Rates and pathways of CH₄ oxidation in ferruginous Lake Matano, Indonesia

This study evaluates rates and pathways of methane (CH₄ ) oxidation and uptake using ¹⁴ C-based tracer experiments throughout the oxic and anoxic waters of ferruginous Lake Matano. Methane oxidation rates in Lake Matano are moderate (0.36 nmol L^-1  day^-1 to 117 μmol L^-1  day^-1 ) compared to other lakes, but are sufficiently high to preclude strong CH₄ fluxes to the atmosphere. In addition to aerobic CH₄ oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH₄ oxidation in Lake Matano's anoxic ferruginous waters. Here, CH₄ oxidation proceeds in the apparent absence of oxygen (O₂ ) and instead appears to be coupled to some as yet uncertain combination of nitrate ( $$ ), nitrite ( $$ ), iron (Fe) or manganese (Mn), or sulfate ( $$ ) reduction. Throughout the lake, the fraction of CH₄ carbon that is assimilated vs. oxidized to carbon dioxide (CO₂ ) is high (up to 93%), indicating extensive CH₄ conversion to biomass and underscoring the importance of CH₄ as a carbon and energy source in Lake Matano and potentially other ferruginous or low productivity environments.