Japanese Journal of Forest Environment

Study of radioactive contamination in forest ecosystem due to the Fukushima Daiichi accident

Shinji Kaneko, Tatsuhiro Ohkubo

Article type: Preface
2013 Volume 55 Issue 2 Pages 67-68
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_67

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Absorption properties of the Cs in the bark of Cryptomeria japonica and Quercus serrata

Kaori Iwase, Rie Tomioka, Yuuki Sugiura, Tutomu Kanasashi, Chisato Tak ...

Article type: Article
2013 Volume 55 Issue 2 Pages 69-73
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_69

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To clarify the mobility of radiocesium (^<137>Cs) deposited in tree bark, we investigated the absorption properties of the Cs in the bark as the first step, using stable isotope (cold) ^<133>Cs. We compared absorption/desorption properties of ^<133>Cs with alkali metals, sodium (Na), potassium (K), and rubidium (Rb), in the bark of sugi (Cryptomeria japonica) and konara (Quercus serrata), which distribute a lot in Fukushima. Each alkali metal ion was absorbed to grinded bark by shaking with the 1 mol m^<-3> chloride solution of each alkali metal. Then, each alkali metal absorbed on the grinded bark was continuously extracted using 1 mol m^<-3> acetic acid ammonium (CH_3COONH_4) and 1 mol m^<-3> nitric acid (HNO_3) solution. In both tree species, Na^+ and K^+ were extracted almost same as or slightly more than absorbed amount in the bark. On the other hand, ^<133>Cs^+ and Rb^+ were extracted 57.6% and 38.3% in bark of sugi and 20.6% and 30.2% in bark of konara, respectively, therefore, most of absorbed ^<133>Cs^+ and Rb^+ seemed to be strongly fixed/absorbed in the bark. ^<137>Cs was extracted from the konara bark which was collected at Fukushima prefecture using the same procedure as above. As the result, ^<137>Cs extractability in konara bark was very low with 0.1 to 0.4%, except the sample after extraction by CH_3COONH_4 in the bark collected in Iwaki city. In this study, it was clarified that Cs fixed/absorbed in the tree bark is not easily removed.

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Soil physicochemical properties of experimental sites in forests contaminated by radioactive materials due to the Fukushima Daiichi Nuclear Power Plant accident

Shinji Kaneko, Shigeto Ikeda, Akio Akama, Satoru Miura, Masamichi Taka ...

Article type: Article
2013 Volume 55 Issue 2 Pages 75-81
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_75

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To predict the behavior of radiocesium derived from the Fukushima Daiichi Nuclear Power Plant accident in a forest ecosystem, soil survey and sampling were performed in five experimental plots at three sites in Fukushima prefecture, Kawauchi-mura, Otama-mura and Tadami-machi, and the physicochemical properties of the soils were examined. The humus type was mull-type and the amount of O horizons was lower than that of European forest soils. The soils had a generally high carbon content and showed low pH. CEC was generally high and exchangeable cations were low. However, the content of exchangeable K was relatively high for the uppermost horizon. The clay content was 16-24% for all soils and the soil texture was CL, SiCL and SCL. The mull-type humus and thin O horizon suggest that the decomposition rate of O horizon is expected to be so high that the radiocesium in the O horizon will rapidly migrate to the mineral soil surface. It is suggested that plant absorption might be limited because the soils contain sufficient clay and exchangeable potassium.

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Radiocesium contamination in suburban forests in Kashiwa city, Chiba Prefecture

Kenji Fukuda, Natsumaro Kutsuna, Toru Terada, Mohammad Reza Mansournia ...

Article type: Article
2013 Volume 55 Issue 2 Pages 83-98
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_83

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Radioactive cesium contamination caused by Fukushima nuclear disaster was investigated in suburban forest patches in Kashiwa city, Chiba prefecture, central Japan. Air dose rate at 1 m aboveground in summer to winter of 2011 was 0.3-0.4 μSv/h either inside or outside the forest patches. Radiocesium concentration of twigs and old leaves of evergreen broad-leaves and conifers was 1.2-8.8 kBq/kg, while that of current leaves of evergreen broadleaved and deciduous trees was 0-2.8 kBq/kg. Most ground beetles collected in summer to autumn of 2011 showed lower concentration than 5 kBq/kg, while mushrooms showed higher concentration with the maxium value of 61 kBq/kg. From measurements of tree branches and wood discs collected from thinned trees, total deposition of radiocesium in the forest patches was estimated. The radiocesium concentration was highest in outer bark of both conifers and deciduous broadleaves and in old leaves of conifers. The contamination level was so high that firewood and compost made in the stand could not be used. Deposition of radiocesium on aboveground parts of forests was estimated as 5.7 kBq/m^2 in a mixed forest of Hinoki and deciduous broadleaves and 3.7 kBq/m^2 in a deciduous oak forest, respectively. Belowground deposition was 85 kBq/m^2 in the deciduous stand. The total amount of radiocesium above- and below-ground was estimated to be 90 kBq/m^2. The soil measurement made in January of 2013 in Konara patches showed that most of radiocesium moved to A layer of the soil, therefore decontamination by litter clearing seemed difficult in these forests.

