RALEIGH, NC Urban stormwater runoff is causing problems for the world's water sources. In the United States, the Environmental Protection Agency found stormwater runoff to be one of the top 10 causes of compromised environments in rivers, streams, lakes, ponds, reservoirs, bays, and estuaries. The pollutants from urban stormwater runoff can harm fish and wildlife populations, foul drinking water, and make recreational areas unsafe.
Researchers from North Carolina State University are looking to rain gardens as one way to remediate the water quality concerns caused by urban stormwater. Rain gardens--also known as bioretention cells--are depressions in the landscape that trap stormwater runoff so microbial activity, filtration/adsorption, and plant uptake can remove pollutants. Typically, the gardens are excavated, backfilled with a filter bed substrate, then planted with vegetation that helps to remove pollutants. "The filter bed substrate is the foundation of the rain garden and gives it the ability to infiltrate runoff, slow drainage, support plant growth, and remove pollutants," explained Helen Kraus, lead author of a study published in HortScience. Kraus and her colleagues designed experiments to assess three different filter bed substrates for their effectiveness in nutrient removal and supporting plant growth.
The research team constructed 12 rain gardens filled with one of three filter bed substrates. The gardens were planted with 16 plant species, and then irrigated with stormwater. The substrates used in the experiments included a sand-based substrate (sand) composed of 80% washed sand, 15% clay and silt fines, and 5% pine bark; a soil-based substrate (soil) composed of 50% sandy loam soil and 50% pine bark; and a slate-based substrate (slate) composed of 80% expanded slate and 20% pine bark. The substrates differed in infiltration and drainage rates as well as chemical composition.
Diverse plant species that inclu
|Contact: Michael W. Neff|
American Society for Horticultural Science