Open Collections

Ing, Lauren Meiko

University of British Columbia

Ebullition of methane (CH₄) from aquatic systems is a significant contributor to global greenhouse gas emissions, and influences water quality by driving vertical mixing. In Base Mine Lake, the first pit lake located in northern Alberta, Canada’s Athabasca Oil Sands Region, ebullition not only releases CH₄ but also transports benthic material and oil to the surface, impacting the lake’s interactions with the atmosphere and surrounding organisms. This study quantified methane ebullition using bubble traps equipped with pressure sensors and gas sampling ports, deployed at five locations over a two-year period. The traps provided 18 continuous records of ebullition under both open-water and under-ice conditions, addressing a research gap in northern lake systems during winter ice cover. A method was developed to process high-frequency pressure data from bubble traps, converting raw measurements into normalized gas depths and fluxes. An average bubble trap flux of 0.381 mm/day (381 mL/m²day) was consistent with on-site eddy covariance system measurements. Spatial variation in ebullition rates was particularly notable at a pockmark location, where fluxes exceeded typical values by one to two orders of magnitude. Gas sampling showed that bubbles were primarily composed of methane, with concentrations ranging from 66-94%. Additionally, ice cores confirmed that ebullition transports oil to the surface of the water column. A strong correlation was observed between falling hydrostatic pressure and increased ebullition. Ebullition events were triggered when total hydrostatic pressure dropped below a critical threshold. Two models were developed to predict these events: one matched normalized depths of observed and modelled fluxes, and the other minimized RMSE using constant pressure thresholds. Quantifying methane ebullition provides insights into the role of pit lakes in oil sands remediation, the viability of pit lakes as aquatic habitats, and the broader implications of methane release for climate change.

Text

2024-10-10

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89379

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/