While monitoring the August release of millions of gallons of stormwater from the Piney Point phosphate plant into Tampa Bay, researchers discovered portions of dying seagrasses and concerning amounts of algae. The most affected areas were Middle to Lower Tampa Bay.
Between August 13 and 25, Piney Point discharged 4.5 million gallons of stormwater near Port Manatee, but Maya Burke with Tampa Bay Estuary Program said water quality results show not much of an immediate impact from those added nutrients, which can feed algae blooms.
"Conditions looked within normal ranges of what we expect to see in the summertime months,” she said. “Usually, water quality isn't at its best in the summertime because we see so much rainfall in our summer months. And that's really providing a lot of the nutrient load that the bay needs to assimilate over the course of a year during that time."
However, scientists did take note of a marine cyanobacteria, previously known as Lyngbya, now labeled Dapis pleousa. It’s commonly referred to as “snot grass” or “gumbo.”
“We observed it in multiple different ways,” Burke said.
When Dapis pleousa is in its early stages, it forms a pinkish white bacterial mat on the sediment.
“It starts to form all these bubbles, so it sort of looks like Sprite has been poured on the bottom of the bay,” she said. “And as it begins to decompose, it sort of lifts off and wraps itself around all of the seagrass blades or anything any other kind of structure that's on the bay bottom.”
This can prevent seagrasses from growing because when they’re covered by algae, they’re unable to process light in order to thrive.
Burke said these conditions point to more long-term effects associated with nutrient loading to the bay.
"It was particularly notable [at] the sites near Cockroach Bay and Port Manatee. There, the seagrass beds, which in years past have been quite vibrant, were looking very poor. You could sort of see things rotting at the base and rolling around on the bay bottom so we were watching loss actively occur."
According to Burke, there’s no clear evidence that puts the blame on last year's historic discharge from Piney Point where over 200 million gallons of nutrient-rich wastewater were released near Port Manatee. Although, she said it’s likely to be exacerbating the seagrass losses.
She said the 2021 wastewater contained 230 milligrams of nitrogen per liter.
“To put that in context ... raw wastewater is usually around 23 milligrams per liter total nitrogen, so 230 milligrams per liter is incredible,” said Burke.
Circling back to the August stormwater release, each liter only contained somewhere between three to four milligrams of nitrogen.
Burke pointed out that while last year’s wastewater event was "incredible," this is an urbanized estuary, where "we all have a nutrient footprint."
She said she’s also concerned about Old Tampa Bay, which is experiencing two other kinds of algae. One of them is a common summertime micro algae called Pyrodinium bahamense, and the other is a macro algae called Caulerpa prolifera that actually looks like seagrass, which Burke said has been a factor in the manatee mortalities on the east coast in Indian River Lagoon.
“Manatees rely on things like seagrass for food, and when they eat something like Caulerpa instead, it's not as dense in calories, and so it helps to contribute to some of the starvation that they are experiencing elsewhere. Fortunately, we're not seeing that in our area right now, but it is something that is an early warning sign that resource managers are concerned about,” Burke said.
The scientists also have some questions about how the negative storm surge from Hurricane Ian could affect Tampa Bay's water and seagrass quality. Instead of pushing water into the bay, the storm sucked it out, leaving seagrass beds and mudflats exposed. Burke said it may have been a positive event by replacing the nutrient-rich bay with cleaner water, or it could have stressed the seagrasses leading to more losses. But there are more questions than answers, she said.
An official seagrass study from partners of the Tampa Bay Estuary Program is expected to conclude by the end of October.
On Friday morning, Piney Point began conducting another stormwater release into Tampa Bay.
