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

Emissions of nitrous oxide from the world’s river networks constitute a poorly constrained term in the global nitrous oxide budget. This nitrous oxide component was previously estimated as indirect emissions from agricultural soils with large uncertainties. 

In the research conducted by Yuanzhi Yao et al., an improved model representation of nitrogen and nitrous oxide processes of the land–ocean aquatic continuum constrained with an ensemble of 11 data products, is presented. The model–data framework provides a quantification for how changes in nitrogen inputs (fertilizer, deposition and manure), climate and atmospheric carbon dioxide concentration, and terrestrial processes have affected the nitrous oxide emissions from the world’s streams and rivers during 1900–2016. 

The results show a fourfold increase of global riverine nitrous oxide 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 nitrous oxide 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 nitrous oxide 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.

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