State's storm-water-cleansing BMPs show only traces of harboring mosquitoes
Bill Lord, here inspecting a constructed wetland, said research shows that "the vast majority of storm-water ponds and wetlands posed only a minimum threat to people as mosquito production grounds."
Photo by Art Latham
Many North Carolina communities have installed various water-quality controlling structures - known as best management practices, or BMPs - to keep polluted, storm-borne surface runoff from contaminating our drinking water.
As the search for the most efficient practices continues, a few researchers have reported that storm-water BMPs in Florida and New Jersey were mosquito breeding grounds.
That's not the situation in the Tar Heel State, according to a researcher in N.C. State University's College of Agriculture and Life Sciences and educators in North Carolina Cooperative Extension's Water Education Network (WEN).
Dr. Charles Apperson, William Neal Reynolds Professor in the Department of Entomology, headed a study in which research technicians Shawn Kennedy and Luma Abu Ayyash slogged through 52 suburban ponds and storm-water wetland BMPs, in 12 coastal and piedmont North Carolina counties, searching for mosquitoes. They collected from 90 to 210 water samples. Dr. Bruce Harrison, a medical entomologist with the state Department of Environment and Natural Resources, identified the mosquitoes in the water samples.
"Public concern over mosquito-transmitted disease agents, especially West Nile Virus, prompted our team to sample storm-water retention facilities for mosquitoes during the 2004 and 2005 seasons," Apperson says.
Happily, the team can report good news: The majority of the tested storm-water management structures did not harbor mosquitoes, although the team did add a caveat.
In the study, "64 percent did not have mosquito populations," says Bill Lord, a WEN member and Extension area specialized agent for environmental education and agriculture. Lord participated in the study by helping to identify sites. "Of those that did, only 12 of the storm-water practices - or about 30 percent - had populations of some significance."
While the team found no evidence of West Nile Virus-carrying mosquitoes, all the mosquito species they collected have been reported elsewhere to be possible vectors for the virus.
"Because most BMPs are near communities, they should be monitored routinely and managed appropriately," says Dr. Bill Hunt, an Extension urban storm-water management specialist in the Department of Biological and Agricultural Engineering. Hunt secured a grant for the study from the N.C. Water Resources Research Institute's Storm Water Consortium.
The BMPs studied included constructed storm-water wetlands, of which the group sampled 18, and standard and innovative wet ponds, with 20 and 14 sampled, respectively.
A constructed storm-water wetland is an artificial marsh created to accept and filter polluted water from parking lots, roads and other impervious surfaces and prevent the polluted water from entering the drinking water supply. Wet ponds are traditional retention basins common in urban areas. Innovative wet ponds combine features of a standard wet pond and a storm-water wetland.
"Wetlands with a variety of vegetation - excepting cattails - tended to have fewer mosquitoes," Apperson says.
"While there was no apparent difference in the mosquito species we found or in how intensely they multiplied in innovative or wetland ponds, compared to standard wet ponds," he says, "our observations suggest that any retention structures containing cattails or willow trees are associated with mosquito production." During the study, technicians were more likely to collect mosquitoes from woody fringe areas of storm-water wetlands and innovative ponds.
Floating detritus accumulating around the base of such plants provides refuges so mosquitoes can dodge fish and other predators. Also, plant stems and tree branches trailing into the water provide shade that can keep water temperatures favorable to mosquitoes.
Hunt and Lord have some advice for storm-water BMP designers and managers: Adopt a maintenance plan that removes woody vegetation and cattails from wetlands every year or two, and consider planting only herbaceous vegetation and not specifying the use of woody plants.
They also encourage using deep pools in storm-water wetlands to provide a continuous refuge for mosquito fish (Gambusia affinis), a significant indicator of few or no mosquitoes.
-Art Latham
As the search for the most efficient practices continues, a few researchers have reported that storm-water BMPs in Florida and New Jersey were mosquito breeding grounds.
That's not the situation in the Tar Heel State, according to a researcher in N.C. State University's College of Agriculture and Life Sciences and educators in North Carolina Cooperative Extension's Water Education Network (WEN).
Dr. Charles Apperson, William Neal Reynolds Professor in the Department of Entomology, headed a study in which research technicians Shawn Kennedy and Luma Abu Ayyash slogged through 52 suburban ponds and storm-water wetland BMPs, in 12 coastal and piedmont North Carolina counties, searching for mosquitoes. They collected from 90 to 210 water samples. Dr. Bruce Harrison, a medical entomologist with the state Department of Environment and Natural Resources, identified the mosquitoes in the water samples.
"Public concern over mosquito-transmitted disease agents, especially West Nile Virus, prompted our team to sample storm-water retention facilities for mosquitoes during the 2004 and 2005 seasons," Apperson says.
Happily, the team can report good news: The majority of the tested storm-water management structures did not harbor mosquitoes, although the team did add a caveat.
In the study, "64 percent did not have mosquito populations," says Bill Lord, a WEN member and Extension area specialized agent for environmental education and agriculture. Lord participated in the study by helping to identify sites. "Of those that did, only 12 of the storm-water practices - or about 30 percent - had populations of some significance."
While the team found no evidence of West Nile Virus-carrying mosquitoes, all the mosquito species they collected have been reported elsewhere to be possible vectors for the virus.
"Because most BMPs are near communities, they should be monitored routinely and managed appropriately," says Dr. Bill Hunt, an Extension urban storm-water management specialist in the Department of Biological and Agricultural Engineering. Hunt secured a grant for the study from the N.C. Water Resources Research Institute's Storm Water Consortium.
The BMPs studied included constructed storm-water wetlands, of which the group sampled 18, and standard and innovative wet ponds, with 20 and 14 sampled, respectively.
A constructed storm-water wetland is an artificial marsh created to accept and filter polluted water from parking lots, roads and other impervious surfaces and prevent the polluted water from entering the drinking water supply. Wet ponds are traditional retention basins common in urban areas. Innovative wet ponds combine features of a standard wet pond and a storm-water wetland.
"Wetlands with a variety of vegetation - excepting cattails - tended to have fewer mosquitoes," Apperson says.
"While there was no apparent difference in the mosquito species we found or in how intensely they multiplied in innovative or wetland ponds, compared to standard wet ponds," he says, "our observations suggest that any retention structures containing cattails or willow trees are associated with mosquito production." During the study, technicians were more likely to collect mosquitoes from woody fringe areas of storm-water wetlands and innovative ponds.
Floating detritus accumulating around the base of such plants provides refuges so mosquitoes can dodge fish and other predators. Also, plant stems and tree branches trailing into the water provide shade that can keep water temperatures favorable to mosquitoes.
Hunt and Lord have some advice for storm-water BMP designers and managers: Adopt a maintenance plan that removes woody vegetation and cattails from wetlands every year or two, and consider planting only herbaceous vegetation and not specifying the use of woody plants.
They also encourage using deep pools in storm-water wetlands to provide a continuous refuge for mosquito fish (Gambusia affinis), a significant indicator of few or no mosquitoes.
-Art Latham