HISTORIC CREEK WATERSHED STUDY

FINAL RESULTS: YEAR 1

By

John F. Meeder

Peter W. Harlem

Amy Renshaw

Southeast Environmental Research Center

Florida International University

Miami, FL 33199

To

Richard Alleman

South Florida Water Management District

West Palm Beach, FL 33406

18 Oct 2001
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EXECUTIVE SUMMARY

The major goals of this study were to: 1) identify a tidal creek site for restoration

of freshwater discharge, 2) determine the predevelopment near shore salinity regime, and

3) determine the discharge of freshwater required to produce the target salinity. This was

done in several stages. The first stage was to identify all the historic tidal creeks along

western Biscayne Bay from the Deering Estate southward to Convoy Point. This was

completed using aerial imagery and ground truthing. This survey resulted in the location

of 48 tidal creeks of which, only several were deemed likely choices because of pollution,

ownership, degree of restoration required, and access problems. The area between the L31E canal and Biscayne Bay from Military Canal to point 800M north of the Military

Canal was selected. This site had a well-developed tidal creek that merged westward into

a freshwater slough and transverse glades. In addition, oyster shell deposits were located

in several areas within this basin indicating that historic conditions were estuarine in

nature. The second stage was to produce a topographic-bathymetric map of the study

area for the present, as well as, historic conditions at the turn of the century. This was

done to determine if restoration success would be likely. The distribution of oyster

deposits, old channels, and flow ways helped to provide a guide for restoration. Creek

cross-section changed greatly from the Bay toward the levee where tidal action did not

maintain the channel. The third stage was to determine a target salinity regime for the

estuarine zone. Using the oyster, Crassostrea virginica’s ecological requirements as the

major paleoecological tool, a target salinity regime of 5 to 15 parts per thousand (ppt) for

the wet season and 10 to 19 ppt for the dry season was established. The final stage was to

calculate the volume of freshwater needed to produce the desired salinity regime. A first

approximation of freshwater delivery required is 10 ac-ft/d during the dry season and 15

ac-ft/d during the wet season. The calculation of required freshwater discharge used a

simple formula balancing water loss against water gain processes. Water loss processes

included evaporation from water bodies, evapotranspiration from marsh surface, tidal

egress volume (calculated for spring tide only), discharge into bay and bay water renewal

time. Water renewal time was very difficult to calculate and was estimated by

calculating tidal volume, bay volume, basin bathymetry, and prevailing wind directions.

The error associated with this calculation was the main reason a post discharge salinity

monitoring program is recommended in order to adjust discharge according to actual field

salinity measurements. We are confident that the figure presented is a reasonable

estimated based upon methodology and funding level. Water gain processes include tidal

ingress (calculated only for spring tides), canal discharge and rainfall.
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INTRODUCTION

Biscayne Bay has undergone numerous anthropogenic changes, most during the

period 1880 to 1980. Changes include the physical regime (Michel, 1976), freshwater

discharge (Buchanan and Klein, 1976), chemical regime (Waite, 1976), sedimentary

environments and processes (Wanless, 1976; Harlem, 1979), and biological regime

(Thorhaug et al., 1976). The most profound changes in the Bay are found in the North

Bay region where most of the bottom, shorelines, and water circulation are highly altered

(Harlem, 1979). North Bay was brackish in nature because of considerable freshwater

discharge from the Everglades and poor circulation to the Atlantic Ocean prior to the

construction of Haulover Cut. North Bay contained many oyster bars, which supported a

small industry at the turn of the century (Smith, 1895; Handbury, 1896; Munroe and

Gilpin, 1930). This industry was lost as a result of increasing salinity associated with the

inlet cut construction, drainage of the Everglades, and the construction of the Intracoastal

Waterway. Other evidence of the estuarine nature of the northern Bay is the fish catch

records, which showed more species and more frequent catches of estuarine dependant

species in and around the Bay (Serafy, 1997) in the past. Lost oyster fisheries associated

with increased salinities is a familiar situation in other areas of Florida such as the Ten

Thousand Islands (Tebeau, 1966; Tebeau, 1991).

