• • CO2 flux in Chinese large and medium reservoirs exhibits strong latitudinal zonation: southern low-latitude basins (e.g., Yangtze, Pearl) show fluxes significantly higher than northern high-latitude basins (e.g., Yellow, Songliao), with a statistically significant negative correlation with latitude (p < 0.05). This spatial pattern is critical for regional carbon budgeting and for prioritizing mitigation efforts in high-emission southern watersheds.
• • Total phosphorus (TP) content is the dominant driver of CO2 flux, showing a positive exponential correlation (p < 0.01). This implies that phosphorus reduction strategies—such as enhanced wastewater treatment and restricted aquaculture—can directly lower emissions, offering a targeted lever for carbon management in eutrophic reservoirs.
• • Reservoir age and latitude are significantly negatively correlated with CO2 flux (p < 0.05), indicating that younger reservoirs and those at lower latitudes emit more CO2. This suggests that aging reservoirs may naturally reduce emissions over time, but new reservoir projects in tropical/subtropical regions require immediate mitigation measures.
• • Physical parameters (reservoir area, pre-impoundment submersion ratio, average water depth) show no significant correlation with CO2 flux at the national scale (p > 0.05), challenging conventional assumptions and emphasizing that biogeochemical factors, not just physical morphology, govern emissions. This finding refines model inputs and improves prediction accuracy for large and medium reservoirs.