[Diffusive Fluxes and Controls of N₂O from Coastal Rivers in Tianjin City]

Rivers are an important emission source of greenhouse gases. To explore the spatial characteristics and influencing factors of N₂O emission from the coastal rivers in Tianjin City, six rivers into the Bohai Sea from different land-use types were selected, and the N₂O concentrations, saturation, and diffusive fluxes were measured using the headspace-gas chromatography method. The N₂O concentration was in supersaturation, and the rivers were the source of atmospheric N₂O. The average concentration, saturation, and diffusive fluxes of N₂O were (23.85±15.20) nmol·L^-1, (309.71±197.38)%, and (27.04±16.46) μmol·(m²·d)^-1, with the ranges of 12.70-115.69 nmol·L^-1, 164%-1502%, and 9.17-244.79 μmol·(m²·d)^-1, respectively. The N₂O concentrations and diffusive fluxes of the rivers presented great spatial heterogeneity, with the sewage river (Huangdipai River)>urban river (Haihe River main stream, Jiyun River)>suburban river (Duliujian River, Yongding Xinhe River)>agricultural river (Chaobai Xinhe River). The N₂O concentration and diffusion fluxes were significantly correlated with salinity, nutrients, and carbon sources. NO₃^--N and TP contributed greatly to the diffusive flux differences. N₂O production and emission greatly related to the nitrogen cycle process in the Tianjin River, and different forms of nitrogen variously contributed to N₂O diffusive fluxes. The salinity gradient had the opposite effect on the N₂O emission in urban rivers and drainage rivers. The N₂O diffusive fluxes of the sewage river in Tianjin were significantly higher than that of other river types. In the future, due to the development of urbanization and the expansion of urban land, more management measures should focus on the hotspots such as the downstream of wastewater treatment plants of sewage rivers, the estuaries of urban rivers, and the residential gathering areas of suburban rivers to reduce N₂O emission.