The estuarine nature of the southwestern coastline and near shore areas of South

Bay is not as well documented. However, the earliest aerial photographs and descriptions

document that freshwater marshes continued almost to the edge of the Bay and that

transverse glades cut across the limestone ridge and spread out into broad sloughs to the

Bay through numerous creeks. These creeks were tidally influenced within a 100M or so

of the shoreline (Figure 1). Freshwater marl soils are presently exposed submerged in

the near shore area documenting sea level rise, saltwater encroachment, and coastline

retreat. This condition is found throughout South Florida (Meeder et al., 1999). Sheet

flow and groundwater discharge both have decreased with Everglades drainage and have

been replaced by canal discharge, which does not have natural timing and is a point

source to the Bay. Parker (1955, 1974) documents that the water table throughout

Miami-Dade County has dropped between 4 to 6 feet since the turn of the century. In

addition, oysters were quite common along the western shore of Biscayne Bay, where

creeks dumped freshwater. The construction of the L-31E protection levee and canal

complex completely eliminated sheet flow to the Bay in the mid 1960’s.

The purpose of this study was to identify a creek system that might be restorable

to predevelopment conditions in terms of coastal salinity regime. In other words, to

reestablish an estuarine zone in the near shore area by discharging water into an historic

creek system that we know supported oysters in the past. The two major tasks were to: 1)

establish a proper salinity regime to target and to 2) develop a model to estimate the

volume of freshwater needed to achieve the target salinity regime.
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SITE SELECTION

The area from Military Canal northwards to Fender Point was selected as a study

site after a characterization of historic Biscayne Bay watersheds was completed (Meeder

et al., 1999), and a review meeting held with the South Florida Water Management

District project manager and National Park Service personnel(Figure 1).

Figure 1. A 1940 aerial photograph illustrating the study area watershed. Note that the

southern branch of the transverse glades slough (large arrow in NW corner of photo) spreads out

and develops into 4 distinct tidal creek systems. Creek No. 2 was selected as the study area.

Note: Tidal influence is defined by the distribution of red mangroves (appear as dark bands along

the coastline and along tidal creek banks and levees).
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SITE CHARACTERIZATION

Ecosystem model: General site description. The purpose of the schematic ecosystem

model is to describe the relationships between ecosystem components and estuarine

salinity and oyster ecology (Figure 2). The two boxes represent the coastal wetland and

the near shore estuarine ecosystems. Ecosystem components or forces not originating

within an ecosystem are identified in circles outside and to the top of the two ecosystem

boxes. The interrelationships between external components (or processes) and

components of the two ecosystems, as well as, between ecosystems are denoted by

arrows. This flow chart is basically what we used to determine both the target salinity and

freshwater discharge required to maintain the target salinity regime. All the components

that drive the hydrology and salinity are approximated and discussed in detail in later

sections.

The coastal wetland system can be described as a red mangrove tall scrub forest,

which occupies a topographic basin bound on the north and south by west-to-east infilled tidal creeks and creek levees and the coastal levee to the east. The creek levee and

coastal levee are covered by taller more diverse forest of red and black mangroves along

the creeks and coastline with tall white mangroves also found landward of the coastal

levee. Creek No. 2 (Figure 1) was a large tidal creek whose headwaters gradually

developed into a freshwater slough. This tidal creek was fed historically by freshwater

discharge from the Everglades and now has potential to receive freshwater from the L31E canal. Wetland water is a mixture of canal discharge, rainfall minus

evapotranspiration (ET) and Biscayne Bay tidal water with episodic additions from

tropical depression storm surges. The proportion of wetland water sources change

seasonally, resulting in seasonal salinity changes related to freshwater discharge, bay

water salinity, rainfall surplus, and tidal height and exchange rate. Salinity controls the

plant species composition and subsequently soil accretion rate. Freshwater discharge,

tide height and storm surge height control suspended sediment concentrations and

import/export.