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Radioactive cesium accumulation in the body of sika deer inhabiting the Oku-Nikko and Ashio regions of Tochigi prefecture in 2012

Masaaki Koganezawa, Yoshitada Tamura, Kei Okuda, Emiko Fukui

Article type: Report
2013 Volume 55 Issue 2 Pages 99-104
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_99

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In 2011, radioactive cesium (^<134>Cs+^<137>Cs) fallout after the Fukushima nuclear accident reached 10,000-30,000 Bq・m^<-2> and 30,000-60,000 Bq・m^<-2>, respectively, in Oku-Nikko and Ashio located 160 km southwest of the Fukushima nuclear power plant in Central Japan. To obtain basic data in elucidating the dynamics of radioactive cesium in the forest ecosystem and its impacts on wildlife in the future, we investigated radioactive cesium concentrations in a total of nine sample categories, including muscles, organs, and gastrointestinal contents obtained from 80 sika deers (Cervus nippon) captured from the Oku-Nikko and Ashio during February and March 2012. We also examined radioactive cesium concentrations in eight food plants consumed by the deer in these regions during the winter period. The investigation revealed that radioactive cesium concentration was highest in the rectal contents in samples from both regions, followed by ruminal contents, muscles, kidneys, liver, heart, lungs, fetus, and amniotic fluids. This elucidated that radioactive cesium was accumulated in the entire body of the deer. Moreover, a prominent difference was found in the radioactive cesium accumulation trend between the deer in the Oku-Nikko and Ashio. We believe this was caused due to variations in the precipitation amount of radioactive cesium and winter food sources in these regions. Additionally, for both regions, radioactive cesium concentration in the rectal contents was higher than that in the ruminal contents and the eight food plants. This suggests that sika deer plays a key role in transferring radioactive cesium through food intake, digestion, and absorption.

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Survey of radioactive contamination of sugi (Cryptomeria japonica D. Don) shoots and male flowers in Fukushima prefecture

Akio Akama, Yoshiyuki Kiyono, Tatsuo Kanazashi, Koji Shichi

Article type: Report
2013 Volume 55 Issue 2 Pages 105-111
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_105

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We measured concentrations of radiocesium (^<134>Cs and ^<137>Cs) in shoots and male flowers of sugi (Cryptomeria japonica D. Don), sampled in Fukushima prefecture in 2011 and 2012, after the Fukushima Dai-ichi Nuclear Power Plant accident. The radioactivities of male flowers and shoots were mainly logarithmic linear to the air dose rates and radiocesium depositions. The measured radioactivities of male flowers ranged between 260 kBq kg^<-1> and < 0.1 kBq kg^<-1> in 2011. In 2012, average radioactivity decreased in the order old needles, one-year-old needles, male flowers, and current-year needles. Some radiocesium was probably absorbed by other organs and translocated within the tree. However, the average radioactivity of male flowers in 2012 was about 40% of the average value for the previous year. Thus, radiocesium absorption by sugi was apparently considerable for a short time after the accident, and subsequent absorption was lower.

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Radioactive cesium contamination of edible wild plants after the accident at the Fukushima Daiichi Nuclear Power Plant

Yoshiyuki Kiyono, Akio Akama

Article type: Report
2013 Volume 55 Issue 2 Pages 113-118
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_113

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Yields of fallen leaves and the compost from a farm forest and their efficacy for paddy rice cultivation in a hilly and lower mountainous area in northern Kanto

Mineaki Aizawa, Tomoe Inui, Hideaki Hirai, Kazutoshi Osawa, Junko Iked ...

