Going West: Nutrient Limitation of Primary Production in the Northern Gulf of Mexico and the Importance of the Atchafalaya River

To investigate controls on phytoplankton production along the Louisiana coastal shelf, we mapped salinity, nutrient concentrations (dissolved inorganic nitrogen (DIN) and phosphorus (Pi), silicate (Si)), nutrient ratios (DIN/Pi), alkaline phosphatase activity, chlorophyll and 14C primary productivit...

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Bibliographic Details
Published in:Aquatic geochemistry 2011-09, Vol.17 (4-5), p.519-544
Main Authors: Quigg, Antonietta, Sylvan, Jason B, Gustafson, Anne B, Fisher, Thomas R, Oliver, Rod L, Tozzi, Sasha, Ammerman, James W
Format: Article
Language:English
Subjects:
alkaline phosphatase
bioassays
Brackish
chlorophyll
dissolved inorganic nitrogen
Earth and Environmental Science
Earth Sciences
Freshwater
Geochemistry
glucose 6-phosphate
Hydrogeology
Hydrology/Water Resources
nitrogen
nutrient content
Nutrients
Original Paper
phosphorus
phytoplankton
Plankton
primary productivity
river deltas
Rivers
Salinity
silicates
silicon
spring
summer
Water Quality/Water Pollution
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Summary:To investigate controls on phytoplankton production along the Louisiana coastal shelf, we mapped salinity, nutrient concentrations (dissolved inorganic nitrogen (DIN) and phosphorus (Pi), silicate (Si)), nutrient ratios (DIN/Pi), alkaline phosphatase activity, chlorophyll and 14C primary productivity on fine spatial scales during cruises in March, May, and July 2004. Additionally, resource limitation assays were undertaken in a range of salinity and nutrient regimes reflecting gradients typical of this region. Of these, seven showed Pi limitation, five revealed nitrogen (N) limitation, three exhibited light (L) limitation, and one bioassay had no growth. We found the phytoplankton community to shift from being predominately N limited in the early spring (March) to P limited in late spring and summer (May and July). Light limitation of phytoplankton production was recorded in several bioassays in July in water samples collected after peak annual flows from both the Mississippi and Atchafalaya Rivers. We also found that organic phosphorus, as glucose-6-phosphate, alleviated P limitation while phosphono-acetic acid had no effect. Whereas DIN/Pi and DIN/Si ratios in the initial water samples were good predictors of the outcome of phytoplankton production in response to inorganic nutrients, alkaline phosphatase activity was the best predictor when examining organic forms of phosphorus. We measured the rates of integrated primary production (0.33–7.01 g C m−2 d−1), finding the highest rates within the Mississippi River delta and across Atchafalaya Bay at intermediate salinities. The lowest rates were measured along the outer shelf at the highest salinities and lowest nutrient concentrations (
ISSN:1380-6165
1573-1421
DOI:10.1007/s10498-011-9134-3