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Fulweiler’s Message in a Bottle

BU prof: estuary mud tells dire eco-story

| From BU Today | By Susan Seligson | Video by Erik Duda

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In the video above, biologist Robinson Fulweiler discusses her coastal ecology research as she and her team collect estuary sediment samples in Waquoit Bay, Falmouth. Photos by Melody Komyerov

For ecologist and biogeochemist Robinson “Wally” Fulweiler, every pungent vial of coastal muck tells a story. Meticulously pieced together in a laboratory that mimics nature, that story is alarming. As she explains, the life-sustaining chemical balance of the planet’s coastal ecosystems is changing dramatically, a result of ever-climbing levels of nitrogen and phosphorous from soil erosion, mining, urban waste, and synthetic fertilizers. In the coastal estuaries and marshes of the Massachusetts shore, Fulweiler, a College of Arts & Sciences assistant professor of earth and environment and of biology, is charting the impact of this destruction, hoping that her findings will raise an alarm about the need to protect these marine resources from further harm.

From the tidal flats of Plum Island to the National Estuarine Research Reserve at Waquoit Bay in Falmouth, she is, in every sense, knee-deep in experiments probing changes in a range of marine nutrients along the Bay State coast. But her lab’s general mission, its “connecting theme,” as she puts it, is the ways that humans have altered coastal systems. From industrial pollution to sewage contamination to straining of resources, the list is long, and much of the damage irreversible, says Fulweiler, whose research focuses on global as well as local impacts of environmental change.

Funded by the National Science Foundation and Sea Grant, a program underwritten by the National Oceanic and Atmospheric Administration, Fulweiler’s work led her and several colleagues to create “The Eutrophication Commandments,” an environmental manifesto published this year in Marine Pollution Bulletin. Commandment number one: “Thou shall protect coastal ecosystems to deliver biodiversity and ecological services.”

A passionate researcher whose lines of inquiry routinely cross from earth science to life science, Fulweiler has a favorite quote, from the ancient Roman philosopher Seneca: “Beyond all things is the ocean.”

Fulweiler stabilizes a 10-foot-tall gas flux chamber to measure the impact of Phragmites on greenhouse gas fluxes.

“We look at all different types of nutrients, but our main focus has been nitrogen,” she says. She and her team routinely burrow into the shallows of Waquoit Bay to fill cylindrical “cores” with sediments. All life requires nitrogen, an inert element that can be found in abundance all around us, as it comprises almost 80 percent of our atmosphere. Humans and other animals get nitrogen from plants or from animals that have eaten plants. For aeons the only organisms capable of using this vital nutrient were so-called nitrogen-fixing bacteria, which amount to less than one percent of all the earth’s organisms, Fulweiler explains. In balance, the nitrogen cycle is an elegant force in sustaining all plant and animal life.

The trouble began in the early 1900s, when humans learned how to fix nitrogen (a process by which nitrogen in the atmosphere is converted to ammonia), for bombs and for fertilizer, adding industrial fixation to the natural process of biological nitrogen fixation. That wasn’t an altogether bad thing; it’s estimated that half the world’s population is alive today because of fertilizer use. But humans have doubled the amount of nitrogen circulating the Earth, and with it comes a proliferation of phytoplankton, or microscopic sea plants. These provide the base of marine food webs, but when they grow in excess or bloom and then die and settle to the bottom of sea floor, they are decomposed by bacteria that gobble up the oxygen they need to survive, a downward spiral.

“It’s a big social and scientific issue,” says Fulweiler. “Every time we excrete we put out nitrogen,” a by-product of most modern human activities, from burning fossil fuels to the sweeping use of commercial fertilizers to produce a diet increasingly dependent on them. According to some estimates, agriculture may be responsible for half the nitrogen fixation on earth.

In fact, even the pandemic use of lawn fertilizers contributes to far-reaching negative impacts in coastal systems, says Fulweiler, who is also the associate director of the BU Marine Program. “We can see the toll on coastal systems when nitrogen comes in; we get these big phytoplankton blooms, and when they die they fall to the bottom of estuaries, where they’re subject to aerobic decomposition—a bacterial process that takes oxygen away from the water column.” Scientists like Fulweiler are churning out the dire data on this process.

“In the Gulf of Mexico, or even in many small local estuaries, if you’re not a fish that can get out of town you’re in trouble,” she says. “A lot of shellfish die, and the low oxygen can kill other fish, too.”

While collecting gas samples, Fulweiler records ambient light and the time of day to calculate fluxes.

Data from Fulweiler’s research, now in its fifth year, and from others around the world are painting a startling map in which most coastal areas, from Chesapeake Bay to the Baltic Sea, are “experiencing anoxic (no oxygen) or hypoxic (low oxygen) conditions in the summertime,” she says. When she and her team bore into the bay floor and come up with sediment, that muck is often full of algae. “It looks like a Brillo pad and smells terrible—you’re not going to find shellfish there,” she says.

After one of their all-day collecting forays in open skiffs, Fulweiler and her team of about eight undergraduate and five graduate students cart core samples as well as samples of the water where they were collected back to their CAS lab, a state-of-the-art, temperature- and humidity-regulated “environmental chamber” with backup generators. “The sediments are full of organisms, mostly bacteria, so they’re invisible to the naked eye, and we want to measure their respiration inside the sediments,” Fulweiler says. “We replace the overlying water with filtered site water and seal the cores with a gas-tight lid.”

Over time, the team carefully extracts water samples and tests them for dissolved nutrients, such as inorganic nitrogen, phosphorous, and silica, as well as dissolved gases, including oxygen, methane, nitrous oxide, and nitrogen gas, called dinitrogen, or N2. The most crucial information—the micro-story that reveals much about the larger picture—is the change, or flux, in these gases over time. “By comparing our most recent measurements with those measured almost 20 years ago in this same bay, we found substantial and surprising changes,” says Fulweiler. “Specifically, we see a decrease in overall benthic, or sea floor, metabolism with an 80 percent decrease in denitrification, the natural microbial process that filters excess nitrogen out of the ecosystem.”

Five years of sediment testing has enabled Fulweiler to weave more threads into a tapestry of existing and future coastal ecosystems. “The worst culprit? Humans, definitely,” she says. Even interventions such as better sewage treatment or decreased fertilizer use “cannot assure a return to a historic ecosystem status,” Fulweiler and her colleagues write in Marine Pollution Bulletin. But, they add, “regardless of the uncertainties, it is clear that action must be taken.” And even though the environmental future often seems grim, the final two Eutrophication Commandments reflect Fulweiler’s commitment to improving it: “Thou shall be patient” and “Thou shall be hopeful.”

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