Aqueous and surface expression of subsurface GHGs: Subsurface mass transfer effects

• Published in: Water research (Oxford) 2020-03, Vol.170, p.115327-115327, Article 115327
• Main Authors: Van De Ven, Cole J.C., Mumford, Kevin G.
• Format: Article
• Language: English
• Subjects: Carbon Dioxide; Dissolution; Emissions; Environmental expression; Greenhouse Effect; Greenhouse gas; Greenhouse Gases; Groundwater; Methane; Multiphase flow; Nitrous Oxide
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2019.115327

Releases of greenhouse gases (GHGs) from the subsurface can result in atmospheric emissions and the degradation of water quality. These effects require attention in today’s changing climate to properly quantify emissions, reduce risk and inform sound policy decisions. Flowing subsurface GHGs, including methane and carbon dioxide, present a risk in the form of two environmental expressions: i) to the atmosphere (surface expression) and ii) to shallow groundwater (aqueous expression). Results based on high-resolution observations in an analog experimental system and analytical modelling show that these expressions depend on the rate of gas flow and the velocity of the flowing groundwater. In deeper systems, the emission of flowing subsurface GHGs could be significantly limited by dissolution into groundwater, adversely impacting water resources without surficial evidence of an underlying issue. This work shows that mass transfer in the subsurface must be considered to quantify, monitor and mitigate risks of leaking subsurface GHGs. [Display omitted] •Dissolution of flowing CO2 gas was studied using visual and analytical techniques.•Flowing GHGs can dissolve into flowing groundwater or be emitted to the atmosphere.•Mass transfer can limit the occurrence of surface emissions of subsurface GHG.•Leak estimates must consider the ratio of mass reaching the surface and dissolved.•Multicomponent mass transfer can alter gas composition reaching the surface.