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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L11601, doi:10.1029/2005GL025449, 2006

Hurricanes, submarine groundwater discharge, and Florida's red tides

Chuanmin Hu

College of Marine Science, University of South Florida, St. Petersburg, Florida, USA


Frank E. Muller-Karger

College of Marine Science, University of South Florida, St. Petersburg, Florida, USA


Peter W. Swarzenski

U.S. Geological Survey, St. Petersburg, Florida, USA


Abstract

A Karenia brevis Harmful Algal Bloom affected coastal waters shallower than 50 m off west-central Florida from January 2005 through January 2006, showing a sustained anomaly of ∼1 mg chlorophyll m−3 over an area of up to 67,500 km2. Red tides occur in the same area (approximately 26–29°N, 82–83°W) almost every year, but the intense 2005 bloom led to a widespread hypoxic zone (dissolved oxygen <2 mg L−1) that caused mortalities of benthic communities, fish, turtles, birds, and marine mammals. Runoff alone provided insufficient nitrogen to support this bloom. We pose the hypothesis that submarine groundwater discharge (SGD) provides the missing nutrients, and indeed can trigger and support the recurrent red tides off west-central Florida. SGD inputs of dissolved inorganic nitrogen (DIN) in Tampa Bay alone are ∼35% of that discharged by all central Florida rivers draining west combined. We propose that the unusual number of hurricanes in 2004 resulted in high runoff, and in higher than normal SGD emerging along the west Florida coast throughout 2005, initiating and fueling the persistent HAB. This mechanism may also explain recurrent red tides in other coastal regions of the Gulf of Mexico.

Received 9 December 2005; accepted 24 April 2006; published 1 June 2006.

Index Terms: 4855 Oceanography: Biological and Chemical: Phytoplankton; 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling (0470, 1050); 1635 Global Change: Oceans (1616, 3305, 4215, 4513).

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Citation: Hu, C., F. E. Muller-Karger, and P. W. Swarzenski (2006), Hurricanes, submarine groundwater discharge, and Florida's red tides, Geophys. Res. Lett., 33, L11601, doi:10.1029/2005GL025449.