Abstract. Coastal lagoons are important sites for nitrogen (N) removal via sediment burial and denitrification. Blooms of heterocystous cyanobacteria may diminish N retention as dinitrogen (N₂) fixation offsets atmospheric losses via denitrification. We measured N₂ fixation in the Curonian Lagoon, Europe's largest coastal lagoon, to better understand the factors controlling N₂ fixation in the context of seasonal changes in phytoplankton community composition and external N inputs. Temporal patterns in N₂ fixation were primarily determined by the abundance of heterocystous cyanobacteria, mainly Aphanizomenon flosaquae, which became abundant after the decline in riverine nitrate inputs associated with snowmelt. Heterocystous cyanobacteria dominated the summer phytoplankton community resulting in strong correlations between chlorophyll-a (Chl-a) and N₂ fixation. We used regression models relating N₂ fixation to Chl-a, along with remote sensing-based estimates of Chl-a to derive lagoon-scale estimates of N₂ fixation. N₂ fixation by pelagic cyanobacteria was found to be a significant component of the lagoon's N budget based on comparisons to previously derived fluxes associated with riverine inputs, sediment-water exchange and losses via denitrification. To our knowledge, this is the first study to derive ecosystem-scale estimates of N₂ fixation by combining remote sensing of Chl-a with empirical models relating N₂ fixation rates to Chl-a.

中文翻译：

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从速率测量和遥感获得的沿海水域N ₂固着的时空模式

摘要。沿海泻湖是通过沉积物埋藏和反硝化去除氮（N）的重要场所。异性蓝藻的繁殖可能会减少N的保留，因为二氮（N ₂）固定可通过反硝化作用抵消大气损失。我们测量了欧洲最大的沿海泻湖库尔斯沙嘴泻湖中的N ₂固定，以更好地了解在浮游植物群落组成和外部氮输入的季节性变化的背景下控制N ₂固定的因素。N ₂固定的时空模式主要由异性蓝藻细菌的丰富程度决定，主要是Aphanizomenon flosaquae在融雪相关的河流硝酸盐输入减少之后变得丰富。夏季浮游植物群落中杂藻蓝藻占主导地位，导致叶绿素-a（Chl-a）与N ₂固定之间有很强的相关性。我们使用了将N ₂固定与Chl-a相关的回归模型，以及基于遥感的Chl-a估计，以得出N ₂固定的泻湖规模估计。根据与河流输入，沉积物-水交换和反硝化损失有关的先前通量的比较，发现浮游蓝藻对N _2的固定是泻湖氮预算的重要组成部分。据我们所知，这是第一个获得生态系统规模的N ₂估计的研究通过将Chl-a的遥感与将N ₂固定率关联到Chl-a的经验模型相结合来进行固定。