the rapidly urbanizing South Carolina coastal zone,
intensive landscape maintenance and turf management are significant
nonpoint source pollutant loadings. The
stormwater best management practice of choice in this region is wet
ponds, the majority of which are brackish lagoons.
Typically, stormwater is piped directly into
the ponds, and their capacity for processing pollutants is limited. These highly eutrophic brackish ponds are
“hot spots” for harmful algal blooms – over 200 blooms from 23
species were documented over the last four years, many associated with
toxins, fish kills or shellfish health effects. Pond nutrient
also impact estuarine eutrophication through surface or groundwater
transport. SCHABP personnel, through
SC Sea Grant-funded project, will test the use of constructed wetlands
supplementary BMP to process stormwater and groundwater nutrients prior
entering detention ponds. The
constructed wetland is designed to enhance denitrification, reducing
input to the pond, improving pond water quality, and decreasing
groundwater nutrient transport to downstream estuaries.
Wetland construction is targeted for
December 2006. Findings thus far from
the baseline study include:
characterization of a 5-month long Microcystis bloom (see previous
high denitrification potential in watershed
high nutrient fluxes into and out of the pond
by stormwater and groundwater.
these ponds exchange
with tidal creeks, they are sources for harmful algal bloom dispersion
adjacent estuaries. Furthermore, flux
measurements indicate that groundwater acts as both a source of
the ponds and a mechanism for transporting nutrients from the ponds. These findings imply that manmade ponds as
presently designed along the South Carolina coast may contribute to estuarine
harmful algal bloom prevalence.