title: Temporal changes in dissolved137Cs concentrations in groundwater and stream water in Fukushima after the Fukushima Dai-ichi Nuclear Power Plant accident.
abstract: The concentration of dissolved137Cs in groundwater and stream water in the headwater catchments in Yamakiya district, located ∼35 km north west of Fukushima Dai-ichi Nuclear Power Plant (FDNPP), was monitored from June 2011 to July 2013, after the earthquake and tsunami disaster. Groundwater and stream water were sampled at intervals of approximately 2 months at each site. Intensive sampling was also conducted during rainstorm events. Compared with previous data from the Chernobyl NPP accident, the concentration of dissolved137Cs in stream water was low. In the Iboishi-yama catchment, a trend was observed for the concentration of dissolved137Cs in stream water to decline, which could be divided into two phases by October 2011 (a fast flush of activity as a result of rapid washoff and a slow decline as a result of soil fixation and redistribution processes). The highest137Cs concentration recorded at Iboishi-yama was 1.2 Bq/L on August 6, 2011, which then declined to 0.021-0.049 Bq/L during 2013 (in stream water under normal water-flow conditions). During the rainfall events, the concentration of dissolved137Cs in stream water increased temporarily. The concentration of dissolved137Cs in groundwater at a depth of 30 m at Iboishi-yama displayed a decreasing trend from 2011 to 2013, with a range from 0.039 Bq/L to 0.0025 Bq/L. The effective half-lives of stream water in the initial fast flush and secondary phases were 0.10-0.21 and 0.69-1.5 y, respectively in the three catchments. The effective half-life of groundwater was 0.46-0.58 y at Koutaishi-yama and 0.50-3.3 y at Iboishi-yama. The trend for the concentration of dissolved137Cs to decline in groundwater and stream water was similar throughout 2012-2013, and the concentrations recorded in deeper groundwater were closer to those in stream water. The declining trend of dissolved137Cs concentrations in stream water was similar to that of the loss of canopy137Cs by throughfall, as shown in other reports of forest sites in the Yamakiya district.
authors.affiliation: Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba 305-8577, Japan. Electronic address: sho.iwagami@gmail.com.
authors.forename: Sho
authors.initials: S
authors.lastname: Iwagami
authors.affiliation: Department of Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Tsujimura
authors.affiliation: Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, Tsukuba 305-8577, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Onda
authors.affiliation: Department of Geoenvironmental Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 305-8572, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Nishino
authors.affiliation: College of Geoscience, School of Life and Environmental Sciences, University of Tsukuba, 305-8572, Japan.
authors.forename: Ryohei
authors.initials: R
authors.lastname: Konuma
authors.affiliation: Department of Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Abe
authors.affiliation: Department of Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Manami
authors.initials: M
authors.lastname: Hada
authors.affiliation: Department of Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Ishwar
authors.initials: I
authors.lastname: Pun
authors.affiliation: Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 739-8526, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Sakaguchi
authors.affiliation: Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 739-8526, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kondo
authors.affiliation: Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, 923-1224, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: Low Level Radioactivity Laboratory, Institute of Nature and Environmental Technology, Kanazawa University, 923-1224, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Miyata
authors.affiliation: Atmospheric Environment and Applied Meteorology Research Department, Meteorological Research Institute, 305-0052, Japan.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Igarashi
mesh_terms: D002588:Cesium Radioisotopes / Q000032:analysis* / Q000737:chemistry; D062406:Fukushima Nuclear Accident; D060587:Groundwater / Q000032:analysis*; D006207:Half-Life; D007564:Japan; D011834:Radiation Monitoring; D045483:Rivers / Q000737:chemistry*; D012995:Solubility; D014875:Water Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry
chemical_list: D002588:Cesium Radioisotopes; D014875:Water Pollutants, Radioactive
keywords: Dissolved (137)Cs; Fukushima Dai-ichi Nuclear Power Plant; Groundwater; Rainstorm event; Stream water