Increased global nitrous oxide emissions from streams and rivers in the Anthropocene

Emissions of nitrous oxide (N₂O) from the world’s river networks constitute a poorly constrained term in the global N₂O budget^1,2. This N₂O component was previously estimated as indirect emissions from agricultural soils³ with large uncertainties^4–10. Here, we present an improved model representation of nitrogen and N₂O processes of the land–ocean aquatic continuum¹¹ constrained with an ensemble of 11 data products. The model–data framework provides a quantification for how changes in nitrogen inputs (fertilizer, deposition and manure), climate and atmospheric CO₂ concentration, and terrestrial processes have affected the N₂O emissions from the world’s streams and rivers during 1900–2016. The results show a fourfold increase of global riverine N₂O emissions from 70.4 ± 15.4 Gg N₂O-N yr⁻¹ in 1900 to 291.3 ± 58.6 Gg N₂O-N yr⁻¹ in 2016, although the N₂O emissions started to decline after the early 2000s. The small rivers in headwater zones (lower than fourth-order streams) contributed up to 85% of global riverine N₂O emissions. Nitrogen loads on headwater streams and groundwater from human activities, primarily agricultural nitrogen applications, play an important role in the increase of global riverine N₂O emissions.