N2O Emissions from a Nitrogen-Enriched River

Nitrous oxide (N 2 O) 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 μM) derived from municipal wastewater effluent and groundwater return flows from irrigated agricultural fields. River water was as much as 2500% supersaturated with N 2 O, and median N 2 O emission rates from the river surface ranged from less than 90 to 32 600 μg-N m - 2 d - 1 . Seventy-nine percent of the variance in N 2 O emission rates was explained by concentrations of total inorganic N in river water and by water temperature. The estimated total annual N 2 O emissions from the South Platte River were 2 × 10 13 −6 × 10 13 μg-N yr -1 . This amount of annual N 2 O emissions was similar to the estimated annual N 2 O emissions from all primary municipal wastewater treatment processes in the United States (1 ). Results from this study indicate that N-enriched rivers could be important anthropogenic sources of N 2 O to the atmosphere. However, N 2 O emission measurements from other N-enriched rivers are needed to better quantify this source.