Decoding the sources (and sinks) of N₂O in aquatic ecosystems

Abstract

Flowing aquatic ecosystems (e.g., rivers, streams, drains, estuaries) both transport nitrogen and host variable biogeochemical nitrogen reactions, which makes it difficult to identify the origin of the nitrous oxide (N₂O) these systems emit to the atmosphere. This may explain why surface water nitrate concentrations (commonly used to predict aquatic N₂O emissions) turn out to be a poor proxy for N₂O: data from a range of coastal wetlands, streams, and rivers across Australia and New Zealand show that low nitrate waterways can be both net N₂O sources and sinks. Here I bring together observations over temporal (diurnal and tidal cycles) and spatial (within and between systems) scales across a range of aquatic ecosystems to demonstrate the potential of isotopic (δ15NN₂O, δ18ON₂O) and isotopomer site preference (SPN₂O) data to deconvolute the drivers of aquatic N₂O.