The spatiotemporal influence of atmospheric nitrogen deposition on basin nitrogen exports based on CMAQ-SWAT model

• The atmospheric deposition impacts on nitrogen exports of the basins were evaluated. • The CMAQ-SWAT coupling model were used. • The peak of atmospheric nitrogen deposition exports occurs in wet season. • High slope area and urban land had larger atmospheric nitrogen deposition exports. Atmospheric nitrogen (N) deposition has become an important non-point source contributing to surface water pollution and a critical challenge in river water quality management. Most existing studies focused on how atmospheric N deposition affect river N fluxes on basin or regional scales, whereas research on the spatiotemporal variability of its impact on riverine N exports remains limited. In this study, an air quality model (Community Multiscale Air Quality, CMAQ) was coupled with a watershed model (Soil and Water Assessment Tool, SWAT) to accurately quantify N deposition fluxes across spatial and temporal scales and to trace their migration pathways. The integrated framework was applied to the Xiaoqing River Basin, a coastal watershed in eastern China. Results showed that atmospheric N deposition contributed 2.6 % to the total N export at the river outlet, with the highest monthly contribution in July (4.3 %). Atmospheric nitrate deposition accounted for 4.6 % of the total nitrate export, peaking at 11.4 % in July. During the wet season, 64.7 % of the annual atmospheric N deposition export occurred. Topography, land use/cover, and atmospheric N deposition flux jointly affected the spatial distribution of deposition-derived N exports, with higher contributions observed in steep-slope and urban areas. The coupled model effectively resolved the spatial-scale mismatch between atmospheric deposition patterns and watershed responses, providing new insights into the cascade processes linking atmospheric N emissions to aquatic environmental impacts. Graphical abstract