Effects of radiocesium inventory on (137)Cs concentrations in river waters of Fukushima, Japan, under base-flow conditions

Shinya Ochiai; Shinji Ueda; Hidenao Hasegawa; Hideki Kakiuchi; Naofumi Akata; Yoshihito Ohtsuka; Shun'ichi Hisamatsu

doi:10.1016/j.jenvrad.2015.03.005

Effects of radiocesium inventory on (137)Cs concentrations in river waters of Fukushima, Japan, under base-flow conditions

J Environ Radioact. 2015 Jun:144:86-95. doi: 10.1016/j.jenvrad.2015.03.005. Epub 2015 Mar 27.

Authors

Shinya Ochiai¹, Shinji Ueda², Hidenao Hasegawa², Hideki Kakiuchi², Naofumi Akata³, Yoshihito Ohtsuka², Shun'ichi Hisamatsu²

Affiliations

¹ Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan. Electronic address: sochiai@ies.or.jp.
² Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan.
³ Department of Radioecology, Institute for Environmental Sciences, 1-7 Ienomae, Obuchi, Rokkasho, Kamikita, Aomori 039-3212, Japan; National Institute for Fusion Science, 322-6 Oroshi-cho, Toki City, Gifu 509-5292, Japan.

PMID: 25827575
DOI: 10.1016/j.jenvrad.2015.03.005

Abstract

To investigate the behavior of nuclear accident-derived (137)Cs in river water under base-flow conditions, concentrations of dissolved and particulate (137)Cs were measured at 16 sampling points in seven rivers of Fukushima Prefecture, Japan, in 2012 and 2013. The concentration of dissolved (137)Cs was significantly correlated with the mean (137)Cs inventory in the catchment area above each sampling point in both sampling years. These results suggest that the concentration of dissolved (137)Cs under base-flow conditions is primarily determined by the (137)Cs inventory of the catchment area above the sampling point. However, the concentration of particulate (137)Cs did not show a clear relationship with either the mean (137)Cs inventory or the dissolved (137)Cs concentration, thus indicating that particulate and dissolved forms do not effectively interact in rivers. To evaluate the contribution of the (137)Cs inventory within catchment areas, we analyzed relations between the (137)Cs concentration and the mean (137)Cs inventory over the area within certain flow path lengths that were traced along the river and slope above the sampling point. Coefficients of determination for dissolved (137)Cs concentrations were highest for the longest flow path, i.e., the whole catchment area, and lower for shorter flow paths. Coefficients of determination for particulate (137)Cs concentrations were only moderately high for the shortest flow path in 2012, whereas the values were quite low for all flow paths in 2013. These results suggest that dissolved (137)Cs can originate from a larger area of the catchment even under base-flow conditions; however, particulate (137)Cs did not show such behavior. The results also show that under base-flow conditions, dissolved and particulate (137)Cs behave independently during their transport from river catchments to the ocean.

Keywords: Base-flow; Catchment inventory; Fukushima Dai-ichi Nuclear Power Plant accident; Radiocesium; River water.

MeSH terms

Cesium Radioisotopes / analysis*
Fukushima Nuclear Accident*
Japan
Models, Theoretical
Particulate Matter / analysis
Radiation Monitoring*
Rivers
Seasons
Water Pollutants, Radioactive / analysis*

Substances

Cesium Radioisotopes
Particulate Matter
Water Pollutants, Radioactive