Studies on Brackish and
stormwater detention ponds sampled by the
SCHABP range in salinity from low brackish to marine, and not
type of HAB is associated with salinity properties.
In general, dinoflagellate and raphidophyte blooms
are relatively prevalent under mid-brackish to marine conditions
al. 2002, Lewitus et al. 2003, 2004), while cyanobacteria are commonly
dominant phytoplankton species in low brackish waters.
For example, a compilation of samples from
2002-2003 demonstrates the occurrence of several different potentially
cyanobacterial species spanning all salinities, but 85% of these
salinity < 20 ppt and 66% below 10 ppt (Fig. 1).
It is important to note that these are not
freshwater ponds – they experience tidal exchange, the salinity
dictated by the
distance from tidal creeks and the hydrological properties of surface
groundwater flow. Assuming that the
salinity distribution in Fig.5 reflects habitat preference, another
point is that salinity optima vary between cyanobacterial species. Among the four most prevalent species, Oscillatoria
occurred most often in low salinities (67% occurrence
at 1 to 7.5 ppt), Microcystis
occurred in salinities ranging from 2 to 10 ppt (73%),
and Anabaena ranged
from 5 to 20 (69%), and Planktothrix’s distributional pattern
of potentially toxic cyanobacterial species at various salinity ranges
samples collected from South Carolina lagoonal ponds in
cyanobacterial hepatotoxins that have
caused animal poisonings and human health problems, usually through
water and recreational activities. During the summer of 2000, a Microcystis
spp. bloom occurred in Lake Edmunds, a freshwater-to-low
in Charleston, SC.
In the summers of 2001
and 2002, monitoring
studies on cyanobacteria and microcystin were conducted in this pond,
2002, regulation of growth and toxin production by M.
aeruginosa cultures were studied. In
both years, microcystin was consistently
detected in water samples. In 2003, we added other freshwater
pond in Charles Towne Landing, a public park, and Goose Creek reservoir, formerly a
water source and now a site of recreational activity (Fig. 2). The primary bloom producing species found in
all bodies of water were Microcystis aeruginosa, Anabaena
and Aphanizomenon flos-aquae. Goose Creek Reservoir Power Plant
only site consistently below 1 ppb, the threshold of safe levels
World Health Organization guidelines. Highest whole water toxin
greater than 10 ppb, occurred during June and July for all other sites.
2 and 14, 2003, the toxin content of Lake Edmunds Shaffer Road was 1926 ppb (whole
water) and 316 ppb
During the Lake Edmunds survey, an inverse
observed between pond phosphate concentration and microcystin levels. In
laboratory experiments, toxin production was higher in
growth phase than stationary phase, independent of the type of nutrient
limiting growth (N or P). We conclude
that the potential for microcystin production is greatest in actively
cells, and that the inverse relationship between microcystin and P in
samples reflects post-bloom periods of nutrient depletion after
accumulation. Predictably, increased nutrient loading would lead to
ambient concentrations of microcystin not only by supporting higher Microcystis biomass, but by prolonging
the period of active cellular division in bloom populations.
The low to mid-brackish
ponds are almost always
phosphate-rich and support high biomass cyanobacterial blooms. Such blooms can contain mixed cyanobacterial
populations and exhibit successions of dominant types, or remain
dominated by a
single species over time (Fig. 3).
Temperature and salinity (top), occurrences
of potentially toxic cyanobacterial species (middle), and abundance of
species (bottom) in samples from a South Carolina lagoonal pond from June
biomass blooms can be sustained for long periods and are common visual
odiferous nuisances to residents and tourists.
The public is less aware of the toxic potential of
these blooms. Nevertheless, our studies
indicate that high
microcystin concentrations are commonly associated with these blooms. For example, toxin levels analyzed by ELISA
were always > 1 ppb, and ranged to > 10,000 ppb from September
November 2004 in a Kiawah Island brackish pond (Fig. 4). The Microcystis bloom lasted five
months. For comparison, the World Health Organization threshold for
drinking water is 1 ppb.
Temperature and salinity (top) and Microcystis
abundance and microcystin concentrations (bottom) in a South Carolina lagoonal pond from
to mid-January 2005. Note that high
biomass (> 100,000 cell/ml) was sustained throughout this 5-month
period. Abundance estimates are the means
from 3 sampling sites within the pond.
Microcystin concentrations for each site are shown
scale). This is the pond used to test
the use of constructed wetlands as a supplementary BMP to mitigate pond
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