日本海の孤島からみた地球環境 : 大気中の微粒子を取り込むバイオマット中の微生物

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Acid precipitation is caused mainly by the oxidation of atmospheric SO_2, NO_2 and C0_2. Aerosol particles containing these oxides, fly ash and mineral dust are cycling on a global scale. NO_2 concentration, rainwater and air dust in the atmosphere have been investigated by electron microscopy. Rainwater sampled (May 29^<th> 2008) from the solitary island of Hekura-jima (Wajima, Ishikawa Prefecture), located in the Sea of Japan, was strongly acidic (pH 4.8) and high in electrical conductivity (EC). This is despite the fact that Hekura-jima has no industry or cars and as such, is believed to be less polluted than other areas in the same prefecture. NO_2 concentrations measured at Hekura-jima (May 28-29^<th> 2008) and at the uninhabited island of Ohshima, in the city of Wajima, Ishikawa Prefecture, (July 22-23rd 2008) indicated quite low values. The acid rain, sulfur materials and mineral dust were found deposited on the surfaces of black pine trees located to the northwestern side of Hekura-jima, suggesting that these atmospheric pollutants originate from surrounding countries rather than from local sources. Scanning electron micrographs of aerosol dust sampled from Hekura-jima on May 27-29^<th>, 2008, showed evidence of atmospheric pollutants of fly ash, sulfuric mineral dust of gypsum and pollen from pine trees. On this basis, it can be assumed that air pollution occurred frequently not only in industrial areas but also in certain solitary and uninhabited islands of Japan. White and green microbial mats were observed on tuff rock located at the uninhabited Ohshima Island suggesting that acidic rainwater that had seeped into the rock was subsequently exuded from cracks within the rocks. X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) analysis of the green microbial mats collected from Ohshima Island showed mainly amorphous Al-Si materials. Optical and transmission electron micrographs of the green microbial mats showed various living microorganisms of diatoms and filamentous cyanobacteria within the granular particles. The living microbes clearly demonstrated a blue fluorescence under UV irradiation. Spherical materials were found inside the filamentous cyanobacterial cells, and chlorophyll was found inside the cocci cells of the microbes. On the other hand, opaque spherical materials of fly ash coexisted with microbes within the diatom cells. An energy dispersive X-ray (EDX) analysis of the fly ash indicated that the main components were Al and Si. In addition, it was found that the granular materials were also composed of Al and Si. The abundant diatoms and filamentous microbes associated with the submicrometer Al-Si chemical compositions of the particles suggested an environmental co-ecosystem comprised of green microbial mats and Al-Si bio-clay mineralization. Environmental interactions between the aerosol particles, rainwater, tuff rock, and microorganisms at the uninhabited Ohshima Island showed a particular natural circulatory system. The diatoms, cyanobacteria and silicate bacteria were found to trap and feed on the mineral dust of Al-Si particles and fly ash collected from the ecosystem of the green microbial mats. The amorphous granular particles of mineral dust and fly ash have a correlation with microorganisms in which they act as carriers of atmospheric pollutants. These particles also play an important role in the environmental purification ability.
2009-04-10

日本海の孤島からみた地球環境 : 大気中の微粒子を取り込むバイオマット中の微生物

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