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In situ measurement of dissolved methane and carbon dioxide in freshwater ecosystems by off-axis integrated cavity output spectroscopy.

Authors
  • Gonzalez-Valencia, Rodrigo
  • Magana-Rodriguez, Felipe
  • Gerardo-Nieto, Oscar
  • Sepulveda-Jauregui, Armando
  • Martinez-Cruz, Karla
  • Anthony, Katey Walter
  • Baer, Doug
  • Thalasso, Frederic
Type
Published Article
Journal
Environmental Science & Technology
Publisher
American Chemical Society (ACS)
Publication Date
Oct 07, 2014
Volume
48
Issue
19
Pages
11421–11428
Identifiers
DOI: 10.1021/es500987j
PMID: 25209573
Source
Medline
License
Unknown

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.

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