UI Researchers Find River Structure is a Key Factor in Greenhouse Gas Emissions
April 11, 2017
Vehicle exhaust, fossil fuel emissions and other pollutants are familiar contributors to climate change. But more innocuous natural resources, like rivers and streams, contribute as well. A research team led by the University of Idaho has found that the form and structure of rivers and streams is an important factor in greenhouse gas emissions — and small rivers produce more than big ones.
Civil engineering Associate Professor Daniele Tonina and postdoctoral researcher Alessandra Marzadri at the University of Idaho, along with their partners at the University of Notre Dame in Indiana and the University of Trento in Trento, Italy, have used these findings to develop a new model to predict emissions at a global level. Their work was published today in the Proceedings of the National Academy of Sciences.
Microbial communities in streams and rivers take in nitrogen compounds, then may release nitrous oxide (N2O) that makes its way into the air. Nitrous oxide is a greenhouse gas, air pollutant and contributor to climate change.
The team studied rivers and streams of different sizes and shapes and in different biomes and climatic conditions across the globe in an effort to better understand the role of surface and subsurface processes in the emission of N2O.
“Rivers produce 10 percent of the entire human-caused nitrous oxide emitted in the world,” said Tonina, who conducts research at the Center for Ecohydraulics Research at the University of Idaho Boise. “Considered over a 100-year period, it has 298 times more impact per unit mass (global warming potential) than carbon dioxide.”
Current equations used to predict nitrous oxide emission levels do not take river morphology into consideration. But Tonina and his team’s research gives a better understanding of why all rivers do not produce the same amount of N2O.
The primary source of N2O emissions from a stream or river varies depending on the size of the waterway, the researchers found. In streams, most of the N2O is produced in the near subsurface and at the interface between the water and the sediment. In larger rivers, most of the N2O is produced in the water-sediment interface and in the water column.
Understanding this was key in creating a prediction model.
With this new understanding of the role of surface and subsurface processes in emissions of N2O, scientists will now be able to more accurately quantify the effect of human activity and natural processes on N2O production.
“We developed a model that can be used at large continental and even global scale,” Tonina said. “The new model provides the needed feedback to help quantify human impact on climate change at the global scale, and it could be used by agencies to provide scientific basis and data to help climate-related decisions in different parts of the world.”
Martha Dee, a co-author of the paper and a graduate student at the University of Notre Dame, said it’s exciting to be able to place field measurements into the context of this analysis.
“We now have a framework that predicts N2O production without having to measure it directly, which will be powerful tool for predicting how environmental change alters greenhouse gas emissions in streams and rivers," Dee said.
This research is supported by National Science Foundation Awards 1344661 and 1344602 and by the European Communities 7th Framework Programme under Grant Agreement 603629-ENV-2013-6.2.1-Globaqua.
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