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Project, and Lake Belt Storage Projects. The Coastal |
Wetlands Project has the objective of restoring the historic water supply patterns through wetlands to the |
southern Biscayne Bay. Wastewater reuse has the potential to affect bay water quality. The remaining projects listed all directly affect the amount of fresh water |
available to Biscayne Bay. |
To guide a science-based, adaptive-management approach to water-management planning, a conceptual |
ecological model of Biscayne Bay was developed |
based upon a series of open workshops involving researchers familiar with Biscayne Bay. Since the adaptive management process for CERP is the context in |
which this conceptual model was developed and will |
be used, the emphasis of the Biscayne Bay CEM is on |
the relationship between the bay ecology and the mainland shoreline and freshwater sources. |
EXTERNAL DRIVERS AND ECOLOGICAL |
STRESSORS |
In the Biscayne Bay Conceptual Ecological Model |
(Figure 2), the two principal drivers applicable to the |
Comprehensive Everglades Restoration Plan (CERP) |
are watershed development and water management. |
They exert their effects through four principal stressEXHIBIT 7 |
Browder et al., Biscayne Bay CEM 857 |
ors: toxicant and pathogen inputs, altered solids and |
nutrient inputs, altered freshwater inflow, and operation of physical structures, particularly water-control |
structures and maintenance of infrastructure. Altered |
freshwater flow is the stressor that CERP will most |
directly affect and includes flow volume, velocity, timing and spatial distribution. CERP may indirectly affect the input of solids, nutrients, toxicants, and pathogens. |
Construction of the major canals through the Everglades and dredging of natural tributaries and transverse glades that carried fresh water to Biscayne Bay |
resulted in lowered regional and coastal water tables |
(Parker et al. 1955), reduced water storage in the watershed, decreased ground-water flow to the bay, and |
the elimination of many tributaries. Drainage of the |
watershed greatly affected the natural salinity gradients and ecotones from the Everglades through coastal |
wetlands and tidal creeks into the bay, and reduced or |
eliminated critical estuarine habitat for bay species requiring low-to-moderate salinity waters. In addition, |
constructed drainage systems result in pulsed, pointsource discharge degrading estuarine habitat near canal |
mouths by creating biologically damaging zones of |
bottom scouring and rapid salinity fluctuations. Departures from natural salinity patterns are ecologically |
damaging to many species because salt concentration |
affects growth, survival, reproduction, and other critical physiological processes in both plants and animals |
(see, for example, Kinne [1971]). The general lowering of the water table on the east-coast ridge and diversion of both surface and ground water into canals |
has degraded not only estuarine habitats within the |
bay, but also adjacent coastal wetland communities, |
including herbaceous freshwater marshes and coastal |
mangrove wetlands that were once functionally connected to the estuarine habitats. The few coastal tropical hammocks that remain have also been detrimentally affected by the lowered water table (M. Roessler, |
pers. comm.). |
The bay has also been significantly affected by the |
watershed development made possible by water management (Alleman et al. 1995). Before drainage of the |
watershed, urban and agricultural development was restricted to the highest ground along the Atlantic Coastal Ridge, consisting of hammocks and pinelands (University of Miami and SFWMD 1995). As land was |
drained, development encroached into lower lands and |
former wetlands. Today, most new development is occurring in former wetlands. |
Development has had many detrimental consequences. The continued loss of open, pervious land |
increases stormwater runoff velocity and pollutant |
loads and reduces the quantity of water storage in the |
watershed. Other dramatic changes occurred in northern Biscayne Bay as a result of dredging and filling. |
Bottom dredging resulted in the loss of seagrass beds |
in northern Biscayne Bay and has affected the stability |
of bay sediments and the capacity to assimilate nutrients and trap particulates. Stormwater runoff from urban development has increased the bay’s exposure to |
contaminants and excessive nutrients. At the same |
time, the filling and destruction of coastal wetlands has |
eliminated natural filtering capacity. The dredging of |
inlets at Haulover and Government Cuts significantly |
increased salinity in northern Biscayne Bay (Wanless |
1969, Wanless et al. 1984), changing much of it from |
an estuarine to a more marine system. |
Biscayne Bay’s water quality has improved substantially in the past 30 years because of the elimination |
of direct discharge of sewage into the bay and other |
pollutant-control measures (McNulty 1970, Alleman et |
al. 1995, DERM 2005a). Parts of North Biscayne Bay |
now support substantial seagrass beds. Extensive seagrass beds have always been characteristic of South |
Biscayne Bay. In recognition of its exceptional values, |
the State of Florida has designated the bay and its |
natural tributaries as Outstanding Florida Waters, and |
as such, they receive the highest level of state protection from degradation. Present water quality generally |
meets or exceeds federal, state, and local standards for |
recreational use and propagation of fish and wildlife. |
Nonetheless, the bay still receives dissolved nutrients, |
trace metals, organic chemicals, and suspended sediments via stormwater runoff, sewage overflows, discharges from industrial facilities or vessels, and canal |
discharges. Canal water typically has lower dissolved |
oxygen and clarity and higher concentrations of contaminants than receiving waters of the bay. |
ECOLOGICAL ATTRIBUTES |
Ecological attributes of the overall health of the Biscayne Bay ecosystem include four types of habitat: |
seagrass meadows, mangrove forests, herbaceous wetlands, and benthic faunal communities (both soft bottom and hard bottom). Ecological attributes that have |
been defined because of their special relevance and |
utility for monitoring and reporting the state of the bay |
include pink shrimp (Farfantepenaeus duorarum Burkenroad), blue crabs (Callinectes sapidus Rathbun), |
stone crabs (Menippe mercenaria Say), oysters, estuarine fish communities, fish and bottlenose dolphin |
(Tursiops truncatus Montagu) health, crocodiles (Crocodylus acutus Cuvier), West Indian manatees (Trichechus manatus latirostris Linnaeus), and wading |
birds. |
EXHIBIT 7 |
858 WETLANDS, Volume 25, No. 4, 2005 |
Seagrass Habitat |
Large areas of the bay bottom support seagrass communities because sediment depth and nutrients are sufficient, water depths are shallow, and water clarity is |
high. Seagrass has been documented to cover up to |
64% of the bay bottom (DERM 1985). There is very |
little area of bare bottom with sufficient sediment to |
support seagrass except where there has been a physical disturbance such as dredging. Seagrass beds function as vital habitat to support critical life stages of a |
variety of ecologically important and commercially or |
recreationally valuable species. At least seven species |
of seagrasses occur in Biscayne Bay: turtle grass |
(Thalassia testudinum Banks & Soland. ex Koenig), |
shoal grass (Halodule wrightii Aschers.), manatee |
grass (Syringodium filiforme Kuetz.), three species of |
Halophila, including H. johnsonii (Eiseman), which is |
a federally-listed protected species, and Ruppia maritime (Linnaeus). Distribution of seagrass species is |
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