Interannual Variation in Methane Production Across a Permafrost Thaw Gradient

Monday, 15 December 2014
Brittany Aiello Verbeke1, Paige Elizabeth Clarizia2, Carmody K McCalley2, Samantha Lynn Werner3, Avni Malhotra4, Sophia A Burke2, Patrick M Crill5, Jeffrey Chanton6 and Ruth K Varner3, (1)Florida State University, Tallahassee, FL, United States, (2)University of New Hampshire Main Campus, Durham, NH, United States, (3)Univ New Hampshire, Durham, NH, United States, (4)McGill University, Montreal, QC, Canada, (5)Stockholm University, Stockholm, Sweden, (6)Florida State Univ, Tallahassee, FL, United States
Methane (CH4) is an important greenhouse gas whose emissions from high-latitude ecosystems are highly sensitive to climate change. Warming and permafrost loss is causing a vegetation shift in northern peatlands from well-drained palsas to graminoid-dominated wetlands, resulting in increased CH4 emissions. Understanding CH4 production patterns across this vegetation transition and under varying environmental conditions is important for improving the accuracy of models used to predict future emissions. We measured CH4 fluxes, porewater profiles of carbon dioxide (CO2) and CH4 concentrations, along with δ13C along a permafrost thaw gradient in Stordalen Mire, Sweden spanning a vegetation transition from palsa to Sphagnum and graminoid dominated wetlands. Measurements were made in the summers of 2013 and 2014, which had lower and higher average temperatures, respectively. Across years, CH4 fluxes increased in sites dominated by the graminoid species Eriophorum angustifolium. A change in C isotopes indicates a shift from hydrogenotrophic to increasingly acetoclastic production with thaw. Comparison between years showed considerable interannual variability in both porewater and emitted CH4, likely driven by large differences in temperature and cloud coverage. Porewater CH4 concentrations increased in sites with Eriophorum vaginatum, but decreased for Eriophorum angustifolium and showed almost no variation in Sphagnum sites. Carbon dioxide concentrations were variable in E. vag sites, but increased for E. ang and Sphagnum sites. Methane fluxes showed a different pattern, higher emissions in 2014 were only observed at the wettest graminoid site, while 2014 fluxes were similar or lower in the drier Sphagnum and Eriophorum vaginatum sites. These results show the value of multi-year data sets for understanding interactions between plant communities and environmental conditions in describing CH4 dynamics and will improve our ability to predict and understand future CH4 emissions.