Florida estuaries-fragile buffers against a rising ocean
By Dinah Voyles Pulver, firstname.lastname@example.org
To anyone who has reeled in a prized redfish or plucked an oyster from the water and eaten it straight out of the shell, the value of a healthy Florida estuary needs little explanation. Created by an earlier period of rising seas, Florida’s estuaries are fragile zones where fresh water flowing from springs and rivers mingles with salt water in a balance that ebbs and flows in a rhythm set by weather and phases of the moon.
The estuaries provide a sheltered, nutrient-rich environment for abundant marine life and serve as nurseries for the surrounding oceans. They also generate billions of dollars of economic impact each year from commercial and recreational fishing, boating and bird-watching. And, for much of the state, they provide a buffer against tropical storms and hurricanes.
Now, scientists and advocates warn these estuaries could be redefined as they become Florida’s last stand against the encroaching sea.
Rising sea levels “will reshape the coastline of Florida in ways that are almost difficult for humans to wrap their arms around,” said Duane DeFreese, executive director of the Indian River Lagoon Council. “It’s hard for us to look 50 or 100 years ahead, but it’s going to change dramatically.”
Already, rising seas and warmer temperatures bring higher tides, greater erosion, higher salinity and increasing acidity along the bays, sounds and lagoons that surround Florida. Dying trees have been documented in coastal forests in the Big Bend region along the Gulf Coast south of Tallahassee as saltier water moves inland. Erosion is eating away at shell middens in Mosquito Lagoon, in the northern end of the Indian River Lagoon.
Scientists with the National Oceanic and Atmospheric Administration predict sea levels could rise around three feet as early as 2070 in Florida, using mid-range scenarios. Their higher-end scenarios show a three-foot sea level rise could occur within about 30 years.
One study by The Nature Conservancy found a 3.2-foot rise in sea level would cause the loss of more than 170,000 acres of coastal forest and 63,000 acres of tidal flats in six estuary systems along Florida’s Gulf Coast between Pensacola Bay and Charlotte Harbor.
‘Nursery for the oceans’
Estuaries are often called cradles of the sea because of the tremendous variety of marine species that spend at least part of their life cycles there, such as green turtles, bull sharks, tarpon and other game fish. seagrass beds, marshes and the tangled roots of mangrove trees that grow in the fragile zones provide food and shelter for myriad species, from delicate seahorses to massive manatees.
“It’s crazy the number of marine organisms that spend some portion of their life cycle in an estuary,” said Edie Widder, chief executive officer and senior scientist at Ocean Research & Conservation Association Inc. in Fort Pierce. “They are a nursery for the oceans.” Given the small amount of real estate they cover, Widder said the estuaries have “an incredibly outsized impact on the oceans.”
Estuaries drive a lot of the economy of the United States, said DeFreese.
The reason estuaries are so valuable — and so fertile — is because they’re transition zones, where nutrients that run off the land help increase the productivity, said Jim Culter, senior scientist and program manager at Mote Marine Laboratory in Sarasota.
Changes in the balance of nutrients or in the balance of fresh and salt water can have a big impact. Studies by the U.S. Geological Survey have found that salinity increases during droughts can cause blue crabs to move upstream, and decreases in fresh water can reduce oyster populations.
As sea levels rise, Culter said the ocean will move farther inland and areas that host the fragile balance of salt and fresh water will shrink. Many estuaries already suffer from issues unrelated to sea level, such as loads of pollution and severely altered watersheds that provide either too much or too little fresh water.
A Geological Survey study released in June examined 28 years of data collected in 10 Florida estuaries that support commercial shellfish harvesting. The study, by John Lisle and Leslie Robbins, published in the journal “Estuaries and Coasts,” found the water in estuaries is getting more acidic, which limits availability of the components of calcium carbonate — crucial for animals such as oysters to build their shells. The study also found that oxygen levels in the water are decreasing. Six of the 10 estuaries have increased salinity and three have increasing water temperatures.
