Protocols for Assessing Transformation Rates of Nitrous Oxide in the Water Column

Nitrous oxide (N₂O) is a potent greenhouse gas and an ozone destroying substance. Yet, clear step-by-step protocols to measure N₂O transformation rates in freshwater and marine environments are still lacking, challenging inter-comparability efforts. Here we present detailed protocols currently used by leading experts in the field to measure water-column N₂O production and consumption rates in both marine and other aquatic environments. We present example ¹⁵N-tracer incubation experiments in marine environments as well as templates to calculate both N₂O production and consumption rates. We discuss important considerations and recommendations regarding (1) precautions to prevent oxygen (O₂) contamination during low-oxygen and anoxic incubations, (2) preferred bottles and stoppers, (3) procedures for ¹⁵N-tracer addition, and (4) the choice of a fixative. We finally discuss data reporting and archiving. We expect these protocols will make ¹⁵N-labeled N₂O transformation rate measurements more accessible to the wider community and facilitate future inter-comparison between different laboratories.