A new method for determining stream methane emissions at the watershed scale has been developed by scientists from the U.S. Geological Survey, University of Utah, North Carolina State University and Ohio State University.

Methane has a global greenhouse gas warming potential of up to 28 – 36 times that of carbon dioxide, and can be discharged into streams either naturally or as a consequence of gas development. Methane emissions from rivers and streams have recently been recognized as an important component of global greenhouse gas budgets.

Scientists applied a new method, which involves injecting gas into stream water, for determining the fate of methane discharged into streams. This new method provides an understanding of the percentage of stream methane escaping to the atmosphere as emissions versus in-stream bacterial consumption and oxidation to carbon dioxide. The full report is available online in the journal Environmental Science and Technology.

“This is the first time that gas tracers have been used to look at stream methane emissions on a watershed scale, and further studies are needed,” said USGS scientist and lead author of the study, Vic Heilweil. “Our findings indicate that a large fraction of methane discharged into streams may be reaching the atmosphere instead of being consumed.”

Scientists used a multiple-tracer injection technique, which involves injecting methane, along with bromide and a noble gas (krypton), into a North Carolina coastal plain stream. Scientists then collected water samples downstream of the injection site, which were later analyzed to determine how much methane was left within the stream. They discovered that about 85 percent of the methane was released to the atmosphere along a two-kilometer reach.

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