Northern wetlands in Japan are distributed mainly in eastern Hokkaido with thick deposition of peat, where seasonal frost penetrates at nearly 100 cm deep in mid winter. During summer season, high flux of Methane under anaerobic conditions of wetland was measured as the value of 424 mg/m2day. In the process of frost penetration in early winter, relatively high value of Methane flux was maintained. The decrease of Methane flux value is not to proportional to the decrease of the temperature in upper layers of soil. On the other hand,the summer flux values of Methane highly depend on the upper soil temperature. The activated layers of Methane production may shift from upper to lower positions according to the lowering ground surface temperature in early winter. The amounts of dissolved organic carbon in ground water at lower positions increase in early winter. At the time of initial frost penetration near ground surface, both thermal and chemical conditions in soil layers with high water table are favorable to high Methane production. The time lag of temperature propagation into lower layers makes the Methane production active until the frost arrives at certain depth.

In Kushiro wetland, the critical depth of activated layer was estimated as 40-60 cm based on the temperature profiles in soil, chemical and Redox profiles in ground water. In final stage of freezing,residual Methane at lower layers in soil was captured in frozen layer. In early Spring, thawing proceeded downward and arrived at certain depth. Stored Methane with high concentration was released resulting the burst of Methane flux from ground surface.

Masami FUKUDA
Institute of Low Temperature Science
Hokkaido University
Kita19 Nishi 8  Kita-ku
Sapporo 060  JAPAN  
Tel +81-11-706-5492
Fax +81-11-706-7142
E-mail:Masami.Fukuda@LT.hines.hokudai.ac.jp