Wednesday, May 28, 2008 - 9:15 AM
369

Carbon sources for methanogenesis and utilization of methane-derived carbon in sediments from an arctic lake: An experimental study using stable isotope tracers

Anne E. Hershey1, Robert M Northington1, Matthew C Bostick1, and Steve C. Whalen2. (1) Biology, UNC - Greensboro, 312 Eberhart, Greenboro, NC 27402, (2) Environmental Sciences and Engineering, UNC, Chapel Hill, NC 27599

Recent studies have shown high rates of methanogenesis and methane oxidation in arctic lake sediments, and that CH4-derived carbon is a significant component of the diet of the dominant consumer, larval Chironomus.  In a laboratory experiment we evaluated carbon sources for CH4 production and oxidation, and assessed CH4 utilization by Chironomus in sediments from an oligotrophic arctic lake. Intact sediment cores with introduced Chironomus were incubated with ambient DOC, 13C-labeled algal DOC, or 13C-labeled acetate.  Algal DOC was preferentially metabolized to CO2 and did not stimulate CH4 production.  Methane production was significantly higher in acetate-treated cores compared to control cores or algal-DOC treated cores, and both methyl and carboxyl groups were converted to CH4, illustrating that both acetoclastic and hydrogenotrophic pathways of methanogenesis were important.  Chironomus acquired 13C from all labeled sources.  Results indicate that algal DOC was not the primary substrate supporting CH4 production and are consistent with estimates based on natural abundance studies of carbon utilization by Chironomus of both CH4-derived carbon and carbon processed through aerobic pathways, and further illustrate the significant role of sediment microbial processes compared to particulate detrital pathways in supporting production of higher trophic levels.


Web Page: methanogenesis, DOC, methane oxidation

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