Vegetation Density Modulates Spatiotemporal Variations of CO₂ Emission in Urban Aquatic Systems

Urban aquatic systems serve as significant contributors to atmospheric carbon dioxide (CO2) emissions, playing a critical role in greenhouse gas (GHG) budgets. Aquatic vegetation is widely implemented in urban water management for ecological restoration and landscape construction, while its spatial configuration and planting density critically regulate the CO2 flux (FCO2) at the water–air interface. This study examines spatiotemporal variations and environmental drivers of FCO2 across different vegetation patterns in the Qingshangang (QSG) River and Lihu Lake (LH) continuum. The FCO2 exhibited pronounced seasonality, with significantly higher emissions during the wet season (QSG: 74.76 ± 61.95 mmol/m2/d; LH: 62.81 ± 39.08 mmol/m2/d) compared to those during the dry season (QSG: 40.13 ± 44.89 mmol/m2/d; LH: 9.41 ± 15.02 mmol/m2/d). Structural equation model (SEM) identified dissolved oxygen (DO) and pH as key direct controls of FCO2, while dissolved organic matter (DOM) contributed indirectly. Sites with dense emergent macrophytes exhibited significantly higher FCO2 levels, highlighting vegetation density as a primary factor shaping spatial heterogeneity in CO2 emissions. Our findings emphasize the need to consider vegetation spatial distribution in urban aquatic ecosystem design and management for greenhouse gas mitigation strategies.