Organizers: Masamichi Takahashi (Forestry and Forest Products Research Institute, Japan), Frédéric Coppin (Institut de Radioprotection et de Sûreté Nucléaire, France) & George Shaw (Nottingham University, UK)
Modelling of radionuclide transfer and ambient dose rates in the Fukushima forest ecosystem: a preliminary study.
Gonze, M., Calmon, P., Mourlon, C., Hurtevent, P., Coppin, F., Simon-Cornu, M., Debayle, C., Gurriaran, R. (Institut de Radioprotection et de Sûreté Nucléaire, France; marc-andre.gonze@irsn.fr; philippe.calmon@irsn.fr; christophe.mourlon@irsn.fr;
pierre.hurtevent@irsn.fr; frederic.coppin@irsn.fr; marie.simon-cornu@irsn.fr; christophe.debayle@irsn.fr; rodolfo.gurriaran@
irsn.fr), Thiry, Y. (National Agency for Radioactive Waste Management (Andra), France; yves.thiry@andra.fr), Yuichi, O.
(University of Tsukuba, Japan; onda@geoenv.tsukuba.ac.jp).
The Fukushima nuclear accident in northeastern Japan led to high atmospheric depositions of volatile fi ssion products, such as cesium, iodine, and tellurium isotopes. The radioactive concentrations and ambient radiation levels are particularly high in forest ecosystems, due to the effi cient interception of airborne radionuclides by forest canopies. In the next decades, the contamination is likely to be dominated by cesium-137, given its long physical half-life (i.e., 30 years) and its long-term recycling between the abiotic/biotic forest compartments. Accordingly, the long-term management of contaminated forest areas is of great environmen-tal, economic, and social concerns for Japanese authorities. In 2013, French and Japanese researchers launched an integrated environmental project which aimed to better understand and predict the fate and transport of gamma-emitting radionuclides in the forested Fukushima landscape. A special emphasis was put on the long-term processes controlling the cesium-137 cycle within forest ecosystems, and the possible exportation to freshwaters through watershed run-off. The project combines fi eld measure-ments, from meter to regional scales, in addition to mechanistic modelling of long-term cesium dynamics and ambient dose rates.
The overall objectives, modelling approaches, and preliminary results will be presented.
Distribution and migration of radiocesium in the forest ecosystem after the Fukushima Daiichi Nuclear Power Plant accident. Kaneko, S., Akama, A., Ikeda, S., Miura, S., Kiyono, Y., Tanaka, H., Kajimoto, T., Saito, S., Tonosaki, M., Kuroda, K., Takano, T., Takahashi, M. (Forestry and Forest Products Research Institute, Japan; kanekos@ffpri.affrc.go.jp;
akama@ffpri.affrc.go.jp; ikedas@ffpri.affrc.go.jp; miura@ffpri.affrc.go.jp; kiono@ffpri.affrc.go.jp; hirop@ffpri.affrc.go.jp;
tkaji@ffpri.affrc.go.jp; stetsu@ffpri.affrc.go.jp; tonosaki@ffpri.affrc.go.jp; kurodak@ffpri.affrc.go.jp; ttakano@ffpri.affrc.go.jp;
masamiti@ffpri.affrc.go.jp).
Forests have been widely contaminated by radiocesium due to the accident at the Fukushima Daiichi Nuclear Power Plant in eastern Japan. To recognize the distribution and behavior of radiocesium in forest ecosystems, we established fi ve plots in three areas with different contamination levels (134Cs+137Cs: 10–30, 100–300, and 1 000–3 000 kBq/m2) in Fukushima prefecture. In summer 2011, radiocesium was distributed at levels of 25–45, 30–43, and 19–28% for tree, litter layer, and surface soil (0–5 cm depth), respectively, for Japanese cedar (Cryptomeria japonica) forests, while for Japanese red pine (Pinus densifl ora) and deciduous hardwood forests, radiocesium was distributed at levels of 18–19, 47–50, and 22–26% for tree, litter layer, and surface soil (0–5 cm depth), respectively. Changes in distribution from 2011 to 2012 involved a decline in radiocesium in the tree and litter layer, while radiocesium in surface soil increased in every forest type. Consequently, more than half the radiocesium was distributed in surface soil at a depth of 0–5 cm in summer 2012. These results suggested that radiocesium was highly captured by the canopy of Japanese cedar forests due to the high leaf biomass, while radiocesium migrated rapidly from the tree canopy and litter layer to the surface soil in 2 years due to washout, litter fall, and decomposition of organic matter.
