A stable isotope technique for measuring production and consumption rates of nitrous oxide in coastal waters

Abstract

The coastal ocean is a globally important source of atmospheric nitrous oxide (N 2O), yet understanding the behaviour of N 2O in the near-shore water column is often hampered by allochthonous inputs of N 2O and the potential for concurrent production and loss processes. A method has been developed to simultaneously measure rates of N 2O production resulting from ammonium oxidation, and rates of production and loss due to denitrification, in regions of high N 2O activity. Water samples are incubated with 15N-labelled substrates ( 15NH 4 +, 15NO 3 − or 15N 2O) and time-series measurements of 15N 2O concentrations are made by purge-and-trap gas chromatography/mass spectrometry (P+T GC/MS). Analytical precision is maintained at ∼±1% by the use of a fully labelled N 2O internal standard ( 15N 2 18O). Some N 2O production rates obtained as part of a series of measurements in a coastal embayment (Bedford Basin, Nova Scotia) are shown.