Nitrous oxide emissions in the Shanghai river network: implications for the effects of urban sewage and IPCC methodology

Global nitrogen (N) enrichment has resulted in increased nitrous oxide ( N 2 O ) emission that greatly contributes to climate change and stratospheric ozone destruction, but little is known about the N 2 O emissions from urban river networks receiving anthropogenic N inputs. We examined N 2 O saturation and emission in the Shanghai city river network, covering 6300 km 2 , over 27 months. The overall mean saturation and emission from 87 locations was 770% and 1.91 mg N 2 O‐N m −2  d −1 , respectively. Nitrous oxide ( N 2 O ) saturation did not exhibit a clear seasonality, but the temporal pattern was co‐regulated by both water temperature and N loadings. Rivers draining through urban and suburban areas receiving more sewage N inputs had higher N 2 O saturation and emission than those in rural areas. Regression analysis indicated that water ammonium ( NH 4 + ) and dissolved oxygen ( DO ) level had great control on N 2 O production and were better predictors of N 2 O emission in urban watershed. About 0.29 Gg N 2 O‐N yr −1 N 2 O was emitted from the Shanghai river network annually, which was about 131% of IPCC 's prediction using default emission values. Given the rapid progress of global urbanization, more study efforts, particularly on nitrification and its N 2 O yielding, are needed to better quantify the role of urban rivers in global riverine N 2 O emission.