Vasyl Yoschenko

Morphological defects in native Japanese fir trees around the Fukushima Daiichi Nuclear Power Plant.

After the accident at the Fukushima Daiichi Nuclear Power Plant (F1NPP) in March 2011, much attention has been paid to the biological consequences of the released radionuclides into the surrounding area. We investigated the morphological changes in Japanese fir, a Japanese endemic native conifer, at locations near the F1NPP. Japanese fir populations near the F1NPP showed a significantly increased number of morphological defects, involving deletions of leader shoots of the main axis, compared to a control population far from the F1NPP. The frequency of the defects corresponded to the radioactive contamination levels of the observation sites. A significant increase in deletions of the leader shoots became apparent in those that elongated after the spring of 2012, a year after the accident. These results suggest possibility that the contamination by radionuclides contributed to the morphological defects in Japanese fir trees in the area near the F1NPP.

Radiocesium distribution and fluxes in the typical Cryptomeria japonica forest at the late stage after the accident at Fukushima Dai-Ichi Nuclear Power Plant.

The Fukushima-derived radiocesium distribution in the typical Japanese cedar (Cryptomeria japonica D. Don) forest ecosystem was determined. In four years after the Fukushima accident, about 74% of the total radiocesium inventory was localized in soil, 20% was in the litter, and only 6% was associated with the aboveground biomass. Most of the radiocesium that was initially intercepted by the tree canopies has been already transported to the ground surface. The importance of the processes for removal of radiocesium from the tree canopies decreased in the order litterfallxa0>xa0throughfallxa0>>xa0stemflow. Within the tree compartments, the largest radiocesium activity fraction, about 46%, was observed in old foliage, which indicates that the process of removal of the initial deposit from the tree crowns has not yet completed. The aggregate soil-to-wood transfer factor was 1.1⋅10-3xa0m2xa0kg-1xa0d.w., which is close to the geometric means of transfer factors recommended by IAEA for other coniferous tree species. Further studies in Fukushima forest are necessary to assess the variation of this parameter under various soil-landscape conditions. Presence of the residues of the initial deposits does not allow to obtain the accurate values of the annual radiocesium fluxes in the ecosystem. Based on the conservative assumptions, the ranges of the fluxes were estimated. Analysis of the flux structures shows that up to percents of the total radiocesium activity in the ecosystem may be involved into biogenic cycling.

Vertical distribution of radiocesium in soils of the area affected by the Fukushima Dai-ichi nuclear power plant accident

Presented are results of the study of radiocesium vertical distribution in the soils of the irrigation pond catchments in the near field 0.25 to 8 km from the Fukushima Dai-ichi NPP, on sections of the Niida River floodplain, and in a forest ecosystem typical of the territory contaminated after the accident. It is shown that the vertical migration of radiocesium in undisturbed forest and grassland soils in the zone affected by the Fukushima accident is faster than it was in the soils of the 30-km zone of the Chernobyl NPP for a similar time interval after the accident. The effective dispersion coefficients in the Fukushima soils are several times higher than those for the Chernobyl soils. This may be associated with higher annual precipitation (by about 2.5 times) in Fukushima as compared to the Chernobyl zone. In the forest soils the radiocesium dispersion is faster as compared to grassland soils, both in the Fukushima and Chernobyl zones. The study and analysis of the vertical distribution of the Fukushima origin radiocesium in the Niida gawa floodplain soils has made it possible to identify areas of contaminated sediment accumulation on the floodplain. The average accumulation rate for sediments at the study locations on the Niida gawa floodplain varied from 0.3 to 3.3 cm/year. Taking into account the sediments accumulation leading to an increase in the radiocesium inventory in alluvial soils is key for predicting redistribution of radioactive contamination after the Fukushima accident on the river catchments, as well as for decision-making on contaminated territories remediation and clean-up. Clean-up of alluvial soils does not seem to be worthwhile because of the following accumulation of contaminated sediments originating from more contaminated areas, including the exclusion zone.

