Department of Marine Sciences, University of Georgia , Athens, Georgia 30602-3636, United States.
Environ Sci Technol. 2017 Mar 21;51(6):3157-3164. doi: 10.1021/acs.est.6b03483. Epub 2017 Mar 3.
Nitrification is a two-step process linking the reduced and oxidized sides of the nitrogen cycle. These steps are typically tightly coupled with the primary intermediate, nitrite, rarely accumulating in coastal environments. Nitrite concentrations can exceed 10 μM during summer in estuarine waters adjacent to Sapelo Island, Georgia, U.S.A. Similar peaks at other locations have been attributed to decoupling of the two steps of nitrification by hypoxia; however, the waters around Sapelo Island are aerobic and well-mixed. Experiments examining the response to temperature shifts of a nitrifying assemblage composed of the same organisms found in the field indicate that ammonia- and nitrite-oxidation become uncoupled between 20 and 30 °C, leading to nitrite accumulation. This suggests that nitrite peaks in coastal waters might be explained by differences in the responses of ammonia- and nitrite-oxidizers to increased summer temperatures. Analysis of field data from 270 stations in 29 temperate and subtropical estuaries and lagoons show transient accumulation of nitrite driven primarily by water temperatures, rather than by hypoxia. Increased climate variability and warming coastal waters may therefore increase the frequency of these nitrite peaks, with potential ecosystem consequences that include increased NO production, NO toxicity, and shifts in phytoplankton community composition.
硝化作用是氮循环中连接还原侧和氧化侧的两步过程。这些步骤通常与主要中间体亚硝酸盐紧密耦合，很少在沿海环境中积累。在美国佐治亚州萨佩洛岛附近的河口水中，夏季亚硝酸盐浓度可超过 10 μM。其他地方也出现了类似的峰值，这归因于硝化作用的两个步骤因缺氧而解耦；然而，萨佩洛岛周围的水域是好氧且充分混合的。对由与野外相同的生物体组成的硝化组合体对温度变化的响应进行的实验表明，在 20 至 30°C 之间，氨氧化和亚硝酸盐氧化解耦，导致亚硝酸盐积累。这表明，沿海水域中亚硝酸盐峰值可能是由于氨氧化菌和亚硝酸盐氧化菌对夏季高温的反应不同所致。对 29 个温带和亚热带河口和泻湖的 270 个站点的现场数据分析表明，亚硝酸盐的短暂积累主要是由水温驱动的，而不是由缺氧引起的。因此，气候变化的增加和变暖的沿海水域可能会增加这些亚硝酸盐峰值的频率，从而对生态系统产生潜在的后果，包括增加 NO 的产生、NO 的毒性以及浮游植物群落组成的变化。
