The development of Fe-nodules surrounding biological material mediated by microorganisms |
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| Authors: | Hidekazu Yoshida Koshi Yamamoto Yuki Murakami Nagayoshi Katsuta Toru Hayashi Takeshi Naganuma |
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| Institution: | (1) Nagoya University Museum Material Research Section, Nagoya University, Nagoya 464-8601, Japan;(2) Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan;(3) Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency (JAEA), Mizunami, Gifu, Japan;(4) Department of Dental Pharmacology, Asahi University, Hozumi, Gifu, Japan;(5) Graduate School of Biosphere Sciences, Hiroshima University, Kagamiyama 1-4-4, Higashi Hiroshima, Japan |
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| Abstract: | Takashikozo is a phenomenon of Quaternary sediments in Japan. They are cylindrical Fe-oxyhydroxide nodules that form as plaques round
plant roots, where Fe is preferentially concentrated to develop a solid wall. Structural features suggest that after the roots
have decayed, the central space where the roots were situated acts as a flow path for oxidized water. Analysis of microbial
16S rDNA extracted from the nodules identified iron-oxidizing bacteria encrusted round the roots where they are the likely
initiators of nodule formation. Direct microscopic observation revealed an accumulation of Fe-oxyhydroxides that fill the
pore spaces and is also likely to be linked with the encrusting microbial colonies. Geological history and nanofossil evidence
suggest that these Fe-nodules may have been buried at a depth of up to several tens of meters for at least 105 years in reducing Quaternary sediments. Thus Fe-oxyhydroxide nodules that have formed in a geological environment at the
interfaces between water and rock by microbial mediation can persist under reducing conditions. If this is the case, the phenomenon
is significant as an analogue of post-closure conditions in radioactive waste repositories, since it could influence nuclide
migration. |
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| Keywords: | Fe-nodules Reducing sediments Microorganisms Analogue |
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