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Ian's storm surge changed Sanibel's freshwater lake environments and now brings a new algae concern

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Posted at 6:21 PM, Feb 15, 2023

SANIBEL, Fla. — Like many things in Sanibel, after Hurricane Ian, the environment changed significantly. Ponds that once were freshwater before the storm, are now saltwater. That is due to the 8 to 14 feet of storm surge that occurred on Sanibel. And now, that change going back to freshwater could be a slow-go to reverse.

“I expect it to last 1 to 4 years depending on the pond,” said Dr. Serge Thomas with Florida Gulf Coast University’s Water School. Hurricane Ian’s storm surge changed these lakes and ponds in 24 hours' time.

“All the life that was in those lakes pretty much died off immediately,” said Mark Thompson, a research associate with the Sanibel Captiva Conservation Foundation. “We lost fish. We lost plants. We lost everything that depended on them to survive in our freshwater habitat.”

The changes in salinity are being studied separately by both SCCF and FGCU’s Water School. Both organizations are clear that these changes could cause algae blooms of all types over the next few years.

“We are going to get different kinds of algae blooms in our lakes that people haven’t seen before, just because they are in different habits than before,” said Thompson. “But, there is always going to be some kind of algae that wants to bloom no matter what kind of water you have in your system.”

But why? Dr. Serge Thomas said it is due to the nutrient loading that was in the freshwater lakes prior to Ian.

“Most of the ponds or lakes I study in Florida are phosphorus limited, so phosphorus is one of the major nutrients that create algae to bloom,” said Dr. Thomas. “And now they’re saltwater so I can use this as if there is a shift between the phosphorus limitation to a nitrogen limitation. The problem is that nitrogen is found in very high concentrations in those ponds, so now you have a nutrient nitrogen-rich pond that is in salt water, which actually triggers the algae blooms.”

Thompson agrees. He says the best thing we can do is wait it out. And when these become freshwater ecosystems again, we then can address the potential algae issue and remove nutrients that can spark new blooms.

But there’s really not much you can do other than wait for the rain. Once we get rain in the system, it will start fresh again, and we then can look at the proper plants in the yard to proper plants in our lakes to control the nutrients.

The clear consensus is it will take some time for the systems to flush themselves out and return to their pre-Ian status. Dr. Thomas adds that this research is key because it hasn’t been well documented after previous hurricanes and this could help other locations prepare and recover.