Methane, a heat-trapping greenhouse gas about 25 times more potent than carbon dioxide, is produced naturally by the breakdown of organic matter by microbes in oxygen-poor environments. Although wetlands are considered the largest natural source of this gas, the scale of emissions from northern lakes (located between about 54°N and 73°N) and the degree by which these releases differ seasonally are not well understood.
To further investigate these processes, Jammet et al. have taken advantage of newly developed sensors to generate a high-resolution record of methane releases in adjacent wetland and lake ecosystems in northern Sweden, in the Stordalen mire near the town of Abisko. Their study ran from mid-September 2012 through the end of May 2013, a period that encompassed the region’s entire winter and spring seasons.
Although the team found no detectable methane emissions from the lake while it was covered by ice, during the spring the lake was the landscape’s largest source of methane, with cumulative releases nearly twice as high as that of the wetlands. These emissions totaled an estimated 53% of the lake’s annual emissions, with 84% of the spring release occurring over a period of just 11 days. These findings refine previous estimates of spring methane releases from seasonally ice-covered lakes, which had varied from 3% to 84% of the annual emissions.
The researchers attribute the observed springtime spike to the mixing of the lake following ice breakup, a process that “stirs” the lake, breaking down its thermally stratified layers and bringing sediment and methane generated during the winter toward the surface. These findings suggest that spring is a critical period for methane releases in northern lakes and that similar processes could control the springtime release of methane in comparable lake-dominated landscapes found in Canada, Siberia, and the Nordic countries. The researchers further suggest that the magnitude of these effects will likely change as rising temperatures continue to shorten the ice cover season and accelerate methane production. (Journal of Geophysical Research: Biogeosciences, doi:10.1002/2015JG003137, 2015)
—Terri Cook, Freelance Writer
Citation: Cook, T. (2016), High methane emissions detected during subarctic lake melt, Eos, 97, doi:10.1029/2016EO044573. Published on 29 January 2016.