Urban lakes as significant sources of greenhouse gas (CO, CH, and NO) 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∙d for CO, 3.1 ± 0.3 mmol∙m∙d for CH, and 12.4 ± 1.0 μmol∙m∙d for NO. The lake emitted 614.9 tons of CO, 68.6 tons of CH, and 0.84 tons of NO throughout the year. CO levels were positively correlated with dissolved organic and inorganic carbon, while CH peaked in winter due to increased anaerobic decomposition. NO concentrations were strongly linked to nutrient levels. Furthermore, statistical analysis showed that urban lakes demonstrated significantly greater CH and NO 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.