東京湾海水中のメタン濃度とその変動(<特集>東京湾およびその集水域内の物質循環)

概要

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Seasonal changes in the methane concentration of seawater were measured in highly eutrophic, Tokyo Bay. Methane concentrations varied from 27.8 to 1850nM during May 1991 to December 1992 and were always supersaturated with the atmospheric methane. During the spring and summer seasons, when bottom water became anoxic, dissolved methane was observed to accumulate (maximum 929nM). There were inverse correlations between dissolved oxygen and dissolved methane in bottom water, when dissolved oxygen concentrations in the bottom water fluctuated. Throughout the experimental period, fluctuations of methane concentrations at mid-depth were relatively small. Particularly during summer, methane concentrations in surface water frequently increased to the same levels, or became higher than concentrations in bottom water. The source of methane in these surface waters were attributed to lateral transport from the near shore zone. From fall throughout winter, methane concentrations decreased and resulted in uniform distribution through the water column. Methane oxidation activities measured in June and August, 1991 in surface and bottom water were extremely low. The calculated diffusive flux from the bay surface to the atmosphere were 1.5-11mgCH_4/m^2/d.
日本地球化学会の論文
1994-03-24