Hustle and flow: USF studies how water moves in Tampa Bay
ABOARD THE R/V W.T. HOGARTH — The research vessel motored off downtown St. Petersburg, its back deck loaded with squat, concrete trapezoids.
Painted blue and labeled “USF” and “FDEP,” the blocks were essentially anchors, 2,500 pounds apiece. Tucked within each was a small, $18,000 sensor.
Bob Weisberg, a physical oceanographer at the University of South Florida, stood on deck with a gaggle of students and colleagues. They donned orange vests and hard hats, and they stepped carefully around the trapezoids.
Over the 78-foot R/V W.T. Hogarth’s gunwales, the bay slipped calmly by, reflecting the morning sun on a warm Tuesday in May.
Soon the researchers would deliver the sensors to the bottom of the bay, where they will sit for months, measuring the velocity of water. The Florida Department of Environmental Protection is helping pay for the work.
Scientists need velocity data to better understand an aspect of the bay that Weisberg believes is underappreciated: the way it moves.
Many advocates and scientists worry about the nutrients that pollute the bay from sewage, fertilizer and other runoff. But Weisberg said people do not think as much about the currents and tides that push that contamination around.
“Where does this stuff go?” he asked rhetorically. “Everything else flows from the circulation.”
The estuary is more like a highway than a stagnant bathtub. Water moves constantly. Tides and winds push the sea, while freshwater dumps out of rivers such as the Hillsborough, colliding with the briny gulf.
The importance of circulation became clear last year as scientists struggled to track the impact of a 215-million gallon wastewater release from the old Piney Point fertilizer plant property. A model built years before by Weisberg and his students showed the pollution could have moved throughout Tampa Bay.
Where those contaminants ended up mattered. They may have helped feed the Red Tide bloom that plagued the region through last summer.
Weisberg was confident in the model before Piney Point, but his team has always wanted more data to test it. Before, they primarily verified the model’s accuracy against observations from a monitoring station below the Sunshine Skyway bridge.
Piney Point, though an environmental crisis for the region, proved to be a boost for science — spotlighting the importance of consistent research and offering a unique opportunity to study the consequences of wastewater discharges.
After the disaster, the USF researchers successfully pitched the Department of Environmental Protection on installing four current monitors in shallower areas outside the bay’s main shipping channel. The team will also deploy sensors to track water quality metrics like salinity and pH level.
About $395,000 will help cover the first year of buying and deploying equipment, according to Jay Law, a physical oceanographer and head of operations in Weisberg’s lab.
“Piney Point is the reason for this funding,” Weisberg said bluntly. The research cruise was his last before retirement.
Thomas Frazer, dean of USF’s College of Marine Science, said scientists are “always responding to some environmental disturbance of some kind.” Piney Point, he said, showed where they could “shore up” their data collection and monitoring.
The Hogarth chugged for hours between four Coast Guard towers — raised platforms topped by metal spires — where the researchers chose to deploy the monitors.
The crew used a winch to heft the concrete trapezoids off the deck and over the water. They lowered the blocks below the surface slowly and released each from the winch.
A trio of divers jumped off the deck, swimming below to unhook a harness from the concrete and to measure the depth of each sensor — between 11 and 23 feet.
Once deployed, the technology should work without much maintenance. Every hour, Law said, the monitors send a series of acoustic pings, one per second for six minutes. Those pings travel up the water column before reflecting off pieces of sediment and plankton drifting in the current. The pings return at different pitches — a phenomenon known as the Doppler effect.
“It’s just like when you hear a train go by,” Law explained. “The pitch changes.”
The monitors use this pitch variation to calculate the velocity of sea currents. After about four months, Law said, the researchers will retrieve memory cards full of data. They will compare those observations to their model, refining it as needed.
Weisberg used the model before Piney Point to study storm surge and forecast the movement of Red Tide — naturally occurring, toxic algae that can feed upon nutrients in human pollution. He once helped police figure out whether a body that washed ashore could have drifted from a nearby marina.
The additional data should boost confidence in the model, he said, and provide more definitive answers about how water moves in different parts of the bay. But he expects surprising questions to surface, too.
A lifetime in science, he said, has taught him a basic principle: The more you learn, the more you realize how much you still don’t know.
Check out the model
To see the USF Ocean Circulation Lab’s model, including a Red Tide forecast, visit ocgweb.marine.usf.edu