The estuarine ecosystem has direct exchange with the coastal wetland ecosystem

through links between hydrology. The interrelationships among hydrologic components

determine salinity and suspended sediment’s ultimate fate. Tides (tidal water at this

location is a mixture of Biscayne Bay seawater and Mowry Canal (C-103) discharge),

groundwater discharge, rainfall surplus, and water renewal times interact to produce the

near shore water and salinity regimes. Estuarine salinity and sufficient water currents to

maintain sediments in suspension are required for oyster development. Water and

suspended sediments are almost freely exchanged with Biscayne Bay, which is

controlled, by bathymetry, wind strength and direction, freshwater discharge, and tide

height. The proposed estuarine zone bottom types range from outcropping bedrock in the

southern area to an organic rich marine sandy mud with considerable skeletal material,

mostly mollusk fragments. This marine sediment generally thickens towards the north

and west. Exposed freshwater marl and mangrove peat is common along the shoreline.
5

The model also was used to address the two major concerns in the feasibility of

rehydration of the tidal creek system and development of the estuarine zone which are: 1)

has the marsh topography changed from deposition and erosion processes so much that

effective freshwater delivery will not be able to be achieved, and 2) has the coastal

basin’s characteristics been altered so that reestablishment of the estuarine zone is

unlikely? The several ecosystem components or rates at which they work may be

affected by changes in topography and water delivery patterns, both spatially and

temporal. Examples include: freshwater retention time in the wetland and estuary can be

increased or decreased by changes in basin volume and channel flow through the wetland

and into the estuarine basin can be highly altered or lost entirely. These questions are

further discussed later in this section.

Figure 2. The schematic ecosystem model. The two boxes represent the two ecosystems;

coastal wetlands and near shore Biscayne Bay. The circles above or outside the ecosystem
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boxes are components that affect the two ecosystems from outside the systems by management

of natural forces such as rainfall. The components inside the ecosystem boxes represent the

major components of each respective system and the arrows describe the relationships between

each ecosystem component.

Aerial photography. The first step to answering the above two questions was to look at

serial aerial photography of the study area in order to establish visual changes (Figure 3).

Aerials from 1928, 1940, 1992 and 1998 were used intensively and other imagery from

the 1960-70’s was consulted. Several changes are very noticeable: 1) the width of the

mangroves along the coast and along the tidal creek increase with time, 2) the entire marl

prairie habitat (light in color) was replaced my mangroves (prior to the early 1970’s), 3)

the embayment north and northwest of the island silted in and was covered by

mangroves, and 4) about 30M of coastline erosion has occurred. The magnitude of

observed changes in the system required more detailed studies of both present and past

conditions.

Figure 3. Aerial photography used for historic change analyzed. Scale is the same for the four

photos. The L-31E structure was not present in 1928 and 1940. Note: the island south of the

point shows an origin further offshore than the area it presently occupies.
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Present topography/bathymetry. The second step was to define present

topography/bathymetry using standard surveying methods to produce a topography map

of the coastal wetlands with a 25mm elevation contour. Standing water levels were also

used to supplement survey lines. The bathymetry map contour interval was 30cm

(Figure 4). Contour patterns were produced by wading transects at high tide. The

locations of the survey and depth control lines are also presented.

Figure 4. Topography of wetlands in 2.5cm elevation contours. Survey was made using a level

with accuracy of 1cm/100M. We closed each shot and only made shots less than 50M. If closure

was off by more than 1cm, we reshot the elevation. Water levels in the marsh at high slack tides

were also used to supplement survey lines. Bathymetry depth contour intervals are 30cm and

were produced by wading transects at high tide.

