Editor’s note: This story is part of a series, The Wild Side of Sea Level Rise, which explores the basic research behind ocean expansion and its impacts on coastal ecology.
If you drive north on I-95 between Brunswick and Darien, Georgia and peek over the overpass, your eyes will be drawn to a tranquil sea of grass that stretches for miles toward the Atlantic Ocean. But a closer look at these wetlands reveals something else. A giant outdoor experiment called SALTEx.
When one thinks about climate change, the mind is naturally drawn to the big shifts. Giant glaciers will melt into the sea; huge hurricanes will batter cities like New York or New Orleans. But on Georgia’s Altamaha river delta and sea islands, the effects of sea level rise are already being felt, like tiny cuts. The wound is slow.
SALTEx isn’t just a lab in the wilderness, it’s a time machine. It is a large-scale simulation of one devastating side effect of rising seas: saltwater intrusion into freshwater habitat. SALTEx shows what happens when this slow wound becomes an ulcer. Salts seep into tiny pores in the soil and stick. Toxic microbes multiply in the soil, each one burping out a microscopic amount of poisonous gas. Plant roots, the glue of the marsh, begin to recede, and the land sinks.
This gradual exposure to more saltwater is poisonous for freshwater wildlife, and the problem isn’t limited to marshes on the coast. Saltwater is pushing further upstream into rivers. Already, centuries-old trees are beginning to die miles from the shore as the ocean migrates inland into freshwater rivers.
The SALTEx project is part of the Georgia Coastal Ecosystems Long-term Ecological Research (LTER) project. There are 25 LTER sites worldwide funded by the National Science Foundation that study long-term transitions in different ecosystems. Marine scientist Merryl Alber directs the Georgia Coastal Ecosystems project as well as the University of Georgia Marine Institute.
Unlike a typical science study, which lasts three to four years, Alber and her colleagues run single projects that extend for a decade or longer. By taking extra time, the researchers can dig deeper into the myriad nature of ecosystems.
The salt marshes of the Altamaha river delta and its barrier islands are a sort of ecological cathedral. This coastal region shows what happens in a relatively pure environment. Researchers here devote much of their time to studying the alarming and already-very-present outcomes of sea level rise. And if wildlife becomes imperiled here, it may spell worse tidings for other coastal habitats.
Do It Yourself Sea Level Rise
With sea level rise, each tide chips away an ecosystem that has existed for 5,000 years.
Our tour of SALTEx began at Meridian dock, about 10 miles away from the actual study site. We reached the dock at dawn, as a fog hung thick and low over the marshes north of Darien, Georgia. Alber along with wetland scientists Christ Craft, Ellen Herbert and Dontrece Smith welcomed us near the landing, with a white ferry bobbing behind. The ferry is the primary means of transport between the mainland and the marine institute’s camp on nearby Sapelo Island.
Smith began this workday, as he does four mornings per week, by using a motorized pump to lift 4,000 pounds of ocean water into a giant plastic tank loaded onto a pickup truck. Once done, we drove through Darien, where live oak trees line two-lane roads like a guard of honor.Their branches extend in a salute with spanish moss drooping like oversized sleeves.
We park by the entrance of a long levee that acts as one of SALTEx’s borders. Fire ants scurry everywhere, and frenzied mosquitoes bite through clothes. One bites my lip within seconds of opening the car door. We walk along a levee, the ground hard and sandy, until we reach the boardwalk.
Craft and Alber developed the idea for SALTEx in 2010. Building anything in a marsh is challenging. The soft ground and heat want to absorb or rot most materials like a swamp monster. So Craft and Herbert, who are based at Indiana University, recruited a platoon of students and technicians to put a plan in action.
Over the next two years, their team performed pilot studies and gained land permits from the U.S. Army Corps of Engineers to construct a 1,250-foot boardwalk through the soggy marsh. The foot-wide boardwalk is made from plastic lumber that allows light and water to penetrate. The support structures are recycled plastic four times heavier than plywood. It took a year of assembling and laying out the segments — plank by plank — to build the boardwalk.
In April 2014, the SALTEx team began treating this freshwater habitat with saltwater. The team obviously can’t drive a heavy truck and its saltwater tank directly onto a muddy marsh, so they’ve built a 110-foot-long PVC pipe to link the pickup to two holding containers adjacent to the plots.
“The river is just on the other side of those trees,” Craft said. “We have a 1,000-foot pipe that goes out there to pump freshwater. We mix fresh and saltwater to our desired concentration in these holding tanks, and then Dontrece pumps the water to the plots over a 3,000-foot network of pipes.”
SALTEx is organized into a grid of 30 squares — 10-by-10 meter plots. Each plot has four species of freshwater plant and a fountain spout connected to the holding tanks. The plots are either controls or receive one of two saltwater treatments: press or pulse.
