Differential patterns and controls of N₂O emission from coastal rivers with varying land uses and salinity in northern China

River ecosystems are significant sources of nitrous oxide (N₂O). However, the patterns and regulating mechanisms of N₂O emissions in coastal rivers under the combined influence of urbanization and salinity gradients remain insufficiently explored. Therefore, this study investigated coastal rivers in Tianjin, located in the temperate climate zone of northern China, and classified six rivers according to dominant land-use types. Through field sampling and monitoring across four seasons, a total of 296 water samples and 74 sediment samples were collected and analyzed. We systematically examined the intensity, spatiotemporal variations, and key factors controlling N₂O emissions from these coastal rivers. N₂O fluxes in coastal rivers followed the order of Sewage river (1.75 ± 1.44 μmol m⁻² h⁻¹) > Mixed rivers (0.88 ± 0.91 μmol m⁻² h⁻¹) > Urban river (0.63 ± 0.27 μmol m⁻² h⁻¹) > Agricultural rivers (0.55 ± 0.20 μmol m⁻² h⁻¹). The N₂O fluxes in the Sewage river were considerably higher than those in the other river types (p < 0.05), and all rivers exhibited the lowest N₂O fluxes in autumn. Water nitrogen and phosphorus concentration primarily controlled the N₂O emissions in the coastal rivers of Tianjin, whereas salinity played a significant regulatory role. Thus, the default emission factor recommended by the Intergovernmental Panel on Climate Change overestimated the N₂O emission potential of the coastal rivers by 2.36–4.33 folds. This highlighted the need to revise this factor for systems strongly influenced by urbanization and human activities to improve the accuracy of regional and global riverine N₂O emission inventories. These findings provide crucial empirical monitoring data for N₂O emissions across different coastal river typologies, serving as an essential step toward correcting systematic overestimations and fundamentally improving future GHG inventories.