A new study has found that levels of a powerful greenhouse gas called nitrous oxide has risen by more than 20 percent over the last century.
The source could be traced to the growth of nitrogen fertilizers and the cultivation of crops that return nitrogen to the soil naturally. Some of the nitrogen entering streams is converted to nitrous oxide.
According to Stephen Hamilton, a Michigan State University professor, nitrous oxide exists at low levels in the atmosphere, but is responsible for 6 percent of climate warming and also contributes to stratospheric ozone destruction.
"And on a per molecule basis, its global warming potential is 300-fold greater than carbon dioxide," he said.
Jake Beaulieu of the Environmental Protection Agency and team members conducted experiments on 72 U.S. rivers and streams. They studied the production of nitrous oxide from the process of denitrification, in which bacteria convert nitrates to nitrogen gases.
"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," Hamilton said.
The study concluded that the growth of this greenhouse gas can be cut short by reducing the use of fertilizer and other sources of nitrogen.