Topography defined one major tidal creek (No. 2, Figure 1). It was a topographic

high from the levee eastward approximately 200M where it attained a channel

morphology with well-developed channel levees which disappeared approximately 150M

from the coast (Meeder et al., 2000). At the point where the natural creek levees were

reduced the creek channel tended to break up into ill-defined channels. A poorly defined

slough crossed west to east approximately 150M south of the main channel and

connected several small tree islands. The last tidal creek was approximately 300M south

of the main creek and is highly disrupted by a drainage canal. This canal should be

backfilled or it may pirate freshwater and delivery straight to the Bay to the southernmost
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part of the proposed estuarine zone. Between the two large creeks from the levee to a

distance eastward of 450M was a topographic basin of nearly 10cm in relief. The area,

approximately 100M wide between 450 and 425mm in elevation, was a near continuous

band north-to-south and forms the eastern rim of the interior basin. The marsh east of

550M from the levee had irregular topography as the marsh was dissected by numerous

small distributaries and marsh loss (perhaps post Hurricane Andrew subsidence) to the

eroding shoreline. Along the shoreline, a coastal levee was the highest feature near the

coast, but in this area was discontinuous.

The proposed estuarine zone had a maximum depth of 20cm at high tide. The

maximum depth was located south of the island and was an earlier Holocene creek

channel. Offshore of the fringing mangroves along most of the coastline was a thin

marine mud or inundated red mangrove peat, which was exposed during most wet season

low tides and most of the dry season. This narrow zone frequently had very little aquatic

vegetation cover. The bottom deepened at a rather constant rate from the shoreline to the

depth of approximately 125cm, where the water depth increased at a faster rate. Between

the channel and the island approximately 45cm of sediment covered the bedrock, forming

a shoaling wedge shaped sediment body. The island was approximately 120M in length

and 40M in width and is aligned in a southeast-northwest direction. The island was made

up of oyster rich skeletal material. At high tide the island was almost totally inundated

and red mangrove trees cover most of the island. This island was first believed to be a

dredged canal spoil bank. However, no channels were located anywhere near it, and the

coastal canal almost directly to the west did not exhibit oyster shells along the banks or in

adjacent soils. Furthermore, skeletal material was found offshore of the island for a

distance of at least 100M, suggesting that the island has migrated landward with sea level

rise. The area north and west of the island was very shallow, and historic channels were

frequently not observable. Scattered lenses of oyster shells were found in this area.

Creek mouths were very narrow and emptied into small embayments.
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Figure 5. Survey and probe transect core locations.

Sediment/soil analyses. The third step was to take soil cores and sediment depths along

transects in order to determine soil types, origins, sequences and depths. Core locations

are found in Figure 5, with more detail found in Meeder et al. (2000) for the creek sites.

Core descriptions are in Appendix A. Soil cores were collected in 8cm diameter

aluminum core tubes using a simple piston coring device to minimize compaction.

Compaction was measured for each core and was minimal except for fibrous peat at the

creek sites. Soil profiles were described with special interest to the uppermost contact

between the surface and immediately underlying soil types.

The basic soil types found were: 1) marl, 2) marly peat, 3) red mangrove peat, 4)

black mangrove peat, 5) sandy mud, and 6) skeletal sand-gravel. Marls were not found at

the surface in the study site. Marls are calcium carbonate (low Mg calcite, a stable

mineralogy) produced by periphyton (Gleason, 1975). They form dense, impermeable

sediments with either a freshwater or low salinity molluscan assemblage. Typical

freshwater pulmonates are abundant in freshwater and the marsh clam, a cerithid, and

abundant hydrobiids are found in the more saline marls. The more saline marls also tend

to have much less organic material, a reflection of sparse Eleocharis cover rather than

denser Cladium.
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A carbonate mud rich red mangrove peat (marly peat) rarely more than 10cm in

thickness was found at the surface in small areas near the center of basins where

mangrove cover was not complete. Within a marly peat horizon, the organic content

increased upwards rapidly at the expense of carbonate mud (marl) content. Skeletal

component was a fresh-to-low salinity mollusk assemblage. Fewer large Polinices were

found than in the underlying marls. Most organic material was red mangrove root

material with a secondary component of leaves locally.

Red mangrove peat was the most common surface soils in the wetlands and also

in a small portion of the estuarine zone. Red mangrove peat was highly organic in nature

(60% by dry weight or more), consisting primarily of root fibers (Meeder et al., 1998).

The mollusk assemblage was characteristically one of more saline to marine conditions.

