Cs vertical migration in a deciduous forest soil following the Fukushima Dai-ichi Nuclear Power Plant accident

Nakanishi, Takahiro   ; Matsunaga, Takeshi; Koarashi, Jun   ; Atarashi-Andoh, Mariko  

To investigate Cs mobility deposited on the forest floor because of the Fukushima nuclear accident, we investigated the vertical migration of Cs through seepage water, using a lysimetric method. The study was conducted in a deciduous forest soil over a period spanning two months to two years after the accident. Our observations demonstrated that the major part of Cs in the litter layer moved into the mineral soil within one year after the accident. The topsoil prevented migration of Cs and the annual migration below a 10 cm depth accounted for 0.1% of the total Cs inventory. The migration of Cs by seepage water was undetectable from the vertical distribution of Cs inventory in the soil profile. In the present and immediate future, most of the Cs deposited on the forest floor will probably remain in the topsoil successively, although a small but certain amount of bioavailable Cs exists in forest surface soil.