Vertical distribution of radiocesium in coniferous forest soil after the Fukushima nuclear power plant accident

This study deals with the description of the vertical distribution of radiocaesium (Cs-137 and Cs-134) in a representative coniferous forest soil, investigated 10 months after the Fukushima radioactive fallout. During soil sampling, the forest floor components (understory plants, litter (Ol-) and fermented layers (Of)) were collected and treated separately. The results indicate that radiocesium is concentrated in the forest floor, and high radiocesium transfer factor observed in the undergrowth plants (3.3). This made the forest floor an active exchanging interphase for radiocesium. The raw organic layer (Ol + Of) holds 52% (5.3 kBq m(-2)) of the Fukushima-derived and 25% (0.7 kBq m(-2)) of the pre-Fukushima Cs-137 at the time of the soil sampling. Including the pre-Fukushima Cs-137, 99% of the total soil inventory was in the upper 10 cm, in which the organic matter (OM) content was greater than 10%, suggesting the subsequent distribution most likely depends on the OM turnover. However, the small fraction of the Fukushima-derived Cs-137 at a depth of 16 cm is most likely due to the infiltration of radiocesium-circumscribed rainwater during the fallout before that selective adsorption prevails and reduces the migration of soluble Cs-137. The values of the depth distribution parameters revealed that the distribution of the Fukushima-derived Cs-137 was somewhat rapid. (C) 2014 Elsevier Ltd. All rights reserved.