By Jamie Groh | UF News
Heavy rains causing repeated river flood intrusions into Florida’s freshwater springs are changing the function of the clear natural resource. Recently published findings from University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers Paul Donsky and Matt Cohen reveal that these intrusions can cause flow reversal worsening already present problems.
The intrusions force dark, murky river water back into the normally clear springs that push fresh water out. The reversed flow results in cloudy conditions that, when coupled with other problems like low oxygen levels and declining submerged aquatic vegetation, can exacerbate algae blooms that have long been blamed primarily on nitrate levels.
“We surveyed 62 springs throughout the Suwannee and Santa Fe River and found very few that had aquatic vegetation,” said Donsky. “There was zero vegetation present at the springs which experience frequent intrusion disturbances.”
The study shows that the impacts of flooding extend beyond individual events sustaining darker water, lower oxygen levels, and accelerating the loss of underwater plants, the perfect recipe for harmful algal growth.
“It’s a lot like wildfire research,” Donsky explained. “In fire ecology, there’s a regular frequency of disturbances that’s manageable for the forest. If you increase the number of forest fires, eventually the forest becomes destabilized and can’t recover.”
Across the sites studied, the researchers identified clear tipping points that help explain why some freshwater systems recover while others do not. Springs that are flooded by nearby rivers more than 20% of the time were far less likely to have underwater vegetation. Once the vegetation is gone, oxygen decreases and fast-growing algae takes over, making it difficult for native plants to return after the disturbances.
“We really want to protect the submerged aquatic vegetation in the springs that’s home for fish, food for invertebrates, provides oxygen, and stabilizes the sediments,” said Donsky. “Anything that’s driving a loss of that aquatic vegetation is something we want to prevent for the ecosystem as a whole.”
The study also comes with a note of caution for water managers. Researchers warn that efforts to replant aquatic vegetation in springs may not be effective unless flooding conditions are also addressed.
“It’s caused by rain events. Rivers can rise very quickly,” said Donsky. “As the river rises higher, it’s forcing the fresh spring water back, reversing the springs’ flow.” When humans take water out of the ground, that worsens the problem, decreasing the springs’ ability to push back against the murky river water and prolonging flood events.
While the research focuses on Florida, the takeaway reaches much further as heavier rain, stronger storms, and more unpredictable flooding are becoming more common trends.
Researchers say what they are seeing in Florida could offer an early glimpse into how other waterways nationwide may change as river flooding becomes more prevalent and harder to predict.