Evaluating radioisotope‐based approaches to measure anaerobic methane oxidation rates in lacustrine sediments

Abstract

The microbial anaerobic oxidation of methane (AOM) is the dominant sink for methane in anoxic sediments. AOM rate measurements are essential for assessing the efficacy of the benthic methane filter to mitigate the evasion of this potent greenhouse gas to the atmosphere. Incubation techniques with trace amounts of radiolabeled substrate (typically 14 CH 4 ) represent the most sensitive approach for methane oxidation rate measurements. Yet, radiotracer application can be performed in different ways, rendering the comparability of AOM rate measurements in field and laboratory investigations problematic. We compared four different 14 CH 4 -based shortterm incubation approaches to quantify methane turnover rates in lake sediments. Three of the applied methods yielded similar and reliable downcore rate profiles. They provided clear evidence for AOM with maximum rates of 15 nmol cm −3 d −1 at~17 cm sediment depth. Using the short-term slurry incubation (SL) method, however, we were unable to detect the AOM activity maximum that we observed with the other approaches. We hypothesize that changes in the microbial structure and disruption of physical interactions due to mixing of sediments negatively affected the activity of AOM communities and longer incubation times are necessary to enhance the sensitivity of this approach. Minor variabilities in rate measurement that we found in the non-SL incubations may be related to small-scale sediment heterogeneity, differential partial methane loss during sample handling, and/or an uneven application of the radiotracer. Whole-core incubations interfere the least with the in situ conditions, but the ultimate choice of the AOM rate measurement method will depend on the individual sampling requirements.

Abundance and biogeography of methanogenic and methanotrophic microorganisms across European streams

“…(2016) and Su et al. (2019). In brief, for PMP, the sediment was incubated for 5 weeks in an air‐tight vial at 16°C in the dark.…”

Methanogenesis exceeds CH4 consumption in eutrophic lake sediments

“…Recent evidence demonstrates slurry incubations may suppress sediment CH 4 oxidation rates in lake sediments compared to intact cores or subcores (Su et al 2019). In contrast, other work has suggested slurrying may stimulate higher rates of CH 4 production in lake sediments (Frenzel et al 1990) or O 2 consumption in freshwater sediments (Flemming and Trevors 1990) compared to core incubations.…”

Manganese/iron‐supported sulfate‐dependent anaerobic oxidation of methane by archaea in lake sediments

“…A radiotracer 14 CH 4 technique (Iversen and Jørgensen ) was chosen to obtain depth‐specific ex situ AOM rate profiles in the sediments. A 20 μ L gas bubble of 14 CH 4 /N 2 (> 2.5 kBq, American Radiolabeled Chemicals) was applied and directly injected to the whole core through predrilled side‐holes at a depth interval of 2 cm (Su et al ). Subsequent incubations were performed at in situ temperature (4°C) in the dark.…”

“…Subsequent incubations were performed at in situ temperature (4°C) in the dark. After incubation, the core was extruded and triplicate samples (~ 4 mL) were collected from 2‐cm sediment slabs using 20‐mL cut‐off syringes, and transferred into vials with aqueous NaOH (5% wt:wt) to stop bacterial activity (e.g., Su et al ). 14 CH 4 activity was measured in the residual methane (as CO 2 after combustion), the CO 2 produced by AOM, and the remaining biomass via liquid scintillation counting (Blees et al ; Steinle et al ).…”