Fluxes of N2O at the sediment‐water and water‐atmosphere boundaries of a nitrogen‐rich river

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Abstract
The biogeochemistry of N2O was studied in a reach of a small river in Massachusetts which receives wastewater treatment plant effluent. Fluxes of N2O across the sediment‐water and water‐air interfaces were measured using a mass‐balance approach in which gas exchange coefficients were measured in situ. The observed atmospheric flux averaged 0.25 mg N2O m−2 h−1, and was among the highest reported fluxes for aquatic systems on a per‐area basis, although the significance of such rivers as global N2O sources may not be large. The largest fraction of the N2O released to the atmosphere was produced in the treatment plant per se. During the cold season, N2O was produced in the river sediment; during the warm season, the sediment was a sink for N2O. Throughout the year, water column production was minimal. During the season when N2O was consumed by the sediment, the benthic N2O flux could be predicted by a simple oxygen penetration depth model.