Stephanie A. Ewing Jennifer W. Harden Ruth K. Varner Kimberly P. Wickland Joshua C. Koch Christopher C. Fuller Kristen L. Manies M. Torre Jorgenson Carmel E. Johnston 2014 <p><span>Permafrost soils store over half of global soil carbon (C), and northern frozen peatlands store about 10% of global permafrost C. With thaw, inundation of high latitude lowland peatlands typically increases the surface-atmosphere flux of methane (CH</span>₄<span>), a potent greenhouse gas. To examine the effects of lowland permafrost thaw over millennial timescales, we measured carbon dioxide (CO</span>₂<span>) and CH</span>₄<span><span>&nbsp;</span>exchange along sites that constitute a ~1000 yr thaw chronosequence of thermokarst collapse bogs and adjacent fen locations at Innoko Flats Wildlife Refuge in western Alaska. Peak CH</span>₄<span>exchange in July (123&nbsp;±&nbsp;71 mg CH</span>₄<span>–C m</span>⁻²<span><span>&nbsp;</span>d</span>⁻¹<span>) was observed in features that have been thawed for 30 to 70 (&lt;100) yr, where soils were warmer than at more recently thawed sites (14 to 21 yr; emitting 1.37&nbsp;±&nbsp;0.67 mg CH</span>₄<span>–C m</span>⁻²<span><span>&nbsp;</span>d</span>⁻¹<span><span>&nbsp;</span>in July) and had shallower water tables than at older sites (200 to 1400 yr; emitting 6.55&nbsp;±&nbsp;2.23 mg CH</span>₄<span>–C m</span>⁻²<span><span>&nbsp;</span>d</span>⁻¹<span><span>&nbsp;</span>in July). Carbon lost via CH</span>₄<span><span>&nbsp;</span>efflux during the growing season at these intermediate age sites was 8% of uptake by net ecosystem exchange. Our results provide evidence that CH</span>₄<span><span>&nbsp;</span>emissions following lowland permafrost thaw are enhanced over decadal time scales, but limited over millennia. Over larger spatial scales, adjacent fen systems may contribute sustained CH</span>₄<span><span>&nbsp;</span>emission, CO</span>₂<span><span>&nbsp;</span>uptake, and DOC export. We argue that over timescales of decades to centuries, thaw features in high-latitude lowland peatlands, particularly those developed on poorly drained mineral substrates, are a key locus of elevated CH</span>₄<span><span>&nbsp;</span>emission to the atmosphere that must be considered for a complete understanding of high latitude CH</span>₄<span><span>&nbsp;</span>dynamics.</span></p> application/pdf 10.1088/1748-9326/9/8/085004 en IOP Publishing Effects of permafrost thaw on CO2 and CH4 exchange in a western Alaska peatland chronosequence article