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 p eriod of 43 days covering the summer season in high-arctic, NE Greenland. M easurements 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 temperatu res and water table level in the late part of the summer, whereas the thick ness 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 fo r the seasonal variations in flux. The proportion of C returned to the atmo sphere as CH4 relative to the total C cycling was around 2%, which is simil ar 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 productio n (NPP) is adapted to reproduce CH4 exchange rates for periods when no meas urements 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 measur ements were made.