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agricultural areas; and TON concentrations are higher in wetland and urban areas than
in agricultural areas (Britt and Cheesman 1992; Lietz 1999; Haag et al. 1999; US DOI
NPS. 2003; Caccia and Boyer 2007; Migliaccio et al. 2008). Given the oligotrophic
nature of these waters the system responds very rapidly to small nutrient enrichment,
especially to increases of phosphorous, the limiting nutrient (Brand 1988, 2001).
Turbidity
Most turbidity in Biscayne Bay is produced by re-suspension of bottom
sediments, both naturally and anthropogenically generated. Natural agents of
resuspension are water currents (tidal driven), wind-produced waves (climate related)
and extreme events (storms and hurricanes). Anthropogenic re-suspension occurs
when boats are grounded and from boat wakes, as well as from canal discharges.
Storm induced turbidity is the principal mechanism for re-suspension along the reef
tract. The area north of BNP adjacent to Key Biscayne is affected by high turbidity from
the Miami River, caused by re-suspended flocculants (Harlem, 1979). Turbidity
problems in Biscayne National Park are reasonably well understood with good data on
the sources as well as the effects on organisms. As long as dredging projects are
restricted and boat usage regulated, this problem will be minimized. Turbidity in
northern sections of the Bay has been a long term problem and is likely to get worse as
the downtown Miami area continues to grow and the seaport is expanded.
Microbial contamination
Miami-Dade County beaches are regularly tested and other sites are
occasionally tested for microbial contamination. Typical microbial groups of concern
include fecal coliforms, enterococci, Clostridium perfringens, and coliphage and known
pathogens such as Escherichia coli, Serratia marcescens, and human enterovirus.
Endemic problems are largely confined to areas north of BNP and may not relate to
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conditions within the Park. High concentration of fecal coliform bacteria in the C-8
(Biscayne) Canal, the C-7 (Little River) Canal, the C-6 (Miami River), C-6 (Miami River)
Lower Segment, and the C-6 (Miami) Canal, within the Biscayne Bay Basin, have
rendered these waterbodies impaired. Threats posed by microbes are not only for
humans but for biota in general. Four bacteria have been previously implicated in coral
disease, Aurantimonas coralicida: white plague (type II) (Richardson et al. 1998),
Serratia marcescens: white pox (Patterson et al. 2002), Vibrio shilonii: bleaching
(Kushmaro et al. 1997), and Vibrio coralliilyticus: bleaching and necrosis (Ben-Haim and
Rosenberg 2002), although the cause of such infections is not uniquely linked to a
specific pathogen (Polson et al. 2008). Studies of pathogens attached to atmospheric
particulates suggest that deposition of fungi and bacteria to the Park from outside by
aerosol means is quite likely to occur. Some concerns have been raised for this to be a
driving force for the coral declines seen in recent years but proof is inconclusive.
Microbial contamination from terrestrial sources does occur and is a potential problem
for Biscayne National Park. Given that data is sparse so the threat is inferential.
Pesticides and herbicides
Key et al. (2003) examined pesticides attributed to contaminated canal discharge
levels in grass shrimp and found correlation between reduced levels of
acetylcholinesterase enzyme and canal chemicals at Military and North Canals. Cantillo
and Lauenstein (2004) analyzed samples from South Biscayne Bay and Manatee Bay
for contaminated marine sediment. Eight types of pesticide were found in seawater
samples including atrazine, metolachor, CEAT, CIAT (metabolized herbicides),
chlorpyrifos, diazinon, malathion, and 4,4’DDE (DDT metabolite). The majority was
found at highest levels at the upstream sites associated with the canal network, at the
mouths of the canals. Metolachlor was present at all sites sampled. Two sites, Princeton
Canal mouth and Florida City Canal mouth had high levels of ethoxylates which can be
an endocrine disruptor. Carriger and Rand (2008) assessed the aquatic risk caused by
atrazine, metolachlor, malathion, chlorpyrifos and endosulfan in south Biscayne Bay
and found that atrazine was the most frequently detected pesticide but only at low
levels. Harman-Fetcho et al. (2005) studied pesticides associated with agricultural
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runoff to the canal network and found that there were seasonal variations and that
harvest season when endosulfan is commonly used had a higher hazard potential.
Seba (1969) reported pesticides associated with surface microlayers in Biscayne Bay
were related to atmospheric transport and deposition.
Past and present use pesticides and herbicides have been consistently detected
in canals and near-shore locations along the southern portions of the bay. For example,
atrazine and some of its metabolites are present in almost all water samples collected in
the freshwater environments at concentrations up to approximately 100 ng/L and also in
coastal areas at lower levels 5-10 ng/L. A similar trend is also evident for the herbicide
metolachlor. However, the water quality guidelines for these herbicides are several
orders of magnitude above the environmental concentrations thus unlikely to produce
detrimental effects. Legacy pesticides, mainly p,p’-DDE (metabolite of DDT) is often
found in canal sediments and occasionally in areas immediately adjacent to canal
discharge points (Princeton, Military, Mowry, North and Florida City canals and at Black
Point Marina). Gardinali et al. (2008c) examined the levels of endosulfan in fish tissues
from BNP and Everglades National Parks and reported that endosulfan sulfate is
generally present in areas of Everglades National Park near the Homestead Agricultural
Area but seldom detected in coastal areas of Biscayne Bay.
Metals
Judge and Curtiss (1977) examined sediment samples from the middle of
Biscayne Bay (just north of the park) for heavy metal contamination and found little
difference between most areas sampled except for lower values near Fisher Island and
a sink for metals in sediments near the mouth of the Miami River. They expressed the
concern that south Biscayne Bay may have been polluted by waters from Miami River
flowing south under Rickenbacker Causeway. Schroeder and Thorhaug (1980)
examined uptake of trace metals into seagrass blades finding higher levels in tissues
than in the surrounding water. Miller (1984) analyzed the runoff from several different
basins types in South Florida and found the highest lead runoff was from a commercial
(shopping center) type basin. Cantillo and Lauenstein (2004) analyzed samples from
South Biscayne Bay and Manatee Bay for contaminated marine sediment. The total
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trace metals (Cu, Zn, Ni, Pb, Cd, Hg, Ag) found in sediments at the mouths of five
canals studied indicated toxic conditions were likely. Lidz (2002) reported initial results
of surface sediment samples analyzed for heavy metals and concluded that Cu, Pb, and
Zn were highest near marinas in the northern parts of the bay, that metal contamination
decreased southward and seaward. Among the trace metals, Copper, Arsenic, and
Lead have been reported in sediments of the bay at concentrations that are above the
national median for the NOAA NS&T Mussel watch program and in some cases above
the 85th percentile. However, all the values reported for south Biscayne Bay away from
the influences of marinas are below the ―probable effects level‖ (PEL) or the sediment
quality assessment guidelines (SQAGs) for coastal sediments used in Florida to assess
sediment contamination. With regards to mercury levels in biota, Evans et al. (2008)
reported mercury levels in fish samples from Florida Bay and Biscayne Bay with highest