Scaling Nitrous Oxide Emissions Along Stream Networks Depends on Streambed Morphology

Abstract:

Streams can be hotspots of nitrous oxide (N₂O) emissions resulting from microbial denitrification. Although the key role of streams in transforming reactive inorganic nitrogen is widely recognized, recent estimates of N₂O emissions from aquatic ecosystems by the Intergovernmental Panel on Climate Change (IPCC) may be largely underestimated in part due because current estimates do not capture mechanisms underlying inorganic nitrogen transformations along stream and river networks. Here, we demonstrate that stream hydro-morphology strongly influences N₂O emissions, and we provide an integrative methodology for upscaling local biogeochemical processes to the catchment scale using a Damköhler number, which accounts for the complex interplay between stream hydro-morphology and biogeochemical characteristics of streambed sediments. Application of this theoretical framework to the large dataset collected as part of the 2nd Lotic Intersite Nitrogen eXperiment (LINXII) confirms that stream morphology is a major driver of N₂O emissions from streams, and provides a foundation for scaling to rivers, which are in need of empirical testing.