Managing the irradiated forest of the Chernobyl Exclusion Zone for nature conservation, fi re protection, and biomass fuel production. Oliver, C. (Yale University, USA; chad.oliver@yale.edu), Zibtsev, S. (National University of Life and Environmental Sciences of Ukraine, Ukraine; sergiy.zibtsev@nauu.kiev.ua), LaRoche, D. (United Nations Environmental Programme, USA;
dal1727@gaw.com), Goldammer, J. (University of Freiburg, Germany; johann.goldammer@fi re.uni-freiburg.de).
The 260 000 ha of irradiated landscape designated as the Chernobyl Exclusion Zone (CEZ) will remain a health threat even after Confi nement II of the failed reactor is completed in 2015. Most of the CEZ contains pine forests on sandy soils that are in imminent danger of burning, creating further problems downwind for crops and inhalation. There are confl icting and controversial future visions for the CEZ. At one extreme is a proposal for intensive harvesting and use of the timber for bioenergy and at the other extreme, a vision of a biodiversity reserve with no management. A balanced approach is being developed by the Global Environmental Facility of the United Nations Environmental Programme using a triad approach. It proposes to combine reserve areas, areas of active management for fi re reduction and habitat restoration, and other areas where biomass fuel can be grown intensively and used to produce energy in a safe manner. The approach is expected to accomplish the combined goals of irradiated fi re risk reduction, biodiversity protection, carbon sequestration in the forest and, through the use of wood energy, commodity production to pay for the proactive management.
Biogeochemical cycling of radiocaesium in contaminated forest area: an overview. Thiry, Y. (National Agency for Radioactive Waste Management (Andra), France; yves.thiry@andra.fr).
Following atmospheric deposition of radiocaesium from the Chernobyl and Fukushima plume, a primary source of forest tree contamination was direct dry or wet interception of aerosol-derived radiocaesium by the canopy, followed by translocation from foliar surfaces to structural components of the tree. Further changes in tree and soil contamination after the initial fallout were due to two main processes. The fi rst was a dominant self-decontamination process of the tree canopy, affected by throughfall and litterfall. This process was rapidly followed by root uptake which continued over time. The long-term radiocaesium cycling in a forest ecosystem is, however, far from a simple formula between soil and tree. Our study aimed to document different forest
peculiarities and infl uential processes by addressing a series of scientifi c questions. How signifi cant is the capacity of a forest to recycle radiocaesium? Why is the initial interception of radiocaesium by forest canopy so important? What is the role of forest soil horizons as a sink or source of radiocaesium? What are the natural processes and associated fl uxes which control the radiocaesium biological cycling? These different aspects will be illustrated with data gained through complementary fi eld studies (Chernobyl remote zone, Fukushima area, Red Forest) or experimental approaches.
Inside contamination of Japanese cedar tree by radiocesium from the Fukushima Nuclear Power Plant accident. Yoshida, H. (Tokyo Metropolitan University, Japan; yoshida-hirohisa@tmu.ac.jp), Ogawa, H. (Fukushima Forestry Research Center, Japan;
ogawa_hideki_01@pref.fukushima.jp), Hirano, Y., Igei, S., Yokota, K. (Tokyo Metropolitan University, Japan; hirano-yurika@ed.
tmu.ac.jp; igei-shigemitsu@ed.tmu.ac.jp; kahori-yokota@ed.tmu.ac.jp), Murakami, K., Kumata, A (Fukushima Forestry Research Center, Japan; murakami_kaori_02@pref.fukushima.jp; kumata_atsushi_01@pref.fukushima.lg.jp).
