for living organisms. Fujino et al. (Chap. 11) reported variations in the 137 Cs radioactivity transfer and accumulation in two large aquatic insect species, the Caddisfly Stenopsyche marmorata Navas (Trichoptera) and the Dobsonfly Protohermes grandis (Megaloptera), in four streams. Differences in the concentration factors among the four streams may reflect differences in the morphology at the study sites. Yoshimura (Chap. 12) has shown radiocesium contamination to freshwater environment including litter, stream algae, sand substrate, aquatic insects, and fish. Radioactive Cs concentration in algae and aquatic insects varied irregularly, but was consistently higher in aquatic insects in pools than in stream riffles.

1.4

Integrated Research on Fate of Radiocesium in a Lake and a River System

Last two chapters assessed the impacts of radiocesium on fishes in a lake and river systems. Chapter 13 has shown the temporal dynamics of 137Cs in the aquatic ecosystem of Lake Onuma on Mt. Akagi in Gunma Prefecture. Watanabe et al. estimated the effective ecological half-life of 137Cs in fishes and lake water by using survey data of 137Cs concentration collected from 2011 to 2017 and single- and two-component decay function models. The estimation of 137Cs mass balance in Lake Onuma suggests that 137Cs may be eluted from lake bottom sediment to sustain the lake water concentration. Kurikami (Chap. 14) discussed the relationship between radiocesium migration in forest and fish contamination by using a model and environmental monitoring data. Radiocesium sources in forest transferred to fish were changing with time from litter layer of the forest floor to the organic soil underlying the litter layer. The temporal variation of inventory of 134Cs and 137Cs in surface soil estimated by aircraft survey was reported by JAEA (2020). The export of radiocesium deposited on the ground surface from watershed is 1–2% during 2011–2016 (Ueda et al. 2013; Osawa et al. 2018; Taniguchi et al. 2019, etc.). Radiocesium concentration in freshwater decreases with increasing time exponentially (Nakanishi and Sakuma 2019; Taniguchi et al. 2019). Freshwater fishes also show the decline in radioactivity of 134Cs and 137Cs with increasing time after the FDNPP accident. Fitting patterns of decline trend is two decay forms, depending on fish species (Suzuki et al. 2018). However, the radioactivity of 137Cs in river and lake waters is 1–2 orders of magnitude higher than that before the FDNPP accident. Major part of 137Cs deposited to freshwater environment is still remained in watershed in Tohoku and Kanto area. Therefore, it is still important to monitor 137Cs radioactivity in freshwaters and

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living in fish to provide information for predicting future concentration changes and some nuclear disease. Acknowledgments The map of research sites reported in this book was made by Dr. Shinya Ochiai of the Low Level Radioactivity Laboratory, Kanazawa University, Japan. The edition work was supported by Mrs. Yuka Kounishi and Mrs. Ayako Matsuda of the Institute of Nature and Environmental Technology, Kanazawa University. We deeply appreciate the above named persons.

