<p>A one-year monitoring campaign was carried out in 13 representative rivers in Jiashan County, Zhejiang Province, to systematically investigate the spatiotemporal heterogeneity and driving mechanisms of CO₂ and N₂O in plain river networks. The results indicated that CO₂ concentrations in main channels, tributaries without, and those with submerged macrophytes all followed a “higher in summer (1.89 mgC/L, 1.76 mgC/L, 1.33 mgC/L), lower in winter (1.07 mgC/L, 0.99 mgC/L, 0.44 mgC/L)” pattern. For N₂O, main channels exhibited a “higher in spring (2.12 µgN/L), lower in autumn (1.3 µgN/L)” trend; tributaries without submerged macrophytes showed a “higher in spring (4.42 µgN/L), lower in summer (2.54 µgN/L)” pattern, whereas tributaries with submerged macrophytes demonstrated a “higher in summer (1.82 µgN/L), lower in autumn (0.88 µgN/L)” variation. Submerged macrophytes significantly inhibited greenhouse gas concentrations. Compared with tributaries lacking macrophytes, dissolved CO₂ and N₂O levels were 44% and 47% lower, respectively, in those with macrophytes. Additionally, CO₂ concentrations in macrophyte-rich tributaries were significantly lower than in main channels. The drivers of CO₂ and N₂O varied among river types, with CO₂ mainly regulated by physicochemical factors and N₂O strongly linked to nitrogen and organic matter. These findings highlight that submerged macrophytes substantially reduce dissolved CO₂ and N₂O concentrations and limit their accumulation in plain river networks, providing important implications for ecological restoration strategies and for improving regional greenhouse gas inventories.</p>