Net sediment production of methane, distribution of methanogens and methane-oxidizing bacteria, and utilization of methane-derived carbon in an arctic lake

Our study illustrates that methanogenesis and methane oxidation within the sediments of a small arctic lake are spatially variable, and using an integrated set of approaches, strongly suggests that fine-scale patterns of spatial variability in distribution of methane oxidizing bacteria (MOB) and methanogens are related to the nature of bioturbation and utilization of MOB by Chironomus larvae. Greater net sediment methane production occurred at a lake depth where concentrations of both methanogen and MOB DNA in the sediments were higher. The ratios of MOB/methanogen DNA on tubes and in the sediment supported the hypothesis of microbial gardening of MOB only at the lake depth where net methanogenesis was relatively high. Chironomus hindguts contained higher concentration of methanogen DNA and showed a trend toward higher concentration of MOB DNA compared to foreguts. The underlying mechanism for differential distribution of methanogen and MOB DNA across the gut needs further investigation, but the pattern suggests that the relationship between Chironomus larvae, methanogens, and MOB is more complex than simply feeding on and assimilation of MOB as may be implied by low delta C-13 of larvae. Vertical distribution into the sediment profile of methanogens and MOB DNA reflects the oxygen regime of the overlying water and was consistent with reports of Chironomus bioturbation activities on particle distribution within the sediment profile.