Seasonal Growth Stimulation of Sub-Temperate Estuarine Phytoplankton to Nitrogen and Phosphorus: An Outdoor Microcosm Experiment

• Published in: Estuaries 1998-03, Vol.21 (1), p.145-159
• Main Authors: Flemer, David A., Livingston, Robert J., McGlynn, Sean E.
• Format: Article
• Language: English
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biomass; Biomass production; Brackish water ecosystems; Estuaries; Experimental design; Fundamental and applied biological sciences. Psychology; Limnology; Marine ecology; Microcosms; Nitrogen; Nutrient concentrations; Nutrients; Phytoplankton; Plankton; Surface water; Synecology
• ISSN: 0160-8347; 1559-2723; 1559-2758; 1559-2731
• DOI: 10.2307/1352553

A study of nutrient limitation of phytoplankton biomass production with emphasis on nitrate-nitrogen ( NO3-)and ortho-phosphate-phosphorus ( PO43-)was conducted in Perdido Bay, Alabama-Florida. The experimental design employed 18-l outdoor microcosms operated in a static renewal mode. Phytoplankton growth responses (i. e., growth stimulation) measured as chlorophyll a (chl a) fell into three principal categories: primary P stimulation occurred mostly during the cooler months at the upper bay (tidal brackish) and mid bay (lower mesohaline) stations; a total of 12 out of 36 experiments; primary N stimulation occurred mostly during the warmer months primarily at the mid-bay station and infrequently at the upper and lower bay stations (upper mesohaline); a total of 7 out of 36 experiments; and N+P costimulation occurred primarily during the warmer months in the upper bay and mid bay and during both warmer and cooler months in the lower bay; a total of 17 out of 36 experiments. Primary P stimulation was generally associated with high ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) (ratio range: 18 to 288). Conversely, primary N stimulation was associated with decreasing DIN:DIP ratios (range 8-46). Redfield ratios of particulate organic N (PON) to particulate organic P (POP) often indicated N limitation (i. e., values often less than 10). PON:chl a ratios often indicated N sufficiency, but three occasions were noted where PON:POP and PON:chl a ratios were not congruent. It is difficult to reconcile the inorganic and organic N and P ratios with the relatively low DIP and DIN concentrations. The phytoplankton assemblage appeared not to be strongly nutrient-limited but, given a nutrient increase, responded differentially to N and P, both seasonally and along the longitudinal salinity gradient. Grazing pressure in concert with nutrient limitation was advanced as an hypothesis to explain N+P co-limitation.