As Hurricane Ian zeroed in on the Florida peninsula, a receding Tampa Bay was a sure sign there was tropical trouble on the way.
It reminded a lot of locals of Hurricane Irma, which also had drained the bay five years earlier. Ian’s “reverse storm surge” unveiled similar scenes: An exposed seafloor. Boats sitting in marinas empty of water. Curious bystanders ignoring meteorologist warnings and taking a closer look at the strange phenomenon.
But with water back in the bay and the storm long gone, researchers now wonder: Did Ian’s reverse storm surge, which lowered water levels by more than 7 feet in some areas, change the amount of nutrient pollution in Tampa Bay? And, if so, what does that mean for the bay’s health?
“When it comes to nutrient management in the bay, hurricanes are one of the multiple, interacting stressors that can influence bay health,” Elise Morrison, an assistant professor at the University of Florida’s Department of Environmental Engineering Sciences, wrote in an email.
Morrison and a team of UF researchers have sampled nutrients, including algal bloom-fueling nitrogen and phytoplankton, biweekly in Tampa Bay since April 2021 — just as the Piney Point wastewater disaster was beginning to unfold. For Ian, they collected water samples before and after the storm at four sites throughout the bay: the Piney Point Creek, Bishop Harbor, Joe Bay and St. Joseph Sound.
While the UF analysis wraps up, researchers at Texas A&M-Corpus Christi who studied a similar reverse storm surge in Corpus Christi Bay during Hurricane Harvey in 2017 say nutrient pollution “changed significantly” in the days after Harvey’s landfall.
Once the water level dropped by 3 feet — what researchers called the “hydrologic pull” — there were increases of ammonium and then a large pulse of nitrate and saltier water about two weeks after landfall, according to a study published last month in Frontiers in Marine Science, a peer-reviewed journal highlighting human interactions with oceans.
“There is a connection between the land and the sea,” said Dorina Murgulet, a professor of hydrogeology at the university and an author of the study. “When sea level drops abruptly, you have a strong pull on groundwater going toward the sea. It carries the nutrients into the bay at a faster rate than normal.”
Generally, whether reverse storm surge is a silver lining or a drawback for estuary health depends on what each estuary needs and doesn’t need.
“It could be good, because it might be supplying nitrogen in a nitrogen-depleted estuary. But it could also be bad, and bring a pulse of new nutrients that could trigger algae blooms,” Murgulet said in an interview.
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A preliminary report indicates that Hurricane Ian sucked more water out of Tampa Bay than Irma did in 2017, which was the last time a major hurricane sparked the eerie phenomenon.
At its most extreme, water in Tampa Bay receded more than 7 feet, 1 inch below sea level, according to the National Weather Service’s post-hurricane report. It happened at the mouth of Hillsborough Bay just after 7:30 p.m. on Sept. 28.
That’s roughly a foot more than during Hurricane Irma, which drained the bay a maximum 6 feet, 1 inch below sea level at the entrance of McKay Bay in 2017, according to Tyler Fleming, a meteorologist at the National Weather Service in Tampa Bay.
“The tides don’t normally go anywhere near that far negative in the bay,” Fleming said. Low tide typically lowers the bay’s water level 2 feet or less.
The unique shape of Tampa Bay, paired with Ian’s location, created what Fleming refers to as a “funnel effect.” As the storm approached the peninsula south of the bay area, a counterclockwise wind started to coax water out. With nowhere to go but out of the mouth of the bay, the receding water effect is amplified, Fleming said.
Usually, it takes between one and three months for water quality impacts to become more clear in the estuary after events like Hurricane Ian, according to Ed Sherwood, executive director of the Tampa Bay Estuary Program.
“The water quality implications from both the negative surge and the subsequent large inflows from Ian’s rains aren’t likely to immediately manifest in the Bay,” Sherwood wrote in an email. “We should learn more about water quality benefits and impacts from the storm’s passage over the next several months in Tampa Bay proper.”