At first sight, all is still at the bottom of Snakeden Branch Stream. Just 20 miles east, downtown Washington, D.C., bustles and hums. Here, though, there is only water, sand, and rubble.
Or so it seems. Curiously, what looks like a stone on the stream bed begins to shimmy deeper into the soft sediment beneath it. As the stone continues to burrow, concentric ellipses appear across its surface, shot through with streaks of amber and ochre-like sun rays shining through the water above. Suddenly, the stone seems to split open. As a smooth white appendage emerges from within it, it becomes apparent that this is not a stone at all.
It is a freshwater mussel.
“They are just the coolest,” said Denise Bruesewitz, with a wide smile and an impassioned look rarely imparted toward these unassuming invertebrates.
Bruesewitz, associate professor of environmental studies, is at the early stages of a project focused on reintroducing freshwater mussels—also called unionids—to two recently -restored urban streams in Reston, Va. In each stream, she and her collaborators will measure the effect these mussels have on removing pollution and, in the process, shed light on their astounding capacity for improving once-degraded waters.
Despite their inconspicuous nature, freshwater mussels are remarkable animals. They come in an extraordinary array of shapes, sizes, and patterns. More than 300 species live in North America alone, and individuals can live for more than 100 years.
Moreover, mussels play a crucial role in enhancing water quality. As they siphon water—as much as a bathtub’s worth every day—through their gills to feed, mussels also filter out bacteria and pollutants, acting like living water purifiers. In this way, their presence is vital to the health of freshwater ecosystems, and by extension, to us.
Yet, unionids are among the most endangered groups of organisms in the United States. Before the invention of plastic, most buttons were made from the opalescent interiors of mussel shells. Populations declined sharply as demand for buttons rose. Pollution has exacerbated this loss, as have dams, which sever river connectivity and make it impossible for mussels to expand their ranges via the host fish to which their larvae attach.
“In some states, there are healthy programs of growing mussels in labs, and in those places, there are efforts to try to restore populations,” Bruesewitz said. “But there’s much less work out there that quantifies the way these mussels impact water quality and stream ecosystems. That’s the piece that’s pretty unique about this study.”
In January Bruesewitz and her collaborators—including stream ecologist Sally Entrekin at Virginia Tech, hydrologist Brendan Foster of the U.S. Geological Survey, mussel expert Jess Jones from U.S. Fish and Wildlife, and Chester Zarnoch, professor of biology at CUNY Baruch College—visited Reston to select two sections of each stream for the study. Mussels will be planted in one section of each stream, and not in another. For five years, beginning in August, Bruesewitz and her collaborators will measure changes in pollutant levels, nutrients, suspended sediments, macro-invertebrate community diversity, and several other water-quality metrics between the stream sections.
Notably, they will track changes in nitrogen cycling. In certain forms, nitrogen is a nutrient essential for life; in excess, however, it can lead to serious issues such as toxic algae blooms and hypoxic conditions, under which parts of a given water body become completely devoid of oxygen. Mussels contribute to a process called denitrification. “It’s sort of like the magic bullet for nitrogen pollution because it just removes the nitrogen from the water completely and converts it to harmless nitrogen gas in the atmosphere,” Bruesewitz said.
Bruesewitz hopes the study will demonstrate how effective these mussels can be as a means of improving water quality, especially in urban areas like Reston, where small streams often suffer from legacies of degradation. Depending on the results, she and the research team envision writing a series of technical papers and reports to management agencies vouching for the value of mussels as a form of aquatic bioremediation.
Water has long fascinated Bruesewitz, who grew up in northern Illinois enamored with the humble vitality of the freshwater all around her. “Like a lot of kids in the ’90s, I was really impacted by environmental news and early conversations around climate change,” she said. “We all have special bodies of water near us where we live, whether they’re little streams or lakes. And they do a lot of important work for us. And a lot of times, they go unnoticed or unappreciated.”
Bruesewitz had her first experience with freshwater ecology as an undergraduate at Winona State University in Minnesota. She studied competition between invasive zebra mussels and caddisflies in the Mississippi River. “It was really interesting,” she recalled, “and just felt exactly like the kind of thing I wanted to do.” Through one of her professors, she landed a volunteer position with the U.S. Geological Survey in Lacrosse, Wis. There, she started studying the ways that nitrogen is delivered and processed in the upper Mississippi River as part of a project aimed at understanding connections between nitrogen and the hypoxic zone in the Gulf of Mexico.
Inspired by this work, Bruesewitz enrolled in graduate school at the University of Notre Dame in Indiana. “I was going to sort of pull the two pieces of my undergraduate work together and understand how zebra mussels impacted nitrogen cycling in the Mississippi River,” she said, describing her original trajectory toward a master’s degree. Ultimately, however, she decided to turn this research into a Ph.D. project.
For her first postdoc, Bruesewitz traveled to the Rotorua Lakes area of New Zealand to study how watershed land-use activities, such as agriculture, affected nitrogen removal through denitrification across several lakes. Her second postdoc took her to the University of Texas Marine Science Institute (UTMSI) in Port Aransas to research nitrogen and carbon cycling in coastal areas.
“I really became interested in connectivity, how nutrients are processed as you go from a river down into an estuary and then further out toward the ocean,” she said. At UTMSI, Bruesewitz was faced with a decision: stay and teach there or take a professorship at Colby. A mentor at UTMSI with connections to Whitney King, the Dr. Frank and Theodora Miselis Professor of Chemistry at Colby, said working at Colby would be a dream job for him. The choice was clear.
Since coming to Colby in 2012, Bruesewitz’s research has remained focused on understanding and enhancing the health of freshwater systems. In addition to the mussel study, Bruesewitz is working on four other externally funded collaborative projects—an impressive and uncommon feat.
Three of these projects center around cyanobacteria, sometimes referred to as blue-green algae, which are capable of producing harmful blooms. With one cohort of colleagues, Bruesewitz is investigating the use of autonomous robots for modeling and predicting blooms in lakes up and down the east coast; with another group from the Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine, she is examining environmental DNA as a tool for monitoring different cyanobacteria strains. A third project with collaborators at the University of Maine finds her looking into lake sediments for ancient traces of gloeotrichia—one type of cyanobacteria—to learn how the deep past might provide clues to understanding blooms today.
As a fourth project, Bruesewitz is modeling a Department of Environmental Studies capstone course on the USDA-funded “Coast-Cow-Consumer” project with Nichole Price at Bigelow to investigate how adding marine supplements to cattle feed can mitigate methane emissions from cows.
When asked what drew her toward pursuing so many projects at once, Bruesewitz replied, “I really enjoy building these long-term collaborations with smart, creative scientists that are interested in similar things.” She has worked with some colleagues, like Chester Zarnoch from the mussel study, for more than a decade and on many projects.
Bruesewitz also values the relationships she has formed with Colby students.
“It’s why you work at a place like Colby—you get the chance to really build connections with students, especially if you work with them multiple years in a row,” she said. “You really get to build out a great friendship, as well as see their interests grow and learn what they want to do after Colby.”
Students working with Bruesewitz can explore lab work as well as fieldwork in a multitude of aquatic habitats and engage with other scientists at every step of the research process. She anticipates student involvement in the mussel project will commence in the summer of 2024.
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