Microbial oxidation significantly reduces methane export from global groundwaters.

Area of Science:

• Environmental Science
• Microbiology
• Geochemistry

Background:

• Methane in groundwater is a growing environmental concern due to its release into surface environments.
• Microbial oxidation is a key process for methane consumption, but its rates in groundwater are not well understood.

Purpose of the Study:

• To quantify in situ microbial methane oxidation rates across a wide range of methane concentrations in German aquifers.
• To identify microbial communities involved in methane oxidation.
• To estimate the global impact of groundwater methane oxidation on methane release.

Main Methods:

• Ultra-low-level ¹⁴C-labeling to measure methane oxidation rates.
• Analysis of methane concentrations spanning five orders of magnitude.
• Microbial community analysis to identify dominant methanotrophs.

Main Results:

• Methane oxidation rates were strongly correlated with methane concentrations, ranging from 0.001 to 74.28 µgC L^-1 d^-1.
• Methane turnover times varied from days to weeks at low concentrations and months to decades at high concentrations.
• Specific microbial groups, including gammaproteobacteria and anaerobic methane-oxidizing archaea, were associated with high oxidation rates.

Conclusions:

• The groundwater microbiome acts as a critical methane filter, removing approximately 66% of groundwater methane globally (167–778 Tg CH₄ y^-1).
• High methane concentrations can lead to incomplete oxidation, increasing the potential for methane release.
• Understanding these microbial processes is crucial for predicting methane fluxes from groundwater.