Craft described “press” plots as chain smokers because they receive continual saltwater exposure throughout the year. Pulse plots, in contrast, are occasional smokers that get hit with salty water only during September and October.
Pulse plots simulate what happens during drought conditions when the water volume coming down the river is low. Ocean water fills the void by moving further upstream at high tide. During droughts, salt concentrations in the river near SALTEx can jump 25-fold — from 0.2 to 5 practical salinity units. So the team is using water with 5 practical salinity units to press and pulse plots, even though they predict droughts will become more severe and more frequent in the future.
Stepping into the marsh between the SALTEx plots, we’re immediately surrounded by five-foot tall cutgrass, which, as its name suggests, can slice through skin. Twinkie-sized grasshoppers crawl on its treacherous blades. Other marsh plants, like primrose willow, smartweed and pickerelweed fill the plots too. It’s low tide, and tiny crabs traipse in the mud.
On the surface, they’ve found what you would expect: higher salinity kills freshwater plants. But the plants are dying much faster than anyone expected. And the real changes are happening underground, Herbert says.
“The marsh grass is extremely productive. The amount of biomass and plant material that they produce every year is on par with tropical forests,” she said. “That biomass and plant material is part of the physical structure of these soils. Live and dead roots from the plants build the volumes of the soils.”
Marsh plants hold the sediment together, not only with their roots but also, when they die, with their corpses. The plants are the glue. Normally, with rising oceans, the marshes would have the natural ability to grow vertically against sea level by accumulating dead plant material, Hebert said. But the researchers have learned that elevated exposure to saltwater stunts this replenishment. By using a sedimentation erosion table, in essence a narrow pipe driven 50 feet into the ground, Craft has found that marsh plots at SALTEx are sinking – at twice the normal rate.
“We expected this sort of degradation and decline of the marsh over about a four or five-year period, but we’re seeing it in the second year of the study. It’s happening faster than we thought,” Craft said.
The significance of this finding is troubling. As saltwater intrudes and more plants die, the marsh sediment will likely begin to degrade and dissolve. The result: the marsh land will sink, allowing more ocean water to creep onto the coast.
At the root of the problem is a shift in soil chemistry. Seawater has a lot of sodium chloride — that’s the common salt in our saltshakers — but it harbors other dissolved salts too, like sulfate. Some microorganisms use sulfate as fuel to grow and reproduce. They’re called sulfate-reducing bacteria, and they produce hydrogen sulfide gas.
More seawater means more hydrogen sulfide gas. That’s a problem because this gas is toxic to freshwater plants, Craft said.
Extra salinity also poisons a kind of bacteria that allow freshwater wetlands to serve as nature’s kidneys.
“Creeks and rivers are like arteries that feed our waste from cities and farms toward the ocean. Wetlands clean out the muck and waste,” Alber said. Nitrate is a major water pollutant in this waste.
Microbes called denitrifying bacteria are vital to the health of freshwater wetlands and removing waste. Denitrifying bacteria take nitrate and turn it into nitrogen gas, which is a key component of our atmosphere.
“When you add seawater, it poisons these bacteria, and so the wetlands’ ability to remove nitrogen and keep the water clean is going to be compromised,” Craft said.
Bald Eagle Squatter
At SALTEx, scientists have artificially simulated saltier conditions. But downstream, saltwater intrusion is occurring naturally, and you can see the impact.
We left SALTEx just before noon and hopped on a speed boat at nearby Two-way Fish Camp. We snaked south through branches of the river until we were just an eyeshot away from the Buttermilk Sound, four miles downriver from SALTEx.
A field of brackish marsh spread before us. Saw grass and wheatlike spartina grass formed the leading edge, while black needlerush poked up behind and filled the rest of our views. And just 300 yards from us, tall woody skeletons sprung from the marsh. These centuries-old bald cypress trees stood like starved sentinels. Grey spanish moss clung to the faded bark, which split as if festered with bursting boil. In the leafless branches, bald eagles had built nests. Known as snags, these dying cypresses feel like ghosts of the marsh.
“We think of this area as an analog to sea level rise. As the estuary becomes saltier, and the saltwater moves into these historically freshwater areas that would have been dominated by charismatic tidal marsh trees like cypress and tupelo gum,” Herbert tells me through ruby red sunglasses. She has an energetic spirit that comes naturally to a freshly minted doctorate and the determination and grit required to work in a damn swamp.
“What you see behind us are the dead snags, and the grasses moving in underneath,” she said. “Obviously that’s a huge transition for the ecosystem, both in terms of the species that want to exist there and the physical structure of the estuary.”
