Algal blooms return to Florida Bay
November 8, 2017
FLORIDA BAY — Algal blooms, which kill fish, suffocate seagrass and make life harder for those who rely on the Everglades estuary for their livelihoods, have surfaced again this year.
Bob Johnson, director of the National Park Service’s South Florida Natural Resources Center, says that large areas of Florida Bay are beset by blooms, which is not surprising after Hurricane Irma and more recent weather events churned up the nutrient-rich bay bottom, one of many likely contributors to the problem.
Pete Frezza, a local fishing guide and research manager for Audubon’s Everglades Science Center, says he’s noticed algal blooms in different areas of the bay.
“It’s gotten pretty bad,” Frezza said. “There is very little water in the bay now that doesn’t have some type of bloom. The only place that looks fine is the areas where there are strong Atlantic tides near the Keys.”
Frezza points to dead seagrass as one possible culprit, as it releases nutrients that feed algae when it decays. About 22,000 acres of seagrass meadows died after a drought in 2015, which likely helped feed algal blooms that appeared shortly thereafter.
“We had a massive amount of floating seagrass come into Florida Bay from the Gulf of Mexico during Irma,” Frezza said. “A lot of that grass most likely sunk into the bay, and when that plant matter breaks down, that’s another release of nutrients.”
Another potential source of nutrients is freshwater flow from the Everglades via central Florida, namely Lake Okeechobee. Frezza says that while Florida Bay relies on freshwater flow, much of what comes into the bay now is nutrient-laden and carries pollutants.
“More freshwater flow is something we want, but this water is moving through agricultural areas (and) urbanized areas where there are high concentrations of nutrients,” Frezza said. “We have a lot of water moving into the bay with elevated nitrogen and phosphorus levels, which can spur the growth of these blooms.”
A reservoir to be built south of Lake Okeechobee, which would store and filter water before it flows south, is in the works, and Frezza says the reservoir could be a significant factor in preventing future algal blooms.
“I imagine (the reservoir) would have helped the situation, absolutely,” Frezza said. “That reservoir will allow for a timely distribution of water, as well. That certainly could help.”
Steve Davis, an Everglades Foundation ecologist, is less sure that runoff is contributing to the algal bloom this year. He points to dead seagrass and an intense rainy season as likely factors in the most recent algae threat.
“It’s not any upland source of pollutants,” Davis said. “It’s not freshwater inflow that’s a bad thing, it’s just that we’ve got all this dead grass out there. Once the (nutrients) are released into the water, algae is much faster growing and more adept at taking up nutrients than seagrass, which has to grow roots and become stable and needs lots of light.”
Drought, which killed off so much seagrass in 2015, is not an issue this year, as rain has reduced salinity levels in Florida Bay significantly, according to Davis. Though the threat of drought killing off seagrass is not currently an issue, past die-offs still potentially haunt the bay when it comes to the formation of algae.
Another factor is that while many believe that Irma actually flushed out the bay, it also blew seagrass and other nutrient-rich plant material into it, which has created conditions which can allow algae to flourish.
“We saw this type of phenomenon with Wilma and in previous storms. Lots of grass and mangrove leaves get moved around and deposited,” Davis said. “We can’t discount the contribution of that (seagrass die-off) to what we’re seeing today in terms of having a compromised Florida Bay.”
National Park Service testing of chlorophyll-A levels, which indicate the presence of algae and cyanobacteria, are sky-high in some parts of Florida Bay, according to Johnson.
“Our last measurement post-Irma (indicates) that we have very high levels of chlorophyll-A in the water column,” Johnson said. “The (Florida Department of Environmental Protection) standard for central Florida Bay is about 2.2 micrograms per liter. We’re up to about 30 to 40 in that part of the bay.”
Other areas of the bay measure at as much as 200 micrograms per liter, according to Johnson, meaning that it’s all but certain that a major algal bloom event is not only happening now, but is likely to persist for some time.
“Some of this is expected, but the problem is that it’s happening right after the prior seagrass die-off and algal bloom. That’s why it’s likely going to persist longer than we’d normally see,” Johnson said, adding that the current bloom could last “for six months or so.”
Davis says it’s tough to pin down one factor that may be causing the current bloom among sediment disruption, the release of nutrients from dead seagrass and other foliage, and other possible contributors.
“If the seagrass beds were healthy and intact, it may not have been so bad,” Davis said. “I can’t say that without a controlled experiment, and when you’re working with Mother Nature it’s hard to have a controlled experiment of this scale.”
Paul Tejera, a local fishing guide who recently ran a backcountry tournament to benefit guides, told the Free Press that the fishing in that tournament and in his experience so far this year has been “very good,” indicating that the nascent bloom may not yet be affecting fish and other wildlife populations.
That’s welcome news for the many industries that rely on a healthy fish stock to survive, though if an algal bloom is indeed taking hold in Florida Bay, those conditions could rapidly change.
As scientists and others continue to monitor the situation, Frezza says those who haven’t ventured out into Florida Bay much past the coastline may not have noticed much change yet, though he says some in Key Largo are already complaining about the quality of the water.
“It’s all in their backyards in Key Largo, but it’s not as bad there as it is in the central bay,” Frezza said. “I don’t think people realize how much worse it looks.”
For him and everyone else who is concerned with the health of Florida Bay, another widespread bloom would hardly be a surprise, as Frezza says they happen now with disturbing regularity.
“It’s large in extent. This is not unprecedented, though,” Frezza said. “To have a (bloom) this big is a little odd, but algal blooms are common now.”