Sea level rise threatens to eat away the Everglades

December 13, 2018

By Dr. Steve Davis, Chief Science Officer

Read our Chief Science Officer, Dr. Davis', article in the South Florida Sun Sentinel.

For those of us living along the lower east coast of Florida, the Everglades is a backyard wilderness, the source of our drinking water and an important hurricane buffer. It is also a flat, low-lying wetland with an imperceptible slope, making it quite vulnerable to sea-level rise.

Once a 50-mile-wide “River of Grass” extending from Lake Okeechobee to Florida Bay, the Everglades is now divided by canals and levees into units we know as Everglades National Park, Big Cypress National Preserve and the Water Conservation Areas.

Now half its original size, the remaining Everglades ecosystem still encompasses more than 2.5 million acres and consists of a variety of habitats that are adapted to extremely low nutrient levels and a range of flooding conditions by either freshwater or saltwater. Scientists have been investigating what is likely to happen to the Everglades when those flooding patterns are altered by rapid rates of sea-level rise.

Many people assume that as sea level rises, mangroves will gradually migrate landward, replacing freshwater sawgrass near the coast. This landward migration of mangroves and other coastal habitats is well documented, and there is strong evidence that this process has been exacerbated further by water management activities, which reduce freshwater flow from the Everglades to the coast.

It doesn’t take a scientist to see the effects. Anyone who drives to Flamingo or Key Largo can observe how far the mangroves have advanced inland over the last few decades.

Given that mangroves provide valuable coastal wetland habitat, trading sawgrass for mangroves may not be such a bad thing, right? Unfortunately, it is not that simple.

The interaction of water, salinity and plants can dramatically affect the integrity and elevation of the soil that supports these habitats.

In freshwater sawgrass marshes and salty mangroves of the Everglades, organic soils (called peat soils) develop under persistent flooding. Peat soils are comprised of plant matter that accumulates faster than it decomposes, forming a blanket of sorts on top of South Florida’s porous limestone bedrock.

In the deepest freshwater marshes, peat soils average 2 to 3 feet in thickness. In Everglades mangroves, peat soil thickness can exceed 10 feet.

When we deprive marshes of freshwater, peat soils break down, resulting in soil loss. In fact, it has been estimated that some marshes in the park have lost as much as 3 feet of soil elevation in the era of water management.

A more complicated and destructive outcome results when freshwater marshes, which are already receiving less freshwater, are increasingly exposed to saltwater before mangroves become established. An example is Cape Sable, the landmass at the southwestern-most tip of Florida.

Read the full article here: http://www.sun-sentinel.com/opinion/fl-op-viewpoint-sea-level-rise-everglades-coast-20180702-story.html