As our boat pilot and marine scientist Jacob Shalack swung our speeder around, Herbert explained that this trend won’t just be transformational near the ocean, but could also seep deep inland. We zoomed 15 miles upstream, where the team monitors the threat in a patch of freshwater forest that is naturally being exposed to increasing amounts of saltwater with each rising tide.
“There’s probably 15 different tree species in here,” Craft said pointing one by one. “Two species of gum — tupelo gum and black gum as well. There’s wet oaks in here, red maple, and then there’s this big understory of palmetto that also grows in drier areas.”
All of these trees are at risk. Two years ago, the team donned a thin steel belt around 40 cypress trees. The belt — called a dendrometer — tracks the tree’s growth rate as the trunk expands. By measuring the tree’s “waistline” at regular intervals, the team can determine if saltwater intrusion is slowing the trees’ growth and ultimately killing them.
“We think the growth rates will go down, but we’re going to make our first set of measurements this winter,” Craft said.
After lunch at Mud Cat Charlie’s, we venture back to Meridian dock for the afternoon ferry to nearby Sapelo Island. As we cruise across the sound, I chat with Alber about the legacy of the University of Georgia Marine Institute, which is housed there.
An Emerald Isle Of Grass
Sapelo Island is an emerald relic of the Ol’ South. Unlike nearby sea islands like Saint Simon’s or Hilton’s Head, which became resorts about a century ago, Sapelo has remained unblemished. On the barrier island’s north side, green marshes and live oak forests exist alongside deserted plantations called Chocolate and Raccoon Bluff, names that betray the area’s pre-civil war roots. To the south, fewer than 60 residents occupy the historically all-black, former slave community of Hog Hammock — the island’s sole town. A handful of paved roads, dubbed the Autobahn, wind from Hog Hammock to the Long Tabby grass air strip and south to an old lighthouse near Nanny Goat beach and the marine institute.
Sapelo Island is also considered the birthplace of coastal ecology, Alber said.
During the early 1900s, Sapelo was owned by Detroit-based automotive pioneer Howard Coffin, who kept the island as a speculative ranch and private getaway. He entertained guests like aviator Charles Lindbergh and presidents Calvin Coolidge and Herbert Hoover. When the Great Depression ruined Coffin, R.J. Reynolds Jr., a tobacco tycoon and future co-creator of Delta Airlines, purchased most of the island in 1934.
Ironically, these two industrialists kept Sapelo from industry. Rather than build beach condos, they allowed nature to persevere. Causeways to the mainland eventually became too expensive to justify, so the marshy island remained unburdened by modernity.
“If you fly over at night, you’d likely miss the island. Without light pollution, it blends into the dark salt marsh and ocean on the Atlantic shelf,” Alber said. McIntosh county, where Sapelo and the Altamaha delta, remains the least developed area on the Georgia coast.
Sometime in the late 1940s or early 1950s, RJ Reynolds met Eugene Odum, a biologist at UGA whom some regard as the father of modern ecology.
“Odum came out here to see rare birds, and they met. The legend goes that they shared a bottle of scotch and Reynolds was impressed by Odum’s passion for ecology,” Alber said.
And so the UGA Marine Institute was born. Ultimately, Reynold’s wife, Annemarie Schmidt, bequeathed their land to the state of Georgia, which converted much of the island into a nature preserve.
When we arrived, Alber gave us a tour of the converted dairy complex that Reynolds donated for the institute’s home. Aquamarine tiles line the floors. A milking room now houses big autoclaves for sterilizing beakers. We pass by a drying oven, where plant specimens are preserved by baking. It smells like herbs roasting on Thanksgiving. Step outside, and you’ll face a courtyard and a fountain covered with stone turkeys.
In the 1950s and 1960s, the institute became a haven for long-term research. Rather than work on a project for days or weeks at a time, scientists could spend years on an outdoor investigation. In the early decades, it wasn’t unusual for scientists to make the marine institute their home, while they made landmark discoveries. For instance, biologist John Teal lived on the island from 1955 to 1959, in which time he recorded the first carbon budget for a marsh. His 1962 publication on the work would ultimately lead to the discovery that salt marshes are an enormous carbon sink.
Salt marshes can store twice to four times as much carbon as mature tropical rainforests. Once a place like the Amazon reaches its full capacity, meaning no more land can be covered by terrestrial plants, the rate at which the forest continues to be a sink for atmospheric carbon dioxide levels off. In salt marshes, that is not the case. They become larger sinks for CO2 as plant matter builds and buries organic carbon in the sediments.
“If we lose these habitats to sea-level rise, it’s possible that more carbon and other greenhouse gases will be left in the atmosphere, which could exacerbate global warming,” said UGA biochemist Chuck Hopkinson, who has continued Teal’s work by examining how rising seas influence salt marsh evolution and the maintenance of carbon cycles.
