Exchanges of Methane between Lakes and the Atmosphere in Hokkaido, Subarctic Climate Region, Japan

Abstract

Dissolved methane concentrations (DM) at twelve major lakes in Hokkaido, the northernmost island in Japan were observed in the open water season during 2006 ~ 2009 to estimate diffusive flux from lake surfaces to the atmosphere. An inverse relationship between lake size and DM was obtained in lakes in Hokkaido as was found for the European boreal lakes. All lake images larger than 0.001 km 2 were obtained by image processing of map data and area and number distributions were analyzed in order to calculate mass fluxes of diffusive methane. Total area of all (1,269) lakes in Hokkaido is 809 km 2 . Regional diffusive flux of methane from lakes to the atmosphere in Hokkaido was estimated to be 0.581 Gg CH 4 yr -1 . Average diffusive flux density (per lake area) was about 0.718 g CH 4 m -2 yr -1 . This is a similar value to that in European boreal lakes on no-permafrost inland areas. Extremely high flux was found in Lake Abashiri-ko, one of highly eutrophic, meromictic lakes.