Article type: Article
2013 Volume 55 Issue 2 Pages 119-126
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_119

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In order to understand the past integrated use of farm forests and agricultural fields in a hilly and lower mountainous region in northern Kanto, as well as the production of rice using organic materials, we measured the mass of raw fallen leaves gathered from a farm forest, the mass of yielded compost made from fallen leaves, and the mass of raw fallen leaves and compost supplied to paddy rice fields. Based on our results, we estimated the area of farm forest required to foster a 1-ha paddy rice field. We also performed experimental cultivation to assess the efficacy of the fallen leaves and compost in terms of nutrient composition. We found that at least 5 Mg/ha of raw fallen leaves was obtained from the forest, and 1 ha of farm forest was necessary to cultivate a 1-ha paddy rice field using these organic materials. Analysis of nutrient composition indicated that the total amount of nitrogen in these organic materials did not meet the general recommended quantity. The quantities of phosphate and potassium in these organic materials were less than 10% of the general recommended level. However, these organic materials were expected to be effective fertilizers containing small amounts of phosphate and potassium for the soil in which excessive amounts of phosphate and potassium had accumulated. In 2011, the yield of cultivated rice using raw fallen leaves and compost was not so low, namely, 80% of that produced with conventional cultivation using chemical fertilizers, but was roughly equivalent to that produced with no fertilizer application, indicating the limited efficacy of these organic materials.

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The evaluation of the forecasting method of beech crop in Yamagata prefecture

Yoshiki Endo, Takayuki Mori, Satoshi Ito, Hiromasa Koyama

Article type: Article
2013 Volume 55 Issue 2 Pages 127-132
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_127

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It is desirable if we can forecast the seed crop of beech forests for successful regeneration or wildlife management. Prediction method of seed crop had already been proposed in Hokkaido, in which two conditions were required for good crop, i.e. mass flowering (> 500 of flowers/m^2) and more than 20 times of increase from previous year in flower production to escape from natural enemy. Above conditions cannot be identical in Yamagata, because climatic condition and abundance of natural enemies may be different from those in Hokkaido. Matsui et al. (2009) had already pointed out that conditions for good seed crop in Yamagata would be more than 350 female flowers/m^2 and more than 10 times of flowers than those of the previous year. However it has been regarded less reliable due to the short period of investigation. In this study, we added data from other study sites and years and re-evaluated the Masui's method. Seed trap census revealed that the Matsui's method is valid to predict the seed crop in Yamagata. In addition, when a beech forest produced more than 350/m^2 of flowers, it would simultaneously satisfied the another condition. This means if only we can estimate flower production of next year by shoot sampling and flower bud observation, prediction of next year's crop is possible. Without traps, this method can be more convenient and versatile tool.

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A bagging experiment to evaluate the effect of predispersal predation exclusion on nut viability in beech (Fagus crenata Blume)

Hideyuki Ida, Masanobu Hotta, Yasuo Ezaki

Article type: Report
2013 Volume 55 Issue 2 Pages 133-137
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_133

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We conducted an experiment to evaluate the effectiveness of preventing predispersal predation on nut viability in beech (Fagus crenata Blume) by bagging a single canopy tree in an old-growth stand of central Japan over two consecutive years with different nut production. To prevent predation on predispersal nuts, the bagging treatment began in mid June of both years. Seed trap sampling of fallen nuts and direct sampling of cupules were also conducted to monitor seasonal changes. Although viable nuts were less productive in the sample beech than in the surrounding beech stand, the bagging treatment increased the proportion of viable nuts from the sample beech by approximately eight fold in the first year (from 4.9% to 41.3%) and five fold (from 2.4% to 12.5%) in the following year. Thus, at an individual level, predator exclusion by bagging increased the percentage of viable nuts by reducing predispersal predation. The results of this experiment confirm that predispersal insect predation is a major factor controlling the viable nut rate in beech.

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Responses of microbial community to soil warming in warm-temperate evergreen broad-leaved forests

Xin Wang, Takayuki Nakatsubo, Akiko Sasaki, Shinpei Yoshitake, Naishen ...

Article type: Report
2013 Volume 55 Issue 2 Pages 139-143
Published: December 25, 2013
Released on J-STAGE: April 03, 2017

DOIhttps://doi.org/10.18922/jjfe.55.2_139

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To elucidate the effect of climate warming on the soil heterotrophic microbial community in warm-temperate, evergreen broad-leaved forests, we conducted a soil-warming experiment in a secondary forest located in the city of Higashi-Hiroshima in western Japan. We established ten trench plots (1 m × 1 m) with root barriers to prevent root regrowth in the forest. The plots were divided into warming and control treatments. Infrared heaters were used to increase the soil temperature of the warming plots by about 2.5℃ for three years. We used phospholipid fatty acid (PLFA) analysis to examine the composition of the soil heterotrophic microbial community. There were no significant differences in the total content of PLFAs (TotPLFAs) and fungal PLFAs (FungPLFAs) between the warming and control plots. However, warming caused an increase in the amount of bacterial PLFAs (BactPLFAs), the result being a lower ratio of FungPLFAs to BactPLFAs (F/B ratio) in the warming plots. In addition, PLFAs characteristic of gram-negative bacteria increased in the warming plots. The results indicated that the soil heterotrophic microbial community in this warm-temperate, evergreen broad-leaved forest was sensitive to climate warming.

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