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| Titel |
Towards prediction of redistribution of fallout radiocesium on forested area discharged from Fukushima Nuclear Power Plant |
| VerfasserIn |
Satoru Miura, Michio Aoyama, Eriko Ito, Koji Shichi, Daisuke Takata, Masumori Masaya, Nobuhito Sekiya, Natsuko Kobayashi, Naoto Takano, Shinji Kaneko, Keitaro Tanoi, Tomoko Nakanishi |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109109
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| Publikation (Nr.) |
 EGU/EGU2015-8989.pdf |
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| Zusammenfassung |
| Redistribution of fallout 137Cs on forested area discharged from Fukushima Nuclear Power
Plant (FNPP) is an issue of major concern for the people in Fukushima and its surrounding
areas. To approach this question we investigated global fallout 137Cs (137Cs-GFO) from
nuclear weapon tests in the atmosphere in the 1950s and 60s, and 137Cs distribution
derived from FNPP (137Cs-FK) within the whole trees contaminated directly. We
examined concentrations and amounts of 137Cs-GFO in surface soils (0–5, 5–15
and 15–30 cm in depth) of 3470 samples at 316 sites all over Japan, which were
collected just before the accident of FNPP. We determined 137Cs-GFO activities by NaI
well-type scintillation counter with its accuracy verified using measurements by
a germanium detector. We divided 316 sampling sites into 10 groups separated
by one longitudinal line and four transversal lines on the terrain of Japan islands,
then analyzed rainfall and geomorphological effects on 137Cs-GFO inventories. In
addition to this dataset, we collected three whole tree samples of 26 year-old Quercus
serrata at a contaminated area by FNPP accident in April, 2014 and examined
concentrations of 137Cs-FK of above- and belowground tree parts by a germanium
detector.
We estimated an average of 137Cs-GFO inventories of forest soils in Japan to be 1.7 ± 1.4
kBq m-2 as of 2008. 137Cs-GFO inventories varied largely from 0–7.9 kBq m-2 among the
country and accumulated greater in the north-western part along the Sea of Japan
side. We detected rainfall effect on 137Cs-GFO inventories, which were greater
where winter rainfall was large. As for vertical distribution of 137Cs-GFO, 44% of
137Cs-GFO remained within the uppermost 5 cm of soil profiles whereas the rest
of 56% existed in 5–30 cm in depth. This indicated that considerable downward
migration of 137Cs-GFO has happened during these fifty years in forest soils in
Japan. However, multiple linear regression analysis by geomorphological factors
related to soil erosion, such as inclination angle or catchment area calculated from
DigitalÂElevation Model, showed almost no significant effects on distribution of
137Cs-GFO.
With regard to tree samples directly contaminated by FNPP accident, concentrations of
137Cs-Fk of coarse roots and stem woods were 100–400 Bq kg-1. Concentrations of
137Cs-Fk of fine to medium roots and branches were higher ranging 400–2000 Bq kg-1. The
concentrations of belowground and aboveground tree parts showed the same levels according
to the size of organ. This indicated that 137Cs-Fk went around the whole tree within these
three years. We figured from the findings about 137Cs-GFO and 137Cs-Fk above that the
contaminated roots of trees could be a source of 137Cs transport from trees to soils.
Distinguishing biological migration of 137Cs between plants and soil from the secondary
surface and vertical physical migration of 137Cs in the soils is a clue to come closer to an
important reliable prediction of future distribution of 137Cs discharged from FNPP. |
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