In late 2004, a series of three tropical storms crossed the Florida peninsula. These storms increased the daily discharge of water onto the West Florida shelf to ~20 times the normal volume. Associated with this increased flux of water was a subsequent pulse of fertilizer containing the inorganic nitrogen nutrients nitrate, nitrite, and ammonium. Inorganic nitrogen nutrients are the limiting reactant for phytoplankton. During primary production, phytoplankton consume these nutrients, effectively removing them from the seawater and converting them to biomass. Large pulses of nutrients into water masses can cause phytoplankton blooms, which can lead to decreased oxygen, marine life mortality, and negative economic impacts. A red tide was initiated in January 2005 and persisted until January 2006. This is an unusually long-lived event for a toxic algal bloom. Just after the third hurricane, a research expedition mapped sea-surface nutrients using high sensitivity fluorometric methods and collected water samples from various depths which were analyzed on-shore via absorbance based methods. Normally the West Florida shelf chlorophyll concentration is ~1 mg chlorophyll per m-3. Satellite estimations during the red tide event indicate that the average chlorophyll concentration was 0.104 mg chlorophyll m-3 over an area of 67,500 km2 and a depth of 25 m. The average integrated flux of inorganic nutrients over the mapped area of ~3,600 km2 and a depth of ~21 m was found to be able to support 2.57 mg chlorophyll m-3. When this amount of chlorophyll is diluted into the volume of the satellite estimations, which is similar in size to West Virginia, the resultant chlorophyll concentration would be 0.118 mg chlorophyll m-3. This data indicates that runoff could be responsible for ~10% of the sustained red tide bloom.

Primary production is greener on the other side: Influence of hurricanes on the West Florida shelf

255th National Meeting (2018)

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