Scientists Map Methane in World’s Rivers and Streams, Find Surprising Sources and Human Impacts on Emissions

Freshwater ecosystems account for half of global emissions of methane, a potent greenhouse gas that contributes to global warming. Rivers and streams, especially, are thought to emit a substantial amount of that methane but the rates and patterns of these emissions at global scales remain largely undocumented.

Now, thanks to an international effort to better understand these processes, a study published today in Nature provides the first glimpse into the global rates, patterns, and drivers of methane emissions from running waters. That glimpse confirms that rivers and streams do, indeed, produce a lot of methane and play a major role in climate change dynamics. But the study also reveals some surprising results about how – and where – that methane is produced.

A profile picture of Emily Stanley.
Emily Stanley.

“We expected to find the highest methane emissions at the tropics, because the biological production of methane is highly sensitive to temperature’ says Emily Stanley, a professor at the University of Wisconsin-Madison’s Center for Limnology and co-author of the Nature report. Instead, she says, their team found that methane emissions in the tropics were comparable to those in the much colder streams and rivers of boreal forests and Arctic tundra habitats.

Temperature, it turns out, isn’t the primary variable driving aquatic methane emissions. Instead, the study found, “the amount of methane coming out of streams and rivers regardless of their latitude or temperature was primarily controlled by the surrounding habitat connected to them,” Stanley says. How warm the water was mattered less than what kinds of habitat it connected to.

Rivers and streams in boreal forests and polar regions at high latitudes are often tied to peatlands and wetlands, while the dense forests of the Amazon and Congo also supply the waters running through them with soils rich in organic matter. Both systems produce substantial amounts of methane because they often result in low-oxygen conditions where the microbes that break down all of that organic matter produce methane as a by-product.

However, not all high methane rivers and streams come by these emissions naturally. In other parts of the world, freshwater methane emissions are primarily controlled by human activity in both urban and rural communities.

‘Humans are actively modifying river networks worldwide and, in general, these changes seem to favor methane emissions,” says Gerard Rocher, lead author of the report and a postdoctoral researcher with both the Swedish University of Agricultural Sciences and the Blanes Centre of Advanced Studies in Spain.

Habitats that have been highly modified by humans – like ditched streams that drain agricultural fields, sections of rivers below wastewater treatment plants, or concrete stormwater canals – also often host the high organic matter, low oxygen level conditions that promote methane production.

While unfortunate, these results of human modification also point to some good news, Rocher says. “One implication of this finding is that freshwater conservation and restoration efforts could lead to a reduction in methane emissions.” Slowing the flow of pollutants like fertilizer, human and animal waste or excessive topsoil loads into rivers and streams would help head off the ingredients that lead to high methane production in our freshwater systems.

A map of the world showing methane emissions from rivers.
A global map shows the modeled yearly average emissions for rivers across the globe. The tropics, along with the Arctic, are particular “hot spots.” Image courtesy: E. Stanley

Stanley agrees that, “from a climate change perspective, we need to worry more about systems where humans are creating circumstances that produce methane” than the natural cycles of methane production. When it comes to freshwater rivers and streams, at least, conservation efforts could not only promote healthier waterways, they could also, quite literally, help clear the air.

But, Stanley says, that is just one take-home message from the study.

Their work also underscores how important teams of scientists working to compile and examine gigantic datasets has become to understanding the sheer scope of climate change. This current report is the result of a multi-year collaboration between the Swedish University of Agricultural Sciences, Umeå University, the University of Wisconsin-Madison and several other institutions across the globe.

Stanley first began to compile a dataset on river and stream methane emissions with her graduate students back in 2015. When she found herself stuck at home and unable to do fieldwork during the COVID-19 pandemic, she realized it was a great time to begin updating that dataset in the hopes it could help predict methane emissions at global scales. That dataset proved pivotal to the study and her international team of colleagues used it, as well as methane measurements collected on rivers and streams across several countries, state-of-the-art computer modeling and AI-assisted machine learning, to “massively expand” the bigger picture of methane emissions.

“We now have a lot more confidence in methane estimates” thanks to all of that work, Stanely says. She and her colleagues hope their study leads to better understanding of the magnitude and spatial patterns of all sources of methane into Earth’s atmosphere and that it can help improve the large-scale models scientists currently use to predict the future state of our climate. Knowing where, and why, such a potent greenhouse gas gets produced can help prepare society for the changes to come and point to potential solutions to curb emissions.

A PDF of the article, “Global methane emissions from rivers and streams” is available here.

Media Contacts:

Emily Stanley:; 608-263-2567; 608-213-3715

Adam Hinterthuer:, 608-630-5737

Gerard Rocher: