2010 President's Report

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Nitrous oxide may be known to some as laughing gas, but it’s a serious—and growing—threat to the planet’s atmospheric ozone layer.

“Nitrous oxide is the leading human-caused threat to the atmospheric ozone layer, which protects the Earth from the sun’s harmful ultraviolet radiation,” says Stephen Hamilton, professor of ecosystem ecology and biogeochemistry at Michigan State University’s Kellogg Biological Station.

While much of the conversation about greenhouse gases has focused on carbon emissions, the amount of the potent greenhouse gas nitrous oxide has increased by more than 20 percent over the past century.

Now Hamilton and a team of researchers have raised another red flag with a study that indicates the role of rivers and streams as a source of nitrous oxide in the atmosphere appears to be three times higher than previously estimated.

While many studies have focused on how nitrogen in agricultural soils contributes to the production of the ozone-depleting gas, little attention has been paid to nitrous oxide created as a result of nitrogen that leaches into waterways.

Hamilton and researchers from the Environmental Protection Agency gathered data on 72 rivers and streams throughout the United States. They studied the production of nitrous oxide from denitrification, the process by which microorganisms convert nitrates to nitrogen gas.

Nitrogen occurs naturally in soils in which crops are cultivated. But the use of nitrogen fertilizers for lawns and crops increases the amount of nitrogen available to microbes in the soil that produce nitrous oxide. About half of the fertilizer used on crops escapes into rivers and streams where some of the nitrogen is converted into nitrous oxide.

Unfortunately, nitrogen is a necessary evil, since it’s essential to growing food crops.

“This problem is mostly linked to agriculture production,” says Hamilton. “We can’t stop growing food, but we can be more efficient about how we do it. In the past four to five decades, we’ve used nitrogen fertilizer liberally. We need to find ways to lessen that impact, either by using incentives and subsidies or by developing new technologies to manage it.”

So how can we change our behavior without affecting food production?

Hamilton projects that in the coming decade, the United States could have a carbon exchange system that will make payments to farmers for reducing their use of nitrogen fertilizer.

In the meantime, the Intergovernmental Panel on Climate Change has revised its estimates based on the findings of this study, which was published in Proceedings of the Academy of Sciences.

With increased understanding of how much nitrous oxide is making its way into the Earth’s atmosphere and where it originates, everyone from scientists to policy makers to the public can make better-informed decisions.

Thanks to Spartan scientists, a more accurate picture of the problem is helping create the kind of changes we all can live with.

For more information:

Stephen Hamilton

W. K. Kellogg Biological Station

KBS Long-term Ecological Research in Row Crop Agriculture Program

This research is supported by the National Science Foundation and MSU AgBioResearch.