The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

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• 作者：Alexander E. Parker ; ^{aeparker@sfsu.edu} ; Victoria E. Hogue ^{vhogue6417@gmail.com} ; Frances P. Wilkerson ^{fwilkers@sfsu.edu} ; Richard C. Dugdale ^{rdugdale@sfsu.edu}
• 关键词：San Francisco Estuary ; primary production ; phytoplankton ; carbon ; ammonium ; nitrate
• 刊名：Estuarine ; Coastal and Shelf Science
• 出版年：2012
• 期刊代码：79_02727714
• 类别：env
• 出版时间：1 June, 2012
• 卷：104-105
• 期：Complete
• 页码：91-101
• 文件大小：608 K

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 (NH₄) and nitrate (NO₃) concentrations. Using dual-labeled ¹³C/¹⁵N 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 NO₃, and not NH₄, use. Results from kinetics experiments demonstrated higher specific uptake rates (V_MAx) for NO₃ compared to NH₄ in the SFE. Finally, dissolved inorganic carbon and nutrient drawdown ratios in the enclosures from the chronically high NH₄ 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 NH₄ uptake (only 20%of that based upon NO₃). Historical changes in wastewater practices have increased the proportion of NH₄ to the DIN pool in the SFE leading to reduced access to NO₃ by phytoplankton. This may help to explain some of the reduced primary production and phytoplankton biomass observed there since the 1970s.