Effects of macrophytes on gaseous nitrogen emissions and nitrogen removal from sediments in a shallow eutrophic lake

Anthropogenic nutrient enrichment in lakes and subsequent increases of greenhouse gas emission are major global problems affecting the ecosystem function of lakes. In this study, laboratory experiments were carried out to investigate the effects of diel dynamics of dissolved oxygen (DO) cycles, induced by macrophyte photosynthesis and respiration, on nitrous gaseous emissions and nitrogen removal from sediments of a macrophytes-dominated eutrophic lake. We found that macrophytes significantly enhanced the diurnal fluctuation of DO in water and increased sediment oxygen levels. The fluxes of N₂O and N₂ showed substantial diurnal variation with the fluctuation of DO. Moreover, macrophytes-dominated sediments were characterized by significantly higher potential nitrification and denitrification compared to non-vegetated control sediments. The concentrations of TN and NH₄ ⁺-N in macrophytes sediments were significantly lower than those in controls. Based on the evaluation of N transformation pathways, we found that nitrogen uptake by macrophytes and N₂ emissions were the dominant pathways for N removal from macrophytes-dominated sediments. The results provide scientific basis for the ecological restoration of eutrophic lakes.