Spatiotemporal variability and controlling factors of indirect N2O emission in a typical complex watershed

•Spatiotemporal fluctuations of riverine N2O emissions were identified.•The main influencing factors of the temporal and spatial variation were revealed.•Key transport processes for riverine N2O emissions were highlighted.•The critical environmental variables in the riverine physicochemical indicators were clarified.•Relative importance of environmental factors was quantified. The mechanisms of N2O emissions from inland rivers remain poorly understood because of the high variability of dissolved N2O concentration and the complexity of influencing factors. Thus, it is necessary to research the spatiotemporal patterns and influencing factors to understand the driving mechanisms of riverine N2O emissions. We combine the Soil and Water Assessment Tool (SWAT) outputs with established empirical equations to identify the spatiotemporal fluctuations of riverine N2O emissions and evaluate model performance through field measurements in a typical watershed. The spatiotemporal hotspots of N2O emissions are then determined, and the relative importance of environmental variables is further determined by correlation and attribution analysis. The results indicate that the riverine N2O emissions are relatively high from August to October, which accounted for 35.38% of the annual emissions. Temporal changes are attributed to agricultural activities and meteorological factors. Agricultural activities such as planting and fertilization lead to increased diffuse nitrogen loads on the land surface. Meantime, heavy precipitation events enhance the transport of nutrients, resulting in changes in nitrogen levels in the river. Spatial analysis shows that the urban watersheds (191.22 ± 156.19 μmol m−2 d−1) are the hotspots of riverine N2O emission, which are 1.55–3.03 times that of non-urban rivers. Spatial variations are mainly affected by riverine physicochemical indicators for different watersheds. Sewage from various sources received by urban rivers provides appropriate environmental conditions for N2O production, and transports large exogenous dissolved N2O. Furthermore, salinity (r = 0.80; p