Rivers may be emitting significant amounts of nitrous oxide as a result of effluents from wastewater treatment plants and agricultural fields, according to a study by the U.S. Geological Survey.

In the atmosphere, nitrous oxide acts as a catalyst in ozone depletion. The government study shows nitrous oxide emissions along the South Platte River in Colorado and Nebraska, where the measurements were taken, are comparable to some of the highest known emission rates in the world.

Per molecule, nitrous oxide causes more destruction to the Earth's protective layer than chlorofluorocarbons, and it warms the planet about 200 times as effectively as carbon dioxide.

The total annual nitrous oxide emissions from the South Platte River are similar to the estimated annual nitrous oxide emissions from all primary municipal wastewater treatment processes in the United States, according to the article.

"If this one river system is similar to others, then nitrous oxide emissions from rivers could be a major human-made source of N2O to the atmosphere," said U.S. Geological Survey hydrologists Peter McMahon, Ph.D., and Kevin Dennehy, who conducted the one-year study.

However, the researchers point out that measurements from other rivers are needed before drawing any final conclusions.

Few published accounts exist of nitrous oxide emissions from an inland river, said McMahon and Dennehy. Most nitrous oxide studies have focused on wastewater treatment plants, agricultural fields, forests and lakes, they said.

As with many rivers in the U.S., the South Platte receives wastewater effluent from municipalities and groundwater return flows from irrigated fields. The measurements were taken along a 450-mile stretch of the river from North Platte, Neb., to just above Denver, Colo.

The nitrous oxide being released by the Platte River is the same gas used by the dentist as an anaesthetic and by drag racers to increase the power of their engines. The difference lies in the concentration of the gas, said McMahon.

The federal study was published in the Jan. 1 issue of Environmental Science and Technology, a journal published by the American Chemical Society.