Fossils were usually few but included the marsh clam, Littorina, Melampus, and

cerithids. Near shore red mangrove peats may contain a marine mollusk fauna, because

of onshore transport during storm tides.

Black mangrove peat differed from red mangrove peat in a black rather than red

color, and the presence of pnuemataphores, as well as, root material as common soil

constituents.

A gray to light brown, sandy mud with various amount of larger skeletal material

dominated by a diverse marine mollusk fauna was the dominant surface sediment type in

the proposed estuarine zone. In some locations near tidal creek mouths the marine

mollusk skeletal component may be replaced by freshwater pulmonates from reworking

and seaward transport processes.

Oyster gravels with a matrix of marine sand and mud form, thin, local lenses and

one sizeable oyster bar were found. Most oyster skeletal material was fragmented with

large single valves common. Double valves and small clusters of oyster shells were also

found in some lenses and in the large bar (the island).

Vertical soil sequences recorded two basic, highly repetitive sequences. The first

sequence was found throughout the coastal wetlands. In this sequence freshwater marl

was replaced rapidly upwards into a transitional marly peat (from 1 to 10cm thick), and

then to a surface red mangrove peat. In general, peats thinned away from the creeks and

coastline. Peats thinned away from the creeks and coastline because the time for peat

accretion decreased away from creeks and the coastline. This is indicative of a condition

progressively becoming more saline with decrease freshwater discharge.

The second repetitive vertical sequence was found in the near shore area. In this

sequence either freshwater marl, or more saline red mangrove peat, was overlain by

marine skeletal rich sandy mud. The contact between the two strata was usually very

sharp. The marine sandy mud was usually less than 40cm thick and frequently including

thin (3 to 15cm thick) oyster skeletal lenses. Most oyster lenses, except the oyster barisland were buried by 15cm of marine sediments. This sequence represented an abrupt

change from fresh water conditions to estuarine and then a more open marine salinity
11

regime. The loss of live oysters was reflective of the lost of freshwater discharge as sea

level has rose producing conditions too saline for oysters. Although mollusk

assemblages can be used to determine paleosalinity, we did not differentiate assemblages

beyond fresh and marine in this study because oyster paleoecology produced better, more

precise paleosalinity data. Oyster paleoecology is addressed in the next section.

Distribution of surface sediment types in the coastal wetlands was rather simple.

Red mangrove peat was found at the surface throughout almost all of the coastal

wetlands. In the center of large basins where mangroves were not very dense, marly peat

was found. In addition, black mangrove peats were found as thin shoestring deposits

along old tidal creeks and behind the coastal levee in places.

Offshore of the fringing mangroves along most of the coastline was a thin marine

mud or inundated red mangrove peat, which was exposed during most wet season low

tides and most of the dry season. This narrow zone frequently had very little aquatic

vegetation cover. The bottom deepened at a rather constant rate from the shoreline to the

depth of approximately 125cm, where the water depth increaseed at a faster rate. This

water depth increase is inversely related to the depth of sediment. Seaward of the narrow

nearshore zone the surface sediments were mostly marine muds and sands between 0 and

45cm in thickness. North and west of the historic channel thin lenses of oyster shells

were found as scattered patches. The maximum water depth was located in this earlier

Holocene creek channel that was located approximately 100M south of the island. Basel

sediments in this creek bed were highly organic, very dark brown to black marls with

limestone clasts and freshwater mollusk shells. South of this ancient creek channel only

patchy, thin sediments overlaid bedrock. Between the channel and the island

approximately 45cm of sediment covered the bedrock. The surface sediments were

marine muds and sands with a varying component of skeletal material up to 20cm thick.

This overlaid and abruptly contacted either freshwater marl to the west and marl or

mangrove peat to the north. The island was approximately 120M in length and 40M in

width and was aligned in a southeast-northwest direction. The island was made up of

oyster rich skeletal material overlaid by red mangrove peat. At high tide the island was

almost totally inundated with the exception of the red mangrove tree cover. This island

was first believed to be a dredged canal spoil bank. However, no channels were located

anywhere near it, and the canals that were present along the mainland do not exhibit

oyster shells along their banks or in adjacent soils. Furthermore, skeletal material was

found offshore of the island for a distance of at least 100M, suggesting that the island has

migrated landward with sea level rise. Creek mouths were very narrow and empty into

small embayments.
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Figure 6. Cross sectional depiction along north-to-south transect 1.

