N2O emissions from a nitrogen-enriched river

Nitrous oxide (N2O) emissions from the South Platte River in Colorado were measured using closed chambers in the fall, winter, and summer of 1994-1995 . The South Platte River was enriched in inorganic N (9-800 mu M) derived f rom municipal wastewater effluent and groundwater return flows from irrigat ed agricultural fields. River water was as much as 2500% supersaturated wit h N2O, and median N2O emission rates from the river surface ranged from les s than 90 to 32 600 mu g-N m(-2) d(-1). Seventy-nine percent of the varianc e in N2O emission rates was explained by concentrations of total inorganic N in river water and by water temperature. The estimated total annual N2O e missions from the South Platte River were 2 x 10(13)-6 x 10(13) mu g-N yr(- 1). This amount of annual N2O emissions was similar to the estimated annual N2O emissions from all primary municipal wastewater treatment processes in the United States (I). Results from this study indicate that N-enriched ri vers could be important anthropogenic sources of N2O to the atmosphere. How ever, N2O emission measurements from other N-enriched rivers are needed to better quantify this source.