Land use types control solid wash-off rate and entrainment coefficient of Fukushima-derived Cs, and their time dependence

Wakiyama, Yoshifumi*; Onda, Yuichi*; Yoshimura, Kazuya  ; Igarashi, Yasunori*; Kato, Hiroaki*

This study provides the results of observations of plot-scale Cs wash-off from various land uses (two uncultivated farmlands, two cultivated farmlands, three grasslands and one forest) from 2011 to 2014. Annual Cs wash-off rate ranged from 0.0026 to 7.5% per year, and more vegetation cover resulted in lower sediment discharge. Cs concentration observed in uncultivated farmland plot decreased with time and the rate was lower than those of riverine, suggesting that contributions of Cs from the upslope area may be insignificant to that in riverine. A negative relationship between Cs concentration normalized by initial deposition amount and sediment concentration in runoff water was found. Cultivation appeared to cause enhanced soil erosion and resulted in constant relatively low Cs concentration. A contribution of coarse organic matter to Cs wash-off was suggested in the forest, which had relatively high Cs concentration and low sediment discharge.