Freshwater bodies emit more greenhouse gases than thought

The world's rivers and streams pump about 10 times more methane into our atmosphere than scientists estimated in previous studies, new research suggests.

Do not underestimate the babbling brook. When it comes to greenhouse gases, these bucolic water bodies have the potential to create a lot of hot air.

According to a new analysis in the journal Ecological Monographs, by researchers at the University of Wisconsin-Madison and colleagues,

The new study also found that human activity seems to drive which streams are the biggest contributors.

"Scientists know that inland waters, like lakes and reservoirs, are big sources of methane," said study lead author Emily Stanley, professor at University of Wisconsin-Madison in the US.

Yet accurately measuring emissions of methane from these sources has remained a challenge.

But over the years, measurements taken by Stanley and her lab members seemed to indicate that rivers and streams may produce more methane than scientists had previously known.

The team created a database of measured methane flux (the exchange of the gas between water and atmosphere) and methane concentrations measured in streams and rivers using data from 111 publications and three unpublished datasets.

The research team then used two different methods to calculate the best estimates of global methane emissions from the data. They found the emissions to be an order of magnitude higher than scientists had previously reported.

The result was "very surprising," Stanley said.

Methane from freshwater is often a byproduct of bacterial metabolism, as they break down organic matter under low-oxygen conditions, like in the sediment at the bottom of a lake.

As the climate warms, the contribution of greenhouse gases from natural sources likes rivers, streams and wetlands is expected to increase because higher temperatures accelerate this bacterial breakdown, releasing more carbon dioxide and methane.

The findings appeared in the journal Ecological Monographs.