The Impact of Community-Driven Methane Oxidation on the Fate of Fugitive Methane in Shallow Groundwater
Bibliographic record
Abstract
Petroleum development from unconventional reservoirs has increased global concerns over the impacts of fugitive methane on freshwater aquifers and the climate. Although methane leakage from wells is well-documented, information regarding the consequences on groundwater is limited. To address these concerns, a comprehensive, multidisciplinary investigation of the migration and fate, and oxidation of fugitive methane in shallow aquifers was conducted. Ten weeks of methane injection and thirty-six weeks of monitoring using surface efflux and ground-penetrating radar measurements, aqueous and isotope geochemistry, 16S rRNA amplicon sequencing and microbial cell counts, was conducted at the CFB research aquifer in Borden, Ontario, Canada. The results showed that a significant fraction of methane vented to the atmosphere while an equal portion persisted in the aquifer despite active growth of methanotrophic bacteria. Methane oxidation in the aquifer was relatively ineffective due to oxygen-limitation. Furthermore, this study demonstrated that even small-volume releases of methane gas can cause extensive and persistent free phase and solute plumes emanating from leaks, that are detectable only by contaminant hydrogeology monitoring at high resolution. The influence of methane, oxygen and alternate electron acceptors such as nitrate on methane oxidation and microbial communities was investigated further using sand-packed, continuous culture mesocosms. The mesocosms were inoculated with groundwater from the methane injection experiments and maintained for thirty-six weeks with varying methane and oxygen concentrations. Methane oxidation was found to be strictly dependent on oxygen and led to the enrichment of 13C in residual methane. Nitrate stimulated the growth of nitrate-reducing bacteria but did not significantly impact methane oxidation. Methylotrophic populations were shown to persist for many weeks in the absence of methane, making them a powerful marker for active as well as past methane leaks. Amplicon and shotgun metagenome sequences of samples from the mesocosms revealed complex bacterial communities consisting of non-methylotrophs alongside Alphaproteobacterial and Gammaproteobacterial methylotrophs. Metaproteome analyses and biomass delta 13C values determined from the metaproteome demonstrated communal methane oxidation in the mesocosms by identifying several non-methylotrophic populations that co-metabolized methane-derived C1 substrates such as methanol, formaldehyde and formate. Altogether, this work expands current knowledge on the migration and fate of methane in shallow aquifers, showing that effective detection and monitoring of methane in groundwater requires high-resolution multidisciplinary approaches, with potential implications for minimizing the impacts of gas exploration from unconventional reservoirs.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".