Urban lakes as significant sources of greenhouse gas (CO2, CH4, and N2O) emissions: insights from field measurements and statistical analyses

Urban lakes contribute to global greenhouse gas (GHG) emissions driven by both natural processes and anthropogenic activities. In this study, we conducted seasonal sampling and analysis of GHG concentrations and water chemistries in Xuanwu Lake, Nanjing, China. Concurrently, we observed pore water chemistry within the lake bottom sediments. Radon isotope activity in lake water was also measured. Then, this study expanded to a broad understanding of urban lake GHG emissions by conducting a meta-analysis of over 100 lakes of similar size but various types (urban vs. non-urban). Xuanwu Lake is a net source of GHG, with mean annual diffusive fluxes of 10.2 ± 9.3 mmol∙m⁻²∙d⁻¹ for CO₂, 3.1 ± 0.3 mmol∙m⁻²∙d⁻¹ for CH₄, and 12.4 ± 1.0 μmol∙m⁻²∙d⁻¹ for N₂O. The lake emitted 614.9 tons of CO₂, 68.6 tons of CH₄, and 0.84 tons of N₂O throughout the year. CO₂ levels were positively correlated with dissolved organic and inorganic carbon, while CH₄ peaked in winter due to increased anaerobic decomposition. N₂O concentrations were strongly linked to nutrient levels. Furthermore, statistical analysis showed that urban lakes demonstrated significantly greater CH₄ and N₂O emissions compared to non-urban lakes. These findings emphasize the need for further research and targeted mitigation strategies to address GHG emissions from urban lakes, especially in the context of increasing anthropogenic pressures and climate change.