Methane emissions from different ecosystem structures of the subarctic tundra in Western Siberia during midsummer and during the thawing period

Methane emission was measured using a static chamber method at seven different ecosystem structures of the subarctic tundra oil the Yamal Peninsula (West Siberian Lowlands, Russia) in August 1995 midsummer) and June 1996 (spring thaw). The results obtained represent one of the most extensive data sets available for Siberian tundra and confirm the significance of this area as an important source of atmospheric methane. Mean midsummer emission rates (4.24-195.3 mg CH4 m(-2) d(-1)) were higher than mean rates reported for wetlands between 65-70degreesN in Alaska, Sweden and Russia. The highest emission rates were measured ill a lake terrestrialization mire which was always flooded, the lowest rates at a dry site in a polygonal mire. Mean emission rates during spring thaw ranged from 0.16 to 56.2 mg CH4 m(-2) d(-1). These rates increased at 4 out of 5 sites from 2.4-15.1 mg CH4 m(-2) d(-1) at the beginning of the measuring period to 24.2-156 mg CH4 m(-2) d(-1) at the end. The water-table level was the crucial parameter influencing spatial variation of methane emission rates, while temperature was the most important factor controlling temporal variation, especially during spring thaw. However, short-term changes of air temperature had no effect, and diurnal variation of methane emissions was never detected. In addition to the direct influence of temperature oil methanogenesis, the indirect effect on soil thawing was apparent. Increasing thawing depth was positively correlated with methane emission. Rapid alterations of the water table also resulted in large episodic methane emissions. Methane emission exceeded the calculated methane production in spring, suggesting that accumulated methane from the previous year was also released. The results show that considerable methane emission occurs even in the spring without an active vegetation cover and without plant-mediated methane transport. This is a consequence Of high methane production rates even at low temperatures, and of methane release via diffusion as the main transport pathway from the soil into the atmosphere.