表層型メタンハイドレートの研究開発に係る環境影響評価

抄録

Two types of methane hydrate have been identified in the deep ocean areas around the Japanese archipelago. The sand type is buried literally in the deep sand layers, whereas the surface type exists just beneath the seabed or in the relatively shallow mud layers. These are attracting attention as the next generation of domestic energy resources in Japan, and the Ministry of Economy, Trade and Industry (METI) has been promoting research and development of methane hydrate. The authors are participating in a research and development project on surface methane hydrates and are conducting environmental impact assessment of methane hydrate development on the marine environments from physical, chemical, biological and ecological aspects. Here, we present the environmental impact assessment in this project and the progress of the research to date. We have been actively introducing various new techniques of field-observation protocols and analytical methodologies to improve and optimize environmental impact assessment for methane hydrate development. A novel technology of highly sensitive stable isotope probe method combined with conventional geochemical and genetic analyses revealed the importance of complex microbially-mediated processes in sediments to reduce the methane flux from the seabed to the over-lying seawater. Laboratory exposure experiments with comprehensive gene expression analysis were conducted to investigate the potential effects on benthic organisms induced by various environmental disturbances including high turbidity, low oxygen, high methane, hydrogen sulfide and low salinity. This study was conducted as a part of the methane hydrate research project funded by METI (the Ministry of Economy, Trade and Industry, Japan).