References Agriculture, Forestry and Fisheries Research Council (2020) A map of spatial distribution of radiocesium in farmland soil in 2011 and 2012. https://www.affrc.maff.go.jp/docs/press/pdf/ 120323_03_bunpuzu.pdf. Accessed 27 Dec 2020 Chino M, Nakayama H, Nagai H et al (2011) Preliminary estimation of release amounts of 131I and 137 Cs accidentally discharged from the Fukushima Daiichi Nuclear Power Plant into the atmosphere. J Nucl Sci Technol 48:1129–1134. https://doi.org/10.1080/18811248.2011. 9711799 Fisheries Agency (2020) Results of the monitoring on radioactivity level in fishes products. https:// www.jfa.maff.go.jp/e/inspection/index.htm. Accessed 27 Dec 2020 Fukushima Prefecture (2015) Response to the Fukushima Daiichi Nuclear Power station accident. https://www.pref.fukushima.lg.jp/uploaded/attachment/146178.pdf. Accessed 27 Dec 2020 Geospatial Information Authority of Japan (2020a) Fundamental geospatial data. https://www.gsi. go.jp/kiban/index.html. Accessed 12 Jul 2020 Geospatial Information Authority of Japan (2020b) Global map Japan. https://www.gsi.go.jp/ kankyochiri/gm_japan_e.html. Accessed 12 Jul 2020 Japan Atomic Energy Agency (JAEA) (2020) Database for radioactive substances monitoring data. https://emdb.jaea.go.jp/emdb/en. Accessed 14 Jul 2020 Katata G, Ota M, Terada H et al (2012) Atmospheric discharge and dispersion of radionuclides during the Fukushima Dai-ichi Nuclear Power Plant accident. Part I: source term estimation and local-scale atmospheric dispersion in early phase of the accident. J Environ Radioact 109:103–113. https://doi.org/10.1016/j.jenvrad.2012.02.006 Katata G, Chino M, Kobayashi T (2015) Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model. Atmos Chem Phys 15:1029–1070. https://doi.org/10.5194/acp-15-1029-2015 Kinoshita N, Sueki K, Sasa K et al (2011) Assessment of individual radionuclide distributions from the Fukushima nuclear accident covering contra-eastern Japan. Proc Natl Acad Sci U S A 108:19526–19529. https://doi.org/10.1073/pans.1117296108 Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) (2011) Air dose rate results of the fourth airborne monitoring survey. http://radioactivity.nsr.go.jp/ja/contents/ 5000/4901/24/1920_1216.pdf. Accessed 25 Dec 2011 Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) (2013) Results of the (i) Sixth Airborne Monitoring Survey and (ii) Airborne Monitoring Survey outside 80 km from the Fukushima Dai-ichi NPP. https://radioactivity.nsr.go.jp/en/contents/7000/6099/24/ 203_e_0301_18.pdf. Accessed 28 Dec 2020 Ministry of Land, Infrastructure and Transport, Japan (2020) National land numerical information. https://nlftp.mlit.go.jp/ksj/index.html. Accessed 12 Jul 2020 Nagao S, Kanamori M, Ochiai S et al (2013) Export of 134Cs and 137Cs in the Fukushima river systems at heavy rains by Typhoon Roke in September 2011. Biogeosciences 10:6215–6223. https://doi.org/10.5194/bg-10-6215-2013

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Nagao S, Kanamori M, Suzuki K et al (2017) 134Cs and 137Cs radioactivity in river waters from the upper Tone River. Bunseki Kagaku 66:243–249. (in Japanese). https://doi.org/10.2116/ bunsekikagaku.66.243 Nakanishi T, Sakuma K (2019) Trend of 137Cs concentration in river water in the medium term and future following the Fukushima nuclear accident. Chemosphere 215:272–279. https://doi.org/ 10.1016/j.chemosphere.2018.10.017 Nakanishi TM, O’Brien M, Tanoi K (2019) Agricultural implications of the Fukushima Nuclear Accident (III). Springer, p 133 Niizato T, Nakanishi T, Funaki H et al (2014) Progress within the F-TRACE project. In: 2nd Casium workshop: meeting challenge for Fukushima recovery. https://fukushima.jaea.go.jp/ fukushima/result/pdf/pdf1410/2-2_Niizato.pdf. Accessed 28 Dec 2020 Nuclear Regulation Authority, Japan (NRA) (2020) Monitoring information of environmental radioactivity level. https://radioactivity.nsr.go.jp/ja/list/512/list-1.html. Accessed 20 Sept 2020 Onda Y, Taniguchi K, Yoshimura K et al (2020) Radionuclides from the Fukushima Daiichi Nuclear Power Plant in terrestrial systems. Nat Rev Earth Environ 1:644–660. https://doi.org/ 10.1038/s43017-020-0099x Osawa K, Nonaka Y, Nishimura T et al (2018) Quantification of dissolved and particulate radiocesium fluxes in two rivers draining the main radioactive pollution plume in Fukushima, Japan (2013–2016). Anthropocene 22:40–50. https://doi.org/10.1016/j.ancene.2018.04.003 Saito K, Tanihara I, Fujiwara M et al (2015) Detailed deposition density maps constructed by largescale soil sampling for gamma-ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident. J Environ Radio 139:308–319. https://doi.org/10.1016/j.jenvrad. 2014.02.014 Suzuki K, Watanabe S, Yuasa Y et al (2018) Radiocesium dynamics in the aquatic ecosystem of Lake Onuma on Mt. Akagi following the Fukushima Dai-ichi Nuclear Power Plant accident. Sci Total Environ 622–623:1153–1164. https://doi.org/10.1016/j.scitotenv.2017.12.017 Takenaka C, Hijii N, Kaneko N, Ohkubo T (2019) Radiocesium dynamics in a Japanese forest ecosystem. Springer, p 65 Taniguchi K, Onda Y, Smith HG et al (2019) Transport and redistribution of radiocesium in Fukushima fallout through rivers. Environ Sci Technol 53:12339–12347. https://doi.org/10. 1021/acs.est.9b02890 Tsuruta H, Nakajima T (2012) Radioactive materials in the atmosphere released by the accident of Fukushima Daiichi Nuclear Power Plant. Chikyukagaku (Geochemistry) 46:99–111 Ueda S, Hasegawa H, Kakiuchi H et al (2013) Fluvial discharges of radiocesium from watersheds contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident, Japan. J Environ Radioact 118:96–104. https://doi.org/10.1016/j.jenvrad.2012.11.009