Depositional model. A depositional model is used to recreate historic topography. The

model is based upon: 1) topography, 2) aerial photographic interpretation of changing

plant distribution and plant cover/soil type relationships and 3) soil core transects.

Topography is presented in Figure 4. A time sequence of aerial photographs was

assembled in order to document the distribution of vegetation and changes in plant

(especially mangrove) distribution through time (Figure 2). Two basic plant

communities existed historically; red mangrove and gramminoid prairie marsh. The red

mangrove forest produced a peat soil, the gramminoid prairie a carbonate marl soil. As

mangroves replaced the prairie, the soil becomes more organic rich until the mangrove

forest formed a continuous canopy which reduced and ultimately excluded periphyton in

the prairie community and thereby stopped marl production. Using aerial photographs,

the spread of mangroves and mangrove peats over different time intervals, and the

thickness of the soil produced in each time interval along transect was determined

(Figure 6). Mangrove peat thickness above the marl along the transect subtracted from

the present topography gave us an approximation of the historic topography. A three

dimensional soil surface map was then generated to display these changes allowing for

analysis of rehydration feasibility. Almost all cores showed a red mangrove peat

overlying freshwater marls with the overlying peats found in various thickness.

The coastline and tidal creeks were first exposed to marine conditions and

mangrove propagules. As freshwater discharge decreased with time, the mangroves, and

therefore mangrove peats migrated away form the tidal creeks producing a thinning

wedge of surface peats (Figure 6). By measuring the advance of mangroves away from

the tidal creek at points documented in aerial photographs, and coring at these points, we

established the rates of mangrove accretion. Marl accretion rates ranged from 1 to

2mm/yr. (Meeder et al., 1998) and red mangrove peats approximately 5mm/yr. at this

site. By 1972 mangroves had invaded and covered the entire wetlands. Therefore, in the
13

center of the basin marls have been accreting for 44 of the last 72 years. The 1928 time

line would then be 4.4 cm beneath the mangrove-marl contact. Over the period of this

study, therefore, the basin topography has increased through time because of the faster

rate of mangrove accretion over marls and mangrove peats have been accreting for a

longer period of time along the creek margins than in the center of the basin.

Chronostratigraphy and serial aerial photography. Analyses (of a time series of

aerial photographs: 1928, 1940, and 1992) documented major changes in vegetation

patterns and coastal morphology (Figure 1) (Meeder et al., 2000). Changes in vegetation

patterns coincide with changes in soil type. This was documented by a series of soil

cores along the 100M transect from the historic creek south into the historic prairie.

Freshwater prairie with marl soils was replaced by mangroves and marly peats.

Therefore, the contact between underlying marl soils and overlying peats were used as a

time line. This is not the most precise method to define a time line as we recognize that

the transformation from marl to peat occurred over a 15 year period. The shift started

along the tidal creeks and expanded towards the basin center. Radiometric dating

methods (Pb210 and Cs) might provide a tighter time line but numerous problems and

assumptions must be overcome. However, for the scope of this work the precision was

adequate, and radiometric dating was very expensive for what it might add. Throughout

the study area, including the nearshore bay, a more marine strata (ranging from 5 to 30

cm thick) overlaid a freshwater marl of mangrove peat. This contact, usually very

distinct especially in the Bay, was considered a time line, which we placed at

approximately 1935. A three dimensional depositional model based upon present

topography and soil accretion since loss of fresh water delivery was produced. Four

major changes were documented: 1) marsh marl soils were replaced by faster accreting

mangrove peat soils, 2) loss of upper tidal creek channel morphology, 3) siltation and

mangrove colonization of tidal creek embayment, and 4) abrupt change in estuary from

non marine to marine sediments. Soil accretion rates were related to the type of surface

community producing and/or modifying them (Meeder et al., 1999). Freshwater marl

rates usually accrete at the rate of 1 to 3mm/yr., sawgrass peats at 5 to 12mm/yr., and

mangrove peat accretion rates can be much higher (Meeder et al., 1996). Using aerial

photographs from different years we documented the spread of mangrove and mangrove

peat with increased saltwater encroachment. When sites along this gradient were cored,

the thickness of mangrove peat overlying freshwater marl was consistent with most

mangrove annual accretion rates (Parkinson et al., 1993; Meeder et al., 1996).

