Florida cape vulnerable to rising seas

Sediment carried into Lake Ingraham by canals dredged a century ago at Cape Sable are gradually filling the lake with acres of mud flats.
Sediment carried into Lake Ingraham by canals dredged a century ago at Cape Sable are gradually filling the lake with acres of mud flats.

From the sky, Florida’s rugged tip looks like a scrap of emerald green lace: marshes and mangroves and tree islands all knit together by ribbons of creeks and lakes.

But at Cape Sable, a remote outpost where the Atlantic meets the Gulf of Mexico, the coast is fraying.

Usually, geological change is so slow that “you never see something in your lifetime,” Audubon Florida biologist Peter Frezza said recently as he piloted his boat around acres of mud flats filling Lake Ingraham. “But we’re watching this happen.”

For more than a decade, scientists have seen the cape as the tip of the sword in climate change. Sliced open by canals dug through the marl dividing marshes from the bay a century ago by Henry Flagler’s land company, the cape is particularly vulnerable to rising seas. Flagler was hoping to drain the wetland and lure homesteaders and ranchers.

No one ever came that far south — swarms of mosquitoes were said to suffocate cattle — but the canals widened. And as they expanded, the coast and marshes where crocodiles nest and migrating birds refuel for transcontinental flights started collapsing like a sandcastle pounded by waves.

Wildlife managers are now in a race. The more saltwater flows into marshes, the faster they die. And the faster marshes die, the more damaging nutrients from the dead sedge and other vegetation wash into the bay.

Scientists think they have a fix. Simply plug the canals. But getting money to repair a problem accessible only by boat — and easily lost in the long list of Everglades restoration projects — has been tough. Three years ago Everglades National Park constructed $7 million dams to plug the two most damaging canals using federal stimulus grants. Now, tired of waiting for work to continue, the nonprofit Everglades Foundation has supplied $143,000 to the park service, half the cost of completing an environmental assessment needed before more money — an estimated $10 million — can be sought to plug four smaller canals.

“With the canals plugged, we may not be able to stop” the damage, said acting park superintendent Bob Krumenaker. “But we can slow down the action and make the system more resilient for a considerably longer time.”

As early as the 1950s, wildlife managers spotted trouble at the two main canals, the East Cape and Homestead. Originally dug only 15 to 20 feet wide, the canals broadened to 10 times their width with the constant scouring by tides. Workers erected earthen dams to stop the canals from widening. But hurricanes and erosion washed away the dams. About 2005, damage started increasing exponentially, Frezza said.

“Even in the last three years the rate water is moving in and out is truly astonishing,” said Carol Mitchell, deputy science director at Everglades and Dry Tortugas National Parks.

At the Raulerson Brothers Canal at the western tip of Lake Ingraham, water rushes down the canal at low tide in white-capped rapids. One morning last month, Tom Van Lent, the director of science and policy at the Everglades Foundation, pointed to three feet of exposed grass and mangrove roots, a sign of just how quickly the marsh has shrunk “like letting air out of a mattress.” A side creek that Van Lent said was impassable five years ago sends water gushing out.

Scientists fear that all the nutrients washing out of the dying marsh could profoundly damage the bay. In 1992, when a massive algae bloom turned much of Florida Bay into a smelly, slimy dead zone, scientists believe the trigger was nutrient run-off. In recent years, the amount of algae-feeding nutrients in Lake Ingraham has remained much higher than in the Everglades to the north.

“We’ll never know what triggers an algae bloom,” Van Lent said. “But adding nutrients to Florida Bay is not a good thing.”

On the flip side, sediment carried by incoming tides over the last 30 years has dramatically changed Lake Ingraham. Once a freshwater lake, it is now salty and filled with acres of barren mud flats. Audubon’s Frezza said the food chain has shrunk, with small fish declining and larger fish and seabirds going elsewhere to hunt.

“It’s not quite the dead sea, but it’s pretty bad,” Van Lent said.

Park officials hope to complete the environmental assessment within the next 18 months, Krumenaker said. The assessment will look at whether plugging the four remaining canals — the Raulerson, East Side Creek, Slagle’s Ditch and House Ditch — can slow the process and improve water quality. Once the assessment is complete, the park hopes to begin the arduous process of finding money, teaming up with nonprofits to go after grants.

“We’ll talk to anyone who’s interested in this project and has a checkbook,” Krumenaker said.

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