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

Abstract

Riverine environments, such as streams and rivers, have been reported as sources of the potent greenhouse gas nitrous oxide ([Formula: see text]) 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 [Formula: see text] production precludes predictions of [Formula: see text] emissions along riverine networks. Here, we analyze [Formula: see text] emissions from streams and rivers worldwide of different sizes, morphology, land cover, biomes, and climatic conditions. We show that the primary source of [Formula: see text] 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 [Formula: see text] production is bounded between two [Formula: see text] emission potentials: the upper [Formula: see text] emission potential results from production within the benthic-hyporheic zone, and the lower [Formula: see text] emission potential reflects the production within the benthic-water column zone. By understanding the scaling nature of [Formula: see text] production along riverine networks, our framework facilitates predictions of riverine [Formula: see text] emissions globally using widely accessible chemical and hydromorphological datasets and thus, quantifies the effect of human activity and natural processes on [Formula: see text] production.