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Northern (>40°N) wetlands have been suggested as the largest natural source of methane (CH4) to the troposphere. To refine our estimates of source strengths from this region and to investigate climatic controls on the process, fluxes were measured from a variety of Minnesota peatlands during May, June, and August 1986. Sites included forested and unforested ombrotrophic bogs and minerotrophic fens in and near the U.S. Department of Agriculture Marcell Experimental Forest and the Red Lake peatlands. Late spring and summer fluxes ranged from 11 to 866 mg CH4 m−2 d−1, averaging 207 mg CH4 m−2 d−1 overall. At Marcell Forest, forested bogs and fen sites had lower fluxes (averages of 77 ± 21 mg CH4 m−2 d−1 and 142 ± 19 mg CH4 m−2 d−1) than open bogs (average of 294 ± 30 mg CH4 m−2 d−1). In the Red Lake peatland, circumneutral fens, with standing water above the peat surface, produced more methane than acid bog sites in which the water table was beneath the moss surface (325 ± 31 and 102 ± 13 mg CH4 m−2 d−1, respectively). Peat temperature was an important control. Methane flux increased in response to increasing soil temperature. For example, the open bog in the Marcell Forest with the highest CH4 flux exhibited a 74‐fold increase in flux over a three‐fold increase in temperature. We estimate that the methane flux from all peatlands north of 40° may be on the order of 70 to 90 Tg/yr though estimates of this sort are plagued by uncertainties in the areal extent of peatlands, length of the CH4 producing season, and the spatial and temporal variability of the flux.

No abstract

Over a 6‐week period from July 3 to August 10, 1988, we made measurements of the flux of methane by enclosure techniques from major tundra environments in the Yukon‐Kuskokwim Delta of Alaska (60°45′N). Emissions from wet meadow tundra averaged 144 ± 31 mg CH4/m2/d and ranged from 15.6 to 426 mg CH4/m2/d, varying with soil moisture and temperature. Flux from the drier upland tundra was approximately 2 orders of magnitude lower and averaged 2.3 ± 1.1 mg CH4/m2/d. Consumption of ambient levels of methane was sporadically measured at these drier sites, and emissions ranged between −2.1 and 18.1 mg CH4/m2/d. Tundra lakes emit methane from the open water surface as well as from fringing aquatic vegetation. The presence of vegetation significantly enhanced flux over open water rates. Average fluxes from a variety of sites with vegetation ranged between 62.7 and 153.5 mg CH4/m2/d. Calculated diffusive fluxes from open water varied with lake size, the large lakes emitting 3.8 mg CH4/m2/d and small lakes emitting an average of 77 mg CH4/m2/d. An updated estimate of global emissions from tundra indicates an annual flux of approximately 11 ± 3 Tg CH4.