The Scientist Who Reads a Lost History in the Mud

Hard working and tough as nails, Grace Brush did what others couldn’t—she teased out the mystery of the Chesapeake Bay.

Published November 1, 2017

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“Let’s drive to Soldiers Delight,” says Grace Brush. So out we go up Baltimore’s treeless Reisterstown Road and down county back roads through Maryland’s thick summer green. Suddenly, we’re among hills with sparse grass and a slightly scrubby forest. This is Soldiers Delight Natural Environment Area, a serpentine barren that looks out of place in this lush country. It’s a peculiar landscape and Brush is a paleoecologist, an expert in the history of landscapes. She views landscapes the way physicians view bodies: systems of interconnected parts, changing with time, resilient until they’re not.

Brush is 86 years old, so we stump cautiously along paths that are interrupted by corrugated pavements of silvery gray-green serpentine rock. It’s a little hard for her to navigate, though she’s paying less attention to her balance than to the rock itself. Serpentine was born directly from the Earth’s mantle and when it weathers, she says, “you don’t get much soil.” The dirt that does weather out is shallow, low in plant nutrients, and doesn’t hold water, so few tree species grow here. Brush points out what does grow—blackjack and post oak, sassafras, greenbrier, grasses, and ferns—and stops to examine the individuals. Our progress is slow but relentless.

In the early 1800s, Soldiers Delight’s serpentine was found to contain chromite, and this area and the nearby barrens were mined; for a while, Baltimore County was the world’s largest supplier of chrome. Brush walks me to the open-pit Choate Mine, talking about how the mines and later the invasive suburbs meant that natural wildfires were quickly stamped out. But “grasslands need fires,” she adds, and without fires, “Virginia pine moved in.” Beginning in the 1960s, a group of ecologically minded citizens lobbied to protect the area, cut the pines, and set up controlled burns. The serpentine barrens are now returning to their normal abnormality, which includes many rare wildflowers.

Brush takes a wildflower identification book out of her jacket and stops to identify tiny flowers on thready plants, though we’re a little early in the wildflower season. “We’ll come back,” she says. We came in the first place because Brush wanted to show me what she means by “landscape,” that is, space plus time, cause and result, from the rock to the dirt to the plants; birth, destruction, restoration.


Brush’s true love and deepest expertise is in an entirely different landscape, that of the Chesapeake Bay. She was 41 years old and living in Baltimore about the time the bay was found to be dying. The Chesapeake is an estuary, the world’s third largest, created in part by 150 rivers that drain 166,000 square kilometers and flow into the Atlantic Ocean. Thus, the bay is a mixture of fresh and salt water. It has 3,600 species of plants and animals, and its watershed area has 18.1 million humans. Its fisheries are worth billions of dollars and they employ tens of thousands of people.

Historical photo of oyster fishing on Chesapeake Bay
Early European settlers were struck by the abundance of oysters in the Chesapeake Bay, noting that they “lay as thicke as stones,” and for centuries fishermen raked in large catches. But in the 1970s, the catches began declining in an alarming way. Photo by Granger Historical Picture Archive/Alamy Stock Photo

But in the early 1970s, the Chesapeake was rapidly losing oxygen, fish, oysters, and plants. The loss coincided with the growth of the environmental movement, and the newly created US Environmental Protection Agency (EPA) began funding scientists, including Brush, to figure out what was wrong with the Chesapeake and how to fix it.

Ecological landscapes are notoriously complex, with many variables and an unknown number of unknown connections: “When we try to pick out anything by itself,” the famous naturalist John Muir once wrote, “we find it hitched to everything else in the Universe.” Ecologists wanting to restore a broken landscape must deal with not only that complexity, but also with shifting baselines. That is, ecologies change with time, shifting naturally through stability to instability to the next stability. So one of the big questions facing ecologists is: to which stability should restoration return?

Brush’s approach to the problem was meticulous, elegant, and obvious: before fixing the Chesapeake, figure out the long history of its shifts and changes. With colleagues and generations of graduate and undergraduate students (whom she carefully credits), she took core samples of the bay’s sediments, the oldest of which date back a little over 14,000 years. In the sediments, she counted pollen grains and other tiny indicators of what was growing on the land and what was living in the water, and assembled an ecological history of the bay.

The project took decades of detailed work. For the past 40 years, Brush has thought through the complex living arrangements of the bay landscape, identifying every variable and measuring each one to see how the Chesapeake got from then to now. “Gracie chasing down the past,” says Walter Boynton, an ecologist at the University of Maryland. Core by core, variable by variable, methodically, precisely, Brush pieced together evidence of the relationships between failing fisheries, river sediment, the sudden disappearance of underwater grasses, and a bay with a serious chemical imbalance.

