Topic: College of Sciences and Humanities

December 28, 2010

The potent greenhouse gas nitrous oxide, which contributes to climate change and stratospheric ozone destruction, is coming from North America's streams and rivers at three times the previously estimated rate, says a Ball State University biologist who co-authored a major report.

Emissions of nitrous oxide from freshwater around the globe is being caused by human activities, such as fossil fuel combustion and intensive use of fertilizers, said Melody Bernot, a Ball State biology professor and one of the researchers for "Nitrous Oxide Emission from Denitrification in Stream and River Networks."

Environmental Protection Agency (EPA) researcher Jake Beaulieu was joined by 25 colleagues in the research effort, which was published Dec. 20 in the Proceedings of the National Academy of Sciences (PNAS).

"We were surprised to see this much nitrous oxide coming from rivers and streams across North America," Bernot said. "Most people think about gases coming from cars and factories, not freshwater streams."

Bernot has been part of the research team investigating nitrous oxide emission since 2001, part of project funded by the National Science Foundation (NSF) under Patrick Mulholland of Oakridge National Laboratory. The group, which has published multiple papers on related issues, collected data from 72 streams across the continent.

"It is clear that human activity is contributing to climate change and destruction of atmospheric ozone at much higher levels than previously thought," Bernot said.

Researchers found that human-caused nitrogen loading into river networks is a potentially significant source of nitrous oxide through a microbial process called denitrification.  When summed across the globe, river networks are the source of at least 10 percent of global anthropogenic nitrous oxide emissions to the atmosphere, three times the amount estimated by the Intergovernmental Panel on Climate Change (IPCC).

Bernot believes the report is another piece of evidence that humans are contributing to changes in the planet's climate. The report estimates that nitrous oxide accounts for six percent of human induced climate change.

"Changes in agricultural and urban land-use practices that result in less nitrogen being delivered to streams may reduce nitrous oxide emissions from river networks," she said.