To see what this means for carbon cycles, the team built a tower in the middle of a salt marsh near the Duplin River, which drains from the island into the Atlantic ocean. The tower continuously measures the exchange of carbon between the marsh and the atmosphere (10 measurements every second).
“When you look at the flux tower data, the rate of carbon dioxide exchange drops very rapidly when the marsh becomes flooded,” Hopkinson said, as we teetered on a narrow footbridge, seven feet above the muddy, crab-covered ground.
When high tides flood the marsh, scientists suspect that much of the carbon that would normally be trapped in the sediment is being caught by the tidal water and drained out of the marsh at low tide. Analysis of water samples collected at the mouth of the tidal creek that floods and drains the flux tower marsh confirms this.
“Right now, our preliminary estimates are that maybe 10 or 50 percent of the carbon dioxide that normally would have gone to and from the atmosphere is going out in the tidal creek water,” Hopkinson said.
That’s a concern because that extra carbon seeps into other environments, like the ocean, and can get released back into the atmosphere.
$2 Billion Squeeze
So what does saltwater intrusion at the Altamaha river mean for the rest of the coast?
The Chesapeake Bay, where marsh ecologist Matthew Kirwan works is dealing with the fastest rate of sea level rise along the Atlantic coast. Kirwan’s family has lived along the bay for thousands of years, so he’s had a front seat to the transformation.
“Next to the Blackwater National Wildlife Refuge, I can see places where my relatives used to have a vegetable garden. I can see places where there were strawberry fields that then became trees and now all that’s left is marsh with dead trees above it. They were growing strawberries there until maybe four years ago,” Kirwan said.
Much of the bay is rural, so for now, there is room for marshes to migrate inland. On the whole, the Chesapeake Bay is losing as much marsh to sea level rise as it’s gaining through inland intrusion. However, there are spots where migrating marshes are starting to bump into land developments.
Such is the case for the Chesapeake’s Blackwater National Wildlife Refuge. The refuge has lost more than 5,000 acres of tidal marsh over the last century. “Outside of Louisiana, Blackwater is the posterchild for marsh loss in the world, said Kirwan, who works at the Virginia Institute of Marine Science and for the Virginia LTER.
There too, the rapid marsh loss is a threat to the wildlife, which is slowly losing its protected home. In response, the state and some conservation groups are buying the farmland that surrounds the refuge. As of January, they had purchased about 2,300 acres or about half of what’s been lost to sea level rise. However, there are no guarantees if this solution will work long-term, especially with Maryland residents.
And similar to the Altamaha delta, as waters rise, the coastal forest is dying too, but Kirwan doesn’t think that’s all bad.
“If you go out in the field and look at where the marsh meets the land, a pessimist is going to see a lot of dead and dying trees. An optimist sees a beautiful marsh growing under those dead trees. That new marsh is providing a wonderful habitat for some birds. It’s sequestering a lot of carbon, and it’s protecting us from storms,” Kirwan said.
Back along the Altamaha river, Alber is concerned that there isn’t room for freshwater landscapes to move inland as sea levels rise.
A 2010 study commissioned by the U.S. Environmental Protection Agency found that residential development in McIntosh County had recently experienced a surge, and a 2012 report by the Georgia Conservancy says the county has “the largest percentage of residential land threatened by flooding due to sea level rise.” For the Georgia coast in general, Climate Central says that $2.5 billion in property value sits on land less than three feet above the local high tide line. This report predicts sea levels in this region to rise by a foot by 2050 and close to four feet by 2100.
“There’s no place for the tidal fresh forest to move further upstream, because those areas are developed. So there’s concern about what will happen to the wildlife that depend on these areas,” Alber said. “If there were no humans on the landscape, this would probably just roll into new areas. But that isn’t something that can happen here.”
In the future, coastal residents will be forced to decide whether to vacate or protect themselves through coastal armouring. As a defense against sea level rise, people are building physical structures, like bulkhead or riprap, to block the oncoming waves. Kirwan says 20 percent of the Chesapeake Bay is armored, but these structures doom the marsh by preventing migration.
I spent a night on a Sapelo Island in one of the marine institute’s dorms. It resembled a beachside bungalow, except its vista was of a vast salt marsh. Generations of researchers have lived in these houses during their long studies at the institute. Decades earlier, Chuck Hopkinson lived for 10 years with his family in an adjacent house. His second daughter was born there.
On the beach that night, I scanned the night sky for the Big Dipper and the North Star. It’s always comforting to know where you’re going. High above us, a plane flew over, with passengers who likely couldn’t see this dark marshy island, and its uncertain future.