Morphological abnormalities in Japanese red pine (Pinus densiflora) at the territories contaminated as a result of the accident at Fukushima Dai-Ichi Nuclear Power Plant

Our research, carried out in 2014-2016xa0at eight sites in the radioactive contaminated territories of Fukushima Prefecture, showed that the young trees of Japanese red pine (Pinus densiflora) are sensitive to radiation. Irradiation induced cancellation of the apical dominance in this species. The effect is similar to that observed in young trees of Scots pine growing in the Chernobyl zone. At the same time, we did not observed any morphological abnormalities in mature trees of Japanese red pine. The probability of cancelling the apical dominance in Japanese red pine increased to 0.11 and 0.14 in the two less irradiated populations, and to 0.5 and 0.9xa0at sites were the absorbed dose rates were approximately 14 and 25xa0μGyxa0h-1, respectively. Most of the observed abnormalities appeared in the second whorl after the beginning of exposure. No new abnormalities were observed in the fifth whorl. This temporal pattern is similar to those reported for Scots pine in Chernobyl and for Japanese fir in Fukushima. Additional detailed studies are necessary for interpretation of the observed temporal pattern and, in general, for explanation of the mechanism of formation of the morphological abnormalities.

Natural attenuation of Fukushima-derived radiocesium in soils due to its vertical and lateral migration

Processes of vertical and lateral migration lead to gradual reduction in contamination of catchment soil, particularly its top layer. The reduction can be considered as natural attenuation. This, in turn, results in a gradual decrease of radiocesium activity concentrations in the surface runoff and river water, in both dissolved and particulate forms. The purpose of this research is to study the dynamics of Fukushima-derived radiocesium in undisturbed soils and floodplain deposits exposed to erosion and sedimentation during floods. Combined observations of radiocesium vertical distribution in soil and sediment deposition on artificial lawn-grass mats on the Niida River floodplain allowed us to estimate both annual mean sediment accumulation rates and maximum sedimentation rates corresponding to an extreme flood event during Tropical Storm Etau, 6-11 September 2015. Dose rates were reduced considerably for floodplain sections with high sedimentation because the top soil layer with high radionuclide contamination was eroded and/or buried under cleaner fresh sediments produced mostly due to bank erosion and sediments movements. Rate constants of natural attenuation on the sites of the Takase River and floodplain of Niida River was found to be in range 0.2-0.4 year-1. For the site in the lower reach of the Niida River, collimated shield dose readings from soil surfaces slightly increased during the period of observation from February to July 2016. Generally, due to more precipitation, steeper slopes, higher temperatures and increased biological activities in soils, self-purification of radioactive contamination in Fukushima associated with vertical and lateral radionuclide migration is faster than in Chernobyl. In many cases, monitored natural attenuation along with appropriate restrictions seems to be optimal option for water remediation in Fukushima contaminated areas.

Radioactive contaminated forests in Fukushima and Chernobyl

ABSTRACT This paper compares the scale and consequences of radioactive contamination of forest ecosystems following the Chernobyl and Fukushima accidents. The Chernobyl deposition in the zone closest to the reactor site (the “near zone”) presently consists of 137Cs, 90Sr and isotopes of transuranium elements, while the only long-lived radionuclide in the Fukushima release was 137Cs. Radiocesium deposition levels in the near zones of the two accidents are similar. We compare the effects of radiation on forest ecosystems and forestry following the two accidents. Acute radiation after the Chernobyl accident caused death of Scots pine (Pinus sylvestris L.) forests close to the power plant and created zones of sublethal and moderate damage at greater distances. Acute radiation dose rates were much lower after the Fukushima accident, and lethal damage to forest species was not reported. Under chronic radiation conditions, the same morphological abnormalities (cancelling of apical dominance) occurred in young populations of Scots pine in the Chernobyl zone and Japanese red pine (Pinus densiflora Siebold & Zucc.) and Japanese fir (Abies firma Siebold & Zucc.) in the Fukushima zone. During the early stages after both accidents, a general trend of gradual decrease of radionuclide inventories in aboveground forest biomass occurred due to leaching with precipitations and removal with litterfall. In Chernobyl forests under certain conditions, this was followed by a period of increase of radionuclide inventories in the biomass due to root uptake. The radiocesium root uptake parameters for a wide variety of forest species, types, and soil conditions must be determined for prognosis of further redistribution in Fukushima forests.

