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Island time

Little-known barrier islands are helping VCU researchers unlock the mysteries of coastal ecosystems and climate change.


Virginia’s barrier islands seem as if they are made from the sands of time, quickly moving and taking a new shape with each turn of an hourglass. The landscape of this chain of more than a dozen islands located off the Eastern Shore is incredibly dynamic, which allows Virginia Commonwealth University researchers to study the impacts of both global warming and natural shifts in the environment in real time.

The islands take the brunt of the Atlantic’s wave energy because they stand in front of Virginia’s shoreline, which makes them the first warning bells for the consequences of climate change, said Julie Zinnert, principal investigator at VCU’s Coastal Plant Ecology Lab and assistant professor in the Department of Biology in the College of Humanities and Sciences.

“We are looking at the environment and how it’s responding to climate change and both oceanic and atmospheric drivers because the plant communities here are really at the forefront of the terrestrial and ocean boundary. They are the sentinels of climate change,” Zinnert said.

The islands show how rising sea levels and temperatures can shape coastal areas. Their eroding shorelines recede several hundred meters in a span of months, which causes woody shrubs to fall into the sea. Shrubs that favor higher temperatures and grasses native to warmer environments, such as green stalks of sea oats from farther south in the U.S., are thriving as they never have before.

But not all changes are due to global warming. Shifting geography is also at the heart of a barrier island’s nature. New dunes continuously form and swales — depressions between dune ridges — deepen. A path once laboriously maintained across one island’s two-mile width is now completely overgrown with blackberry thickets, shrubs and grasses that must be parted with a machete after several months of neglect. The land masses themselves also migrate due to wave energy and shifting sediment.

The constant erosion and other dynamics of these islands could serve as a warning to areas such as New Jersey’s Long Beach Island, and Miami, where sea level rise impacts urban development.

Living in these regions is a gamble, said Donald Young, Ph.D., professor of biology and senior associate dean of finance and administration in the College of Humanities and Sciences.

“It’s a harsh environment. It’s not to be conquered by us,” Young said. “We need to learn to appreciate and live with it.”


A wealth of knowledge

Zinnert and Young work with other scientists at the Virginia Coast Reserve Long-Term Ecological Research station, located in Oyster, a short boat ride from the islands. Zinnert said their observations of natural and global warming-induced climate changes allow scientists to infer how barrier islands around the world may be impacted in the future, and it informs environmental education efforts and policy decisions.

“Our work provides the community with the knowledge of how plant ecology interacts with the physical environment to enhance conservation and management of these dynamic ecosystems,” Zinnert said.

Researchers in VCU’s biology department and experts from several entities on the East Coast form the VCR LTER. The University of Virginia holds the primary grant for the site and the islands themselves are maintained by The Nature Conservancy.

Young was VCU’s primary investigator at the site for 24 years before Zinnert took the lead two years ago. The university’s work has been funded by the National Science Foundation for more than 25 years, with supplemental grants from other sources.

The research station is one of nearly 30 across the country in the Long-Term Ecological Research Network, which is the largest and oldest ecological research network in the United States. The LTER has been funded by the NSF since 1980, with the purpose of solving ecological problems that can span several decades and geographical areas.

Edward Long, an undergraduate who majors in chemistry, removes soil from a soil core to be analyzed for bulk density and other factors.
Julie Zinnert, Ph.D. and her students in the Coastal Plant Ecology Lab perform a bucket burial experiment on Hog Island.
Zinnert explains experimental design to undergraduate student Austin Tuley before sampling light intensity across grassland and thickets.

Changes wrought by man and nature

Many of the islands in the chain are literally disappearing due to erosion, according to VCR LTER’s continuous research record.

“The islands are very beautiful. It’s one of those things people don’t know exist in their very own state, and the fact is they’re rapidly changing,” Zinnert said. “There are pictures that exist of homes that used to be on the islands that are now in the waves because the islands are rapidly retreating due to sea level rise, and it’s so dramatic just in our very short time.”

Satellite imagery collected from 1984, 1988, 2011 and 2016 show that 10 of the islands — Metompkin, Cedar, Parramore, Hog, Cobb, Wreck, Ship Shoal, Myrtle, Smith and Fishermans — have shrunk by 27 percent since 1984. At the same time, shrub cover has spread over 40 percent of the landscape, much of which was formerly grasslands behind sand beaches.

