title: In situ measurement of dissolved methane and carbon dioxide in freshwater ecosystems by off-axis integrated cavity output spectroscopy.
abstract: A novel low-cost method for the combined, real-time, and in situ determination of dissolved methane and carbon dioxide concentrations in freshwater ecosystems was designed and developed. This method is based on the continuous sampling of water from a freshwater ecosystem to a gas/liquid exchange membrane. Dissolved gas is transferred through the membrane to a continuous flow of high purity nitrogen, which is then measured by an off-axis integrated cavity output spectrometer (OA-ICOS). This method, called M-ICOS, was carefully tested in a laboratory and was subsequently applied to four lakes in Mexico and Alaska with contrasting climates, ecologies, and morphologies. The M-ICOS method allowed for the determination of dissolved methane and carbon dioxide concentrations with a frequency of 1 Hz and with a method detection limit of 2.76 × 10(-10) mol L(-1) for methane and 1.5 × 10(-7) mol L(-1) for carbon dioxide. These detection limits are below saturated concentrations with respect to the atmosphere and significantly lower than the minimum concentrations previously reported in lakes. The method is easily operable by a single person from a small boat, and the small size of the suction probe allows the determination of dissolved gases with a minimized impact on shallow freshwater ecosystems.
authors.affiliation: Biotechnology and Bioengineering Department, Cinvestav, Avenida IPN 2508, Mexico City, San Pedro Zacatenco, D.V. 07360, Mexico.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Gonzalez-Valencia
authors.forename: Felipe
authors.initials: F
authors.lastname: Magana-Rodriguez
authors.forename: Oscar
authors.initials: O
authors.lastname: Gerardo-Nieto
authors.forename: Armando
authors.initials: A
authors.lastname: Sepulveda-Jauregui
authors.forename: Karla
authors.initials: K
authors.lastname: Martinez-Cruz
authors.forename: Katey Walter
authors.initials: KW
authors.lastname: Anthony
authors.forename: Doug
authors.initials: D
authors.lastname: Baer
authors.forename: Frederic
authors.initials: F
authors.lastname: Thalasso
mesh_terms: D000413:Alaska; D002245:Carbon Dioxide / Q000032:analysis*; D017753:Ecosystem; D060106:Lakes / Q000737:chemistry*; D008567:Membranes, Artificial; D008697:Methane / Q000032:analysis*; D008800:Mexico; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods
chemical_list: D008567:Membranes, Artificial; D002245:Carbon Dioxide; D008697:Methane