Megan Clevenger and Miles Neilson don’t mind getting stuck in the mud.
In fact, the University of Mary Washington environmental geology majors have developed a keen appreciation for the slick, estuarine deposits that lie below the surface of the Potomac River.
Under the guidance of Professor of Geology Neil Tibert, they’re exploring the wetlands along the Potomac, digging up the muddy clay and analyzing the sediment to examine the impact of sea-level rise in the Chesapeake Bay watershed.
“We’re able to see how the river looked thousands of years ago,” said Neilson, a senior from Williamsburg. “If we can understand how the bay reacted to sea-level rise in the past, we can predict what’s going to happen to this area in the future.”
Their results, which they presented earlier this month at the Geological Society of America conference in Baltimore, are eye-opening.
“Our data shows sediment and sea-level rise during the last century are two to three times the global average,” said Tibert, who has studied erosion and the climbing water level along the Potomac since he arrived on UMW’s Fredericksburg campus 13 years ago. “In the coming centuries, we’re looking at impact in meters, not centimeters, which is what you would expect with global warming from melting ice.”
Their research, now in its second year, is supported by a four-year $74,000 grant from the U.S. Geological Survey.
Until now, the central regions of the Chesapeake Bay area have garnered little scientific notice, said Tibert. He believes that is about to change. As one of the largest estuaries in the world, Tibert said, the watershed may be a bellwether for understanding sea-level rise in other regions of the globe.
The unprecedented changes in sea level will mean significant flooding of existing infrastructure in the Chesapeake Bay region, said Tibert, a native of the Bay of Fundy in Nova Scotia.
“Look at Tidewater,” he said. “Look at Richmond. All of the cities are at the fall line, where oceans begin and rivers end. Every highway, every bridge will feel the impact in the next 50 to 100 years. We’ll need to start planning now to know where we are going to put our highways and bridges.”
For the past two summers, the trio spent several days a week on the University’s 22-foot research boat, known as the UMW Eagle 1, trolling the Potomac wetlands around Colonial Beach and Westmoreland County. The boat, equipped with coring and geophysical equipment, allows the UMW researchers to study the sediment deposits below the river bottom. A new boat, currently under construction, will replace the Eagle 1 in 2016. To be known as the UMW Eagle II, it will be rigged with a covered pilot house to provide much-needed cover to protect the sensitive electronic instrumentation.
The group also works in collaboration with a geology team of undergraduates from Salem State University in Massachusetts under the guidance of Associate Professor Brad Hubeny.
The researchers locate sediment changes in the river bottom with a CHIRP (Compressed High-Intensity Radar Pulse) detector that penetrates the water and records changes of sediment thickness, providing a subsurface record of the region’s sedimentation history.
“With the CHIRP detector, I can look at the bottom and everything buried underneath the bottom,” said Neilson, whom Tibert calls “the CHIRP man” because of his adeptness at operating the high-frequency sonar device. “It’s like an X-ray of the ocean floor.”
From the boat or waist-deep in a marsh tidal flat, they drop long tubes below the surface to take samples and record sediment changes.
“It gives us a better understanding of how thick the sediment is and how far it extends,” Tibert said. “We see where changes are occurring. We see faults or tributary channels that were once active below surface. We want to understand what’s contributing to these extra sedimentary layers.”
They also record the water temperature and salinity, and are able to reconstruct both sea level and climate changes over time by studying oysters and other tiny organisms that live in the bay.
Once the samples are taken, Clevenger’s work begins. Embracing her “Mud Queen” nickname, she processes the sediment samples and cuts them into centimeter-sized sections. Back in the classroom lab, she burns the samples in a furnace to measure the amount of organic matter, and examines sticks, seeds or shells within the sample that are sent off to Woods Hole Oceanographic Institution for Carbon 14 dating.
“Our oldest sample was 5,000 years old,” said Clevenger, a native of Oswego, New York, who earned a zoology degree before coming to UMW. “It’s amazing to work with something that old.”
They also discovered Colonial oyster beds, including one near Stratford Hall that no longer exists. They’ve been buried by sand and silt washed into the water from farming and development since the Industrial Revolution.
“Oysters have been a source of income and food for the past several hundred years,” said Tibert. “People’s livelihood depends on those oysters.”
While the old oyster beds can’t be re-established, he said that recent efforts to grow new oyster beds have been successful.
Neilson will graduate in December and Clevenger in May, but the hands-on experience with Tibert has helped shaped their future. Both are looking at graduate schools and careers in environmental research.
“It’s one thing to read in a scientific journal about these studies on sea-level rise,” Neilson said, “but it’s mindboggling to know you’re part of something groundbreaking, something so much larger than yourself.”
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