The estuaries, the scientists concluded, are being affected by changes taking place worldwide, including increasing levels of carbon dioxide in the atmosphere, development along the coast and increased nutrients in the water. The estuaries studied included St. Joseph, Cedar Key, south Tampa Bay, the St. Johns River North and three sections of the Indian River Lagoon.
Additional pressure from a changing climate and rising sea levels will cause further damage, said coastal ecologists and estuary advocates. Some, such as Arnoldo Valle-Levinson, a professor in the University of Florida’s Civil and Coastal Engineering department, wonder if sea level rise is partly to blame for ongoing troubles in the Indian River Lagoon, which has been plagued in recent years by toxic algal blooms, vanishing seagrass and fish kills.
‘A game of inches’
To describe how sea level rise might change things, scientists at Mote Marine Laboratory say when seas rise two feet in Sarasota Bay, the very lowest tides will be where today’s highest tides are.
Nuisance high tides already occur across the state, said Randall Parkinson, a coastal geologist affiliated with Florida International University.
In June, a NOAA study reported the average annual frequency of high tide flooding in the continental U.S. hit an all-time record in the past year. In Florida, new records for number of days with high tide flooding were set in Naples and Cedar Key between May 2017 and April 2018, and all 17 tide stations had high tide flooding above frequencies seen nearly 20 years ago.
That trend is expected to continue, likely at an accelerated rate, the study’s authors concluded, exacerbated by a combination of high astronomical tides, winter storms and tropical storms.
Hurricane Irma’s impacts were felt across much of Florida in September 2017, but it was just one of several named and unnamed storms that caused trouble over a period of months during the fall and winter.
Incremental rises in sea level are increasingly making communities along estuaries more vulnerable, with the potential for adding thousands of dollars in flood damages, said DeFreese. “This is a game of inches.”
As rising seawater penetrates farther and farther inland into tidal and freshwater creeks, it will gradually change the function and form of wetlands and other ecosystems that surround the estuaries, said Parkinson, who is preparing a vulnerability assessment for the Indian River Lagoon.
Estuaries will become saltier, and areas of brackish water along the waterways will shrink. The areas of estuaries that fluctuate in salinity will be more compressed and move upstream in the creeks and rivers that feed freshwater to the estuaries.
Modeling the future
Scientists have been able to look at how rising sea levels will impact coastal wetlands and forests by using the “Sea Level Affecting Marshes Model,” developed in the 1980s to study the impacts of the changing climate. Scientists can put in decades of data, including water level measurements and elevations, and examine potential impacts across a system.
Laura Geselbracht, a senior marine scientist at the Florida Chapter of The Nature Conservancy, started by looking at Apalachicola Bay, eventually expanding the study with her colleagues across the northern Gulf Coast and as far south as Tampa Bay and Charlotte Harbor. They looked at how sea level rise would impact coastal habitat and human communities along six estuaries.
“One thing we did notice is that with, say, as little as 0.6 meters of sea level rise — about a foot and a half — you see significant changes,” said Geselbracht. “And in some areas we’ve already seen significant changes.
“In places like the southern Big Bend, you can see sea level rise in action,” she added. “You can see where it’s been and what impact it has had.”
They concluded more than 170,000 acres of coastal forest could be lost with a 39-inch increase in sea level in the Gulf of Mexico, a rise that NOAA’s mid-range scenarios project could happen in some locations along the Gulf by 2070.
The study found 63,000 acres of tidal flats could be lost across the six estuaries, including 36,000 acres in Tampa Bay. When tide flats and dunes are lost, said Geselbracht, “urban areas become more vulnerable to coastal storms.”
They checked their model by putting in decades worth of data collected at Waccasassa Bay, near Cedar Key on the Gulf Coast, to see if it would accurately project the changes now occurring. It did, said Geselbracht.