Part I

Rivers and Lake Environment

Chapter 2

Differences in Radiocesium Export in River Systems 1 and 5 Years After the Fukushima Daiichi Nuclear Power Plant Accident Seiya Nagao, Masaki Kanamori, Hiroki Uemura, Shu Tado, Akie Shimamura, Toshiki Morokado, Seiichi Tomihara, Shun Watanabe, Kyuma Suzuki, and Shinya Ochiai Abstract Studies on the migration of radiocesium, 134Cs and 137Cs, deposited on the ground surface in the Tohoku and Kanto areas are important for understanding their external doses and effects on the ecosystems of freshwater and coastal environments. This chapter focuses on the spatiotemporal variations in radiocesium in river systems with a wide range of accumulation in catchments. Research has been conducted on eight river catchments with different characteristics and radiocesium inventories. We investigated the variations in the radioactivity of 134Cs and 137Cs and their existing forms from 2011 to 2016. The monitoring results indicated that the migration behavior of radiocesium from the watersheds, which were highly contaminated, to the Abukuma and Niida Rivers could be divided into two periods: (1) July 2011 to April 2012 and (2) August 2012 to June 2016. However, the migration in the Natsui River, which had a less-contaminated watershed, differed from that of Abukuma and Niida Rivers, indicating wide range of particulate radiocesium at lower turbidity. These results reflect the differences in the existing forms of radiocesium and a decline in the entry of radiocesium to rivers from catchments at both time intervals.

S. Nagao (*) · S. Ochiai Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, Nomi, Ishikawa, Japan e-mail: [email protected] M. Kanamori Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, Japan H. Uemura · S. Tado · A. Shimamura · T. Morokado College of Science and Engineering, Kanazawa University, Kanazawa, Ishikawa, Japan S. Tomihara Aquamarine Fukushima, Iwaki, Fukushima, Japan S. Watanabe · K. Suzuki Gunma Prefectural Fisheries Experiment Station, Maebashi, Gunma, Japan © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 S. Nagao (ed.), Impacts of Fukushima Nuclear Accident on Freshwater Environments, https://doi.org/10.1007/978-981-16-3671-4_2

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Keywords 137Cs · River water · Existing forms · Migration behavior · Particulate radiocesium

2.1

Introduction

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident occurred after the Tohoku Earthquake and tsunami on March 11, 2011. Large amounts of radionuclides were released during March and April 2011 (Chino et al. 2011; Katata et al. 2012) and deposited on land and in the ocean (MEXT 2011). Kinoshita et al. (2011) provided accumulation maps of the radionuclides (129mTe, 131I, 134Cs, 136Cs, and 137 Cs) released by the accident, and the MEXT (Ministry of Education, Culture, Sports, Science and Technology, Japan) summarized the spatial distributions of 134 Cs + 137Cs in surface soil (Takata et al. 2014; Saito et al. 2015) due to their relatively long half-life (134Cs: 2.07 years, 137Cs: 30.1 years), large released amounts, and high external exposure risk. A second migration after deposition on the ground’s surface has been observed for global fallout and the Chernobyl accident (Hirose et al. 1990; Matsunaga et al. 1991, 1998; Konoplev et al. 2002). To better understand the migration behavior of radionuclides derived from the FDNPP in aquatic environments, monitoring research should be conducted in watersheds with different vegetation, geomorphology, and radiocesium accumulation levels. The Japanese government has been conducting much monitoring research in Japan (NRA 2020). Many scientists have published monitoring results obtained at various river systems, such as the spatial variations (Nagao et al. 2014a, b; NRA 2020), temporal variations (Nagao et al. 2015; Taniguchi et al. 2019; Takata et al. 2020a), rainfall effects (Nagao et al. 2013; Ueda et al. 2013; Shinomiya et al. 2014; Yamashiki et al. 2014), and snow-melt effects on radiocesium export (Nagao et al. 2017). Existing forms of radiocesium are also important research parameters for simulating their migration behavior from watersheds to rivers and from the upper to lower river reaches (e.g., Tanaka et al. 2013; Sakaguchi et al. 2015). Sakaguchi et al. (2015) reported the