Spatiotemporal variations of dissolved nitrous oxide concentrations in small water bodies in a typical urban...

Waters in urban landscape are susceptible to nitrogen (N) pollution, potentially leading to supersaturation of dissolved nitrous oxide (N₂O) and making them a source of atmospheric N₂O. However, the spatiotemporal variations and driving factors of dissolved N₂O concentrations in these waters remain unclear. This study examined the spatiotemporal variations of dissolved N₂O in an interconnected river-lake system in a subtropical urban landscape. The annual mean dissolved N₂O concentration was 0.81 μg N L^-1, with a mean N₂O saturation of 304 %, indicating the system could act as a N₂O emitter. Under the influence of daily fluctuations in water temperature and DO, the diurnal variation of N₂O was most pronounced in autumn, with the smallest amplitude observed in winter. Seasonal mean concentrations of dissolved N₂O, N, phosphorus (P), chlorophyll-a (Chl-a) and dissolved oxygen (DO) peaked in winter and were lowest in summer. The central lake had significantly lower dissolved N₂O, N and P concentrations, but possessed higher water temperature, pH, concentrations of Chl-a and DO than its upstream and downstream rivers. Dissolved N₂O concentrations were positively correlated with concentrations of N and P, but negatively with pH, Chl-a, and DO. There was intensifying competition for N between the N₂O producers and algae, particularly in summer or in the central lake area. Therefore, the spatiotemporal variations of dissolved N₂O concentrations were primarily driven by the integrated effects of seasonal conditions, nutrient fluctuations and algal growth. This research can provide essential scientific guidance for developing the effective strategies to control N pollution and mitigate the risk of N₂O emissions from water bodies in urban landscape.