Dynamics of ¹³⁷Cs in Water and Phyto- and Zooplankton in a Reservoir Affected by the Fukushima Daiichi Nuclear Power Plant Accident

Abstract

Lake water, phytoplankton and zooplankton were sampled in a total of 12 quarterly surveys from August 2014 to May 2017 at a reservoir in the Fukushima nuclear disaster area, and variations in dissolved forms of 137 Cs and planktonic 137Cs were observed. Seasonal variations in dissolved 137Cs concentration becoming high in summer and low in winter were observed in the upstream, midstream and downstream areas of the reservoir, but no seasonal or site-specific differences in planktonic 137Cs concentrations or dominant species were found. The concentration factors of 137Cs for phytoplankton and zooplankton were 340 and 1,700, which were comparable to previously reported values. The amount of planktonic 137Cs in the water was less than 1.4% of the total 137Cs in the reservoir water; therefore the effect of plankton on the dynamics of 137Cs in the reservoir was minimal.