Correlating the presence of Sparganium angustifolium with methane ebullition in a subarctic Swedish lake

Methane (CH4) is a greenhouse gas more potent than carbon dioxide. It is released in the Arctic from the seafloor and sediments in melting permafrost regions. Lakes and ponds also emit methane to the atmosphere. Methane production in anoxic lake sediments is often controlled by the amount of available organic material and temperature. It is speculated that the amount and type of submerged aquatic vegetation (SAV) in lakes can also affect methane production in two ways; by either providing a source of carbon (C) for methane production and/or releasing oxygen into the sediment through the roots to hinder production. We sampled SAV at 63 locations on Mellan Harrsjön, a small post-glacial lake in a permafrost setting in sub-arctic Sweden (N 68°21', E 19°02'). We also measured percent cover of the vegetation, dissolved oxygen, temperature, depth and other variables. We found that the most abundant species, Sparganium angustifolium, occurred in areas with high ebullitive methane emissions from previous studies and therefore provides a carbon source for CH4 production. We also found that over a ten day period percent cover of Sparganium angustifolium increased, with increasing water temperatures, from 37 to 49%. With Arctic warming, high latitude lakes are likely to experience an earlier ice-out and later freeze-up. Because of this, SAV growth is likely to increase and provide a more stable carbon source for CH4 production.