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

Abstract

© 2018 John Wiley & Sons Ltd This study evaluates rates and pathways of methane (CH 4 ) 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 CH 4 fluxes to the atmosphere. In addition to aerobic CH 4 oxidation, which takes place in Lake Matano's oxic mixolimnion, we also detected CH 4 oxidation in Lake Matano's anoxic ferruginous waters. Here, CH 4 oxidation proceeds in the apparent absence of oxygen (O 2 ) and instead appears to be coupled to some as yet uncertain combination of nitrate (NO -3 ), nitrite (NO -2 ), iron (Fe) or manganese (Mn), or sulfate (SO 2-4 ) reduction. Throughout the lake, the fraction of CH 4 carbon that is assimilated vs. oxidized to carbon dioxide (CO 2 ) is high (up to 93%), indicating extensive CH 4 conversion to biomass and underscoring the importance of CH 4 as a carbon and energy source in Lake Matano and potentially other ferruginous or low productivity environments.