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首页> 外文期刊>Estuarine Coastal and Shelf Science >The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary
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The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

机译：旧金山河口无机氮形态对初级生产的影响

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摘要

We describe the results of a series of 96-h enclosure experiments conducted using water from stations in the northern San Francisco Estuary (SFE) along a gradient in ammonium (NH_4) and nitrate (NO_3) concentrations. Using dual-labeled ~(13)C/~(15)N tracers, we followed the timing and sequence of primary (carbon, C) production and phytoplankton nitrogen (N) use during experimental phytoplankton blooms. Our results show that diatoms consistently drive the phytoplankton blooms in the enclosures. By tracing both C and N uptake we provide clear evidence that high rates of C uptake are linked to phytoplankton NO_3, and not NH_4, use. Results from kinetics experiments demonstrated higher specific uptake rates (V_(MAX)) for NO_3 compared to NH_4 in the SFE. Finally, dissolved inorganic carbon and nutrient drawdown ratios in the enclosures from the chronically high NH_4 regions of the SFE were substantially lower than predicted from the Redfield ratio, suggesting suppressed C uptake, in relation to other elemental uptake. Our conceptual model of the DIN interactions that lead to higher primary production and phytoplankton blooms in the SFE suggests that higher rates of primary production that accompany phytoplankton NO3 uptake are sufficient to outpace phytoplankton losses, leading to blooms, compared to the lower rates associated with NH_4 uptake (only 20% of that based upon NO_3). Historical changes in wastewater practices have increased the proportion of NH4 to the DIN pool in the SFE leading to reduced access to NO_3 by phytoplankton. This may help to explain some of the reduced primary production and phytoplankton biomass observed there since the 1970s.
机译：我们描述了一系列使用沿旧金山河口（SFE）站的水沿铵（NH_4）和硝酸盐（NO_3）浓度梯​​度进行的96小时围合实验的结果。使用双标记的〜（13）C /〜（15）N示踪剂，我们跟踪了实验性浮游植物开花期间主要（碳，碳）生产和浮游植物氮（N）使用的时间和顺序。我们的结果表明，硅藻始终如一地驱动着围堰中的浮游植物开花。通过追踪C和N的吸收，我们提供了明确的证据，表明高C吸收率与浮游植物NO_3而非NH_4的使用有关。动力学实验的结果表明，与SFE中的NH_4相比，NO_3的特定比吸收率（V_（MAX））高。最后，来自SFE慢性高NH_4区域的围栏中溶解的无机碳和养分吸收比大大低于Redfield的预测值，表明相对于其他元素吸收而言，C吸收受到抑制。我们在SFE中导致更高的初级生产力和浮游植物大量繁殖的DIN相互作用的概念模型表明，与NH_4相关的较低速率相比，伴随着浮游植物NO3吸收的较高初级生产力足以抵消浮游植物的损失，从而导致绽放。吸收量（仅基于NO_3的吸收量的20％）。废水处理方式的历史性变化增加了SFE中NH4在DIN池中的比例，导致浮游植物对NO_3的获取减少。这可能有助于解释自1970年代以来那里观测到的初级生产和浮游生物量减少的情况。

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