A hydrologic model demonstrates nitrous oxide emissions depend on streambed morphology

Rivers are hot spots of nitrous oxide (N2O) emissions due to denitrification. Although the key role of rivers in transforming reactive inorganic nitrogen is widely recognized, the recent estimates of N2O emissions by the Intergovernmental Panel on Climate Change (IPCC) may be largely underestimated. This denotes a lack of reliable and robust methodologies to upscale denitrification, and other biogeochemical processes, from the local to the network scale. Here we demonstrate that stream hydromorphology strongly influences N2O emissions. We provide an integrative methodology for upscaling local biogeochemical processes to the catchment scale with a Damköhler number, which accounts for the complex interplay between stream hydromorphology and biogeochemical characteristics of streambed sediments. Application of this theoretical framework to the large data set collected as part of the second Lotic Intersite Nitrogen eXperiment (LINXII) demonstrates that stream morphology is a key factor controlling emissions of N2O from streams.