The Patterns of Dissolved N2O Concentrations Are Driven by Nutrient Stoichiometry Related to Land Use Types in the Yiluo River Basin, China

The concentrations of dissolved N2O in river systems at the basin scale exhibit significant spatial and temporal variability, particularly under diverse landscape conditions. This study focused on a temperate basin—the Yiluo River (YLR) basin in China—to investigate the variations in dissolved N2O concentrations and the indirect emission factors (EF5r) between the dry and wet seasons. The differences among tributaries were analyzed to assess the impact of land use types. The findings revealed that N2O concentrations and saturation levels were lower during the wet season in both the main streams and tributaries. In the dry season, the N2O concentrations were strongly correlated with NH4+-N, NO3−-N, and oxidation–reduction potential (ORP) (R2 = 0.743, p < 0.001), while in the wet season, the N2O concentrations were correlated with dissolved phosphorus (DP), water temperature (Tw), NH4+-N, and DOC (R2 = 0.640, p < 0.001). Impervious land was identified as the primary source of nitrogen in both seasons, rather than cropland. Natural land, particularly shrubland, demonstrated a notable mitigating effect on N2O accumulation and played a significant role in reducing NO3−-N levels. The YLR basin exhibited lower EF5r values (0.005–0.052%) compared to the default value recommended by the IPCC, with a significant decrease observed during the wet season (p < 0.001). Data analysis indicated that nutrient dynamics, particularly NO3−-N, the ratio of dissolved organic carbon to NO3−-N (DOC/NO3−-N), and the ratio of NO3−-N to DP (NO3−-N/DP), were significantly correlated with EF5r. These results underscore the need to re-evaluate regional N2O emission potentials and provide new insights into mitigating N2O emissions through strategic land use management.