Freshwater from the Everglades Needed to Protect Florida Bay

FLORIDA BAY – PHOTO BY MAC STONE.

Florida Bay is one of the most diverse and productive ecosystems in Florida. It begins where the Everglades, or “River of Grass,” ends near the Florida Keys. Long renowned for its lush seagrass beds, mangrove islands, and spectacular recreational and sport fishing, it is one of the reasons why the Florida Keys is the fishing capital of the world. Florida Bay is an estuary, where freshwater runoff from the “River of Grass” meets salt water from the Gulf of Mexico and Atlantic Ocean, generating a perfect potion that results in a profusion of life. It is no coincidence that it’s a nursery ground for fish, shrimp, lobster, crabs, and countless other species.

However, Florida Bay has been severely damaged by a lack of freshwater flow, resulting in seagrass die-offs in 1987 and again in 2015. This seagrass, which provides habitat for the fisheries that draw millions of people to the Keys each year, is essential to the heart of the ecosystem. Understanding how freshwater gets into Florida Bay from the Everglades is key to understanding how to protect and restore it.

Direct rainfall is certainly an important source of freshwater affecting Florida Bay salinity levels. However, the amount of freshwater that escapes back to the atmosphere through evaporation balances (if not slightly exceeds) annual rainfall. This means that freshwater inflows from the Everglades are even more important in balancing the bay’s salinity levels.

As the drought of 2015 reached its peak in August, salinity levels in Florida Bay were more than double the salt content of ocean water. Stressed seagrass plants died across an area of about 80 square miles of the bay. Why? The drought was centered on the park. There was no freshwater available locally, and evaporation from the bay led to the lethal spike in salinity.

DR. STEPHEN DAVIS COLLECTING DEAD SEAGRASS IN FLORIDA BAY AFTER HURRICANE IRMA.

Some say this is normal, and that Florida Bay succumbing to drought is simply the result of Florida Bay being a “rainfall-driven” ecosystem. However, if we look into Florida Bay’s sediments, which give us a glimpse into its past, we don’t see evidence of extreme high salinity before the Everglades was diked and drained. In fact, what we see was that the bay was less salty, reflecting the higher historical input of freshwater from the Everglades.

There is no debate among Florida Bay experts that the Everglades is and always has been an important source of freshwater to Florida Bay. Further, there is no technical debate as to how freshwater from the Everglades gets into Florida Bay . Freshwater gets into Florida Bay directly through Taylor Slough and the C-111 Panhandle wetlands and indirectly through the much higher volume of flows from Shark River Slough that dilute nearshore waters and wrap around Cape Sable before entering into western and central Florida Bay.

Rainfall and evaporation are still the same; whereas, inflows from these Everglades sources have been cut by more than 50%. This is due to the compartmentalization and disconnection of the Everglades from Lake Okeechobee that now results in excess water being discharged to the Caloosahatchee and St. Lucie rivers rather than south to the Everglades and Florida Bay. The impact of these changes is most acute during drought.

How do we fix this? Any increase in freshwater inflows—whether from Shark River Slough or Taylor Slough—during drought will improve salinity conditions across Florida Bay. In 2015, direct inflows to the bay from Taylor Slough were not possible because of the local drought. We can’t create water where it doesn’t exist. On the other hand, indirect inflows to the bay from Shark River Slough were precluded by closure of the water conservation areas, which did have water. Further upstream, there was also water available in Lake Okeechobee. However, without storage south of the lake, we were unable to utilize any of these historic sources.

If we want to drought-proof Florida Bay, we need storage that allows us to connect and treat water supplies from the north to where the water is needed in the south. Re-directing that freshwater under the bridges along Tamiami Trail and into Everglades National Park will improve salinity conditions across Florida Bay. If we don’t do this, Florida Bay will continue to be on a knife’s-edge from year-to-year reflecting the “rainfall-driven” artefactual state of the current management system that so many misunderstand as being a natural condition.

MAP OF EVERGLADES NATIONAL PARK SHOWING NATURAL FLOW PATHS FOR FRESHWATER INFLOW TO THE BAY (BLUE) AND HOW THE PATTERN HAS CHANGED (RED). TOTAL INFLOWS TO THE BAY FROM THESE SOURCES HAVE BEEN CUT BY MORE THAN 50%.

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