Methane emissions from an alpine fen in central Switzerland

Abstract

Methane emissions and below ground methane pore water concentrations were determined in an alpine fen at 1,915 m a.s.l. in central Switzerland. The fen represented an acidic (pH 4.5–4.9), nutrient-poor to mesotrophic habitat dominated by Carex limosa, Carex rostrata, Trichophorum caespitosum and Sphagnum species. From late fall to late spring the fen was snow-covered. Throughout winter the temperatures never dropped below 0°C at 5 cm below the vegetation surface. Methane emissions in June, July, August and September were in the range of 125 (±26)–313 (±71) mg CH4 m−2 day−1 with a tendency to decrease along the summer season. Mean methane pore water concentrations at a depth of 20–40 cm below the vegetation surface were 526 (±32) μM in June and in the range of 144 (±10)–233 (±7) μM in July, August and September. At a depth of 0–20 cm the mean methane pore water concentrations dropped back to <20 μM with an almost linear decrease between 0 and 15 cm. Oxygen pore water concentrations were close to air saturation in the first few centimeters and dropped back below detection limit at a depth of 20 cm. In July and August the pore water concentrations of dissolved organic carbon (DOC) were in the range of 7.2–10.1 mg C l−1 at all depths. The pore water concentrations of acetate, formate and oxalate were in the range of 2.0–8.2 μM at all depths. Methanotrophic and methanogenic communities were quantified using pmoA and mcrA, respectively, as marker genes. The abundances of both communities showed a distinct peak at a depth of 10–15 cm below the vegetation surface.