Recent coastal dune lake outfall events contribute to fresh and saltwater biodiversity By Erika Zambello
In early May of 2018, Eastern Lake in Walton County burst through a sand barrier. Water rushed through the newly created opening into the Gulf of Mexico, mixing the brown-hued currents of the lake with the bright green waves of the saltwater. Eastern Lake was experiencing an outfall event.
Eastern Lake is a coastal dune lake, one of 15 such lakes recognized locally within Walton County. These water bodies are rare, existing in Northwest Florida, New Zealand, Australia, Madagascar, Oregon, South Carolina and a few other locations around the world. Unlike other coastal sandy environments, water collected in coastal dune lakes from rainfall, runoff and groundwater seepage does not percolate quickly through the sandy soil. Instead, lake water remains in shallow depressions all year round, fluctuating with the outfall conditions and weather. The largest fluctuations occur when a dune lake outfalls.
The force of water flowing outward from the lake or inward from the Gulf of Mexico can be dramatic, scouring sand and carving stream channels through the white sand beaches into the gulf, attracting a host of birds and other wildlife species.
Unfortunately, fluctuating water levels in the dune lakes can reveal plastic pollution debris. When Deer Lake connected to the gulf through its outfall in February, plastic toys, water bottle tops and other single-use plastic items littered the marshy edges where the currents had been strongest. This prompted a mini-cleanup by the Choctawhatchee Basin Alliance (CBA) staff to collect debris and use it to educate students across the county about plastic pollution.
Importantly, these outfall events drive the biodiversity of plants and animals of our unique coastal dune lakes.
“The coastal dune lake outlets play an important role in the exchange of saltwater, impacting the physical and chemical conditions of lake water, as well as the plants and animals,” explains Brandy Foley, monitoring coordinator for the CBA. “The exchange of water acts as a pathway for saltwater species to enter the lakes. These intermittent exchanges with the gulf provide an opportunity for fresh and saltwater flora and fauna to coexist and offer a rich habitat and food source to local and migrating species, such as shorebirds.”
Each of Walton County’s coastal dune lakes has its own personality, based on the combination of its size, watershed features, surrounding land uses, and outlet characteristics. Outlet openings vary greatly in length, frequency and duration, and are driven by each lake’s critical high water level as well as prevailing climatic conditions for example, droughts and rain. As a result, some of the dune lakes can be completely freshwater, some brackish, and some salty, with varying degrees of salinity occurring between different lake stages.
To restore the coastal dune lakes, the Choctawhatchee Basin Alliance continually monitors the water for quality indicators, including nutrients and algae levels. Additionally, CBA was awarded a National Fish and Wildlife Foundation Five-Star and Urban Waters grant, which is co-funded through Southern Company and Gulf Power, to remove invasive plant species from several Walton County coastal dunes lakes. As local citizens, we can reduce plastic use in our community, keep sustainability in mind when building near the coast, and strive to conserve the shoreline to make sure our dune lakes are healthy now and for future generations.