“Runoff from agricultural and urban watersheds has increased the availability of nitrogen in streams and rivers, greatly increasing nitrous oxide production rates,” said Jake Beaulieu, a postdoctoral researcher at the Environmental Protection Agency in Cincinnati, Ohio, who along with Jennifer Tank, Galla Professor of Biological Sciences at the University, are the lead authors of a new paper that demonstrates that streams and rivers are a significant source of the nitrous oxide entering the atmosphere.
Nitrous oxide is one of many greenhouse gasses that is entering our atmosphere and wreaking havoc with the environment. However, nitrous oxide is also responsible for the degradation of our planet’s ozone layer.
Its entry into the rivers and streams is the result of the increased use of nitrogen fertilizers and the cultivation of crops that return nitrogen to the soil naturally. The runoff from the farms alongside rivers and streams thus increases the amount of nitrogen available for conversion into nitrogen oxide.
The new study looked at 72 rivers throughout the United States of America, studying the production of nitrous oxide from the process of denitrifaction, whereby bacteria convert nitrates into nitrogen gases. The study has found that the role of rivers and streams as a source for nitrous oxide entering the atmosphere is twice as high as had been estimated by the Intergovernmental Panel on Climate Change.
“Even with more than 99 percent of denitrified nitrogen in streams and rivers being converted to the inert gas, dinitrogen, river networks still contribute to at least 10 percent of global anthropogenic nitrous oxide emissions,” said contributing author Stephen Hamilton, a professor at Michigan State University’s Kellogg Biological Station.
Surprisingly, nitrous oxide is actually a more toxic compound for our atmosphere.
“Nitrous oxide is the leading human-caused threat to the atmospheric ozone layer, which protects the earth from the sun’s harmful ultraviolet radiation,” said Hamilton. “And on a per molecule basis, its global warming potential is 300-fold greater than carbon dioxide.”