Research

Leave it to beavers

As urban growth in the Southeast increases harmful waterway pollutants, Carolina scientists found a natural solution: beavers and their dams.

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Carolina senior Elizabeth Farquhar carefully climbs down a muddy bank and into a stream below with a strange circular device, about 2 feet around, in tow. The flowing water comes up to her knees, and the mud makes walking in the heavy waders she pulled on over her clothes a tricky task — but not one she’s unfamiliar with. She wades to the first pink marker along the bank, places the contraption on the water, and pulls out a stopwatch.

This floating device is a kind of sensor that Farquhar and her fellow researchers use to measure oxygen levels in the water. She waits five minutes before moving downstream to the next pink marker. It feels peaceful here as birds chirp and insects buzz. But then a horn blares from the nearby highway.

Just a few steps away, fast food restaurants, gas stations and office buildings rise up from the pavement. Trash litters the sidewalk and roads as cars speed past, kicking up chemicals and pollutants on the highway every time it rains.

Urban flooding has become an increasingly pressing issue as cities grow and replace soil, grass and plants with concrete, causing city planners to turn to manmade solutions. But the most efficient civil engineers may not be human. The American beaver (Castor canadensis) has become known as a nuisance for its tendency to alter landscapes in neighborhoods through damming, but its knack for flood attenuation may be just what urban planners need.

Farquhar is one of three undergraduate researchers currently working on Carolina geographer Diego Riveros-Iregui’s collaborative project with UNC Charlotte, Georgia State University and Georgia Gwinnett College to determine beavers’ impact on water quality in urban settings and compare their work with manmade retention ponds.

Many people may be surprised to know that there are beaver marshes right in the middle of Durham.

Retention ponds are expensive to build and maintain and can contain less diverse natural life than beaver marshes, according to Riveros-Iregui. Plants, animals, bacteria and phytoplankton play a crucial role in the absorption of nutrients like nitrogen and phosphorus that may otherwise spill into nearby waterways and cause issues such as harmful algal blooms, destruction of habitat and overall disruption to ecosystems. Beavers, on the other hand, are already making dams that slow water down long enough to be absorbed by the abundance of life in their marshes.

“Scientists have studied the role of beavers on water quality for a while,” Riveros-Iregui says. “The part that is different about what we’re doing is that we’re studying beavers in urban environments. These areas of the Southeast are some of the most rapidly growing areas in the United States. But we also know that urban settings are bad for water quality.”

Many people may be surprised to know that there are beaver marshes right in the middle of Durham. Riveros-Iregui’s team is testing sites located behind shopping centers and grocery stores, along highways and near apartment complexes.

An increase in infrastructure like parking lots, buildings and roads decreases the amount of ground that can absorb rainwater, thereby increasing the likelihood of flooding that brings trash, plastics and chemicals into nearby water systems. Some of the most common efforts to attenuate flooding are through building retention ponds in urban areas.

By taking measurements of water quality, depth and flow at inlets and outlets of both beaver marshes and retention ponds, the team can compare what nutrients and chemicals go into and come out of both systems and determine which is more efficient.

“The question really comes to management,” Riveros-Iregui says. “Can we figure out how to manage beaver dams in a way that they can be sustainable? That would be a win-win: We don’t have to remove them, and they’re keeping our streams healthy.”

Farquhar studies environmental science. When plans to study water systems in Ecuador last summer fell through after COVID-19 was declared a global pandemic, she and two other undergraduates — Katie McMahon and Tessa Davis — joined doctoral student Kriddie Whitmore as the first cohort of the multi-year, National Science Foundation-funded project.

Farquhar is excited to lay the groundwork for research with so much potential for real-life impact.

“I hope our work helps show that beavers are not just a nuisance,” she says. “In the future, if developers want to bulldoze over this marsh, we can show them what it’s doing for the area and that it’s actually beneficial.”

Diego Riveros-Iregui is the Bowman and Gordon Gray Distinguished Professor in the department of geography within the UNC College of Arts & Sciences.

Elizabeth Farquhar is a UNC alumna who graduated in May 2021. She majored in environmental science with a marine science minor within the UNC College of Arts & Sciences.

Katie McMahon is a UNC alumna who graduated in May 2021. She double-majored in geography and global studies within the UNC College of Arts & Sciences.

Tessa Davis is a UNC alumna who graduated in May 2021. She majored in environmental science with a biology minor within the UNC College of Arts & Sciences.

Kriddie Whitmore is a doctoral student in the department of geography within the UNC College of Arts & Sciences.

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