アラスカ永久凍土地域の湖沼から大気へのメタン拡散

抄録

Dissolved methane concentrations (DM) at 41 lakes along 4 major highways were observed in the open water season in 2008, 2012 and 2013 to estimate diffusive methane flux from lake surfaces to the atmosphere and to verify an enhancive effect of thawing permafrost on the methane flux in Alaska. An inverse relationship between lake size and DM was obtained in lakes in tundra region as was found for the European boreal lakes. It suggests that no evidence indicating an effect of thawing permafrost on DM was found in these lakes in the tundra region at this moment. 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 area and number distributions were obtained in order to calculate regional mass fluxes of diffusive methane. Total area of all lakes (807,619) in Alaska (northern region from 59°N) is 49,291 km². Regional summer diffusive flux of methane from lakes in Alaska was estimated to be 77 Gg CH₄ yr^–1. Average diffusive flux density (per lake area) was 1.56 g C m^–2 yr^–1.