Nitrogen (N) bioavailability affects phytoplankton growth and primary production in the aquatic environment. N bioavailability is partly determined by biological N cycling processes that either transform N species or remove fixed N. Reliable estimates of their kinetic parameters can help understand the distribution of N cycling processes. However, available estimates of kinetic parameters are often derived from microbial isolates and may not be representative of the natural environment. Observations are particularly lacking in estuarine and coastal waters. We conducted isotope tracer addition incubations to evaluate substrate affinities of nitrification, denitrification and anammox in the Chesapeake Bay water column. The half‐saturation constant for ammonia oxidation ranged from 0.38 to 0.75 μM ammonium, substantially higher than observed in the open oceans. Half‐saturation constants for denitrification—0.92–1.86 μM nitrite or 1.15 μM nitrate—were within the lower end or less than those reported for other aquatic environments and for denitrifier isolates. Interestingly, water column denitrification potential was comparable to that of sedimentary denitrification, highlighting the contribution of the water column to N removal during anoxia. Mostly undetectable anammox rates prevented us from deriving the half‐saturation constants, suggesting a low affinity of anammox. Using these substrate kinetics, we were able to predict in situ N cycling rates and explain the vertical distribution of N nutrient concentrations. Our newly derived substrate kinetics parameters can be useful for improving model representation of N nutrient dynamics in estuarine and coastal waters, which is critical for assessing the ecosystem productivity and function.

中文翻译：

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确定特定位点的氮循环反应动力学可以准确模拟北美大河口的原位氮转化率


氮 (N) 生物利用率影响水生环境中浮游植物的生长和初级生产。氮生物利用率部分取决于生物氮循环过程，这些过程要么转化氮物种，要么去除固定氮。对其动力学参数的可靠估计可以帮助了解氮循环过程的分布。然而，可用的动力学参数估计通常来自微生物分离株，可能不能代表自然环境。河口和沿海水域的观测尤其缺乏。我们进行了同位素示踪剂添加孵育，以评估切萨皮克湾水柱中硝化、反硝化和厌氧氨氧化的底物亲和力。氨氧化的半饱和常数范围为 0.38 至 0.75 μM 铵，远高于在公海中观察到的值。反硝化作用的半饱和常数（0.92-1.86 μM 亚硝酸盐或 1.15 μM 硝酸盐）处于下限内或低于其他水生环境和反硝化菌分离物报道的值。有趣的是，水柱反硝化潜力与沉积反硝化潜力相当，突出了缺氧期间水柱对氮去除的贡献。大多数无法检测到的厌氧氨氧化率使我们无法推导出半饱和常数，这表明厌氧氨氧化的亲和力较低。利用这些底物动力学，我们能够预测原位氮循环速率并解释氮养分浓度的垂直分布。我们新推导的底物动力学参数可用于改善河口和沿海水域氮养分动态的模型表示，这对于评估生态系统生产力和功能至关重要。