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values in Crevalle jacks found in south Florida and in other species associated with |
areas of restricted circulation. |
Anti-fouling agents |
In the past decade, some non-traditional contaminants have also been reported |
in the vicinity of BNP. Organotin (TBTs) related antifouling compounds were reported in |
sediments at the North Canal at Homestead Bayfront Marina and Irgarol 1051, an |
antifouling booster biocide, has also been reported in many marinas in the bay. All |
these pollutants are related only to boating activity and transport beyond their localized |
usage area is not expected. Since TBTs have been banned, Irgarol 1051, in conjunction |
with copper are contaminants that need to be further monitored with respect to marinas |
and boatyards. Maxey (2006) analyzed surface water, seagrass, and sediment for the |
antifouling biocide Irgarol 1051 and its metabolites. Concentrations of Irgarol in surface |
water and seagrass ranged from N.D. to 1239 ng/L and 2.35 ng/g to 225 ng/g, |
respectively. Concentrations of Irgarol in sediments were negligible (< 10 ng/g). |
Bioconcentration factors (BCF) are measurement of the ratio of the chemical |
concentration in a marine organism compared to that of the surrounding water. BCFs |
greater than 1000 are considered to be accumulative, while BCFs greater than 5000 are |
considered highly accumulative. BCF values for Irgarol uptake into seagrass ranged |
78 |
from 60 to 31588. While Irgarol was found at the majority of the marinas sampled, no |
Irgarol was found at any coral reef, the specie reported to be the most sensitive to |
Irgarol. |
PCBs and PAHs |
Lang and coworkers (Lang et al., 2002) reported the abundance and atmospheric |
deposition of a variety of organic contaminants, including polychlorinated biphenyls |
(PCBs) and polycyclic aromatic hydrocarbons (PAHs), in the Miami metropolitan area. |
PAHs are commonly present in many sediment samples but their concentrations are |
relatively low and consistent with background levels in urbanized areas. Marinas, |
however, represent a deviation of this observation and is common to see sediments in |
canals and access areas to major marinas to have elevated concentrations of Total |
PAHs. Litz et al. (2007) reported total PCBs (sigma 73PCBs) present in the highest |
concentrations and 5 times higher in males dolphins with sighting histories in the |
northern, metropolitan area of Biscayne Bay than males with sighting histories in the |
southern, more rural area. All compound classes had higher concentrations in northern |
animals than in southern and are also high as compared to other studies of estuarine |
dolphins and may place these animals at risk of reproductive failure and decreased |
immune function. |
CLIMATE CHANGE |
Increasing concentrations of greenhouse gases in the atmosphere (carbon dioxide, |
methane and nitrous oxide) have been shown to be the primary cause of global |
increase of surface temperatures (IPCC 2007; Karl, et al. 2009), leading to warming of |
the oceans, melting of ice fields and glaciers, and diverse climatic effects, which for |
south Florida entail a number of important issues (Table 5.1), such as: sea level rise, |
changes in rainfall and evaporation patterns affecting the amount of available |
freshwater and potentially causing prolonged droughts and/or flooding; saltwater |
intrusion into the coastal aquifers and public water supply; reduction of coastal |
79 |
stormwater release capacity due to sea level rise (SLR); and changes in tropical storm |
and hurricane activity with increased surge levels (Heimlich et al 2009; Obeysekera |
2011) |
Sea Level Rise |
Because of the sensitivity of vegetation patterns to subtle elevation differences, |
we can expect the coming sea level rise to have a profound effect on the Park’s |
terrestrial vegetation. Landward (uphill) migration of mangrove is already occurring on |
the mainland, partly due to anthropogenic changes to the coastal water delivery |
systems or driven by sea level rise. Wanless (1984) showed the movement of the |
intertidal zone upward at the Coral Gables Waterway, caused by a slight rise in sea |
level during the latter half of the 20th Century. However, the current rate of rise is faster |
and is expected to be the controlling factor on future patterns of terrestrial vegetation as |
more and more of the low coastal margin of the Park becomes inundated by marine |
waters. Coronado-Molina et al. (2003) suggested that mangroves on the mainland |
shore may be better suited to keep up with the sea level rise than those on the Keys, |
due to higher productivity. Harlem and Meeder (2008) showed that sea level rise of only |
1 foot would inundate much of the shoreline of Biscayne National Park at high tide |
which would alter salinity regimes in the coastal area drastically and favor the westward |
(inland) migration of saltwater habitats. |
One aspect of great concern is the release of sediment and its associated |
nutrients and pollutants to the marine system as coastlines erode. There are large |
amounts of the former locked up in coastal sediments which will enter the sea as waves |
and increased currents attack the existing shore deposits. While moving sediments by |
currents is a natural phenomenon and most benthic communities are adapted to some |
amount of sedimentation, the loading potential from rapid sediment adjustments as sea |
level rises can only be considered a negative impact on Bay and especially on |
marine/reef ecosystems. |
Ocean Acidification |
Ocean acidification refers to the ongoing increase in acidity (lowering pH) of the |
Earth's oceans, caused by the uptake anthropogenic carbon dioxide of (CO2) from the |
80 |
atmosphere. This pH reduction causes problems for marine organisms which use |
carbonate molecules (aragonite or calcite) to construct hard body parts or protective |
shells, skeletons, and tests. Included in the affected groups are molluscs, foraminifera, |
coccolithophores, crustaceans, starfish, bryozoans, and corals. Octocorals (soft corals) |
and other marine organisms use calcite for structural support and scleractinian corals |
use aragonite which is the metastable form of calcium carbonate used to build |
skeletons. The Park lies in an area that will be least affected by acidification if the |
models hold true (Guinotte et al. 2006), however, changes in the deep reefs seaward of |
the Park should be expected in the near term and effects will increase in shallower |
waters after 2100. |
81 |
Table 5.1 - Summary of Climate Change Impacts on Southeast Florida’s Water Resources |
(Heimlich et al., 2009) |
Climate change Potential threats to Potential threats of Other effects |
impact fresh water supply severe flooding |
Sea level rise • Saltwater intrusion of aquifer • Compromised stormwater • Barrier islands subject to |
• Inundation of Southernmost drainage systems inundation and washout |
Everglades with seawater • Reduced capacity of canals • Beach erosion |
potentially affecting the and coastal control structures. • Coastal wetlands and |
Biscayne Aquifer in south • Greater potential for flooding southernmost Everglades |
Miami-Dade. due to heavy rain storms and encroachment |
• Reduced groundwater flow hurricanes |
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