Fluxes of nitrous oxide to the atmosphere were measured at 15 sites along the Platte River system from upstream of Denver, Colorado, to its confluence with the Missouri River near Omaha, Nebraska, in October 1994, February 1995, and August 1995. Fluxes of nitrous oxide varied with land use. The highest fluxes occurred downstream from Denver's largest wastewater-treatment plant (21,820 to 36,900 µg-N m-2 d-1), intermediate fluxes were in areas of irrigated agriculture (less than 55 to 3,481 µg-N m-2 d-1), and the lowest fluxes were in undeveloped or nonirrigated areas (less than 55 µg-N m-2 d-1). Nitrous oxide fluxes were positively correlated with water temperature and nitrate concentrations in surface water. Denitrification in riverbed sediments is a probable mechanism for nitrous-oxide production. Fluxes of nitrous oxide to the atmosphere from the Platte River system were similar to, or greater than, published fluxes measured at the air-water interface from nitrogen-rich lakes and from soils associated with grasslands and with temperate and tropical forests. Results from this study indicate that large river systems affected by urban and agricultural land uses could be an important terrestrial source of nitrous oxide to the atmosphere.
1 U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO 80225