Diffusion fluxes of greenhouse gases at the sediment-water and water-air interfaces in a shallow macrophyte-dominated lake

Lakes, acting as sinks/sources of greenhouse gases (GHGs), play a crucial role in regulating global warming. Aquatic plants, a vital component of lacustrine ecosystems, influence the production and emission of GHGs. This influence might further increase the spatiotemporal heterogeneity of GHG emissions, particularly in shallow macrophyte-dominated lakes. In this study, a seasonal sampling of water, sediment, and gas was carried out in four sites, namely the Phragmites communis zone (Phrag), unvegetated zone (unveg), Potamogeton crispus zone (Potam) and mixed vegetation zone (mixed) in Lake Dongping, a shallow macrophyte-dominated lake located in the north of China. The physicochemical properties of water and sediment were analyzed, and fluxes of GHGs at the sediment-water interface (SWI) and water-air interface (WAI) were calculated. The results showed that the nitrous oxide (N₂O) fluxes at the WAI were high in winter, while the N₂O fluxes at the SWI were low in autumn and in the mixed. Methane (CH₄) and carbon dioxide (CO₂) fluxes at both the SWI and WAI were high in summer and in the Phrag, but low in winter and in the unveg. Water temperature was a primary and common determinant for the GHG fluxes at the WAI. Besides, NO₃^- concentrations also affected N₂O fluxes, and water pH affected CO₂ fluxes. Sediment pH and water pH were the key factors for CH₄ and CO₂ at the SWI, respectively. The results suggested the necessity to take seasonal variations and impact of aquatic plants into consideration to improve the estimation of GHG emission in macrophyte-dominated lakes.