Thereafter, the contact between the peat and underlying marls were used as a time line

with the understanding that this time line actually spreads over a time period of

approximately 30yrs. However, this approach is not as unreasonable as it first seems,

because the underlying marl accretion rates are an order of magnitude lower than the

mangroves. Therefore, very little preexisiting topography will be missed by this

approach.
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Figure 7. Three-dimensional topography/bathymetry map illustrating the elevation differences

between historic and present conditions.

Historic topography/bathymetry. Historic conditions were established using serial

aerial photography and soil cores along transects to determine paleotopography (Figure

7). As freshwater discharge slowed and then stopped, the rate of saltwater encroachment

was proportional to the rate of freshwater discharge decline and stoppage. As saltwater

encroachment increased so did the expansion of mangroves over the previous fresh water

marl prairies. Soil core transects across this trend documented a surface layer of

mangrove peat overlying marl that thinned away from the tidal creeks. Because marl

accretion is 5 to 10 times slower than mangrove peat accretion the contact between peat

and marl is used as a time line with minimal error over the period of this study (1928 to

present).
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Figure 8. Historic contours and bathymetry.

DISCUSSION

Present wetland morphology prevents direct rehydration of the historic tidal creek

because of mangrove peat soil accretion in tidal channels west of the point of present

tidal exchange. Freshwater flow and tidal exchange prevent siltation and loss of channel

morphology. The release of freshwater into the system probably will not result in instant

reestablishment of the abandoned creek channel for three reasons. First, as mentioned

already, the tidal creek channel morphology is gone. The topographic basin south of the

creek is more pronounced at present than in 1928 because of the greater rate of mangrove

peat accretion than that of the marl soils in the basin, which has resulted in much higher

channel levees than those of the past. Finally, an old, poorly defined sloughway, or series

of marsh depressions, are located near the center of the basin close to the east-to-west

survey line (visible in the 1940 aerial photograph) and will probably capture the water.

Water will pile up until it overflows the mangrove peat basin margin and erode

downwards forming a new channel. Another probable scenario is that the water will pile

up in the basin until the lowest spot in the basin margin is found; a likely spot for this to

occur is along the abandoned creek at about 250M east of the levee of along the ditch

lying along the southern margin of the basin. The capture of the basin water by the ditch

is the least desirable scenario. The reestablishment of a creek morphology from the levee
16

to the Bay may take a few years to become reestablished depending upon the freshwater

discharge. The more discharge, the faster channelization will occur.

The small embayment at the tidal creek mouth has been reduced in size and depth

by siltation and mangrove colonization. Since 1940, the mangroves have accreted as

much as 40 cm of peat over the embayment muds and freshwater skeletal remains

deposited there by freshwater out flowing currents from the marl prairies.

Reestablishment of the embayments is not likely in areas with thick mangrove peats.

However, the shallow open water areas of the embayment might be scoured and

transported into the Bay with sufficient reestablished freshwater flow. However, the

freshwater retention capacity of our proposed estuarine zone has been irrevocably

diminished in the areas of peat accretion.

In conclusion, historic changes in the wetland and nearshore Biscayne Bay area

are documented, and these changes appear to minor enough that rehydration of a tidal

creek system probably will not be curtailed but may take a few years to reach a new

equilibrium between erosion, deposition and water flow patterns.

