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Science on the Edge

January 25, 2008

Mary Ann Travis
mtravis@tulane.edu
Photography by Paula Burch-Celantano

Along Louisiana Highway 1, cypress-tree stumps stick up out of the marsh grass every mile or so. The gray, bare trees look as forlorn as the splintered docks poking into the Gulf of Mexico at the end of the road on Grand Isle—the last stop on the highway. The dead trees and ruined piers appear to have met similar fates in the path of storms and saltwater intrusion.

Science


Scientists on the edge — Jeff Chambers, Tom Sherry, Torbjorn Tornqvist


At Grand Isle, sea level is rising at a rate of nearly 10 millimeters (.39 inches) per year.

“That’s crazy,” says Torbjörn E. Törnqvist, associate professor of earth and environmental sciences.

The present rate of sea-level rise on the Gulf Coast is four to six times higher than in the previous 1,000 years.

Ever since the Industrial Revolution, factories, cars, air conditioning, computers and other trappings of modern life increasingly have spewed out carbon dioxide. And sea level has risen. Louisiana’s coastal land is on a rapid path to submersion; its wetlands in the shape of spindly claws are becoming more tattered with each storm.

But people in other coastal areas in the United States—and the rest of the world—have no grounds for complacency.

“We think what we’re looking at here is actually a global phenomenon,” says Törnqvist. “Because you know it’s all connected.”

Törnqvist is among a group of Tulane scientists who are investigating the mysteries of sea level rise, coastal sinking, earth faulting, trees growing and dying, and birds and plants relating in complex ways to global climate change.

Louisiana is a wonderland of discovery for these intrepid explorers of the natural world. They are geologists and biologists fascinated by the Earth and its delicate ecosystems. They are rigorous scientists who ask questions, crunch numbers, weigh results and ask more questions.

Tulanian talked to six scientists about their work on the ground in Louisiana—and its local and global implications.

filling the gaps

“On average,” says Törnqvist, who is also the director of the Tulane-based National Institute for Climatic Change Research Coastal Center, “if you just let science go as some kind of self organizing spontaneous process, most important things will get done at some point. But sometimes there are these gaps that nobody jumps on.”

Science


Scientists on the edge — Nancye Dawers,
Michael Blum, Alex Kolker.


Among the gaps in knowledge that Törnqvist is filling are why and how fast land in coastal Louisiana is subsiding and how quickly sea-level rise is occurring.

In 2000, 100 miles above the Gulf of Mexico at a bend in the Mississippi River, Törnqvist and his research team began hand drilling holes in a “shoulder of the road in a swamp.” At the field site, they extracted core samples that date back up to 8,000 years. They also measured the elevation of the samples relative to the present sea level.

Back in the lab, Törnqvist and his team continue to analyze the origin of the sediments in the samples and select materials for age measurement at another specialized lab.

“The idea is that organic matter started accumulating as a result of the rise of the water table,” he says.

By finding out the levels at which organic matter—or peat—has accumulated, Törnqvist can document the rate of sea-level rise.

“We can now say that about 6,000 years ago, sea level was probably a little bit more than 5 meters lower than it is today,” says Törnqvist. And it’s been constantly rising.

Lately, Törnqvist’s doctoral student Juan González, who is completing his PhD thesis this spring, has focused on A.D. 600 to 1600, the period before the Industrial Revolution. During that 1,000-year interval, sea level rose about half a millimeter per year.

Compare the pre-Industrial Revolution half-a-millimeter rise to the present-day 10-millimeter-a-year rise at Grand Isle, and you get an understanding of what Törnqvist means by “crazy.”

While the current rate of sea-level rise elsewhere around the world and elsewhere along the Gulf Coast is not as dramatic as Grand Isle’s, (the mean global rate is currently more than 3 millimeters per year) there is still cause for alarm.

And the alarm bells ring from global warming. Törnqvist is interested in the historic relationship between sea-level change and climate change “because that can tell us something about what might happen in the future.”

“The last time we saw sea level rising at rates more than 3 millimeters per year on the Gulf Coast was about 7 or 8,000 years ago,” says Törnqvist. And that rapid rise in water was because a big ice sheet in Canada was melting.

