Microbial oxidation of methane in the sediments of central and southern Baikal

Methane levels and methane oxidation rates were determined in the sediments from geochemically different areas in the central and southern parts of the low-mineral Lake Baikal. At different stations, integral rates of methane oxidation varied from 60 to 6592 μmol m−2 day−1. Typically, two distinct peaks of methane oxidation rates were revealed, located in the oxic and anoxic sediment horizons. In most cases, the rates of aerobic and anaerobic methane oxidation were comparable. Due to low sulfate concentration in pore water (<0.15 mM), a mechanism different from reverse methanogenesis, which involves methanotrophic archaea and sulfate-reducing bacteria and is common in marine sediments, was probably responsible for this process in Lake Baikal reduced sediments. The possible alternative mechanisms and electron acceptors are discussed.