Concurrent Methane Production and Oxidation in Surface Sediment from Aarhus Bay, Denmark

Abstract

Marine surface sediments, which are replete with sulfate, are typically considered to be devoid of endogenous methanogenesis. Yet, methanogenic archaea are present in those sediments, suggesting a potential for methanogenesis. We used an isotope dilution method based on sediment bag incubation and spiking with 13C-CH4 to quantify CH4 turnover rates in sediment from Aarhus Bay, Denmark. In two independent experiments, highest CH4 production and oxidation rates (>200 pmol cm-3 d-1) were found in the top 0–2 cm, below which rates dropped below 100 pmol cm-3 d-1 in all other segments down to 16 cm. This drop in overall methane turnover with depth was accompanied by decreasing rates of organic matter mineralization with depth. Molecular analyses based on quantitative PCR and MiSeq sequencing of archaeal 16S rRNA genes showed that the abundance of methanogenic archaea also peaked in the top 0–2 cm segment. Based on the community profiling, hydrogenotrophic and methylotrophic methanogens dominated among the methanogenic archaea in general, suggesting that methanogenesis in surface sediment could be driven by both CO2 reduction and fermentation of methylated compounds. Our results show the existence of elevated methanogenic activity and a dynamic recycling of CH4 at low concentration in sulfate-rich marine surface sediment. Considering the common environmental conditions found in other coastal systems, we speculate that such a cryptic methane cycling can be ubiquitous.

Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernförde Bay, SW Baltic Sea

“…A similar close coupling between methane oxidation and methanogenesis in the absence of definite methane profiles was recently proposed from isotopic labeling experiments with sediments from the sulfate reduction zone of the nearby Aarhus Bay in Denmark (Xiao et al, 2017). It is therefore likely that such a cryptic methane cycling also occurs in the sulfate reduction zone of sediments in the Eckernförde Bay.…”

Biogeochemistry, microbial activity, and diversity in surface and subsurface deep‐sea sediments of South China Sea

“…Although the concave‐up shape of methane profile was often interpreted as the diffusion of methane from SMTZ, increasing evidence suggested endogenous methane production could occur in the sulfate‐rich sediments (Maltby et al ; Sela‐Adler et al ; Xiao et al ; Zhuang et al ), as observed in this study. Therefore, the low but detectable concentrations of methane could be a collective result of production, consumption, and diffusion from underlying sediment below SMTZ.…”

Methylotrophic methanogenesis fuels cryptic methane cycling in marine surface sediment

“…The Haps cores were transferred to a PVC core‐liners (diameter 11.8 cm) on deck. The cores were then brought back to the laboratory, kept at in situ temperature (10°C) and processed within 48 h (Xiao et al ). Several Rumohr Lot cores (Meischner and Rumohr ) were taken for geochemical profiles and radiotracer microbial activity measurements.…”

“…The gross CH 4 production and oxidation rates were quantified by amending the natural pool of CH 4 with 13 CH 4 and following the subsequent replacement of the 13 CH 4 by 12 CH 4 from methanogenesis, which is referred to as bag incubation combined with 13 C isotope dilution (Xiao et al ). Briefly, two segments (0–2 cm and 8–10 cm) of sediment were sliced from Haps cores in a glove box with N 2 atmosphere and passed through a 0.5 mm sieve.…”

“…In this study, we tested the role of methylotrophic methanogenesis in surficial marine sediment by combining stable and radioactive isotope labeling techniques. We quantified gross CH 4 production rates by amending the natural pool of CH 4 with 13 CH 4 and following the subsequent replacement of the 13 CH 4 by 12 CH 4 from methanogenesis (Xiao et al ). The contribution from hydrogenotrophic and acetoclastic pathways were quantified by labeling experiments using 14 C‐bicarbonate or 2‐ 14 C‐acetate.…”