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Figure 2.2: Sediment type map for Biscayne Bay bottom (from Harlem et al. 2009)
Little is known about the distribution of soil types within BNP and there seems to
be three soil types inside the park. First, silty marl (carbonate mud) is the dominant soil
type along the west side of the park landward of the mangrove fringes (Gaiser, et al.,
2006b, Ross, et al. 2003). The second major soil type in the Park is peat derived from
mangrove detritus. This is the common soil along the fringe of the coastline, along
former freshwater streams and seeps, and on most of the islands. The third major soil
type in Biscayne National Park are histosols developed under hardwood hammock
vegetation on the barrier islands. These organic soils develop in well-drained upland
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settings that combine relatively high above ground production with some level of
recalcitrance to decomposition (Coultas, 1977; Ross et al. 2003; Harlem et al. 2009).
WATER RESOURCES
Natural habitats in BB have been severely affected by rapid urbanization and
coastal development linked with the growth of the Greater Miami area, and by disruption
of its natural drainage system. Southern BB has been additionally impacted by
agricultural activities. Overall, most of the surface water flow into BB is now controlled
by a system of canals, levees and structures contributing to the bay's transition from an
estuary to a marine lagoon over the last 100 years (Harlem, 1979; 2009). Biscayne Bay
estuarine waters have experienced the impact of anthropogenic interventions since the
early 1900’s, including major disruptions of its hydrology (RECOVER 2009) and
sustained urban and agricultural development. Hence, despite their oligotrophic nature,
BB aquatic ecosystems bear the heritage and signals of such a long and sustained
influence.
Prior to construction of the South Dade Conveyance System coastal wetlands
and nearshore areas in BB maintained estuarine condition most of the year (Smith
1896; Meeder et al. 1999, Meeder et al. 2001) and supported a diverse assemblage of
estuarine biota, including oyster reefs and American crocodile (Kushlan and Mazzotti
1989; SFWMD 1995; SFNRC 2006). The southern bays and sounds have experienced
significant reductions in historical freshwater flows, leading to hyper saline conditions
during extended periods of low rainfall (Wingard et al. 2003, 2004). Nevertheless, BB
remains very productive and its biodiversity is still noteworthy.
These outstanding features have driven the establishment of protected areas
besides BNP and encompassing central and southern BB, among them, the Florida
Keys National Marine Sanctuary, Biscayne Bay Aquatic Preserve, John Pennekamp
Coral Reef State Park, Bill Baggs State Park and Biscayne Bay-Card Sound Spiny
Lobster Sanctuary (Fig 2.3). Furthermore, within the Comprehensive Everglades
Restoration plan there are subcomponents to re-establish estuarine habitat through the
Biscayne Bay Coastal Wetlands (CERP 2010), whose main goals are to re-hydrate
coastal wetlands currently drained by canals and redistribute freshwater flow to the Bay.
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This restoration endeavor might affect salinities in the bay, especially in nearshore
habitats of BNP (Serafy et al. 2001).
Figure 2.3: Protected areas in the vicinity of the Biscayne National Park. EEL= Miami-Dade
Environmentally Endangered Lands; FKNMS = Florida Keys National Marine Sanctuary (from
Harlem et al, 2009).
Rainwater
Given the extension of the Bay’s watershed and the diversity of water sources
entering the Bay the characterization of its climate requires a regional approach,
because components and balances among the freshwater budgets and the marine
inputs play a critical role on WQ and ecosystem responses. Long-term climate data has
been downloaded from the South Florida Water Management District (DBHYDRO)
website (http://www.sfwmd.gov) for the following weather stations: Florida Coastal
Everglades Long Term Ecological Research Station (LTER; 25º51’00‖; 81º22’59‖);
Biscayne National Park
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Tamiami Trail Station (25º45’37‖; 80º49’29‖); Miami International Airport Station
(25º49’01‖; 80º16’59‖); and Joe Bay Station (25º13’28‖; 80º32’28‖). The location of
these stations could provide insight on the loads and flows derived from three major
sources of rain and different settings. Additional to geographical variability, the LTER
and Tamiami stations would provide information on rainwater locally derived from inland
evaporation and recycling (i.e. Everglades), while the Miami station would have a
stronger signal from the Miami urban area, and Joe Bay Station rain data would bear
information on marine contributions to rain water.
Rainfall in South Miami-Dade ranges from 102 to 165 cm yr-1
. The wet season
extends from June to November with a bimodal pattern peaking in summer (June) and
fall (September-October). The dry season spans between December and May (Fig 2.4).
Although there is not enough data to substantiate spatial rain patterns given the lack of
stations on the Bay itself or the keys to the east, it is generally accepted that more rain
occurs over the coastal ridge on the mainland than over the barrier islands (Schmidt
and Davis, 1978).
Little information can be derived from the time-series of Figure 2.4, except for an
important decline of rainfall at Joe Bay station since 1994. The bimodal pattern
observed at most rainfall stations is absent at Joe Bay (Fig 2.4) where data dispersion is
significant. The dry season usually runs between November and April. Higher
precipitation and larger contrast between dry and wet season occurs inland, towards the
Everglades as compared to Joe Bay in the south.
Zcusum charts of long-term precipitation data (Fig 2.5) clearly show the
occurrence of common cycles of diverse spans (for details on construction and
interpretation of Zcusum charts see Appendix 4). Fourier analysis of precipitation timeseries suggests cycles of about 47-50 years; 14 years cycle and its harmonics at 7 and
3½ years; and 1 year (seasonality). A long cycle (~50-year) occurred from 1940s to
1990s and was characterized by higher precipitation rates until early 1970s when a
significant shift to below average rates began and lasted until the early 1990s.
Precipitation changes in early 1990s parallel changes in surface water chemistry,
rainwater chemistry, flows and ecosystem response in South Florida estuaries and
coastal waters (Briceño et al. 2010).
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Figure 2.4: Precipitation time-series and seasonality of precipitation for Florida
Everglades, Miami Airport, Tamiami and Joe Bay weather stations
Miami Station. Rain
0
5
10
15
20
25
Jan-48
Jan-58