Oxidation of methane in the oxic surface layer of a deep lake sediment (Lake Constance)

Summary

Oxygen and methane metabolism were measured using intact sediment cores taken from the profundal (147 m depth) of Lake Constance. Vertical O₂ profiles were determined with O₂ microelectrodes. Oxygen penetrated into the sediment to a depth of about 1.5–2.5 mm. The potential O₂ consumption rates did not differ significantly between various sampling dates and sampling sites on the deep lake floor. Dissolved CH₄ increased linearly between 2 and 20 cm depth resulting linearly between 2 and 10 cm depth resulting in a diffusive flux of about 369 μmol CH₄ m⁻² d⁻¹ into the oxic sediment surface layer as calculated form Fick's law. Activities of methanogenesis were measured in slurried sediment subcores. Integration of these activities over 2–10 cm depth indicated a total production of 1400 μmol CH₄ m⁻² d⁻¹. Incubation of intact sediment cores overlaid with O₂-containing hypolimnetic water resulted in a flux of about 35 μmol CH₄ m⁻² d⁻¹ out of the sediment into the water. However, as soon as dissolved O₂ had decreased to less than about 18 μM O₂, the CH₄ flux abruptly increased to about 480 μmol CH₄ m⁻² d⁻¹. This anaerobic CH₄ flux was similar to the CH₄ production estimated from the vertical distribution of dissolved CH₄, but was much higher than the CH₄ flux measured under aerobic conditions. Therefore, about 93% of the produced CH₄ must have been oxidized within the oxic sediment surface layer by aerobic methanotrophic bacteria which consumed about > 9% of the O₂ flux into the sediment.

Flux studies, O₂ consumptionl CH₄ evasion, CH₄ and O₂ concentration profiles, Methanogenesis, Methanotropy