Time dependence of the Cs concentration in particles discharged from rice paddies to freshwater bodies after the Fukushima Daiichi NPP accident

Yoshimura, Kazuya  ; Onda, Yuichi*; Wakahara, Taeko*

Particulate radiocesium concentration in paddy fields was studied for its parameterization and temporal changes over an extensive area covering various deposition levels of radiocesium after the FDNPP accident. The particulate radiocesium concentration in the paddy field correlated with the deposition amounts, indicating that the entrainment coefficient, defined as the ratio of concentration and deposition amounts, is useful for estimating the particulate radiocesium concentration in a paddy field. Variability of the entrainment coefficient was reduced by correcting the particle size dependency of particulate radiocesium concentration. The entrainment coefficient decreased with time according to a double exponential function. The decrease rate constant of the entrainment coefficient was higher than those of other land uses, thus demonstrating a rapid decrease in the particulate radiocesium concentration in the tested paddy field.