Louisiana is the first coastal area in the United States to experience such extreme sea-level rise and “to suffer the consequences,” says Törnqvist. “But if we don’t do anything, if we just keep doing what we’re doing, sooner or later, people are going to have the same experience in low-lying coastal areas around the world.”

still a mystery

Everyone agrees that Louisiana is sinking. A complicated web of factors contribute to the land’s subsidence: sea-level rise related to global warming, ground compaction related to extraction of oil and the draining of swamps for urban development, dredging of oil-and-gas production canals in the wetlands, and saltwater intrusion killing freshwater marsh grass.
bird
An important element in the loss of wetlands in Louisiana lies at Old River Control, 200 miles northwest of New Orleans. Here is the nexus of the U.S. Army Corps of Engineers’ mighty dam effort to stop the Mississippi River from flooding and from being captured by the Atchafalaya River.

But the single most important factor in wetlands loss, says Törnqvist, “is undoubtedly the fact that we have levees all along the main rivers—the Mississippi and the Atchafalaya—that prevent the wetlands from being nourished with fresh annual layers of sediment, as was the case in the natural state.”

Located 315 miles above the Gulf of Mexico, Old River Control is a structure engineered to keep the majority of the Mississippi River’s flow heading south toward Baton Rouge and New Orleans, preventing it from changing its course and joining the Atchafalaya River.

The Mississippi River previously freely jumped its banks every millennium or so. The river meandered within an arc about 200 miles wide depositing sand and silt for building the land of coastal Louisiana.

Old River Control came online in 1963 and along with the extensive levee system downriver that was constructed in the 1930s as part of the New Deal program has successfully curbed the Mississippi River in south Louisiana from doing what it did for eons—deposit sediment to build land.

The sediment of the river doesn’t build up the delta anymore. The sediment is funneled offshore and falls off into the deep waters of the Gulf of Mexico.

Alex Kolker, a research professor in the Department of Earth and Environmental Sciences, studies marine sediments. He’s charting the depths of Barataria Bay, a body of water near Grand Isle. By crisscrossing the bay in a boat equipped with sonar, he’s gathering data about how fast the delta is sinking. He’s surveying the ever-changing depth of water, trying to put a proverbial measuring stick at the bottom of the bay.

“We know the bay is subsiding, but how fast is still a mystery that I’m busy working on,” says Kolker.

That the wetlands are quickly disappearing, Kolker can tell simply by looking at global-positioning-system maps of the area. Some places where the maps indicate marshland or solid ground, the research boat smoothly glides through water. “The land is no longer there—and the maps can’t be that old,” he says.

Kolker arrived at Tulane in January 2007 with an interest in how climate change and human impacts affect coastal areas. He has done work in Long Island Sound, N.Y., studying wetlands loss. And using data from sites in the Atlantic Ocean—near New York City; Charleston, S.C.; Halifax, Nova Scotia; Stockholm, Sweden; and Cascais, Portugal—he has researched variability in sea-level rise in relation to high- and low-pressure weather systems, wind-driven processes and dynamic sea-level change—the change by storms that is often most damaging to people, property and ecosystems.

The scale of the Louisiana wetlands and coastal ecosystem is much bigger than the Long Island wetlands, which are a blip on the map in comparison, says Kolker.

Barataria Bay is “beautiful and magical,” he says. Grand Isle, the barrier islands, the marshes, lakes, bayous, estuaries, rivers and the Gulf make it a “unique area.”

“Professionally, this is ground zero,” says Kolker. “This is the place to be doing what people in my field do.”

active faults

The way Nancye Dawers views things, the creation of the rich soil of the Mississippi River delta happened almost yesterday.

An associate professor of earth and environmental sciences, Dawers says that the “young” Mississippi River delta was formed in the “recent” past, that is, the last 10,000 years.

Dawers is a structural geologist who studies the evolution of faults in the earth’s subsurface.
She takes the long view—the millions-of-years-old view.

Millions of years before the Mississippi River as we know it began building its present delta, the thick sequence of sediments that underlay it began to fracture, and faults formed in response to the accumulating load of sediment. One of these faults eventually resulted in the formation of Lake Pontchartrain. The lake, which isn’t a lake at all but an estuary where fresh and salt water mix, is, of course, crucial to the situation of the city of New Orleans. While Lake Pontchartrain itself is only a few thousand years old, its northern shore is controlled by an ancient fault system, part of which is known as the Baton Rouge fault.

Most of Dawers’ work has been in the western United States—California, Idaho, Montana and Utah—where seismically active faults have dramatically affected land formations.

She came to Tulane and Louisiana seven years ago, not expecting to find an active fault along the northern margin of the Gulf Coast. But then she heard of a 1944 Mississippi River Commission report that presented evidence of an active fault near Baton Rouge from the Amite River to the Pearl River.

Dawers became intrigued that the Baton Rouge fault had played a major role in the formation of the Lake Pontchartrain Basin.