Grace Brush and her associates take core samples in Chesapeake Bay

Through more than 30 years of coring and analysis, Brush’s research detailed the harmful effects of deforestation, agriculture, and chemical fertilizers on the ecology of the Chesapeake Bay and its species. Photo by David Harp

“Brush’s work was foundational,” says Rich Batiuk, the EPA’s associate director for science, analysis, and implementation.

And she accomplished much of this without tenure and the usual net of academic securities. Some universities gave her not contracts or salaries, but access to work space and graduate students. She funded most of her work with grants, one after another, never sure where the next one would come from. She got her first tenured position at Johns Hopkins University in 1990, when she was 59, an age at which most scientists are past their prime. Her most recent scientific papers were published this year. One of her former graduate students, Daniel Bain, a geologist at the University of Pittsburgh, says “she’s tough as heck.”


Grace Somers Brush is of medium height. She has curly, sandy-gray hair, doesn’t stand quite as straight as she used to, and looks like she’s nobody in particular. If you’re talking mundanities, she’s polite but her attention tends to drift. If you want to know about the silt piling up in the Susquehanna behind the Conowingo Dam, she snaps to, knows exactly what she thinks, says so, and backs it up with evidence.

Brush grew up in rural Nova Scotia, going to a tiny country school with a monthly delivery of books, all of which she read. She spent a lot of time outdoors in the woods and at a nearby lake. “Nova Scotia was totally glaciated,” she says, so her outdoors was a postglacial landscape of bogs, lakes, rocky coasts, and sandy beaches, as well as a northern forest with conifers, maples, hemlocks, and aspens. When she was 13, her only option for continuing education was a boarding school in Antigonish, 40 kilometers from her home; she stayed in the small town to attend St. Francis Xavier University. One of her classes took a field trip to an outcrop called Joggins Fossil Cliffs, a slice through 300 million years’ worth of rock. Some layers revealed fossilized tree ferns that could have grown only in the tropics. That landscape would have looked nothing like the postglacial land she was standing on. Why were landscapes in the same place so different at different times, she later wondered?

In 1956, she finished a PhD dissertation at Harvard University on the ancient pollen from tropical and semitropical plants preserved in 200-plus-million-year-old fossils from the American Midwest. Eventually, she became seriously interested in landscapes. They are profoundly unlike, and each one changes profoundly with time. How does that happen?

By 1969, after a number of short but productive stays in various universities, Brush moved to Baltimore for good, just in time for the discovery that the Chesapeake Bay was sick.


Some 35 million years ago, when the mid-Atlantic coast was even swampier, hotter, and more humid than it is now, a comet or asteroid three to five kilometers in diameter hit the region. It left a crater twice the size of Rhode Island. In time, rivers from the Appalachians began flowing northeast and southeast toward the crater. And about 10,000 years ago, after the last ice age ended, glaciers melted and the sea level rose, flooding the crater and up into the rivers; the biggest river valley, the Susquehanna, became the Chesapeake Bay.

Satellite image and map showing the Chesapeake Bay watershed
Satellite image by NASA, illustration by Mark Garrison

Indigenous Americans made a good living for thousands of years along its shores, hunting and fishing. And early Europeans were much taken with the region. In the early 1600s, Captain John Smith called the Chesapeake “a very goodly bay.” The land around it, he added, was pleasant: “overgrowne with wood,” “well-watered,” and “the vallies very fertill.” In the water were blue crabs, oysters that “lay as thicke as stones,” and “an aboundance of fish, lying so thicke with their heads above the water.” The rivers were large and navigable, and, Smith concluded, “heaven and earth never agreed better to frame a place for man’s habitation.”

Over the next few centuries, the land around the very goodly bay was fished, farmed, urbanized, and industrialized. By the late 1800s, the forests, which had once covered 95 percent of the land, were reduced to just 40 percent. By the early 1970s, the underwater grasses that sheltered many species of fish and crabs—grasses that in living memory had been so thick in the river estuaries that boats couldn’t get through them—were all but gone. It “astonished the fishermen that the grasses disappeared so quickly and completely,” Brush said. The catches of fish and oysters all dropped.

