Variability of Methane in Stordalen Mire Stream Sediments, Abisko, Sweden

Abstract:

Methane emissions from Stordalen Mire in subarctic Sweden have been increasing over the last century with rising atmospheric temperatures. Methane emissions from lakes in this region have shown a positive correlation with sediment and air temperatures. Previous studies have examined CH₄ emissions of these lakes but the primary stream that flows along the edge the mire is understudied. Streams and rivers that exist in permafrost peatland environments are thought to be a pathway for the release of older carbon deposits from thawing permafrost. To understand the potential role of stream morphology and stratigraphy on CH₄ concentrations and contributions to carbon cycling in this system, seven sediment cores were extracted from the stream and one from the adjacent lake. Cores were subsampled at 5cm depth intervals and analyzed for CH₄ concentration, δ¹³CH₄ isotopes, elemental CHNS and sediment grain size. Results from these analyses show that maximum CH₄ concentrations in stream sediments occur at greater depths than in the adjacent lake sediments. Higher CH₄ concentrations are observed in organic C rich layers in both environments. However, in stream sediments, CH₄ appears to be produced within some stratigraphic intervals, but exists in others as the result of transport. Organic C/N ratios of the sediments indicate a predominance of terrestrial organic C but it is unclear whether the sediment organic C is the result of deposition of C from permafrost thaw or C that was deposited through the degradation of modern plant material.