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and taking into account all source waters, this area of fresher |
water would extend along the mainland shoreline to the isthmus bounding the southern end of Barnes Sound. |
When considering questions related to water management |
and freshwater flows from the mainland, the focus within these |
regions shifts westward to water and habitats nearest the coast |
that provide the most sensitive indicators of bay conditions. |
For the purposes of this report, the focus for development of |
targets to assist in the estimation of water for the protection of |
fish and wildlife is placed on two areas: the Coastal Mangrove |
Zone (CMZ) on the mainland of Biscayne National Park, and |
the Western Bay Zone (WBZ), including the seagrass bottom, |
which occurs in the western portion of the South Bay Section |
(Fig. 3). |
Western Bay Zone Target Area. RECOVER has developed |
a performance indicator (SE-6) for CERP restoration efforts |
in Southern Biscayne Bay that describes indicator organisms, |
salinity conditions, and the “nearshore” area in which the performance measure will be applied. The area defined in SE-6 |
has lost historical oyster (Crassostrea virginica) colonies and |
no longer sustains red drum (Sciaenops ocellatus), a species |
that could be restored if habitat conditions were made suitable. Performance measure SE-6 defines “nearshore” as 250 m |
from shore during the dry season and 500 m from shore during the wet season (Fig. 3). The definition of these longitudinal |
bands of estuarine habitat is based on a simple consideration |
of a volume of water entering the bay edge as uniform flow; |
Ecological and Hydrologic Targets for Western Biscayne National Park 5 |
however, there is no analysis in the performance measure that |
explains why 250 and 500 m were chosen as target areas. |
Because the characteristics of the benthic community |
depend on bottom type, we chose to use existing, but stable, |
physical characteristics of the bay bottom to assist in the |
definition of a target area for restoration. Based on benthic |
mapping and evaluation of abundance and distribution of |
benthic community types, the ecology of Biscayne Bay, as a |
whole, is dominated by the soft bottom (approximately 64% |
of the bottom) and hard bottom (17%) benthic communities |
(NOAA 1996). Soft bottom, shallow areas promote seagrass |
communities, whereas hard bottom areas, which occur where |
sediment is non-existent or very thin over a rocky substrate, |
are characterized by soft corals (i.e., sea fans), sponges, and |
isolated coral colonies. |
Examination of geological maps of the bay bottom shows |
that areas affected by freshwater inflows along the coast of |
Biscayne National Park comprise a zone of soft bottom seagrass habitat that extends from Turkey Point to about 1,000 |
m offshore at Convoy Point to some 6,500 m offshore at the |
northern mainland boundary of the park (Fig. 3). The northern sector of this zone is a mix of both soft and hard bottom |
communities. This zone is bounded by the CMZ at the western shore of central and southern Biscayne Bay and by an area |
of hard bottom that occupies the Middle Bay Zone to the |
east. This WBZ historically received freshwater flow through |
coastal marshes and creeks, and groundwater recharge that |
correlated with the wet and dry seasons. |
The bottom type and location of the WBZ, relative to historical freshwater inflows, define a target area of 10,000 acres |
of functional, seagrass-based estuarine habitat in Biscayne |
National Park. In contrast, the RECOVER dry season target |
of 250 m from shore covers about 1,600 acres, or only 16% |
of functional estuarine habitat that could be restored. The |
RECOVER wet season target of 500 m from shore covers |
about 3,200 acres, or less than 1/3 of the estuarine habitat that |
could be restored. It is our understanding that RECOVER |
may consider revising SE-6 in response to the considerations |
discussed here. |
Our description of desired conditions and the analyses |
of ecological and hydrologic targets in the WBZ focus on |
this 10,000 acre area of submerged aquatic vegetation (SAV) |
habitat at the western edge of Central and South Bay, within |
Biscayne National Park. Currently, freshwater is delivered |
through canal structures along the coast. The water deliveries should be stabilized by linking volumes and timing with |
natural coastal marsh hydroperiods and estuarine salinities. |
This change would reestablish high quality nursery habitat for |
important fish and invertebrates in a band of soft bottom/SAV |
habitat from the northern boundary of Biscayne National |
Park south to Turkey Point (Fig. 3). |
Florida Turnpike |
6 South Florida Naturai Resources Center Technical Series (2006:1) |
Submerged aquatic |
vegetation |
Hard bottom |
Eastern extent of Coastal |
Mangrove Zone |
250 meter buffer |
500 meter buffer |
Bay Zone borders |
Area Enlarged |
Atlantic |
Ocean |
Legend |
S-20F |
Barnes |
Sound |
Point |
Biscayne |
Bay |
Key |
Biscayne |
Safety Valve |
Figure 3. RECOVER performance measure focus areas and alternative Western Bay Zone focus area based on submerged aquatic vegetation on the bay bottom. |
Ecological and Hydrologic Targets for Western Biscayne National Park 7 |
ECOLOGICAL TARGETS FOR BISCAYNE |
NATIONAL PARK |
Historical Conditions |
Coastal Mangrove Zone. What we now call the Coastal Mangrove Zone was formerly composed of freshwater |
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