Journal Article Diffusive summer methane flux from lakes to the atmosphere in the Alaskan arctic zone

10 ( 3 )  , pp.303 - 311 , 2016-09
Dissolved methane concentrations (DM) in thirty lakes along Dalton Highway were measured in the open water season in 2008 and in 2012 to estimate diffusive flux from lake surfaces and to verify the enhancive effect of thawing permafrost on flux in the Alaskan arctic zone. An inverse relationship between lake size and DM was obtained in lakes in the regions as was found for European boreal lakes. There was no evidence indicating an effect of thawing permafrost on DM in these lakes. DM in lakes in the taiga region, however, were higher than those in the tundra region. All lake images on a map larger than 0.001 km2 were analyzed, and the area and number distributions were obtained in order to calculate regional mass fluxes of diffusive methane. The total area of all lakes (339,733) in the Alaskan Arctic zone (northern region from 64.00°N) is 25.5 × 103 km2. Regional summer diffusive flux of methane from lakes in the Alaskan arctic zone was estimated to be 22 Gg CH4 yr−1. Average diffusive flux density (per lake area) was 0.86 g CH4 m−2 yr−1, which is similar to that in European boreal lakes.
湖沼表面から大気に拡散するメタンフラックスに及ぼす永久凍土融解の影響を検証するために、2008年と2012年の開水期(8月)、アラスカ北極圏、主にDalton Highway沿いの30湖沼の溶存メタン濃度(以下DMと略記)を観測した。ヨーロッパ寒冷地の湖沼と同等の、湖沼面積が小さいほどDMが高くなる傾向が得られた。これらの湖沼のDMに対し、永久凍土の融解の影響の証拠は認められなかった。一方、タイガ地帯では、上記のツンドラ地帯より有意に高いDMが観測された。0.001 km2以上の全湖沼について面積-個数のヒストグラム解析を行った結果から北緯64度以北の34万湖沼(総面積約26万km2)から大気に拡散するメタンは約22 Gg CH4 yr−1と推計された。湖沼面積あたりフラックスは0.86 g CH4 m−2 yr−1であり、ヨーロッパ寒冷地の湖沼と同様の値であった。

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