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The ecological effects and interrelationships associated with salinity patterns and coastal wetlands are
depicted in the third diamond in Figure 2. Data and
historic accounts document that, in the past, freshwater
inflows to Biscayne Bay were more diffuse and continuous via surface sheet flow, ground water, and
EXHIBIT 7
862 WETLANDS, Volume 25, No. 4, 2005
freshwater ‘springs’ within the bay (Kohout 1967, Kohout and Kolipinski 1967). These conditions generated
a diverse salinity regime, with general gradients near
0 ppt close to the mainland, to 35 ppt or greater in the
open areas of the bay in the southeast. These conditions apparently extended to Manatee Bay off Barnes
Sound at the extreme southern end of Biscayne Bay
(Ishman et al. 1998). Prior to drainage, several small
rivers that flowed into the semi-enclosed northern part
of the bay made it brackish. Natural patterns of salinity
distribution and fluctuation were major determinants
of habitat development, composition of biological
communities within these habitats, and their overall
productivity. Therefore, restoration of more natural
freshwater inflows and associated salinity patterns and
coastal wetlands are necessary prerequisites to restoration of the bay’s natural estuarine diversity and productivity.
Relationship between Salinity Patterns and Freshwater Inflows. Both flow rate and distribution of freshwater inputs to Biscayne Bay have been altered by
construction and operation of the present water-management system (Buchanan and Klein 1976). The system of canals and water-control structures provides a
means to manipulate and control virtually all inflow to
the bay. Altering the historical distribution of freshwater inflow in time and space has had an effect on
patterns of salinity distribution and salinity variability.
Routing freshwater flow to the bay through canals and
away from coastal creeks and wetlands has resulted in
a loss of estuarine habitat. The salinity gradient resulting from large, point-source discharges is very different from that resulting from more diffuse flow
through tidal creeks and wetlands and ground-water
seepage resulting from higher overall water tables. Inflows distributed through coastal wetlands resulted in
a positive salinity gradient from interior wetlands and
a broader mesohaline zone along the shoreline prior to
drainage. Diversion of freshwater runoff into canals
(i.e., point sources) short-circuits coastal wetlands and
does not create positive gradients from interior wetlands outward. Although the general relationship between freshwater inflow and salinity is well known in
Biscayne Bay, this relationship has not been rigorously
quantified within the critical western nearshore zone
and associated wetlands, where the greatest effect of
changes in freshwater inflow patterns can be expected.
Relationship between Freshwater Inflow and
CERP. Changes in upstream water-management
practices will cause changes in freshwater inflow to
Biscayne Bay. Modeling results with the South Florida
Water Management Model (SFWMM) indicate that
CERP’s proposed changes to water-management features and practices in Biscayne Bay’s watershed will
substantially affect freshwater delivery patterns. Exact
relationships between rainfall in the watershed, freshwater delivery patterns, and planned changes to the
water-management system are difficult to define quantitatively. For example, model estimates of daily discharge rates through coastal canal structures bear little
relationship to daily rainfall, suggesting highly unnatural flow patterns. Furthermore, present methods of estimating discharge rates at structures can introduce significant error (Swain et al. 1997) and will need to be
improved to fully investigate rainfall-runoff relationships.
Water Quality
Relationship of Biscayne Bay Water Quality to Water
Quality in Ground Water, Storm Water, and Canal
Discharge. The term ‘‘water quality’’ includes both
abiotic and biotic characteristics; therefore, water quality both influences and embodies major aspects of the
ecological functioning of Biscayne Bay. The processes
that link ecological attributes in Biscayne Bay to
stressors are depicted in diamond 2 of Figure 2. In
general, water clarity in Biscayne Bay is high, except
where and when bottom sediments are disturbed by
wave action or boat traffic. Inorganic nutrient concentrations are naturally low, and phytoplankton in the
water column is not an impediment to light penetration. Open waters of Biscayne Bay are generally characterized by high dissolved oxygen concentration, low
nutrient and chlorophyll concentrations, and high clarity. Sewage-related bacteria, trace metals, and other
toxicants typically occur at low concentrations in Biscayne Bay waters. A primary controlling factor of water quality in Biscayne Bay is the quality of water discharged into the bay. Water quality in a number of
canals and rivers that discharge to the bay is poor in
comparison to the open waters of the bay. Surface waters in some canals in south Miami-Dade County that
discharge into Biscayne Bay contain high levels of inorganic nitrogen.
Water quality can also be affected by ground-water
inputs. In some areas, ground water contains elevated
levels of ammonia nitrogen from landfill leachate and
nitrate-nitrogen from agriculture (DERM 1987, Alleman 1990, Markley et al. 1990, DERM 1993, Alleman
et al. 1995, Lietz 1999, Meeder and Boyer 2001). Submarine ground-water discharge into shallow nearshore
waters is a source of elevated nutrients (Meeder et al.
1997); nutrient concentrations in shallow ground water
(beneath the nearshore bay between Mowry Canal and
Military Canal) are higher than in bay or canal waters
or deep ground water. The structure and operation of
water-management systems, land uses and urban and
agricultural practices, and sea-level rise all affect
EXHIBIT 7
Browder et al., Biscayne Bay CEM 863
ground-water input (and nutrient loading) to Biscayne
Bay.
Biscayne Bay is vulnerable to nutrient loading, especially from phosphorus, the limiting nutrient to phytoplankton growth in Biscayne Bay (Brand 1988). Water-column inorganic and organic nutrient concentrations, turbidity, photosynthetically-active radiation
(PAR), bacteria, plankton taxa, size, and composition
of plankton, as well as phytoplankton biomass, as reflected in chlorophyll and other pigments, can all be
influenced by solids and nutrients received via canal
discharge, stormwater runoff, and ground water.
CERP’s proposed changes in freshwater delivery,
particularly in south Miami-Dade County, may affect
nutrient concentrations and loading to Biscayne Bay.
On the one hand, plans to reroute canal discharge
through coastal wetlands could reduce nutrients reaching Biscayne Bay; on the other hand, wastewater reuse
may increase nutrient or other contaminant loading.
While water-quality targets for wastewater reuse have
been proposed that would protect open waters of south
Biscayne Bay from degradation, it is not yet clear that
achieving these targets is technically and economically
feasible. This will pose problems since the water from
wastewater reuse is a substantial part of total inflow to