Babbling Brooks Bubble up Methane Gas

Nearby brooks may be doing more than babbling. New research shows that these freshwater sources may be an unrealized source of methane, the second-largest greenhouse gas contributor to human-driven global climate change.

In a recent paper published in the journal Global Change Biology, researchers show freshwater may be contributing more methane gas to the environment than has previously been measured.

"There have been recent suggestions that freshwater streams, rivers and lakes are important sources of methane to the atmosphere," University of Wisconsin-Madison graduate student John Crawford, lead researcher who also works for the US Geological Survey in Boulder, Colo., said in a statement.

This discovery has the potential to change how climate scientists and others determine the greenhouse gas budget.

In brooks and other freshwater environments, methane gas comes from the metabolic byproducts of bacteria living in the organic-compound-rich, oxygen-poor sediments. It exists in two forms: as a dissolved gas and encapsulated in bubbles that rise from sediments "like bubbles coming up in a can of soda," Crawford explained. It is these methane bubble capsules that researchers investigated.

Using a gas chromatograph sensor, they were able to determine how much methane was contained in each bubble and the rate of bubble release from Allequash Creek, a tributary of Trout Lake in Vilas County, Wis., as well as Mann Creek, Stevenson Creek and North Creek.

They found there was as much methane in bubbles emitted from Allequash Creek and the surrounding area as had been measured in other wetland and lake environments. And at least 50 percent more methane can be emitted by bubbles in the region as is dissolved in the water.

"We are missing half the story, at least in this area, if we don't include bubbles," Crawford added.

Methane levels in the atmosphere are 150 percent higher than they were before the Industrial Revolution, and the gas can lead to ozone production. Unfortunately, this study cannot accurately assess the contribution these freshwater methane bubbles pose to climate change.