Heidi Nepf has a research apparatus that’s unusual even by MIT standards. Some 2, 000 wooden pegs are randomly lodged in a 1. 25-foot-by-32-foot plexiglass sheet. Attached to each is a willowy “brush, ” made of the same plastic as sandwich bags. (It turns out to have just the right qualities, says Nepf). When the sheet’s flooded with water, those brushes sway gracefully with the flow.
The lab-based model of coastal vegetation — because that’s what it is — is the work of graduate student Marco Ghisalberti. But why “grow” some 2,000 fake plants? Because it’s a way to probe the intricate machinery of real plants. And, says Nepf, an associate professor of civil and environmental engineering, it works.
Those betasseled pegs, she notes, “are good surrogates for many forms of coastal vegetation.” Nepf’s focused on how real plants behave because vegetated zones on the coast play vital roles in our world. For one thing, they’re home to many species of small fish and crustaceans, and serve as nurseries for numerous types of marine creatures.
They and their land-based cousins called wetlands are also pollution fighters. “A lot of runoff from the land contains waste nutrients and contaminated particles,” she notes. “Coastal zones are an important buffer between land and the water.”
Meanwhile, a series of painful sagas, from the failing oyster industry in Maryland’s Chesapeake Bay to the Gulf of Mexico “dead zone” — where fish largely disappear from an area of up to 7, 000 square miles because the water’s oxygen has been depleted by nutrient runoff from the land — testify to the cost of damaging natural filtering systems.
Nepf explores what makes good coastal zones or wetlands tick. Those artificial grasses, for example, help show how the movements of their real-life counterparts affect water flows through and over the plants.
But that’s just one goal. The faculty member, who has a physics background, is interested in issues from the fluid dynamics of the tiny eddies and swirls around a single reed to how entire marshes function. “We still can’t model them well,” she explains. “People have been trying to make the mathematics tractable, but it’s very complicated.”
Longer term, she wants to set the stage for better artificial wetlands — the kind often used in wastewater treatment, for example — and better restoration of resources like coastal grasses.
A graduate of Bucknell and Stanford, Nepf says the practical benefits of her work are a key motivator. But there’s an aesthetic factor, too. “When I was a student, I remember observing some experiments where you put dye in water so you can see how the flow moves,” she says, “and I was just completely enthralled.”