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

Abstract

This study evaluates rates and pathways of methane (CH4) oxidation and uptake using 14C‐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 (NO3−), nitrite (NO2−), iron (Fe) or manganese (Mn), or sulfate (SO42−) 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.

Anaerobic methane oxidation and aerobic methane production in an east African great lake (Lake Kivu)

“…Also, the strong density gradients in Lake Kivu restricts vertical mixing and promotes the accumulation of high CH 4 concentrations in anoxic waters, which slowly diffuse to the oxic compartment, supporting both aerobic and anaerobic CH 4 oxidation. The higher rates observed in Lake Matano than in Lake Kivu may be explained by higher CH 4 concentrations in anoxic waters (up to 480 μmol/L) and greater concentrations of the highly favorable electron acceptor Fe concentrations (up to 170 nmol/L) in the upper anoxic waters (Sturm et al, 2016). Also, vertical mixing in Lake Matano is stronger than in Lake Kivu (Crowe et al, 2008).…”

Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction

“…Lake Matano, Indonesia, is a permanently stratified ultraoligotrophic lake (Crowe et al, 2008). Below its oxic surface waters, Lake Matano's permanently anoxic and stratified waters are highly enriched in iron and manganese, and support the activity of Mn cycling organisms with organic carbon and CH 4 as potential sources of electrons (Crowe et al, 2011;Jones et al, 2011;Kuntz et al, 2015;Sturm et al, 2019). We designed an enrichment strategy to select for microbes capable of anaerobic CH 4 oxidation coupled to soluble Mn(III) reduction by incubating anoxic Lake Matano sediment communities with soluble Mn(III)-pyrophosphate as the electron acceptor (with 2% O 2 in a subset of bottles), and CH 4 as the sole electron donor and carbon source after preincubation to deplete endogenous organic carbon (see Supporting Information for enrichment details).…”

Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes

“…In one instance at Lake La Cruz, the aerobic MOB are suggested to mitigate all CH 4 emissions (Oswald, Milucka, et al, ). In other lakes (e.g., Kabuno Bay of Lake Kivu, Lake Pavin, and Lake Matano), the depth of the water columns allows for oxidation of diffused CH 4 before significant portions can reach the atmosphere (Borges, Abril, Delille, Descy, & Darchambeau, ; Lopes et al, ; Sturm et al, ). In all cases, the CH 4 fluxes in these lakes are estimated to be lower compared to the lacustrine global average CH 4 flux (0.11 mmol m −2 hr −1 ; Aselmann & Crutzen, ).…”