Greenhouse gas emissions hotspots and drivers of urban freshwater bodies in areas of the Yangtze River delta, China

In the modern era, urban freshwater bodies play a significant role in global carbon (C) budgeting, therefore, impacting climate change under rising global mean temperature. However, the trend, magnitude and drivers of greenhouse gas (GHG) emissions in these urban freshwater bodies of China remain uncertain. This study investigated temporal changes in GHG emissions in urban water bodies, including artificial lakes, reservoirs, aquaculture ponds and rivers, within a year in Nanjing city in the areas of the Yangtze River delta of China. In addition, meteorological and hydrochemical parameters were measured to elucidate the key drivers of GHG emissions. The results showed that the average annual flux of carbon dioxide (CO₂) and methane (CH₄) in aquaculture ponds was estimated to be 1355.6 mg CO₂ m⁻² day⁻¹ and 116.6 mg CH₄ m⁻² day⁻¹, followed by that of artificial lakes were 1172.2 mg CO₂ m⁻² day⁻¹ and 44.1 mg CH₄ m⁻² day⁻¹, rivers reached 775.9 mg CO₂ m⁻² day⁻¹ and 23.9 mg CH₄ m⁻² day⁻¹ and reservoirs were 170.1 mg CO₂ m⁻² day⁻¹ and 7.2 mg CH₄ m⁻² day⁻¹, respectively. The results further suggest that although artificial lakes and aquaculture ponds occupied only 23% of the cumulative area under lakes and ponds in the Yangtze River delta, contribute approximately 43%, about 27.5 Gg C, of total fluxes. Furthermore, high concentrations of dissolved organic carbon (DOC) and low dissolved oxygen (DO) coincided with the high GHG emissions. The study suggests that DO, DOC, temperature and wind speed are the key factors impacting the potential of GHG emissions in urban freshwater ecosystems. Strategic mitigation measures in the vicinity of the urban freshwater bodies could efficiently reduce carbon emissions in the future.