Concern was expressed; federal officials took boat trips to see for themselves. Congress created the Chesapeake Bay Program, an unlikely but high-functioning collaboration between 19 federal agencies, 40 agencies in six states and the District of Columbia, 1,800 local governments, 20 academic institutions, and more than 60 nongovernmental organizations. Money—US $27-million—was raised. Blame was laid: overfishing, toxic effluent from industry, sewage—or maybe all these, plus a bust phase in the bay’s normal boom and bust cycle. “I knew about this,” Brush said. “And I thought, ‘Gee whiz, if we could take [sediment] cores we could see what it was like before the fisheries’ decline.’”

Finding Gold at the Bottom of the Bay

Brush’s detailed research is now helping policymakers plan strategies for the Chesapeake’s revival. Video by Michael Fincham/Maryland Sea Grant


To take a core, get into a boat with a couple of muscular students and several one- to two-meter piston tubes. Find a place where the mud should be relatively undisturbed, jam one of the tubes into the mud as far as possible, and then—using the general principles of blood drawing—pull the mud into the tube, and cap and label. Try to do this six to 12 times in each place to be sure of having at least one core with intact sediment layers. Take the cores back to the lab, cut each one down the middle, then slice each half into sections one to two centimeters wide, and look for whatever you’re trying to find.

To learn what was growing where and when, Brush began with pollen grains—her specialty. “Pollen gets everyplace,” Brush says—all over land, rivers, and bays, which is why people call it “pollen rain.” So she and a graduate student first identified and then counted the pollen from plants around one of the Chesapeake’s largest rivers, the Potomac, and did the same for pollen from trees on the river’s banks. Then Brush figured out which plants and trees shed the most pollen, namely oak and ragweed, and used these counts to study the ratio of plants to tree pollen and how that ratio changed with time.

After that, Brush and several of her students studied how quickly pollen and silt each settle out of water. The settling rates were about the same, which meant that the amount of pollen in a layer could be used as a proxy for the rate of sedimentation. Then the team counted the pollen grains in each thin section of more than 100 cores and identified the pollen. After that, the team knew how much sediment the rivers carried at any given time. That “entailed a huge amount of work,” Brush says. “It took me a long, long time to figure that out.”

She then took the pollen counts and sedimentation rates to the historical archives and compiled a timeline of events in the region. Once the Europeans moved in and began plowing the ground, first with wooden plows and then more deeply with metal plows, the sedimentation rate roughly tripled. And as they cleared the land, ragweed, “the most invasive species on Earth,” Brush wrote, moved in and spread across the places that had been logged. In the cores, ragweed went from accounting for less than one percent of the pollen to more than 20 percent. In short, Brush had found that just as pollen could serve as a proxy for sedimentation, ragweed could be used as a proxy for deforestation: “Lots of ragweed,” Brush says, and “you know the forests have been cut.” This had major implications. Cut the forests and rain carries even more sediment into the rivers and on into the Chesapeake.

To find out what the increased sediment was doing to the water, Brush and successive graduate students did more coring throughout the bay. Then they checked the cores for seeds of the underwater grasses that form, in Walter Boynton’s words, “a green wreath around the bay” and provide shelter and food to a variety of bay creatures. In Brush’s cores, the numbers of grass seeds cycled up and down for centuries; and then in the 1970s, they disappeared fast and didn’t reappear. Such a disappearance was unique. “It wasn’t a cycle,” says Boynton. “It was an event. Brush made it clear this was unprecedented.”

So what was killing the underwater grasses? In cores taken from different parts of the bay, Brush and her graduate students counted the tiny jawbones of worms and the fossil remains of certain diatoms, species that lived on the bottom of the bay. The results were telling: as farming increased along the bay, worms and bottom-dwelling diatoms began disappearing along with the grasses. In her counts, Brush could watch the land being cleared of forests, and the rivers carrying more sediment into the bay. And as the sediment and nutrients increased, the bay water became murky: less and less light got through to the bottom. When the light was gone, Brush saw the disappearance of the grasses that depended on the light and the creatures that depended on the grasses.


But those weren’t the only major changes that Brush and her team discovered in the sediment cores. They also recently found an unexpected jump in the level of nitrogen, a raw material that plants need to grow. The jump dated from the earliest European settlement. During the same period, in different cores, Brush noticed that the plants were changing from those that grew in wetlands to those that grew in dry lands. Wetland plants return the nitrogen to the air and dry land plants return it to the soil and then the bay. And because the nitrogen in the bay increased, Brush thought she was seeing a sign that farmers were draining the wetlands.

