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Unique Water Ecosystems

Posted on Mar 01, 2019 in Ecosystem , Coastal dune lakes , March-April 2018

New study reveals diverse plant life in rare coastal dune lakes by Erika Zambello

Looking across a coastal dune lake, I’m first struck by the water reflecting the puffy clouds flying overhead, the waving cordgrass, the deep row of pine trees growing along its shoreline. Just across the white dunes I hear the crashing waves of the Gulf of Mexico, and more often than not, the cry of an osprey soaring overhead.

But beneath the surface of our rare coastal dune lakes, an entirely different world emerges. To study these watery ecosystems, Richie Gray of the Mattie Kelly Environmental Institute (MKEI) and Challen Hyman of MKEI and the Choctawhatchee Basin Alliance (CBA) conducted surveys across the 15 named coastal dune lakes this year, looking specifically at aquatic vegetation.

Coastal dune lakes are bodies of water found in dune ecosystems within two miles of the coast. Though usually isolated, the water levels of the coastal dune lakes fluctuate substantially since they create transitory interchanges with the Gulf of Mexico. The lake-water is composed of both fresh and saltwater that comes from tributaries, groundwater seepage (from uplands and from the gulf), rainfall, exchange with the gulf, and coastal storm surges. The lake-water is generally a black or tea color due to the dissolved organic matter it contains. This is a natural phenomenon, and it’s nothing to be worried about. While these lakes are exposed to normal weather conditions just like any lake, Florida’s coastal dune lakes are also tremendously impacted by many elements of hurricane activity such as a storm’s frequency, strength, tidal flow and duration.

Richard Gray of the Mattie Kelly Environmental Institute takes a water sample.

Because the coastal dune lakes open at different frequencies with the Gulf of Mexico, some are saltier than others. Gray and Hyman found that this saltiness level — divided among brackish (a mix of salt and fresh), freshwater, and between the two, has direct impacts on what plant species can thrive. Fresh lakes overall as a group had the highest number of plant species at 18, followed by 10 in the intermediate lakes and eight in the saltiest water bodies. The same pattern is followed when Hyman looked directly at the average number of species found in any one specific lake or large lake lobe: eight species in freshwater, 4.3 for intermediate water lakes, and 3.3 for brackish systems.

Additionally, Gray and Hyman looked at vegetation coverage using sonar technology. “As you might expect,” Hyman explains, “Coverage across the dune lakes peaks in the warm, summer months, and reaches the lowest levels during the winter.” This is interesting to anglers, who often target vegetation when seeking different fish species.

Since the team only has one year of sampling under their belts, they will continue to collect data to compare vegetation to fish communities within the lakes. Because plants have an important impact on the fishing, swimming, and padding in coastal dune lakes, the more we know about them the more we know about these amazing natural resources in our own backyard.