Purpose Accurately tracing nitrogen (N) sources and clarifying their migration-transformation processes is essential for mitigating riverine N pollution, yet the mechanisms across media and land-use contexts remain unclear. Materials and methods In this study, we assessed and compared the differences in the nitrate content and isotopic compositions (delta N-15-NO3- and delta O-18-NO3-) of surface water, as well as the carbon (C) and N content and their isotope values (delta C-13 and delta N-15, respectively) in the suspended particulate matter (SPM) and surface sediments (SSM) of the Wei River, with respect to various land-use types [i.e. construction land (CL), agricultural land (AL), and forest land (FL)]. Moreover, the N sources in the different media were quantitatively assessed, and the transformation processes were clarified. Results The nitrate content, delta N-15-NO3-, delta N-15 and N content of SPM in the FL were significantly lower than those in AL and CL (P < 0.001). Manure and sewage were the dominant nitrate sources in CL (58.1 +/- 8.5%) and AL (53.3 +/- 19.0%). The SPM found in CL and AL were mainly derived from terrestrial soil (46.7 +/- 21.8% and 44.1 +/- 30.4%, respectively) and effluent detritus (28.2 +/- 15.6% and 24.4 +/- 16.5%, respectively), whereas that in FL primarily originated from terrestrial leaf litter (50.4 +/- 24.8%) and terrestrial soil (26.9 +/- 22.2%). Note that terrestrial soil was the dominant source for the SSM observed across all land-uses types (56.4%-87.2%). Significant positive correlations were observed between delta N-15-NO3- and delta N-15-SPM (P < 0.001) and between delta N-15-NO3- and delta O-18-NO3- (P < 0.001), indicating that the nitrate transformation was mainly influenced by assimilation. However, no significant correlations were observed between SPM and SSM (delta C-13, delta N-15, and C and N contents), suggesting weak vertical mixing in the water column. Conclusions Overall, this study underscores the strong coupling between land-use patterns and N cycling, indicating that effective regulation requires management strategies tailored to specific land-use conditions.