Assessment of radiological efficiency of countermeasures on peat-bog soils of Ukrainian Polissya

In the field conditions, the long-term (2013-2015) small-plots experiment was carried out for evaluation of radiological efficiency of application of ameliorants as the countermeasures for reduction of the 137Cs uptake to herbage at the Peat-boggy (Histosols) soils of Ukrainian Polissya. At the late stage after the Chernobyl accident, the average radiological efficiencies of application of sand (175-200xa0tonxa0ha-1) and ferrocyn (0.2 tonxa0ha-1) as the ameliorants were rather low ranging from 0.8 to 1.6. Application of 4 ton ha-1 of chalk and 5 ton ha-1 of peat ash decreased 1.7-1.9 times the 137Cs activity concentrations in plans. The highest radiological efficiencies, 4.4xa0±xa02.0 and 7xa0±xa02, were reached at applications of chalk-ferrocyn ameliorant (4xa0+xa00.2 tonxa0ha-1) and ferrocyn-bentonite absorbent HZH-90 (30 tonxa0ha-1), respectively.

Radioactive and stable cesium isotope distributions and dynamics in Japanese cedar forests

Dynamics of the Fukushima-derived radiocesium and distribution of the natural stable isotope 133Cs in Japanese cedar (Cryptomeria japonica D. Don) forest ecosystems were studied during 2014-2016. For the experimental site in Yamakiya, Fukushima Prefecture, we present the redistribution of radiocesium among ecosystem compartments during the entire observation period, while the results obtained at another two experimental site were used to demonstrate similarity of the main trends in the Japanese forest ecosystems. Our observations at the Yamakiya site revealed significant redistribution of radiocesium between the ecosystem compartments during 2014-2016. During this same period radionuclide inventories in the aboveground tree biomass were relatively stable, however, radiocesium in forest litter decreased from 20xa0±xa011% of the total deposition in 2014 to 4.6xa0±xa02.7% in 2016. Radiocesium in the soil profile accumulated in the 5-cm topsoil layers. In 2016, more than 80% of the total radionuclide deposition in the ecosystem resided in the 5-cm topsoil layer. The radiocesium distribution between the aboveground biomass compartments at Yamakiya during 2014-2016 was gradually approaching a quasi-equilibrium distribution with stable cesium. Strong correlations of radioactive and stable cesium isotope concentrations in all compartments of the ecosystem have not been reached yet. However, in some compartments the correlation is already strong. An increase of radiocesium concentrations in young foliage in 2016, compared to 2015, and an increase in 2015-2016 of the 137Cs/133Cs concentration ratio in the biomass compartments with strong correlations indicate an increase in root uptake of radiocesium from the soil profile. Mass balance of the radionuclide inventories, and accounting for radiocesium fluxes in litterfall, throughfall and stemflow, enabled a rough estimate of the annual radiocesium root uptake flux as 2xa0±xa01% of the total inventory in the ecosystem.

