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 (378Kb)
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26,418,000 Yen (FY 1994 5,263,000 Yen)
Dissolved methane and nitrous oxide concentrations in Japanese lakes and inland seas were measured. The results were analyzed with the environmental parameters to clarify the controlling factors making the seasonality of the concentration and the emission fluxes. The dissolved methane is monthly measured in an eutrophicated lake, Kasumigaura. The whole lake average was 1 57nM, which was far higher than the atmospheric equilibrium concentration. There was a clear seasonality in the dissolved concentration. The average of the diffusive flux from the water surface was 3.1mg CH4/m2/day. The bacterial oxidation of methane in the water was significant in late summer and autumn. Half of the dissolved methane diffused from the lake bottom sediment is oxidized within the water column. Dissolved nitrous oxide concentration was also measured. The concentration was higher in winter and lower in summer. The oversaturated concentration was around 20% of the equilibrium concentration, showed no seasonality and had no relationship with the dissolved inorganic nitrogen. The dissolved methane concentration of Japanese various lakes, having different trophic levels, were measured. From the relationship between the measured dissolved methane and the trophic levels, a model calculation for the total methane emission was performed. The methane emission was estimated as 1.6 GgCH4/year for the sum of all the Japanese natural lakes. Seasonal change in the methane concentration of seawater was measured in highly eutrophic Tokyo Bay. The sources of methane in these surface waters were attributed to lateral transport from the near shore zone. The calculated diffusive flux from the bay surface was 1.5 gCH4/m2/year, which was larger than that of Lake Kasumigaura. This indicates the possibility of large contribution of marginal sea to the global methane emission.
Methane, Nitrous Oxide, Lake, Inland Sea, Flux