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western BNP shoreline. Road construction produced elevated structures with adjacent
canal-like borrow ditches and levee structures which cross the western coast in many
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places. All these structures are barriers to flow, some affect groundwater, and all
fragment the coastal environments into small disconnected parcels (Fig 5.1). This has a
negative effect on the wetlands themselves and downstream consequences for those
marine/bay ecosystems which depend on both quantity and quality of freshwater
entering the estuary, groundwater flow and dynamics of seawater intrusion.
Assessments of perceived impacts of canal and groundwater discharges to southern
Biscayne Bay include those of Szmant (1987), Byrne and Meeder (1999), Lietz (1999),
Langevin (2000) and Graves et al (2004, 2005). Findings suggest nitrogen-enriched
groundwater enters Biscayne Bay through canals and underwater springs. Szmant
(1987) reported a change in seagrass community composition near the mouth of C-102
and C-103 and found lower salinities and higher water column nutrient concentrations in
the affected areas
Habitat Fragmentation
Habitat fragmentation has both physical and biotic impact. Most fragmentation
occurs on the western coastal zone affecting the coastal wetlands and mangrove fringe.
This compartmentalization of formerly connected wetlands includes urban areas,
canals, roads, and other structures which impede water flow and isolate biota.
Therefore habitat fragmentation is a current problem with fair documentation for the
terrestrial environments, although its potential impacts on the Bay are only inferred.
Dredging and filling for marinas and residential boat access as well as channels dug
through shallow water and bridges/causeways are currently a minimal problem in
Biscayne National Park, but affects the Bay to the north of the Park.
Power Plants
Electrical generating power plants, all run by Florida Power and Light, are located
adjacent to Biscayne National Park. The principal plants are: (1) the Turkey Point
Nuclear facility located just west of the Park’s SW corner and includes a fossil fuel
peaker plant on site; (2) the Cutler Power Plant, located on the shore of Biscayne Bay
northwest of the Park; and (3) one fossil fuel peaker plant which has been permitted
south of the Princeton canal just west of the Park perimeter. Since 2007, the NPS has
expressed concerns about the planned expansion, indicating those plans affect
mangrove wetlands within protected areas, and the recharge area which maintains the
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saltwater barrier line, and would decrease any benefit the CERP Coastal Wetlands
restoration could provide once implemented. NPS also pointed out the lands had been
previously identified as providing wildlife connectivity, and are frequented by several
endangered or threatened species including the Florida panther, indigo snake, wood
stork and state listed wading birds. NPS also expressed concerns about the lack of
supplies of water to meet the plants needs, disposal of same, archeological issues, and
the threats from sea level rise which would leave the facility as an island at some future
stage (NPS, 2007).
WATER QUALITY
Water quality issues of concern for Biscayne Bay and Biscayne National Park are
primarily caused by their proximity to Miami Metropolitan area, home to more than 2.4
million people, and also to agricultural activities in the Homestead area, and even to
agriculture south of Okeechobee Lake whose nutrients pesticides, and agro-chemicals
may be transported along the canal network and brought south to the Biscayne Bay
basin. All waters in Biscayne Bay are Class III, whose designated use is recreation and
propagation and maintenance of a healthy, well-balanced population of fish and wildlife.
Biscayne Bay is also a designated Outstanding Florida Water (OFW). Main water
quality issues are: water turbidity); nutrient loading and enrichment, bacterial
enrichment, chemical compounds derived from runoff, pesticides, and industrial and
stormwater pollutants (Lietz and Meyer 2006; http://www.miamidade.gov). Canal inflow
is the primary loading mechanism for pollutants to the bay followed by subsurface runoff
from the shallow, highly permeable Biscayne Aquifer, which allows rapid movement of
groundwater with direct subsurface connection to the bay and canals (Klein and Hull
1978; Lietz 1999; Alleman et al. 1995). Caccia and Boyer (2007) identified atmospheric
deposition as an important contributor to nutrient enrichment.
Contaminated runoff and groundwater have been identified as major sources of
pollutants (pathogens and toxicants) to the Dade County canal system (Long et al.,
1999, 2000, 2002, 2005), which finally reach the Bay. Polluted waters have been
exposed to leachates from agricultural fields, landfills and municipal dumps, through
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atmospheric deposition of pollutants derived from combustion sources, agricultural
applications, industrial discharges and vehicle emissions, and finally from direct
disposal and point sources. Three groups of contaminants have been consistently
targeted when environmental assessments of Biscayne Bay are conducted: trace
metals, chlorinated pesticides, polychlorinated biphenyls (PCBs) and polynuclear
aromatic hydrocarbons (PAHs).
Early studies of pollution were focused on the impact of raw sewage from open
sewers and septic tanks (Wakefield 1939; Moore et al. 1955; McNulty 1956). The
Mowry Canal had elevated phenol levels (Cheesman 1989) and the bay north of
Rickenbacker Causeway was more affected by chemical contamination and toxicity
than to the south of the causeway (Long et al. 1999). Organophosphates have been
detected in sediments at three sites including Military and North Canals (Cantillo and
Lauenstein 2004), but sediments in open areas of the park have generally low toxicity.
Lidz (2002) reported initial results of surface sediment samples analyzed for heavy
metals and concluded that deformed benthic foraminifera were common near the landfill
(Black Point area).
NOAA conducted intensive regional surveys to describe the incidence, severity,
and spatial extent of adverse biological effects associated with chemical contamination
in Biscayne Bay in 1995. Results showed high levels of sediment contamination and
severe toxicity in several peripheral canals and tributaries, notably the lower Miami
River. The 1995 data also showed sporadic low-level occurrence of sediment toxicity in
southern Biscayne Bay. From 1999 results it is apparent that contaminant plumes and
associated toxicity do not appear to extend seaward of the mouth of the canals in an
appreciable manner. Concentrations of contaminants in the sediments in open areas of
Biscayne and Manatee Bays are generally low (Cantillo and Lauenstein 2004)
Nutrient enrichment
Nutrient loading in Biscayne Bay is correlated to population density (Caccia and
Boyer 2007), agriculture and storm events (Briceño et al. 2010; Migliaccio and Castro
2009). Additionally, climatic cycles and events seem to affect nutrient loading to the bay
with increases in loading rates during wetter years (Caccia and Boyer 2007). Surface
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waters from the three most important land-cover types in Biscayne Bay watershed,
agricultural, urban and wetland cover, have different chemical characteristics. NOx
concentrations are higher in agricultural than in urban or wetland areas; concentrations
of ammonia, TP, and Chla tend to be higher in urban areas than in wetland or