Alvarez, F. ., Texas A&M University at Galves, Galveston, USA, federico.alvarez3@gmail.com
DiMarco, S. F., Texas A&M University, College Station, USA, sdimarco@tamu.edu
Kurtz, J. C., Environmental Protection Agency-Gulf Ecology Division, Gulf Breeze, USA, kurtz.jan@epa.gov
Quigg, A. S., Texas A&M University at Galveston, Galveston, USA, quigga@tamug.edu

SHIPBOARD PHOSPHORUS, NITROGEN AND SILICA NUTRIENT LIMITATION ASSAYS USING IN-VIVO PHYTOPAM FLUORESCENCE IN THE NORTHERN GULF OF MEXICO.

Our objective was to investigate the importance of nutrient limitation of phytoplankton production in coastal waters of the Northern Gulf of Mexico. Resource limitation assays were performed on 8 cruises from the summer of 2005 to the summer of 2007 during NOAA funded Mechanisms Controlling Hypoxia program and EPA's Gulf Hypoxia Modeling Framework program. Twenty-four to forty-eight hour ship board experiments were conducted in which surface water was supplemented with additions of NO3, PO4, SiO4, NO3+PO4, NO3+PO4+SiO4 and with no added nutrients (control) at 50% irradiance. Changes in phytoplankton biomass and photosynthetic activity were calculated from in-vivo fluorescence measured with a PhytoPAM (Pulse Amplitude Modulated) fluorometer. Additional samples were taken to measure chlorophyll concentration using traditional methods. Our findings reveal that phytoplankton could be N-limited, P-limited and occasionally N and P co-limited, but never Si limited in the Northern Gulf of Mexico. The type of nutrient limitation was dependent on water quality (‘brown’, ‘green’ versus ‘blue’ waters) and season. The Mississippi River and Atchafalaya River plumes greatly influence water quality on a seasonal basis, and so, potentially phytoplankton production.

Poster presentation

Presentation is given by student: Yes
Session #:194
Date: 03-05-2008
Time: 17:30 - 19:30