The objective of the study was to evaluate the transportation mechanism of radioactive cesium in the ecosystem at Yamakiya, Kawamata, Fukushima prefecture, from 2011 to 2013. The estimated initial radiocesium deposition was 1 568 000 Bq/m2 (134Cs + 137Cs) in the study area. The sample species from the bark to the pith was obtained by increment borers (12 mm diameter) from the living tree and the sample was cut every 1–2 cm. The concentration of radiocesium in samples under dry states were evaluated by Ge conductor-ray spectrometer SEG-EMS (Seiko EG&G Co. Ltd.). The contamination of the inside of the cedar tree was 100 times lower than that of the bark, and was dependent on the direction and height in 2011. The fi rst stage of inside contamination of the cedar tree was caused by the foliar and bark absorptions. The level of radiocesium in the inner tree was highest in heartwood and phloem in cedar. The radiocesium concentration in heartwood was related to height; however, concentration in the phloem and sapwood was only slightly related to height. In 2012 and 2013, the concentration profi le in the horizontal direction of sapwood was similar; however, concentration in heartwood was homogeneous.
Posters
Radiocesium contamination in Satoyama forests in Kashiwa city, a suburb of the Tokyo metropolitan area. Fukuda, K., Kutsuna, N., Terada, T., Mansournia, M. (University of Tokyo, Japan; fukuda@k.u-tokyo.ac.jp; kutsuna@k.u-tokyo.ac.jp;
terada@nenv.k.u-tokyo.ac.jp; mrmansournia@yahoo.com), Uddin, M. (Government of Bangladesh, Bangladesh; nz_post@yahoo.
com), Jimbo, K., Shibuya, S., Fujieda, J., Yamamoto, H., Yokohari, M (University of Tokyo, Japan; jimbo@nenv.k.u-tokyo.ac.jp;
sshibuya@nenv.k.u-tokyo.ac.jp; juri09a@nenv.k.u-tokyo.ac.jp; yama@k.u-tokyo.ac.jp; myoko@k.u-tokyo.ac.jp).
Radioactive cesium contamination caused by the Fukushima nuclear disaster was investigated in forest patches in Kashiwa city, Chiba prefecture, a suburb of the Tokyo metropolitan area. The forest patches we studied were former Satoyama woodland, which was historically maintained to provide fi rewood and other organic materials. Restoration of Satoyama can enhance its ecological functions, but radiocesium contamination is a barrier. Air dose rate at 1 m above ground in summer to winter of 2011 was 0.3–0.4 µSv/h, both inside and outside the forest patches. The radiocesium concentration was highest in old leaves of conifers and the outer bark of both conifers and deciduous broadleaves and least in wood tissues; however, radiocesium concentration in some part of the stem wood was above the limit for fi rewood (40 Bq/kg). Deposition of radiocesium on the aboveground parts of forests was estimated as 5.7 kBq/m2 in a mixed forest of hinoki and deciduous broadleaves and 3.7 kBq/m2 in a deciduous oak forest. The total amount of radiocesium above- and belowground was estimated as 60–90 kBq/m2, which was much higher than the estimation by government through aircraft measurements.
Transportation of radiocesium from forest to agricultural fi elds. Hirano, Y., Yokota, K. (Tokyo Metropolitan University, Japan;
hirano-yurika@ed.tmu.ac.jp; kahori-yokota@ed.tmu.ac.jp), Ogawa, H., Kumata, A. (Fukushima Forestry Research Center, Japan;
ogawa_hideki_01@pref.fukushima.jp; kumata_atsushi_01@pref.fukushima.lg.jp), Yoshida, H. (Tokyo Metropolitan University, Japan; yoshida-hirohisa@tmu.ac.jp).
The objective of this study was to evaluate the transportation of radioactive cesium from forest to paddy fi elds in the ecosystems at Ogami, Kawamata, Fukushima prefecture, where mushroom cultivation was carried out. The dispersion of radiocesium in the forest (24 ha) and the paddy fi eld close to the forest (40 ha) was evaluated. The forest area consisted of two ridges and one ravine with two irrigation ponds. Comparing the depth profi le of radiocesium concentration on the ridges and the ravine revealed that the transportation of radiocesium from the ridge to the ravine was mainly caused by the transportation of fallen leaves. The depth profi le of radiocesium concentration in the ravine, the irrigation ponds, and the paddy fi elds indicated that radiocesium existed in the litter layer of post-fallout expanded leaves; water-soluble radiocesium was scarcely observed in the soil and the litter in 2013. The decontamination trial of bark from Quercus serrate for mushroom cultivation was also reported.
