Search Results (3)

To analyse the ¹³⁷Cs distribution and migration under various fractions of organic matter layers, this study investigated easily recognizable, originally shaped organic L-fractions, and not easily recognizable, early fermented and fragmented organic F-fractions, of both oak (Quercus serrata) and cedar (Cryptomeria japonica) sampled from Osawa watershed sites at Nihonmatsu City, Fukushima Prefecture, Japan. The organic materials were put on top of soil columns from Field Museum (FM) Tamakyuryo in Hachioji City, Tokyo. The ¹³⁷Cs vertical distribution in forest soil profiles was analyzed using the relaxation mass depth, ho (kg m⁻²). Soil columns with both L and F- organic layer fractions of both oak and cedar, labelled as Oak-L, Oak-F, Cedar-L and Cedar-F with four replications (n = 16), were set up by the laboratory column-based method and kept under five months’ incubation period. Soil columns after incubation were sampled at depths of 0–1 cm, 1–2 cm, 2–5 cm and 5–10 cm. Results of ¹³⁷Cs inventory in the organic fractions showed that 86% (oak and cedar) of the total organic layer fractions ¹³⁷Cs inventory accumulated within the F-layer, indicating that the transformation of litter is a huge source for potentially mobile ¹³⁷Cs, especially the oak F-layer (67% ¹³⁷Cs inventory) and further continuous transfer into the forest soil mineral layers. A higher ho in L treated soils (Oak-L and Cedar-L) compared to the F treatments implied that the low ¹³⁷Cs amounts penetrated faster and deeper due to their water-soluble nature. Furthermore, Cedar-F showed a higher ho of 24.3 kg m⁻² than Oak-F of ho, 14.0 kg m⁻², and a significant positive relationship between ¹³⁷Cs retention and total carbon (TC) (p < 0.05) suggested the influence of soil organic matter on ¹³⁷Cs penetration and retention. The C/N (carbon nitrogen ratio) results revealed that organic matter fractions of high C/N including ¹³⁷Cs, as observed in Cedar-F, in which decomposition does not advance, penetrates soil depths while the organic matter fraction of low C/N, observed in Oak-F, showed that decomposition advanced to release ¹³⁷Cs which was held by adsorption unto the RIP (radiocesium interception potential) of soil surface. In addition, infiltration by water as a transportation process was suggested to largely influence the downward migration and retention of ¹³⁷Cs at lower depths of Cedar-F. Full article

After the nuclear power plant accident in Fukushima, radionuclides were deposited over a large area of local forest. However, almost nothing is known about radionuclide infiltration into trees. Here, we used poplar seedlings as a model to show that radiocesium can enter directly into leaves and bark, moving via ray cells through the symplastic pathways to the xylem and concentrating around the meristems, cork, and vascular cambium. During induced potassium incorporation and reduced seasonal growth, the radiocesium in the meristems of stems mainly passes into abscission tissues such as leaves and heartwood. There is no turnover of radiocesium after it enters the heartwood. Full article

The earthquake and tsunami on 11 March 2011 led to a meltdown followed by a hydrogen explosion at the Fukushima–Daiichi nuclear power plant in Japan, causing the dispersal of abundant radionuclides into the atmosphere and ocean. The radionuclides were deposited onto trees and local residences in aerosol or gaseous forms that were partly absorbed by rain or melting snow. Here, we show that the radionuclides attached to the surfaces of trees, in which some radiocesium was incorporated into the xylem through ray cells and through symplastic pathways. The level of incorporated radiocesium varied based on tree species and age because of the ability of radiocesium to attach to the surface of the outer bark. After four years, the radiocesium level in the forest has been decreasing as it is washed out with rainwater into the sea and as it decays over time due to its half-life, but it can also be continuously recycled through leaf tissue, litter, mulch, and soil. As a result, the level of radiocesium was relatively increased in the heartwood and roots of trees at four years after the event. In private forest fields, most trees were left as afforested trees without being used for timber, although some trees were cut down. We discuss an interdisciplinary field study on the immediate effects of high radiation levels upon afforested trees in private forest fields. Full article