Nitrous oxide emissions from the Ohio River

Because nitrous oxide (N₂O) is a potent greenhouse gas and atmospheric concentrations are on the rise, the potential for N₂O evasion from rivers is of interest.  We measured N₂O emission rates every two weeks from August 2008 through January 2009 at a single site located in the Markland pool of the Ohio River near Cincinnati, Ohio; spatial variability was characterized with emission rates measured once at each of six sites distributed across the 150 km pool.  Emission rates ranged from 8 – 34 μg N₂O-N m^-2 h^-1 at the biweekly sampling sites with the highest rates observed during the summer and fall and the lowest rates during the winter.  All sites in the pool-wide survey were sources of N₂O to the atmosphere with the highest emission rate (630 μg N₂O-N m^-2 h^-1) occurring immediately downstream of Cincinnati where ammonium concentrations exceeded 400 μg N L^-1.  We estimate that the 30 km of river downstream of Cincinnati produced 1.5 times more N₂O than the remaining 120 km of the pool combined.  This research demonstrates that estimates of global N₂O emissions from rivers should consider the significance of nitrogen inputs from urban centers.