Use of stable carbon isotopes to assess anaerobic and aerobic methane oxidation in hypersaline ponds
Metadata[+] Show full item record
Methane oxidation is known to play a significant role in reducing methane (CH4) concentrations in sediments and water columns in a variety of aqueous environments. In marine systems, for example, it is thought that more than 80% of CH[subscript 4] produced is oxidized before reaching the atmosphere. However, under hypersaline conditions, little research has been performed to evaluate methane oxidation. Of the few hypersaline studies undertaken, it is unclear to what extent methane oxidation occurs, although cells of anaerobic methanotrophs have been identified in salinities up to halite saturation. The focus of this study was to investigate anaerobic and aerobic methane oxidation in organic rich microbial mats and endoevaporite crusts of hypersaline ponds. The two main study areas were the Atacama Desert in Chile and Guerrero Negro in Mexico. To track microbial consumption of CH[subscript 4] to carbon dioxide (CO[subscript 2]), [superscript 13]C-labeled CH[subscript 4] was added to the headspace of incubation vials containing mat and evaporite slurries. After incubationing for a period of time between 2 and 90 days, a portion of the biologically produced gaseous headspace was analyzed for [delta][superscript 13]C[subscript CO2]. If methane oxidation was occurring, the measured [delta][superscript 13]C[subscript CO2] values would be more enriched in [superscript 13]C compared to control incubations where no [superscript 13]CH[subscript 4] was added. The largest difference between [delta][superscript 13]C[subscript CO2]values of 13CH4-containing incubations and corresponding controls was approximately + 4 0/00 to + 7 0/00 in anaerobic treatments of microbial mat and evaporite crusts from Salar de Llamara in Chile. The [delta][superscript 13]C[subscript CO2] values for the majority of [superscript 13]CH[subscript 4] treated incubations, including [superscript 13]CH[subscript 4] treatments with added inhibitors, were within ~ 1 0/00 of respective controls. Based on the low amount of 13Cenrichment in [delta][superscript 13]C[subscript CO2] values, it appears that little, if any, methane oxidation is occurring in these hypersaline systems.