Overall, coastal wetlands along the state’s Gulf Coast are likely to change substantially, she said, including inland river floodplains on the northern Gulf Coast. If you squeeze an area where a species occurs, she said, “you’d anticipate you’d greatly reduce the population of that species.”
The marine life affected by these shrinking estuaries are some of “the ones we care most about,” said Culter. “Oysters, blue crabs, clams, scallops, shellfish and things that are common that we fish for.”
That will in turn have an impact on commercial fisheries and their contribution to local economies. The filter feeders, such as clams and oysters, also are important for water quality.
Culter is working on shellfish restoration projects, including placing clams in Sarasota Bay and watching their growth.
Seagrass beds, which form the foundation of marine life in many estuaries, also are expected to feel the impact of rising seas. The grass beds are important because they provide places for marine life to shelter and forage and they absorb nutrients and carbon.
But the grass beds may be one example of an instance where sea level rise will cause changes that might not be considered good or bad, just different.
Deeper water levels are expected to make it more difficult for seagrass to thrive and grow in some locations because the grass can only grow in areas where sunlight can penetrate to the bottom. For example, said Culter, the average depth of seagrass in Sarasota Bay might be six feet. As sea level rises, those grass beds will start to lose their deep edges as the water becomes too deep for the sunlight to reach the grass.
But, depending on water quality, seagrass beds might move to new areas that go underwater. Geselbracht said grass beds might colonize some of the tidal flats as they become submerged.
Transitions among the ecosystems will depend in part on the amount of undeveloped land available for marshes and other estuary features to move to, and how much that migration is blocked by existing development.
As the ecosystems change, studies indicate some species could be “winners,” and others might be “losers.” For example, with salt marsh projected to expand in some areas, it’s possible some animals might benefit, such as the salt marsh vole, an endangered rodent found near Cedar Key. Bird species that use tidal flats, such as the reddish egret, for example, could suffer as the flats shrink.
But no one understands those impacts on species yet, said Jon Oetting, a conservation planner with the Florida Natural Areas Inventory. Much will depend on how rapidly the transitions occur and how much the habitats are separated from each other.
As the marshes expand or shrink, it could have profound impacts on the surrounding estuaries, said Geselbracht. “Some people might think ‘Oh that’s just a marsh,’ but that marsh is worth millions of dollars in recreational and commercial benefits.”
Appraising a marsh
It’s relatively easy to put a monetary value on things like homes, condominiums and infrastructure, said Jennifer Kassakian, a senior associate at Industrial Economics, a consulting firm that has studied the Indian River Lagoon. It’s harder to put a monetary value on ecological resources.
Kassakian has worked on projects that help people understand the value ecological communities provide, economically and otherwise. For example, an estuary has value as a nursery ground for marine species, including commercially important species such as crabs, clams and fish.
Using the same model The Nature Conservancy scientists used, she and a colleague, Jim Neumann, a principal at Industrial Economics, looked at the impacts of sea level rise on wetlands in the Indian River Lagoon.
The study showed there would be “substantial change” in the lagoon, including the loss of irregularly inundated marshes and swamps and substantial gains in acres of mangroves and open water, she said. The study, which looked at the amount of carbon dioxide that could be absorbed by the lagoon and surrounding plants, concluded the estuary would see an increase in carbon storage, but a decrease in productivity.
With a 47-inch rise in sea level, the study concluded the lagoon overall would see a loss of 24 percent of its wetlands.
Wetlands are important because they provide a buffer for storm surge and absorb the energy from waves. “If you don’t have that buffer,” said Kassakian, “if you allow that water to come straight up to people’s houses, that’s a pretty direct impact.”
Estuary groups across Florida are assessing “vulnerabilities” and pinpointing areas where intervention, such as limiting new development, might have the most impact. Several are working in conjunction with the Environmental Protection Agency’s Climate Ready Estuaries program.
“People like simple answers,” said Culter. “They want things to be fixed. That’s not going to happen. It’s going to take a lot of thought and discussion to deal with it.”
