Image: Gerald Herbert/AP
As Hurricane Irma rakes the west coast of Florida, all eyes are on the cities and human lives in the storm's path. But Irma is also hammering the Florida Everglades, and the scientists familiar with this fragile ecosystem are concerned the storm could deliver a devastating blow.
"They're losing out," said Hal Wanless, a geologist at the University of Miami, when asked what's been happening to the Everglades' coastal marshes and mangrove swamps in the wake of recent, powerful hurricanes. According to Wanless, a trifecta of urban development, extreme weather, and climate change has eroded the Everglades' resilience. The system, he said, "is getting set back, it's having trouble keeping up."
A sixty-mile wide river of sawgrass and mangrove forests that used to stretch all the way from Orlando to the Florida Keys, the Everglades is an internationally-recognised ecological treasure, home to alligators, panthers, manatees, crocodiles, more than 300 species of birds, and hundreds of rare or endemic plants. Its very existence is both predicated on water and existentially threatened by it -- but the threat has been dramatically amplified over the past century, by unnatural drainage and development, and by unnatural changes to Earth's climate.
In order make South Florida livable, people had to drain the swamp. That effort began in earnest in the mid 20th century, with the diking and re-routing of Lake Okeechobee, a sprawling pool of freshwater that used to feed water all the way down the sawgrass prairies of the Everglades to Florida Bay. With the construction of thousands of miles of levees and canals, humans were able to tame, contain, and re-direct the lake, draining hundreds of thousands of acres of land directly south of it for sugar cultivation. The coastal floodplains of South Florida, meanwhile, were made suitable for highways, golf courses, and skyscrapers, setting the stage for a massive population boom.
Roughly half of the Everglades has been drained or paved over since developers decided to conquer the land early US explorers described as "hideous" and "abominable." What's left of the formerly formidable ecosystem is far too dry, and plagued by a laundry list of ailments, from seagrass die-offs in Florida Bay when salinity levels get too high in the summer, to toxic algae blooms along Treasure Coast when too much agricultural effluent is sent spewing out of Lake O., to raging wildfires across critical habitats that used to be fully-fledged wetlands.
Compounding the problems caused by the draining of the Everglades is the threat of human-caused climate change. South Florida, which sits on porous limestone substrate often likened to Swiss cheese, faces some of the highest rates of sea level rise in the world, and as the ocean plows further into its freshwater-adapted marshes, it's weakening them even more. The region has seen about foot of sea level rise since the 1930s, with perhaps another three feet to go by the end of the century.
Now, to add insult to injury, we have Irma, the strongest storm to make landfall in the United States since Hurricane Katrina, and one that a growing chorus of scientists are saying isn't quite natural, either. While the extent of the storm's impact on the Everglades won't be known for some time, Wanless said that past storms, particularly Hurricane Andrew, which struck South Florida as a Category 5 in 1992, can help set our expectations.
It was in wake of that storm that the United National put the Everglades on the list of World Heritage sites in Danger.
"Andrew put down 80,000 acres of mangrove swamp," Wanless said, noting that these swamps, which hold about half of their biomass in their massive root systems, literally build land out of the water. As soon as they start to decay, that land disappears. "We were getting subsidence rates of two to four centimeters per year, anywhere along Biscayne Bay or the West Coast of Florida north of Cape Sable," in swamps leveled by the hurricane.
Many of the mangrove stands that were badly hit by Hurricane Andrew, particularly the Ten Thousand Islands region near Everglades City, have since become part of the ocean, Wanless said.
"It becomes a challenge for this mangrove fringe to survive," he said. "They build soil [rapidly], and could probably keep up with a couple feet of sea level rise per century if there weren't hurricanes." But, "we're gonna see a rapid loss of the mangroves in the presence of things like Irma."
That creates problems for inland, freshwater-adapted marshes, which the mangroves help to buffer against both storms and rising sea levels. As saltwater plows inland, it is triggering the collapse of thick, organic peat soils, which in turn leads to more loss of land. "As these soils become exposed to salt, you strongly tip the balance toward a more rapid breakdown," Everglades ecologist Steve Davis told Gizmodo last year.
These changes are evident in Cape Sable, an isolated and rapidly-eroding stretch of mangrove swamp, beach and marsh at the southwest toe of Everglades National Park that's expected to see surges as high as 10 to 15 feet from Irma.
"At a time when we're having over a foot of sea level rise and accelerating each century, it becomes a race between the mangroves coming back and subsidence that leads to open water," Wanless said.
All of this has implications for the millions of people living in South Florida, who rely on a healthy, functioning Everglades to replenish their drinking water supply. Surficial, coastal aquifers are already being contaminated by saltwater intrusion on account of the Everglades being too dry, and as the oceans continue to creep up without enough freshwater recharge from the wetlands, the threat is expected to get worse. Meanwhile, population growth and urban sprawl could double Floridians' water demands by mid-century.
The multi-billion dollar solution to this tangled web of problems is the Comprehensive Everglades Restoration Plan, an Army Corps-led effort to increase the flow of freshwater south from Lake Okeechobee in order to help the wetlands rebuild their strength. Many Everglades ecologists say it's the only way to buy these ecosystems more time, but nearly twenty years after plans were first drawn up, little progress has been made.
"If we'd immediately manage water levels that help mangroves [and marshes] recover from hurricanes and build up peats -- which has not been done -- maybe we could keep building up these wetlands to keep up with sea level, keep freshwater coming so they don't dry out and burn," Wanless said. "Maybe we could hold on to the glades through much of the century. As it is, we're gonna have saltwater intrusion, and coastal erosion."
"Time's running out for the Everglades," he added.