LAUSR

Emissions of nitrous oxide (N 2 O) from the world’s river networks constitute a poorly constrained term in the global N 2 O budget 1 , 2 . This N 2 O component was previously estimated as indirect emissions from agricultural soils 3 with large uncertainties 4 – 10 . Here, we present an improved model representation of nitrogen and N 2 O processes of the land–ocean aquatic continuum 11 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 CO 2 concentration, and terrestrial processes have affected the N 2 O emissions from the world’s streams and rivers during 1900–2016. The results show a fourfold increase of global riverine N 2 O emissions from 70.4 ± 15.4 Gg N 2 O-N yr −1 in 1900 to 291.3 ± 58.6 Gg N 2 O-N yr −1 in 2016, although the N 2 O 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 N 2 O 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 N 2 O emissions. N 2 O emissions from rivers have increased globally by a factor of four between 1900 and 2016, with emissions starting to decline since the early 2000s. Most riverine N 2 O emissions come from smaller streams, driven primarily by the use of nitrogen fertilizers in agriculture.