Slips on the Baton Rouge fault results in subsidence of the area immediately south of it, namely the Pontchartrain Basin. The fault may still be active, Dawers has discovered, although the fault appears to be “aseismic.” Aseismic means it doesn’t produce large earthquakes but rather steady, slow slippage occurs in association with small earthquakes. Some of these earthquakes occasionally are large enough to be felt in the region.

Using high-resolution laser technology and other techniques, Dawers and graduate student Bobby Cosentino are mapping the various segments of the Baton Rouge fault system, trying to determine its long-term history. By measuring the slope of the fault’s topographic scarp—the step it forms in the landscape—they can discriminate between the likely constant, slow displacement of land versus displacement in sudden, large earthquakes.

With another graduate student, Emily Martin, who earned her master’s degree in 2006, Dawers also has explored a fault in southern Plaquemines Parish near Bastian Bay and the town of Empire. They know from early oil exploration data that a subsurface fault exists in the area. There also has been land loss in the area traced to the 1970s—a time of active oil and gas production. However, the pattern of displacement of marshland at this locality is more consistent with a fault than with fluid withdrawal.

The issue of faulting in coastal Louisiana is a controversial topic, says Dawers, because “if faulting is contributing to our subsidence problem, there aren’t any solutions to stopping that process.”

Thousands of years can go by where nothing happens. And then there might be an episode of fault slip. “We just don’t know,” says Dawers, as she continues to look into displacement patterns and slip rates. Like most geologists, she does not predict the future; she seeks to understand processes, both present and past.

katrina’s trees

Global warming probably did not directly cause Hurricane Katrina in August 2005. One high-powered storm drawing on the energy of warm Gulf waters does not precisely correlate to global climate change, most scientists agree.

Ironically, however, the 320 million trees destroyed by Katrina in the forests of Louisiana and Mississippi are actually causing a global warming of their own.

Jeff Chambers, assistant professor of ecology and evolutionary biology, has discovered that the trees killed or damaged in the Katrina storm are releasing more carbon dioxide into the air than all the rest of the trees in the United States can absorb in a year.

Chambers used the same research tools he had been using for 12 years studying wind-disturbance in the Brazilian Amazon rain forests and applied them to the Katrina problem.

Growing, healthy trees act as carbon “sinks” that store carbon dioxide—a greenhouse gas released from other sources into the atmosphere. If carbon is not absorbed, the atmosphere heats up. The decomposing trees of Katrina release carbon instead of taking it in for photosynthesis as they would if they were still alive and growing.

Chambers is associate director of the National Institute for Climatic Change Research Coastal Center (of which Törnqvist is the director). Chambers and his research team used NASA satellite images of the forests before and after the storm to determine the extent of the damage. They also conducted fieldwork at 25 study sites in Louisiana on the East Pearl River. Chambers’ study of Katrina’s dead trees was published by the journal Science in November.

What surprised Chambers more than the staggering number of devastated trees is the impact the decomposing trees are having on the total U.S. carbon sink. “When I first started the analysis, I thought, I’ll bet it will be 20 to 30 percent of the total U.S. sink. It was 100 percent. I was shocked by that.”

He went through the calculations from every angle, but still the figures hold up. And he stands by them.

The impact of powerful, destructive storms is so interesting that Chambers and his research team are launching a study of the carbon effects of all the major hurricanes to hit the United States since 1850.

He also is studying the impact of sea-level rise on coastal ecosystems with other Tulane scientists.

“As a scientist, you are supposed to look at all of it and come up with what’s real—the facts,” he says. And the facts are, “in the aftermath of a hurricane, dead trees release carbon.”

And increased carbon in the atmosphere is a cause of global warming.

And global warming may result in more intense hurricanes.

canaries in the mine

Hurricanes—dramatic, cataclysmic environmental events—are part of the fabric of Louisiana’s ecology, says Tom Sherry, professor of ecology and evolutionary biology.

In the aftermath of Katrina, Sherry is investigating how the Swainson’s Warbler is faring in the bottomland forests of the Pearl River Basin—the same area where Chambers has documented the huge tree loss. This warbler thrives on the kind of “disturbed” habitat that hurricanes create by knocking down old trees. As the ecosystem rebounds, forest undergrowth—vines and such—grows profusely, providing a hospitable habitat for this bird.

Sherry expects that the Swainson’s Warbler—an “indicator species” for the Mississippi
River delta ecoregion—will flourish in the years after the storm.