Zinnert and Young said shrub proliferation contributes to the rapid erosion. Rising temperatures and CO2 levels that are the result of global warming benefit the shrubs.

These plants prevent island rollover, a natural process that constantly changes the landscape of narrow barrier islands and is vital to their existence. Wave energy, much of which is hastened by storms, pushes sediment over the dunes that lay directly behind the shoreline. As a result, sediment is deposited behind the dunes on the mainland-facing side of the islands, which contain swales and marshes.

Zinnert and her students in the Coastal Plant Ecology Lab walk through shrubs and thickets in the center of Hog Island.

As the sediment continues to shift over time, a cyclical pattern is formed that causes the island to move and “roll over” onto itself as more sediment is deposited landward. It’s reminiscent of a bike being propelled forward by a chain rotating over cogs.

“As time goes on, blowouts over dunes will turn marsh into upland. So, the island visibly starts to move on the landscape,” Zinnert said.

Instead of rolling over, large portions of the islands are eroding because shrub roots lock sediments in place and the shrubs themselves are a barrier to sand movement. Cobb Island has undergone one of the most dramatic transformations. The 200 hectare island has lost well over half its land area since 1984.

Some islands are still moving. Parramore, which spans nearly 900 hectares, has a north end covered in woody vegetation and tall dunes that is predicted to erode until it’s narrow enough to move. In order to roll over, an island must be thin enough for sediment to reach its landward side.

Shrubs are not only expanding on barrier islands, they’re taking over many grasslands across the globe. Bayberry engulfs miles of Virginia’s coast, while birch willow and alder have spread in the Arctic. Acacia permeate much of the Serengeti and Australia, and other shrub types are seen throughout the world. The increase in global temperatures allows them to thrive, researchers say. The shrubs are also particularly hardy due to survival mechanisms. They thrive without nitrogen and raise surrounding ground temperatures, which creates microclimates. Shrubs spread aggressively and easily crowd out other plant species.

a. Woody vegetation covers Cobb Island. b. Cobb Island's land mass in 1984. c. Reduced landmass in 2011.

Island harbingers

The lesson taught by Virginia’s barrier islands is to take caution living and developing on these landscapes that are naturally moving with the tides, or eroding due to rising sea levels.

Coastal mainland populations worldwide should also take heed. These disappearing islands are not only sentinels of climate change, they’re guardians of coasts because they help shield the mainland from storm energy. The marshes and lagoons on their landward sides, behind the ocean-facing dunes and beaches, are home to a variety of wildlife.

“Those islands protect the mainland, the fisheries and oyster beds,” Zinnert said. “There are a number of people on the Eastern Shore who sell local oysters from the lagoons, so there’s an economic benefit.”

Other barrier islands along the East Coast in areas such New Jersey, the Outer Banks in North Carolina, and the many islands along the coasts of Georgia and Florida are eroding. Similar to the effects of shrub proliferation, continued development has blocked island rollover by not allowing sediment to move.

Over the last 100 years, the southern portion of Hog Island was eroding while northern end was accreting (growing) due to sediment transfer.

Even before tourism growth and substantial migration to barrier islands, the natural island rollover process slowly condemned abandoned towns to the waves. Broadwater, formerly a small town of about 300 people, was located on the south end of Hog Island, but was uninhabited by the 1930s. In its prime, the town included a bank, school and other markers of municipal life. As the shores eroded, a few homes were barged to the mainland, but the remaining edifices eventually tumbled into the waves. The town is now about a kilometer out to sea.

On Wreck Island, old dock pilings peek out of the waves on the ocean side of the land mass. It’s an odd sight because boats require the protection of smoother waters on an island’s landward side. Over time, Wreck has moved so much it has literally rolled over the dock, which was originally on the island’s opposite side.

To combat both erosion and migration, there are solutions such as levees, walls and the creation of artificial beaches. But these fixes are temporary and expensive.

“We evoke our static world on one that is dynamic and moving,” Young said. “All you can do is build the islands up, put walls up and put people behind the walls. It’s going to be a really interesting next century or two.”

"It’s going to be a really interesting next century or two."
Footnote: Story by Leah Small, University Public Affairs. Photos by Allen Jones, University Marketing. Video by Max Schlickenmeyer, University Marketing.