In the 2010s, scientist Dina Liebowitz scooped up algae-coated tiles from the waters of the Ichetucknee River as visitors bobbed, splashed and floated along the surface in inner tubes.
When the revelers called out with questions, the ecologist condensed years of research into a three-second pitch: She was testing whether snails help keep springs clean.
For a long time, regulators have tried to fix algae problems in the region’s springs by focusing on nitrogen. Newly published results from the Ichetucknee experiments suggest successful restoration will need to consider snails, fish and other algae eaters, too.
“A broken arm and the flu at the same time”
Mushy, green spiderwebs of sink-your-foot-in algae have coated springs throughout north central Florida for decades.
In 2000, a state-mandated Springs Task Force reported nitrate could be the culprit.
Regulators ran with it.
Local, regional and state funders invested in replacing nitrate-leaching septic tanks with sewer systems, lowering fertilizer use on farms and making restoration plans for polluted springs.
“It made so much sense that pollution would be the problem, right?” Liebowitz said. “There was a beauty to thinking that there was a single way to fix this.”
Indeed, scientists agreed that lessening human impact on the region’s springs was a good thing. But research by UF Water Institute director Matt Cohen and other ecosystem scientists around 2010 found a spring’s nitrate levels alone weren’t a good predictor for how much algae it’d have.
“ Springs health is kind of like human health,” said Liebowitz, who completed her Ichetucknee work during her doctoral degree in Cohen’s lab. “You can have a broken arm and the flu at the same time.”
Cohen, Liebowitz and others have since come to understand springs face a range of ailments from urbanization to pesticides to how slowly the water flows, all connected to algae in some way.
Their work identified declining dissolved oxygen as particularly concerning for the health of springs and the critters that live in them. That’s where Liebowitz’s interest in snails, which she calls “little janitors of the springs,” began.
Researchers aren’t yet certain what lowers dissolved oxygen in the region’s springs. Water near the surface tends to carry more oxygen than water deep underground, so one hypothesis is that overpumping of shallow portions of the Floridan Aquifer could leave older, less oxygenated water to come out at springs.
Liebowitz set out to test whether dissolved oxygen levels impacted snails’ cleanup skills.
The experiment
Liebowitz’s snails have hard, black, spiral shells that cover their soft bodies like toppled wizard hats.
They’re common in streams throughout the Southeast and “pretty much everywhere” in the main stem of the Ichetucknee, said Paul Donsky, a doctoral student in Cohen’s lab and co-author of the study.
There, they munch on the very algae swimmers and kayakers avoid.
Liebowitz put snails in underwater enclosures with algae-covered tiles at various spots along the Ichetucknee to test their ability to clean up the goo.
At low levels of algae, the snails did a good job of keeping it low. But when algae levels started high, the snails generally couldn’t keep up (with a few exceptions).
That could be because the algae start as small, single cells but grow into stringy, multicellular mats that are harder to break, Liebowitz said. Snails “could eat the grass, but not the trees.”
Many Suwannee River springs are beyond that algal tipping point, Donsky said. The team’s Ichetucknee study offered one way that could’ve happened, pointing — again — to dissolved oxygen.
The river’s aquatic snails “breathe” underwater by taking in dissolved oxygen through their gills. When researchers placed snail enclosures in Mill Pond, an area of the river with low dissolved oxygen, snails died unexpectedly. The remaining snails struggled to keep up with even low levels of algae.
If low oxygen levels knocked out snail populations in Suwannee River springs, algae may have grown beyond its tipping point. Even if snail numbers recovered, they may not have been able to tackle the forest of algae they now faced.
“My work did not quite get to the place of figuring out exactly what's going on, but dissolved oxygen is definitely a big part of the picture,” Liebowitz said.
Snails ate less and some died when Liebowitz simulated low and very low dissolved oxygen levels, respectively, in later lab experiments. She didn’t test contaminants or habitat changes from low flows but said those might harm snails, too, impairing their cleanup work.
Patricia Spellman, an assistant professor studying hydrology at the University of South Florida, was “really excited” by Liebowitz and Donsky’s study. She said researchers used a realistic number of snails and checked to make sure variables like water flow rates didn’t skew results.
Though Liebowitz did her field work in 2013, Spellman expected results today would be similar. Testing a different spring, though, could be different.
Lafayette Blue, Madison Blue, Troy and Convict springs along the Suwannee River have higher nitrate levels than Ichetucknee springs and occasional reversals, when river water pours into a spring instead of groundwater bubbling out.
“The connection between nitrates and algae proliferation is established,” she said. “If you have continuous nitrate feeding into the system, your grazers are only going to be able to do so much.”
Management implications
Dumping buckets of snails into springs won’t undo algae problems “because there's a reason why they died off in the first place,” Liebowitz said.
That doesn’t mean slime-coated springs will stay that way forever.
Big floods can wash algae away, Donsky said, and reversals can reset the system, too. Work from other members of Cohen’s lab has shown that planting underwater vegetation and bringing up oxygen levels in springs can also help undo algae problems.
“It’s a different pace and a different mechanism to get back to the original,” Liebowitz said, “but it doesn’t mean you can’t get back.”
Regulators’ challenge is deciding which mechanisms to fund.
“ I think it would be nice, from a management perspective, if we could just turn one of the knobs,” said Donsky, who works as a regulator at the Suwannee River Water Management District in addition to his academic research at UF. “But, more likely, these are complex ecosystems. They’re going to have more than one thing going on.”
To date, the Florida Department of Environmental Protection has focused on the nitrate and flow level knobs in Florida springs.
Cohen’s dissolved oxygen hypothesis has gained support in research circles, Donsky said, but “the regulatory structure is not necessarily set up for that yet.” FDEP didn’t respond to WUFT’s request for comment.
In Alachua County, Cohen’s former student Greg Owen is bridging the gap between research and regulation as a senior planner with the Alachua County environmental protection department.
“ I think it helps inform us as to which locations are suitable for restoration,” Owen said of Liebowitz’s work. “We're going to want to look at dissolved oxygen levels because that's one of those key drivers as to where we'll have success or not.”
Owen’s own research in Hornsby Spring found raising dissolved oxygen improved plant and snail survival and slowed algal growth. Removing algae and sediment, the more conventional restoration method, “didn’t seem to have any effect at all.”
Continuously bubbling oxygen into a spring with an air compressor worked well on an experimental scale but would cost millions to do for the whole spring, Owen said. Further testing could see if shorter, temporary cycles with a compressor could help plants take root and let Liebowitz’s “little janitors” keep cleaning up.