Indicator species are so designated by scientists because “if the populations of that species are doing well, then that presumably tells us that the ecoregion the species depends on is doing well,” says Sherry.

Under Sherry’s guidance, Donata Henry, who is now a lecturer in the ecology and evolutionary biology department, did her PhD dissertation research on the Swainson’s Warbler in commercial pine forests. Where growers let the forests develop a little bit wild, undergrowth creeps in, and the warblers are strong and healthy. Such ecology-sensitive commercial enterprises show that it is possible for industry to coexist peacefully with the natural world, says Sherry.

The Northern Swallow-Tailed Kite is another indicator species for the Mississippi River delta ecoregion. But it is not doing well in the bottomland forest of the Pearl River, according to Sherry’s former doctoral student Jennifer Coulson. The kite’s major predator, the Great Horned Owl, is eating kite eggs, chicks and even adult females at the nest. The owl usually stays out of dense forests, which are becoming fragmented or disappearing altogether. It is in the dense forests that the Swallow-Tailed Kite previously thrived.

The forest fragmentation that is hurting the Swallow-Tailed Kite, however, is not attributed to hurricanes, but to another facet of global change—residential land development—in this case, in the Slidell, La., area. As trees are cut down to pave the way for housing tracts, the owl swoops in to diminish the Swallow-Tailed Kite. A bright spot in the saga of Louisiana birds is the abundance of wading birds—Great Egret, White Ibis, Great Blue Heron, Little Blue Heron, Rosette Spoon-bill and Night Heron. Along the coast, these majestic and graceful birds wade in the shallow water of the wetlands and feed on fish, frogs, insects and crawfish.

Sherry and another of his former PhD students, Bruce Fleury, who also is a lecturer in ecology and evolutionary biology, showed that a major cause of these birds’ success is the growth of commercial crawfish aquaculture.

For more than 30 years, Sherry has studied migratory birds that winter in the Caribbean and summer in North America. He has published more than 70 articles and book chapters.

He has seen firsthand the impending extinction of birds in the rain forests and elsewhere. As he studies the impact of climate change on ecosystems, Sherry says he feels an obligation to speak out about the need to protect nature and promote conservation.

“The natural world needs advocates,” he says. “Our evolutionary heritage is at stake.” (See Sherry in “Ask the Expert” on page 9.)

evolution and ecology

Marsh plants in the wetlands of Louisiana have been dying as saltwater intrudes into their freshwater habitats. But plants, especially some sedges and grasses, can evolve quickly. So quickly, says Michael Blum, that evolutionary change can accompany ecological change.

Blum, an assistant professor of ecology and environmental biology, is looking at how wetlands are responding to global climate change and sea-level rise. He’s specifically studying plant response to elevated carbon dioxide and increased salinity.

Marshes, like much of the land in coastal Louisiana, have been built up by sediment from the river, and some marsh plants—sedges, in particular—have dropped seeds that become embedded in the sediment.

At a site near Bayou Lacombe in the Pearl River Basin, Blum and his colleagues are taking sediment cores from the marshes and extracting embedded seeds, some of which are estimated to be more than 800 years old.

The sedge seeds have hard coats conducive to long-term survival. In a laboratory, Blum germinates the seeds and then simulates past, present and future environments of salinity, carbon dioxide and temperature regulation to observe how the plants respond. For the future environment, he pushes the carbon dioxide up to 50 percent more than the carbon dioxide in today’s environment, which is the extreme that some scientists are predicting.

In these experiments, by simulating the outer limits of environmental change, Blum can gauge how quickly marsh plants have adapted to changing climate conditions.

With marshes the first line of defense against storm surge on the Louisiana coast, Blum’s work gives hope that it is possible that marsh plants will become more tolerant of high-salinity conditions.

“The marshes may evolve in place,” says Blum.

Blum is a newcomer to Tulane and Louisiana this year. He previously worked in the marshes of the Chesapeake Bay in Maryland and the outer banks of North Carolina, but he says they are small and finite compared to the marshes of Louisiana.

In the fall, he took his undergraduate “Wetlands Ecology” class to Grand Isle for a field trip. During the trip, Blum was amazed at the marsh landscape and the immensity of Louisiana’s wetlands.

Out in the vast wetlands, “You can lose where you’re at,” says Blum. “Nothing compares to the extent of the coastal marshes of Louisiana.”

Tulanian
Winter 2008

Citation information:

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Page URL: http://tulane.edu/news/tulanian/science-on-the-edge.cfm

Tulane University, New Orleans, LA 70118 504-865-5000 website@tulane.edu