Role of surface and subsurface processes in scaling N₂O emissions along riverine networks

• Published in: Proceedings of the National Academy of Sciences - PNAS 2017-04, Vol.114 (17), p.4330-4335
• Main Authors: Marzadri, Alessandra, Dee, Martha M., Tonina, Daniele, Bellin, Alberto, Tank, Jennifer L.
• Format: Article
• Language: English
• Subjects: Biological Sciences; Physical Sciences
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1617454114

Riverine environments, such as streams and rivers, have been reported as sources of the potent greenhouse gas nitrous oxide (N₂O) to the atmosphere mainly via microbially mediated denitrification. Our limited understanding of the relative roles of the near-surface streambed sediment (hyporheic zone), benthic, and water column zones in controlling N₂O production precludes predictions of N₂O emissions along riverine networks. Here, we analyze N₂O emissions from streams and rivers worldwide of different sizes, morphology, land cover, biomes, and climatic conditions. We show that the primary source of N₂O emissions varies with stream and river size and shifts from the hyporheic–benthic zone in headwater streams to the benthic–water column zone in rivers. This analysis reveals that N₂O production is bounded between two N₂O emission potentials: the upper N₂O emission potential results from production within the benthic–hyporheic zone, and the lower N₂O emission potential reflects the production within the benthic–water column zone. By understanding the scaling nature of N₂O production along riverine networks, our framework facilitates predictions of riverine N₂O emissions globally using widely accessible chemical and hydromorphological datasets and thus, quantifies the effect of human activity and natural processes on N₂O production.