Seasonal change of radiocesium in different age needles and male fl owers of Japanese cedar (Cryptomeria japonica) in Fukushima. Kanasashi, T., Takenaka, C. (Nagoya University, Japan; kanasashi.tsutomu@g.nagoya-u.jp;
chisato@agr.nagoya-u.ac.jp).
Decontamination of radioactive substances from forests is required to recover forestry and to promote residents coming back home to eastern Fukushima. Cryptomeria japonica is an evergreen needle-leaved tree and one of the main plantation species distributed widely in the Fukushima region. The needles grow every year from the top of the previous year’s needles and the male fl owers develop at the top parts of current growth needles. To elucidate accumulation and transportation of radiocesium in trees, we studied the seasonal change of 137Cs in needles of different ages and the male fl owers at four sites in middle and north-eastern Fukushima, beginning in 2011. Radiocesium was detected by gamma ray spectrometry using a high purity germanium radiation detector. The specifi c radioactivity of 137Cs in each part has been obtained from September 2011 and the total activity in each part from December 2012. Because 137Cs was detected in the needles and male fl owers grown after the Fukushima accident, radiocesium was transported from the older needles. Needles grown before the accident showed higher specifi c radioactivity and total activity through all seasons, suggesting that the effects of the direct deposited radiocesium and its absorption had continued.
Radiocesium inventory of forested land in Japan just before the Fukushima Daiichi Nuclear Power Plant accident.
Miura, S., Shichi, K., Ito, E., Kaneko, S. (Forestry and Forest Products Research Institute, Japan; miura@ffpri.affrc.go.jp;
shichi@ffpri.affrc.go.jp; iter@affrc.go.jp; kanekos@affrc.go.jp).
Fallout from nuclear weapon tests in the atmosphere in the 1950s and 1960s dispersed 137Cs across the globe and deposited it on soils. Because 137Cs was deposited at the soil surface, it has been used as a tracer for soil erosion studies. Cesium deposited onto forested land in Japan was expected to be redistributed because of steep mountainous landforms and frequent heavy rains. We examined concentrations and amounts of 137Cs in surface soils (0–5, 5–15, and 15–30 cm in depth) all over Japan just before the accident at the Fukushima Daiichi Nuclear Power Plant. Concentrations of 137Cs in surface soils ranged from below detection limit to >200 Bq/kg and fi t a gamma distribution. Cesium concentrations in the upper soil layers were higher than those in lower layers. Amounts of 137Cs retained on forested slopes varied widely; concentrations were lower in cultivated soils. We analyzed the effects of site and environmental factors on physical movement of contaminated surface soils. This information will be valuable in predicting the long-term dynamics of 137Cs derived from the Fukushima radioactive accident.
Predominant factors in the depth profi le in forest soil of radiocaesium, released by the Fukushima Daiichi Nuclear Power Plant accident. Niizato, T., Abe, H., Watanabe, T., Ishii, Y., Sasaki, Y. (Japan Atomic Energy Agency, Japan; niizato.tadafumi@
jaea.go.jp; abe.hironobu@jaea.go.jp; watanabe.takayoshi@jaea.go.jp; ishii.yasuo@jaea.go.jp; sasaki.yoshito@jaea.go.jp).
This paper discusses the predominant factors in the depth profi les of radiocaesium, released by the Fukushima Daiichi Nuclear Power Plant Accident, in forest soil under the evergreen coniferous and broadleaved deciduous forests of the valley-head of mountain area of Fukushima, northeast Japan. The samples were obtained from ridge, slope, and bottomland in the forest by drilling with a soil sampler and scraping with a scraper plate to a depth of about 40 and 20 cm, respectively. The investigation of soil horizons, a tree census, and a topographical survey were also carried out to characterize the study area. The results show that the concentration profi le of radiocaesium in the uppermost soil horizon was related to the distribution of depositional and erosional area in the forest; that is, the concentration profi le tended to be higher in the depositional area than in the erosional area. Additionally, the decrease in concentration rate from the ground surface to the depth was related to the soil composition, such as organic, clay minerals, and clastics of parent rock. Therefore, not only soil type but also geomorphological aspects should be taken into consideration in the elucidation of the dynamics of radiocaesium in the mountain forests of Fukushima.