Correcting the many existing problems in the estuaries will help make them more resilient to change, said estuary officials on both coasts.
Rather than trying to “slap a Band-Aid” on things, it’s important to think long-term, looking at long-term strategies and large-scale, multiyear projects that can really get to some of the root problems, said Jennifer Hecker, executive director of the Charlotte Harbor National Estuary Program.
Like many estuaries statewide, the watershed around Charlotte Harbor has been greatly altered. Many areas in Hecker’s region are either not receiving enough water or receiving too much water. Utilities in the region are learning to correctly manage the water, she said, “to build communities that will be better protected from the harmful effects of a changing climate.”
If the region can store water and protect its freshwater supplies, said Hecker, the hope is that they will be able to “push back on sea level rise and saltwater intrusion to the greatest degree possible.”
A similar strategy is needed for the Indian River Lagoon, said DeFreese. Every action that makes the lagoon system more resilient to sea level rise comes back to human impacts already identified, he said. “It’s wastewater, it’s stormwater, it’s living shoreline replacement, and it’s getting filter feeders back into the system.”
Parkinson, the consultant studying the vulnerabilities of the Indian River Lagoon, said preparing plans is one thing. Implementing the plans is “a much bigger challenge,” he said. “It requires people to make decisions that may not directly benefit them and it costs money.”
He sees three options for implementing the plans being developed across the state: 1) Protect and defend, 2) Adapt, or 3) Managed withdrawal from low-lying coastal areas.
Saving the shorelines
As groups around the state prepare to protect and defend, retaining or increasing the amount of natural, “living shoreline” is shaping up to be a key strategy. In areas where the shores are lined with marsh grasses, mangroves and oysters, the shorelines have the potential to help the land keep pace with rising sea levels, several scientists said. Safeguarding shorelines could help with the transition of coastal wetlands as seas rise.
Linda Walters, a biology professor at the University of Central Florida, is among those convinced living shorelines will be an important part of the solution. For more than a decade, she has worked with nonprofits, businesses and schools to collect oyster shells, grow mangroves, then place marsh grasses, mangroves and bags of oyster shells along shorelines all over the Indian River Lagoon system.
Once established, oysters provide habitat for birds and fish as well as a hard structure that can protect shorelines from erosion, and wind and wave energy, she said. On the shorelines Walters has developed, the oysters are the initial defenders, providing wave breaks that give the plants time to get established. Marsh grasses help protect mangrove trees, and once the mangroves are established, their intertwined roots begin trapping sediment moving in the water and gradually the surface of the soil rises.
These shorelines with oysters, marsh grass and mangroves can accumulate sediment faster than the sea level is rising in some estuaries, and may help coastal wetlands transition from one kind to another as sea levels rise.
If the water in an estuary is allowed to move naturally up a slope, the mangrove trees will follow that transitional zone, said Candy Feller, a senior scientist and mangrove expert at the Smithsonian Environmental Research Center in Maryland. “In a perfect world, they will keep pace with rising sea levels.”
The problem in Florida is that people like the land-sea margin, said Feller. “They’ve built their houses there and their seawalls and everything.”
Parkinson and others say seawalls aren’t the answer.
"You can’t just build a wall,” because Florida is built on limestone and sand, he said. “The water would just go under or behind the seawall.”
The other option Parkinson raised is withdrawal from the shoreline. It’s “the only plan that is viable in the long term,” he said. “The longer we delay making the right choices, the more difficult it is to implement a plan and the more expensive it’s going to be.”
As DeFreese travels along the Indian River Lagoon, he said he’s beginning to see evidence of change in attitudes toward preparing for long-term sea level rise.
Widder, however, said she still sees too much “head in the sand thinking.”
“This is just going to be catastrophic for us,” she said. “Florida is so vulnerable. For us not to be anticipating the kinds of problems that we’re going to be facing is shortsighted and damaging to all of us.”