Trace gas exchange in a high-arctic valley 2.: Landscape CH4 fluxes measured and modeled using eddy correlation data

Eddy correlation measurements of methane exchange were conducted during a period of 43 days covering the summer season in high-arctic, NE Greenland. Measurements were carried out over a fen area and showed fluxes ranging from no exchange in the early part of the campaign to 120 mg m(-2) d(-1) during midsummer. The emission showed a clear variation related to soil temperatures and water table level in the late part of the summer, whereas the thickness of the active soil layer was a main controlling parameter in the thaw period, in the early part of the season. A model to assess methane emission dependency on physical parameters is found to give a realistic estimate for the seasonal variations in flux. The proportion of C returned to the atmosphere as CH4 relative to the total C cycling was around 2%, which is similar to ratios often reported in literature. On the basis of these findings, an estimate is given for the total summer season emission of CH4, in which a simple model including both physical parameters and net primary production (NPP) is adapted to reproduce CH4 exchange rates for periods when no measurements were undertaken. In this way the total emission of CH4 during the period June 1 to September 1 1997, is found to equal 3.7 +/- 0.57 g m(-2), which is a relatively high rate given the harsh climate in which the measurements were made.