For those living along the lower east coast of Florida, the Everglades is a backyard wilderness, the source of our drinking water and important hurricane buffer. It is also a flat, low-lying wetland with an inconspicuous slope, making it 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 level 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 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.
Anyone who drives to Key Largo can see how far the mangroves have advanced inland over the past few decades. Given that mangroves provide valuable coastal wetland habitat, trading sawgrass for mangroves may sound acceptable, but it’s 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 composed of plant matter that accumulates faster than it decomposes, forming a kind of blanket on top of our 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. 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. In the Everglades, collapsed
areas appear as large puddles surrounded by vegetation. Over time, collapsed areas of marsh merge into larger areas, releasing nutrients into the environment where they wreak havoc in the Everglades and coastal waters. Loss of peat soil can result in the loss of land. When such drastic ecological changes occur so rapidly, it is difficult to predict what chain of events will follow. However, we know that we are accelerating peat collapse and shaping the future coastline of the Everglades under the current system of water management.
Until we restore the flow of freshwater to Everglades National Park, we are short-circuiting the natural transition to mangroves and possibly increasing South Florida’s future coastal vulnerability.
Source: Palm Beach Post, 07/08/2018
Steve Davis, The Everglades Foundation