Radiocesium dynamics in forest ecosystems after the Fukushima Nuclear Power Plant accident: experiences during the initial five years

The accident at the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) in Japan on 11 March 2011, caused by an earthquake-induced tsunami, was classified as one of the world’s largest nuclear accidents, comparable to the accident at the Chernobyl Nuclear Power Plant (ChNPP) in Ukraine on 26 April 1986 (IAEA 2015). The FDNPP accident resulted in massive emissions of radioactive substances into the atmosphere and, subsequently, over a wide area, not only in the vicinity of the FDNPP but also across a vast area in northeast Japan. Forests are the dominant component of the terrestrial landscape in northeast Japan, and they were contaminated to varying degrees by radiocesium fallout from the accident (Hashimoto et al. 2012). During the initial stages of radiocesium contamination after the accident, forests acted as a barrier against direct radiocesium fallout in urban areas and neighborhoods, and radiocesium was subsequently retained in forest ecosystems. Extensive decontamination measures were undertaken to enable residents to return to evacuated areas after the accident. However, some severely contaminated areas were designated as “areas where returning is difficult.” In this regard, in April 2017, 6 years after the accident, evacuation orders were lifted for the areas surrounding difficult-toreturn areas, which are dominated by forests. Decontamination was mostly conducted in residential and agricultural areas and was limited in nearby forest areas, indicating that most of the forests in these zones will remain contaminated. The Ministry of Agriculture, Forestry and Fisheries formulated regulations after April 2012 for the use of forest products, setting permissible levels at 40 Bq kg in firewood, 50 Bq kg in logs for mushroom cultivation, 280 Bq kg in charcoal for cooking, and 400 Bq kg in biochar and leaf litter origin compost (MAFF 2011a, 2011b, 2012); however, no regulations were established for timber for construction use. These regulations differ from those implemented after the ChNPP accident. Although limited information was gathered during the initial period of the ChNPP accident in April 1986, many studies of radiocesium contamination and dynamics in forest ecosystems and forest products commenced soon after the FDNPP accident (e.g. Kato et al. 2012, 2017; Komatsu et al. 2016; Ogawa et al. 2016). Recently, Gonze and Calmon (2017) compiled the results of many early studies to clarify the generic trends of the radiocesium dynamics in 2011–2013. Therefore, the findings from the initial stages of the impact of the FDNPP accident on forest ecosystems are important to complete this information. The first symposium on the FDNPP and the ChNPP accidents, at the annual meeting of the Japanese Forest Society (JFS), was held at Utsunomiya University in March 2012 (Ohkubo et al. 2012). Special sessions on the issues of radioactive contamination and countermeasures in forests and forestry after the accidents were coordinated in the subsequent annual meeting of the JFS (Kaneko and Ohkubo 2013, 2014; Ohkubo and Kaneko 2016). About 40 papers, consisting of approximately 15 oral presentations and 25 posters, were presented and discussed each year over 3 years. The topics covered the distribution and dynamics of radiocesium in forests, transfer factors of radiocesium in various forest products, various types of countermeasures, influence of radiation contamination on forestry, local communities, etc. From this perspective, the Editorial Board of the Journal of Forest Research (JFR) is creating the special feature titled, “Radiocesium dynamics in forest ecosystems after the Fukushima Nuclear Power Plant accident: experiences during the initial five years.” The aim was to collect reviews and articles concerning various aspects of forest ecosystem contamination and the decontamination measures undertaken in the 5 years after the FDNPP accident. The original review and articles belonging to this special feature are included in this issue (vol. 23, issue no. 1) and subsequent issues. This special feature includes a review paper and five original articles, and covers topics such as a comparison of radioactive contamination between Fukushima and Chernobyl forests (Yoschenko et al. in this issue), forest edge effects in radioactivity-contaminated forests (Imamura et al. in this issue), the effects of inoculation with ectomycorrhizal fungi on the accumulation and distribution of radiocesium in konara oak (Quercus serrata) seedlings (Choi et al. in this issue), the mass of the organic layer in the soil affecting downward migration of radiocesium (Ito et al. in this issue), a demonstration of radiocesium absorption through bark into sapwood in Konara oak by stable cesium experiments (Wang et al. in this issue), and differences in shoot positions affecting radiocesium contamination of needles in Japanese fir (Oba et al. in this issue). Over time, radiocesium contamination levels are decreasing and the area of low contamination is expanding after natural decay and weathering of radiocesium. Long-