Rivers May Be Emitting Substance Involved In Ozone Destruction

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 (N2O) acts as a catalyst in ozone depletion. The government study shows N2O 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.

The study is reported in the Nov. 14 web edition of Environmental Science & Technology, a peer-reviewed scientific journal published by the American Chemical Society, the world's largest scientific society. The study also will appear in the Jan. 1 print edition of the journal.

The total annual N2O emissions from the South Platte River are "similar to the estimated annual N2O 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," say USGS 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, according to McMahon and Dennehy. Most N2O studies have focused on wastewater treatment plants, agricultural fields, forests and lakes, they say.

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.