Methane Ebullition and Diffusion From Two Alaskan Lakes and Several Small Ponds

Methane efflux from two lakes and several small ponds located on the North Slope of Alaska was estimated from measurements of ebullition and diffusion. This pilot study was performed over a several-day period during the months of July and August in 2006. Ebullition was measured using bubble traps constructed from 15-inch diameter, inverted funnels. Diffusion was estimated from measurements of dissolved CH4 profiles and use of a boundary layer diffusion model. Stable carbon isotope measurements were performed on CH4 in the collected bubble and water samples to assess methane production and oxidation in the lake sediment and water column. Transects were established on Cake Eater Lake, near Barrow, and on Fog 4 Lake, near the Toolik Lake Research Station. Five small ponds situated on the tundra surrounding Cake Eater Lake were also sampled for dissolved CH4 content. Cake Eater Lake is a large, flat-bottomed, thaw lake with a maximum depth of 1.3 meters along the transect. Fog 4 is a small, potential kettle lake with a maximum depth of approximately 5 meters. Bubble samples of 7 ml or more were found at 8.3% of the sites in Cake Eater Lake over a period of 24 hours with an average CH4 content of 40%. At Fog 4 Lake, 67% of the study sites produced greater than 7 ml of bubbles over 24 hours with an average CH4 content of approximately 55%. Diffusion appears to be a significant contributor to the total CH4 flux in the lakes and in the small ponds. The ponds appear to release more CH4 per unit area through diffusion than the nearby Cake Eater Lake.