Marine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South FloridaMarine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida

RESEARCH - REGULATION OF CARBON FIXATION

Carbon and Nitrogen Dynamics in the Mississippi River Plume-A River in the Ocean

The Mississippi River is the sixth largest river in the world. Rapid depletion of nutrients occurs as salinity increases due to mixing along the plume.

Production is initially light limited near the coast and highest productivity occurs at salinities of ca. 25 . Near-shore production is driven by high nitrate. Nutrient limitation only occurs at salinities >30. Paradoxically, the greatest particulate organic carbon (POC) export in the plume seems to occur in areas of low productivity.

Little is known about the plume's contribution to primary productivity in the Gulf of Mexico. Our estimates of the contribution to the basin-wide productivity are based upon in-situ carbon fixation rates and satellite-derived estimates of the plume's area. Our estimates indicate that the plume accounts for 41% of all surface productivity (top 10 m) in the oligotrophic GOM. Additionally, the plume accounts for 13% of total water column productivity in the olig. GOM, while only covering 2.8% of surface area.

In situ fluorescence (upper panel) and salinity (lower panel) along the plume axis from the Mississippi Delta (left side of the figure) to the oligotrophic Gulf of Mexico (X axis is in km). The plume is < 10 m with salinities between 51-35 ppt.


Flow cytometry of a vertical profile shows the dominance of Synechococcus in the surface waters, with Prochlorococcus below; picoeucaryotes are largely concentrated at the subsurface chlorophyll maximum.


Surface water flow cytometry along the axis of the plume. Synechococcus typically dominated the surface waters within the plume, whereas Prochlorococcus was more abundant outside the plume. The picoeukaryotes (red line) were least abundant (note different scale).


Form IA and form ID rbcL mRNA and primary production along the plume axis. The greatest primary productivity occurred on the shelf, while form IA (Synechococcus-like) rbcL dominated the Rubisco gene mRNA.




Nitrate and ammonium concentrations along the plume axis. Nitrate concentrations exceeded ammonium at 5 of 6 plume stations (top panel). However, ammonium was the preferred nutrient for uptake (bottom panel), even though concentrations were vanishingly small. The high rates of ammonium uptake were the results of high rates of regeneration. Thus, even though initial concentrations of nutrients are high in the plume, tremendous rates of recycling manage to fuel production far into the Gulf of Mexico.

References

Wawrik, B. and J.H. Paul. 2004. Phytoplankton community structure and productivity along the axis of the Mississippi River Plume. Aquat. Microb. Ecol. 35:185-196.

Wawrik, B., John H. Paul, Deborah A. Bronk, David John, Mike Gray. 2004. High rates of ammonium recycling drive phytoplankton productivity in the offshore Mississippi River plume found in the oligotrophic Gulf of Mexico. Aquatic Microbial Ecology 35:175-184.

Wawrik, B., J.H. Paul, L. Campbell, D. Griffin, L. Houchin, A. Fuentes-Ortega, and F. Muller-Karger. 2003. Vertical Structure of the Phytoplankton Community associated with a Coastal Plume in the Gulf of Mexico. Mar. Ecol. Progr. Ser. 251:87-101.


  • To find out more about Rubisco genes in the environment, click here.

  • To learn more about carbon and nitrogen dynamics in the Mississippi, click here.

  • To learn more about the metagenomic analysis of oceanic picoplankton communities click here.

  • To learn more about the relationship between CO2 drawdown and phytoplankton gene expression click here.



Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida
Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida
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Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida Marine Microbiology Group - College of Marine Science - University of South Florida