Acquisition of radioactive cesium in the stems of trees in Japan. Takano, T., Fujiwara, T., Kuroda, K., Abe, H., Youki, S., Akira, K., Yoshitaka, K., Sugiyama, M., Zhang, C., Tonosaki, M. (Forestry and Forest Products Research Institute, Japan;
ttakano@ffpri.affrc.go.jp; fujiwara@ffpri.affrc.go.jp; kurodak@affrc.go.jp; abeq@affrc.go.jp; youki@ffpri.affrc.go.jp; akagawa@
ffpri.affrc.go.jp; kubojima@ffpri.affrc.go.jp; sugicchi@ffpri.affrc.go.jp; chunhua@ffpri.affrc.go.jp; tonosaki@ffpri.affrc.go.jp).
The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 caused radionuclide contamination of the surrounding forest. To determine the degree of stem contamination with radioactive cesium, samples of Cryptomeria japonica, Chamaecyparis obtusa, Pinus densifl ora and Quercus serrata were collected in Fukushima Prefecture from August to November of 2011 and August to September of 2012, respectively. Concentration of radioactive cesium of the bark in 2012 was 60 to 40% of that found in 2011 in all species. This reduction may be due to rainfall and the bark peeling due to the growth of trees. In terms of radioac-tivity of the wood, no clear differences emerged between the 2011 and 2012 samples. However, while sapwood radioacradioac-tivity declined, that of heartwood increased, which led to a more uniform concentration of radioactive cesium in wood. In other species, radioactivity was higher in sapwood. These results of radioactivity in wood suggest the radial migration of radioactive cesium toward heartwood in C. japonica.
Transport of cesium in Japanese bamboo: perspective on decontamination of radiocaesium from bamboo forests. Takenaka, C., Sugiura, Y., Umemura, M., Kanasashi, T. (Nagoya University, Japan; chisato@agr.nagoya-u.ac.jp; sugiura.yuki@b.mbox.
nagoya-u.ac.jp; i040013b@yahoo.co.jp; kogunkandori@yahoo.co.jp).
Bamboo forests, important to people as areas supporting various livelihoods like bamboo shoots, were also contaminated with radiocaesium (137Cs) derived from the serious accident of Fukushima Daiichi Nuclear Power Plant in 2011. The decontamination of 137Cs from bamboo forests is an essential task, but is considered diffi cult because of the existence of a large amount of rhizomes. To propose an effective decontamination procedure for 137Cs, we aimed to clarify the absorption and transport mecha-nisms of cesium in bamboo. Bamboo samples, such as stem, branch, leaves, and rhizomes, were collected from three moso bamboo (Phyllostachys pubescens) forests in Fukushima prefecture. The target bamboos were selected to include stems grown both before and after the accident. Also, we used bamboo samples collected in Aichi prefecture in order to compare the dynamics of stable cesium (133Cs) together with the other elements. We found that the same level of 137Cs was observed in the leaves of stems grown before and after the accident. This result indicated that the uptake ability of old and young bamboo might be similar.
In addition, we discuss the difference of cesium transport to the apex of the shoot and the rhizome.
Impact of forest vegetation on long term recycling of radionuclides at polluted sites. Thiry, Y. (National Agency for Radioactive Waste Management (Andra), France; yves.thiry@andra.fr).
Forest ecosystems are usually long lived and over time accumulate large amounts of biomass. Forest area can thus act as a biospheric sink for numerous pollutants (atmospheric or underground). In addition, many spoils or contaminated industrial soils are afforested for a return to a better ecologically functional system. The stabilization role of forests has been illustrated from different environmental studies. Still, a remobilization of contaminants is likely in case of vegetation-site-climate equilibrium disruption. The long-term impact of perennial vegetation on pollutant biogeochemistry is usually hardly considered in standard risk assessments. In particular, the role of biota in partitioning processes needs further attention for a complete long-term assessment of the contamination dynamics. This contribution aims at deciphering the infl uence of forest biological cycling in the redistribution of different radioactive contaminants with emphasis on the processes involved. At least four study cases will be envisaged: 1) a vast pine forest highly contaminated with radiocaesium originating from the Chernobyl atmospheric fallout; 2) a