[en] Radiocaesium wash-off associated with soil erosion in different land use was monitored using USLE plots in Kawamata, Fukushima Prefecture, Japan after the Fukushima Dai-ichi Nuclear Power Plant accident. Parameters and factors relating to soil erosion and "1"3"7Cs concentration in the eroded soil were evaluated based on the field monitoring and presented. The erosion of fine soil, which is defined as the fraction of soil overflowed along with discharged water from a sediment-trap tank, constituted a large proportion of the discharged radiocaesium. This indicated that the quantitative monitoring of fine soil erosion is greatly important for the accurate evaluation of radiocaesium wash-off. An exponential relationship was found between vegetation cover and the amount of eroded soil. Moreover, the radiocaesium concentrations in the discharged soil were greatly affected by the land use. These results indicate that radiocaesium wash-off related to vegetation cover and land use is crucially important in modelling radiocaesium migration. - Highlights: • Fine soil erosion showed large impact on radiocaesium wash-off. • Exponential relationship was found between vegetation cover and eroded soil. • Radiocaesium concentration in the discharged soil was depending on land use

[en] Forests in Fukushima and neighboring prefectures accumulated atmospheric fallout of radioactive materials after the Fukushima Daiichi Nuclear Power Plant accident. We investigated the initial behavior of ¹³⁷Cs deposited in coniferous forest plantations. Furthermore, we conducted in-situ measurements of radioactivity in coniferous and broadleaf forest canopies. The results of this study demonstrated that more than 60% of the Fukushima reactor accident–derived radiocesium remained in coniferous forest canopies 5 months after initial deposition. Furthermore, in-situ measurements of radiocesium indicated that the radiocesium absorbed in forest canopies has been moving downward through the canopy to the forest floor. (author)

No abstract available

[en] The sampling method of soil contaminated with radioactive materials by the Fukushima power plant accident was established and mentioned here. (M.H.)

[en] The Fukushima Dai-ichi Nuclear Power Plant Accident released large quantities of radionuclides into the atmosphere, with subsequent fallout onto wide area of land surface in Fukushima and its neighboring prefectures. Because approximately 70% of the radiocaesium deposited on land was in forest areas, an analysis of the spatial distribution and transfer of radiocaesium in forested landscapes is necessary to diagnose both the environmental impacts of the accident and the environmental recovery from radioactive contamination. This article summarizes research findings from an investigation into radiocaesium dynamics in terrestrial environments in and around Fukushima prefecture, and gives prospects in future prediction of impacts and recovery. (author)

[en] Highlights: • Ambient dose rate in Fukushima forests was repeatedly measured. • Ambient dose rates in mixed broad-leaved and deciduous forests were higher than evergreen conifers. • Ambient dose rate in evergreen conifer decreased slower than mixed broad-leaved and deciduous broad-leaved forests for the period of 2011–2014. • Decline of dose in evergreen conifer during the period of 2011–2014 was slower than that induced solely by physical decay of radiocesium. • Decline of dose in mixed broad-leaved and deciduous broad-leaved forest was 10–20% faster than the physical decay of radiocesium. - Abstract: Approximately 70% of the total land area affected by the fallout from the Fukushima accident is forested, and therefore monitoring of the ambient dose rate in forest environments is essential to ensure that the population and natural habitats of these areas are protected from radiological hazards. However, there are little available data on the ambient dose rate for forest environments. This study investigated temporal changes in the ambient dose rate in different forest environments of Fukushima Prefecture. We conducted repeated measurements of the ambient dose rate in 2014 and 2016 at the same measurement points as those used by the Ministry of Agriculture, Fishery and Forestry of Japan (MAFF) in 2011. The measurements revealed that the decreasing trend in the ambient dose rate varied among the different forest types and time periods. The ambient dose rate in EGC decreased slower than that induced by the physical decay of radiocesium for the period of 2011–2014. However, such slow declining trend of ambient dose rate was likely followed by quick reduction during the following years (2014–2016 and 2011–2016). On the other hand, in MBL and DBF forests, the ambient dose rate decreased 10–20% faster than that induced solely by physical decay of radiocesium for the observation period 2011–2016.

[en] Radionuclides released to the atmosphere can be deposited onto catchments and water bodies. After the FDNPP accident, subsequent redistribution of radionuclides, mostly radiocaesium, occurred via (i) water run-off in streams and rivers (commonly termed washoff) and (ii) erosion of material from catchments, into water bodies. These processes can affect the extent to which radiocaesium is transferred into edible aquatic organisms from water and aquatic food. After the FDNPP accident, the combination of high rainfall and intensive agricultural land-use contributed to a highly dynamic transfer of radiocaesium from catchments to rivers, lakes and irrigation ponds in Fukushima Prefecture and other neighbouring Prefectures. Various factors affecting the transfer of radiocaesium from catchments to rivers and from freshwater to aquatic organisms are discussed below.

[en] The spatial and vertical distributions of ¹³⁷Cs in surface soils were surveyed and analyzed then correlated with the contents of organic carbon in the hinoki (Chamaecyparis obtusa Sieb. et Zucc.) plantation forest and secondary forest dominated by red pine (Pinus densiflora Sieb. et Zucc.) in Japan. The spatial variation of ¹³⁷Cs activity was observed in the surface soil around the red pine. The average activity of 16 samples around the tree is 42.4 Bq/kg and the standard deviation is 25.9 Bq/kg. This finding indicates the importance in the selection of a sampling site and the number of samples from the surface soils especially around a tree. For the vertical distribution of ¹³⁷Cs activity, it was found that the concentration in the surface soil is highest, 149 Bq/kg in the hinoki stand and 101 Bq/kg in the red pine stand, and decreases with depth. The relationship between ¹³⁷Cs activity and carbon content in the forest soil was investigated in two undisturbed forest stands. The relations were more precisely expressed using an exponential equation than by a linear equation. From the same forest, similar regression equations were obtained. This indicates that the distribution of ¹³⁷Cs could be characterized by the organic carbon content in an undisturbed forest. It is also suggested that the coefficient values in the regression equation help to define the movement of ¹³⁷Cs accompanying the decomposition of organic matter

No abstract available

[en] Vertical profiles of radiocesium in lake sediments were investigated several times in Japanese 5 lakes within 4 years after the Fukushima nuclear accident. Changes in profiles of ¹³⁷Cs activity were commonly detected, such as a decrease in surface sediments and an increase in deeper sediments. ¹³⁷Cs peaks could be found in Lakes Akagi-onuma and Onogawa, but a shape of profile was nearly flat in the top 0 - 18 cm depth in Lakes Kasumigaura and Kitaura in 2014. A comparison with the mass sedimentation rate previously reported indicated that a disturbance of lake sediments (bioturbation and/or physical diffusion) affected the flat profiles observed in Lakes Kasumigaura. ¹³⁷Cs inventories in 5 lakes were 1 - 6 times higher than ¹³⁷Cs deposition on ground surface by the airborne monitoring. The inventory / deposition ratio was related to watershed area / lake area ratio, suggesting that the loads from watershed through inflowing rivers. We hope those observation data to be helpful for modelling radiocesium dynamics in Japanese lakes. (author)