title: Gas-Tracer Experiment for Evaluating the Fate of Methane in a Coastal Plain Stream: Degassing versus in-Stream Oxidation.
abstract: Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements. In this study, dissolved gases (methane, krypton) were injected into a coastal plain stream in North Carolina to quantify stream CH4losses at the watershed scale. Stream-reach modeling yielded gas transfer and oxidation rate constants of 3.2 ± 0.5 and 0.5 ± 1.5 d-1, respectively, indicating a ratio of about 6:1. The resulting evasion and oxidation rates of 2.9 mmol m-2d-1and 1,140 nmol L-1d-1, respectively, lie within ranges of published values. Similarly, the gas transfer velocity (K600) of 2.1 m d-1is consistent with other gas tracer studies. This study illustrates the utility of dissolved-gas tracers for evaluating stream methane fluxes. In contrast to point measurements, this approach provides a larger watershed-scale perspective. Further work is needed to quantify the magnitude of these fluxes under varying conditions (e.g., stream temperature, nutrient load, gradient, flow rate) at regional and global scales before reliable bottom-up estimates of methane evasion can be determined at global scales.
authors.affiliation: Utah Water Science Center, U.S. Geological Survey , Salt Lake City, Utah 84119, United States.
authors.forename: Victor M
authors.initials: VM
authors.lastname: Heilweil
authors.affiliation: Department of Geology and Geophysics, University of Utah , Salt Lake City, Utah 84112, United States.
authors.forename: D Kip
authors.initials: DK
authors.lastname: Solomon
authors.affiliation: School of Earth Sciences, Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Darrah
authors.affiliation: Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University , Raleigh, North Carolina 27695-8208, United States.
authors.forename: Troy E
authors.initials: TE
authors.lastname: Gilmore
authors.affiliation: Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University , Raleigh, North Carolina 27695-8208, United States.
authors.forename: David P
authors.initials: DP
authors.lastname: Genereux
mesh_terms: D001272:Atmosphere; D005740:Gases; D008697:Methane; D009657:North Carolina; D045483:Rivers
chemical_list: D005740:Gases; D008697:Methane