温泉水中でのシアノバクテリアによる炭酸カルシウム鉱物の生成促進と多形への影響

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Geochemical and mineralogical investigations of CaCO_3 precipitation in Anraku hot spring of Kagoshima Prefecture were carried out to evaluate the effects of cyanobacteria on precipitation rates and polymorphism of CaCO_3 minerals. The CaCO_3 precipitates form surface sediments of the hot spring along water passage about 5m length and 10m width. These CaCO_3 sediments consist mainly of aragonite (70〜88 wt.%) with variable amounts of calcite, on which cyanobacterial biofilms were developed. Chemical analysis of the hot spring water collected along the water passage with intervals of 1.5m indicated that the water was highly supersaturated with respect to both aragonite and calcite with SI (log (IAP/K))=0.7〜1.4. Such high SI values seem to be achieved mainly by the result of abiotic CO_2 degassing and also by CO_2 removal due to photosynthesis of cyanobacteria. To evaluate the effect of cyanobacteria, we performed experimental synthesis of CaCO_3 minerals using the hot spring water in the systems with and without cyanobacteria (Phormidium sp.) isolated from the hot spring. The experiment was conducted at 25℃ for 10days under 4,000Lx light condition. Results of the comparative experiment, it was found that the precipitation rates of CaCO_3 in biotic system were enhanced by 1.9 to 3.2 times compared with the abiotic system due to the cyanobacterial photosynthesis which cause rapid increase in solution pH and also in saturation states. In addition, extent of aragonite formation was greatly induced up to 94〜97 wt.% relative to abiotic system by possibly interaction with acidic proteins released from the cyanobacterial cells into the solution.
2007-08-16

温泉水中でのシアノバクテリアによる炭酸カルシウム鉱物の生成促進と多形への影響

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