Red Tide theory suggests storms fed costly bloom

ST. PETERSBURG — Here’s another reason to curse hurricanes: They may have helped fuel the Red Tide that plagued Florida’s west coast last year.

The record rainfall from the four hurricanes that raked Florida in 2004 swelled the aquifer, potentially sending high amounts of nutrients into coastal waters through underground springs, according to a recently published theory from researchers at the University of South Florida and the United States Geological Survey.

Red Tide thrives on those nutrients, which include nitrogen and phosphorus.

Frank Muller-Karger, an oceanography professor at USF’s College of Marine Sciences, warned that more research needs to be done to confirm the theory. Still, Muller-Karger thinks the nutrients pumping out of the underwater springs play a main role.

«I’m not sure if it contributes to the cause of Red Tide,» he said. «But I’m pretty convinced they contribute to maintaining the Red Tide.»

Red Tide, a naturally occurring algae that periodically affects the Gulf Coast, kills fish and other marine life and can cause itchy throats, watery eyes and respiratory problems in humans. Exactly what triggers Red Tide outbreaks remains a mystery.

Muller-Karger and his research colleagues focused on Florida’s underwater springs, or discharges, that pump millions of gallons of groundwater directly into the ocean.

Rivers, the researchers found, provided barely enough phosphorus and far too little nitrogen to sustain the 2004-2005 Red Tide bloom, which caused millions of dollars in losses to the fishing, recreation and tourist industries. Rivers are an important nutrient source, but could not account for such a long-lived and widespread outbreak, they wrote in the study.

Also, there was a lag of a few months between the heavy rains from the hurricanes and the appearance of the Red Tide blooms.

«Rivers would get the nutrients to the coast quite quickly,» Muller-Karger said. «So why the lag?»

Muller-Karger and his colleagues thought the underwater springs, fed by record hurricane rainfalls, could be the culprit.

When rain falls, some of it seeps through Florida’s porous and phosphorus-rich ground and into the aquifer. As it filters through, it picks up the natural phosphorus and nitrogen in higher concentrations than runoff into rivers.

For instance, the Tampa Bay underwater spring alone provides nearly 35 percent as much nitrogen as all north and central Florida rivers draining toward the Gulf of Mexico combined, according to the study published in the June volume of the Geophysical Research Letters.

The water that filters into the aquifer may be further enriched by septic tank effluents and man-made fertilizers.

Muller-Karger and his co-authors, USF assistant professor Chuanmin Hu and USGS researcher Peter Swarzenski, encouraged the use of more funding to pinpoint the locations of the underwater springs off west central Florida so that their volume and nutrient contents can be thoroughly measured.

«It’s a connection that hasn’t received much attention,» Muller-Karger said. «Such a major source of nutrients should receive more consideration.»

Graham Brink can be reached at

[Last modified June 21, 2006, 06:17:51] 

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