As farmers in the Chesapeake cleared more forest, farmed more land, and eventually spread chemical fertilizers rich in nitrogen across their fields, the rivers swept more nitrogen into the bay. So the more nitrogen in the bay, the more photosynthesis fuel for the algae living at the top of the bay.

Grace Brush holds a core sample of Chesapeake Bay sediment

To chart changes in the Chesapeake Bay’s ecology over time, Brush took core samples of the sediments there. The oldest sediment layers in the cores dated back to more than 14,000 years ago. Photo by David Harp

By the middle of the 20th century, algae in the bay were increasing faster than marine organisms could eat them. The algae bloomed in enormous areas of greenery and the blooms, along with the increasing sediment from farming and deforestation, decreased the light at the bottom of the bay. And when the algal blooms died, they sank to the bottom, where they decayed with the help of bacteria that need oxygen. As the decaying algae used up oxygen, the water became anoxic, a dead zone in which fish and oysters perished. “Turn off the light, put in a lot of organisms [at the top],” said Fredrika Moser, director of the Maryland Sea Grant College, “the communities [at the bottom] lose their function.” In fact, the bay “flipped;” life floated on the top, died on the bottom.

The Europeans moving into Chesapeake country brought with them a new civilization rich in technology, but everything they did moved sediment and nitrogen from the land into the water. Eventually, John Smith’s landscape turned into Grace Brush’s. Her research, says former graduate student Emily Elliott, a biogeochemist at the University of Pittsburgh, has taken “a lot of labor-intensive work. It’s taken her 30-plus years to do it. But she tied the land to the water.”


Grace Brush sits next to Chesapeake Bay holding sediment samples
Fascinated by ancient landscapes and how they could change profoundly over time, Brush, a paleoecologist, decided to reconstruct the ecology of the Chesapeake Bay both before and after European settlement in the region. She hoped this would yield clues to the bay’s modern problems. Photo by David Harp

For thousands of years, the bay’s landscape had no set baseline; it shifted through one phase after another, adapting to changes in climate, sea level, fishing, and farming. “The bay had always been a dynamic system,” Brush says. William Ball, her colleague at Johns Hopkins, agrees: a healthy bay “responds, it rebounds,” he says, “and it doesn’t always look the same.” But in the past 300 to 400 years, with humans practicing industrial farming, paving over land, creating pollutants, and generally suiting the landscape to their own interests, the changes, Brush says, came too fast for nature to respond and rebound. “Humans change the systems much faster than nature does,” she says. “Fast change doesn’t allow for adaptation.”

What humans break, they can sometimes fix. Like most studies in ecology, Brush’s research has implications for policy. Her work now allows the bay’s stakeholders to devise targets for its revival, says the EPA’s Rich Batiuk—targets for how much nitrogen to let into the bay, how much oxygen the deep Chesapeake could hold, how many acres of underwater grasses could be restored, how much nitrogen and sediment a healthy bay could handle, how to keep the water on the land.

It’s working: the latest report on the bay documents fewer anoxic areas. The grasses are coming back, the water is clearer. “Things [are] turning the corner,” says Boynton. “People have been busting their butts on this for 30 years, but good things are starting to happen.”


Brush herself cares about policy but avoids the politics. “I stayed out of it. You can lose an awful lot of time and I couldn’t get my hands around the discussions,” she says. “For me, I got a core, I could sample the bay, I could see it. I could get answers.”

“And God bless her for that,” says Batiuk. “When her name is on the work, the science is strong and you can run with it.”

Ball: “She’s a delight. I go into her office with some bug about politics and we end up talking about science. And then I remember why I’m here.”

Batiuk: [laughing] “Working with her is like working with velvet. She talks, everybody goes silent and listens respectfully … and you see things you hadn’t seen. It’s like a smooth thing you want to wrap yourself up with—you feel smarter and you understand the world better.”

“She’s just remarkable,” Moser says.


So Brush continues as she began, though she says she’ll retire in the spring of 2018. She fell recently, tripped over her pant leg near her home and face planted. Her upper lip was lacerated, some teeth were broken. She’s okay now. But after recuperating for a few weeks at home, she’s had a taste of complete retirement; and that, she says, “is not going to work.”

She’ll still retire, but she’s going to need projects. She just had a book come out, called Decoding the Deep Sediments, but it’s a little heavy going and she’d like to write a popular version of it. And she wants to know more about the extra nitrogen in the bay that apparently came from early farmers draining marshes. She doesn’t think she’ll be collecting more evidence, but she’s pretty sure she’s already got the data in existing cores.

“I just have to get busy,” she says.