By Susan Ferris Hill and John H. Tibbetts, South Carolina Sea Grant Consortium
Photo credit: Grace Beahm
According to South Carolina Sea Grant-funded researcher Erik Smith, an aquatic ecologist with the University of South Carolina and the North Inlet-Winyah Bay National Estuarine Research Reserve, there are more than 14,000 stormwater ponds in South Carolina’s coastal region. Developers dig these ponds to capture stormwater runoff, currently an acceptable best management practice for reducing and filtering the amount of surface-water runoff that eventually makes its way into nearby waterways. Stormwater ponds have other benefits as well, such as using the dirt dug for the pond as fill material to lift a nearby site’s elevation, providing habitat for fish and wildlife and adding value to homes built near these sometimes picturesque ponds.
Yet questions are being raised in the scientific community about how stormwater ponds function in coastal watersheds. “Ponds represent a new type of aquatic environment along South Carolina’s coastal zone,” says Smith. “We have essentially replumbed this region by digging a whole lot of shallow bathtubs… Some of these ponds develop in healthy ways, mimicking natural water bodies where fish and wildlife thrive. Many others become ecologically dysfunctional… with implications for coastal water quality that scientists and managers don’t fully understand.”
"We have essentially replumbed this region by digging a whole lot of shallow bathtubs.” Erik Smith, Ph.D., University of South Carolina and North Inlet-Winyah Bay National Estuarine Research Reserve aquatic ecologist
Stormwater ponds also retain some contaminants, including sediments and heavy metals, in particles that gravity draws to the mucky bottom and holds there. This prevents them from being discharged into waterways, says South Carolina Sea Grant scientist John Weinstein, an aquatic toxicologist at The Citadel. And many conventional stormwater ponds collect and concentrate nutrients in the water column. Nutrients, such as nitrogen and phosphorus, are necessary for aquatic life, but when they accumulate in excess, algal blooms that lower dissolved oxygen levels can develop.
Another South Carolina Sea Grant-funded scientist, Dianne Greenfield, director of the South Carolina Algal Ecology Laboratory, which is a partnership between the South Carolina Dept. of Natural Resources and the University of South Carolina Belle W. Baruch Institute, examines coastal phytoplankton—or algae—ecology, physiology and biogeochemistry. Greenfield concentrates her work on the consequences of algal bloom formation. Some algal blooms lead to degraded water quality, and certain types of blooms can cause fish kills. There also are toxin-producing algal blooms which can pose health risks to people, pets and wildlife, although there are no documented human health effects in people who have come into contact with harmful algae in South Carolina stormwater ponds.
As a best management practice, stormwater ponds will continue to be built, but there are ways to make these ponds more effective, efficient and less costly to manage. Developers and local communities, including homeowner associations, could improve water quality in the ponds by using various low-impact development techniques. Constructed wetlands are one way. A typical created wetland has two elements: a wide, thick bench of aquatic and terrestrial plants around its perimeter and a shallow, often boggy, sometimes dry retention area in the center where soils can take up excess nutrients and other contaminants. Using pervious pavers that allow rainfall to filter through them and into the ground below is another. And protecting trees instead of clear-cutting lets the tree roots soak up rainwater and recharge the groundwater, reducing stormwater runoff.
Dan Hitchcock, a South Carolina Sea Grant researcher and biosystems engineer with Clemson University, and a team of scientists are studying how rainwater flows through small watersheds that are characteristic of many undeveloped lands in the region. The research team is trying to determine the seasonal and rainfall event-based mechanics of water budgets and stream flow. “We are working to understand how forest water budgets are related to shallow water tables,” says Hitchcock. “When soils are saturated, such as in winter when trees are dormant, more runoff is generated than in summer. Infiltration—and therefore soil storage—is limited during these months. That potentially causes more stormwater quantity, which must be managed.”
To tie all of this research together, identify knowledge gaps where more research is needed and assist stormwater managers and other stakeholders at the local and state levels, the South Carolina Sea Grant Consortium is in the process of developing a funding initiative. The multi-disciplinary research seeks to develop a sustainable economic- and natural-resource strategy for the construction, use and maintenance of stormwater ponds. The effort will include work to ecologically characterize coastal stormwater ponds in order to understand their functionality and durability. Ultimately, innovative engineering and construction practices will be developed to ensure that current and future ponds function without concerns about possible ecological impacts or costs associated with management and maintenance.
Helpful links for additional information:
Chemical and Biological Contamination of Stormwater Detention Pond Sediments in Coastal South Carolina (final report)
South Carolina Algal Ecology Laboratory
Community Associations and Stormwater Management: A Coastal South Carolina Perspective
Coastal Heritage magazine, “Water’s Edge: Managing Coastal Runoff”
Coastal Heritage magazine, “Slowing Stormwater: Improving Water Quality by Imitating Nature”
