Emission characteristics and influencing factors of greenhouse gas emissions from urban rivers in the Plain River Network region of China

<p dir="ltr">Climate change has emerged as a global focus, and the emission of greenhouse gases (GHG) exerts a crucial influence on global climate change. The patterns and controls of GHG emissions in urban rivers remain unclear. GHG fluxes in different types of urban river in Changzhou city of China were calculated respectively by the floating static chamber method and boundary layer equation method. Ultraviolet-visible (UV-vis) absorption spectrum and three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM) were employed to explore the sources and characteristics of dissolved organic matter (DOM) in rivers. The physical and chemical indicators of river and sediment were monitored on-site and analyzed in the laboratory. Also, the species and quantity of bacteria in the sediment were determined. The Spearman correlation analysis was utilized to identify the key factors influencing GHG emission. The results indicated that, (1) the intensity of sunlight has an effect on the activity of pseudomonas, and thus affects N2O flux; (2) the CO2 flux measured by two methods showed a significant difference and negative correlation (p<0.05), which may because low wind speed influence the robustness of the boundary layer model. Therefore, using only the boundary layer equation method cannot accurately measure GHG of rivers in urban areas with low wind speed (3) the CO2 flux was highly positively correlated with total phosphorus and ammonia nitrogen in water (p<0.01). Pollution control and input control play a crucial role in reducing GHG emissions, (4) DOM in urban rivers is mainly derived from autochthonous sources, which are protein-like substances related to the metabolism of phytoplankton. GHG emission flux is negatively correlated with autochthonous parameters, indicating that the less interference by human activities, the less GHG emission.</p>