Sea Level Rise, South Florida and the Everglades

Sea Level Rise, South Florida and the Everglades

Categories: Blog

Most South Floridians live on porous limestone rock blanketed with a few inches of soil, mere feet above sea level. This, coupled with gradually rising seas, has caused property owners to be rightfully concerned about flooding and property loss.

Over the past 100 years, sea level has risen approximately 8 inches globally. Over the next century, that could increase five-fold.

While flooding in urban areas is always a concern, most South Floridians are utterly unaware of the impact rising sea levels have on the natural landscape of the Everglades. This lack of awareness is, to some degree, understandable. A remarkably resilient ecosystem, the Everglades contains a variety of habitats adapted to a range of flooding from either freshwater or saltwater, so some may wonder why we should be concerned about sea level rise at all in the Everglades.

How the Everglades responds to rising sea levels is a bit complex. The Everglades is a flat, low- lying landscape with a gentle slope — about a 1.5 to 2-inch rise for every mile from the coast. The conventional thinking is that coastal habitats such as mangroves will gradually migrate up this gentle slope with increased penetration of saltwater into freshwater habitats.

This “landward migration” scenario, however, may not necessarily be the rule.

Close-up view of peat collapse along a sawgrass plant in lower Shark River Slough of Everglades National Park. Note the exposed roots.

Cape Sable, a span of beach and freshwater wetland shielding the southwest coast of the Florida peninsula, may provide an instructive glimpse into a potential future scenario. In the 1920’s, the dredging of canals accelerated saltwater penetration into this freshwater marsh habitat.

The outcome was less like “landward migration” and more analogous to the land loss situation in coastal Louisiana.

When we deprive Everglades marshes of freshwater, organic soils (known as peat soils) decompose and disappear, resulting in a rapid loss of soil elevation. In severely dried areas, the soils also become vulnerable to fire. Freshwater plants die and soils begin to breakdown resulting in massive nutrient releases to nearshore habitats like Florida Bay.

Ultimately, the outcome is that collapsed areas created by soil loss are often too deep with saltwater for mangroves to become established. Instead, they remain open water habitats and eventually become seagrass habitats. This phenomenon has already shaped the coastlines of Biscayne and Florida Bays, and accelerating this process will also change the future coastline of the entire South Florida region whether we recognize it or not.

This process is particularly significant for the Everglades. Not only is it the source of our drinking water, it is also our most important protection from sea level rise and storm surge. By not offsetting this saltwater intrusion with restoration of freshwater flow, we are effectively leaving our back door open in a rising flood. For this reason and more, Everglades restoration should be our highest priority.

As for what the future South Florida will look like, excellent monitoring and modeling tools are available to us. We know what today and tomorrow – or perhaps even the next 20 years – will be like.

What will happen over the next 50 to 100 years is less certain.

Although South Florida won’t disappear into the sea anytime soon, there is a clear and growing need to educate citizens about the significance of incremental sea level rise. The first step is to acknowledge the problem.

Beyond that, we must continue to monitor changes in the ecosystems we depend on and prioritize the science needed to understand how future Floridians might be affected. While we don’t want to take too long, time and resources are needed to understand the sea level rise problem and develop the most advantageous options, strategies and solutions.