Using Noble Gases to Compare Parameterizations of Air‐Water Gas Exchange and to Constrain Oxygen Losses by Ebullition in a Shallow Aquatic Environment

• Published in: Journal of geophysical research. Biogeosciences 2018-09, Vol.123 (9), p.2711-2726
• Main Authors: Howard, Evan M., Forbrich, Inke, Giblin, Anne E., Lott, Dempsey E., Cahill, Kevin L., Stanley, Rachel H. R.
• Format: Article
• Language: English
• Subjects: Aquatic environment; Argon; bubbles; Bubbling; Data processing; Dissolved oxygen; ebullition; ecosystem metabolism; Fluctuations; Fluxes; Gas exchange; Gases; Krypton; Metabolism; Modelling; Neon; noble gases; Oxygen; Oxygen production; Photosynthesis; Ponds; Rare gases; salt marsh pond; Salt marshes; Saltmarshes; Sediments; Supersaturation; Water gas; Wind speed; Xenon
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2018JG004441

Accurate determination of air‐water gas exchange fluxes is critically important for calculating ecosystem metabolism rates from dissolved oxygen in shallow aquatic environments. We present a unique data set of the noble gases neon, argon, krypton, and xenon in a salt marsh pond to demonstrate how the dissolved noble gases can be used to quantify gas transfer processes and evaluate gas exchange parameterizations in shallow, near‐shore environments. These noble gases are sensitive to a variety of physical processes, including bubbling. We thus additionally use this data set to demonstrate how dissolved noble gases can be used to assess the contribution of bubbling from the sediments (ebullition) to gas fluxes. We find that while literature gas exchange parameterizations do well in modeling more soluble gases, ebullition must be accounted for in order to correctly calculate fluxes of the lighter noble gases. In particular, for neon and argon, the ebullition flux is larger than the differences in the diffusive gas exchange flux estimated by four different wind speed‐based parameterizations for gas exchange. We present an application of noble gas derived ebullition rates to improve estimates of oxygen metabolic fluxes in this shallow pond environment. Up to 21% of daily net oxygen production by photosynthesis may be lost from the pond via ebullition during some periods of biologically and physically produced supersaturation. Ebullition could be an important flux of oxygen and other gases that is measurable with noble gases in other shallow aquatic environments. Key Points Concentrations of high solubility noble gases in a salt marsh pond are predicted well by wind speed‐based gas exchange parameterizations However, ebullition must occur to explain concentrations of less soluble noble gases, and we infer ebullition rates from neon observations Including ebullition fluxes increased daily net oxygen production by 1–21%, making it an important oxygen flux in this setting