Changes in topography/bathymetry. The major reason historic conditions were

addressed was to determine if conditions have changed so much that reestablishment of

an estuarine zone would be impossible. Although numerous changes are documented

between present and historic conditions freshwater delivery should be able to reestablish

estuarine conditions. The only concern is whether canal water discharged into the study

block will develop channel flow once again or will spread out into sheet flow. If enough

water is delivered we feel that channel flow can be established within a year or two. The

desirability of channel flow over sheet flow is that much less water will need to be

delivered to meet the target salinity than if sheet flow is the major process. The new

creek channel is likely to develop approximately 100M south of the historic channel in

the present center of the depression. As the depression fills channelization will probably

occur through the first breach (old tidal creek channel, many of which are still present in

reduced form 300 to 400 M inland from the coast). In other words, the lowest spot along

the margin of the topographic depression. Several such depressions exist, to the north of

the depression (the historic creek channel), east to the series of abandoned tributaries, or

southeastward to the manmade ditch that crosses a historic channel. This last situation is

the least desirable, because it would deliver water too far south of the proposed estuary,

south of the oyster island, and might not stay in the system as long as delivered further

north. In addition, the straight man made channel would be more efficient in water

delivery but would not carry as much mangrove detritus.
17

PART 1: SALINITY

Historic changes in salinity and the effect on the coastal wetland-nearshore

ecosystem were documented. Three methods are used in this documentation: 1)

chronostatigraphy and serial aerial photography, 2) biogeochemical salinity markers, and

3) invertebrate, especially oyster, paleoecology. In summary, all evidence suggests a

decrease in freshwater discharge associated with an increase of wetland and coastal

salinity. To accentuate the loss of freshwater discharge, a rise in sea level of

approximately 20 cm has occurred during the last 100 yrs (Maul and Martin, 1993). As

conditions became more saline, the nearshore estuarine zone was lost as was the oyster

(Meeder et al 1999) and estuarine-based fisheries (Serafy, 1997). Oysters have rather

specific habitat requirements and therefore oyster paleoecology was used to determine

historic salinity.

A. Oyster distribution at the study site. Sediment probe transects and soil cores

demonstrate the abundance of oysters over a rather large area with a concentration

found in a NW to SE trend. When discussing oyster shells we are restricting our

discussion to level bottom Crassostrea virginica and not mangrove root encrusting

forms. The two forms can be separated easily by overall shape of the shell, especially

the shape of the post settlement and young adult stages shell attachment area (Stenzel,

1971).

1. Present live oyster distribution. At present, live oysters were only found living

on mangrove roots along the shoreline and up the tidal creeks for a distance of

approximately 100m. Oyster and barnacle density on the roots were low, rarely

covering more than 30% of the root surface in areas where the roots were always

subtidal. However, spat attachments and one-year age class oysters were the

norm and larger oysters were very uncommon. The occurrence of live oysters,

however sparse, does indicate that oyster larvae were present.

2. Distribution of dead oyster shells. Dead shells were found in several settings: 1)

at the base of mangroves, along tidal creeks with fell after death from their

attachments on prop roots, 2) throughout the estuarine zone north and west of the

island, 3) from the island southward approximately 150M and eastward 100M

below a thin marine sediment layer (0 to 20 cm thick), 4) small discontinuous

lenses along the tidal creek banks below a surface marine sediment layer (5 to 20

cm thick), and 5) the island in the estuary is basically constructed of oyster shells,

many if not most, were disarticulated but small clumps were common. Many

small clumps were overturned as an indication of transport. The oyster shells

appeared to be concentrated above a freshwater marl or mangrove peat north,

west, and southeast of the island, freshwater marl to the southwest and south of

the island (Appendix 1). The oyster bearing strata away from the reef contained

mostly single valves which is indicative of transport. However, throughout the

strata occasional oysters with both shells and small clumps were found implying

that random spat fall was successful but did not develop further at this site.

Oysters do not have a “hard hinge”, and therefore disarticulate soon after death
18

when not held together by encrusting organisms or buried by sediment. The

island itself overlaid mangrove peats. The island in the estuary zone was at first

thought to be dredged material. However on closer inspection, no channel existed

on either side of the island, the adjacent dredged canal to the west did not have

any outcropping oyster shell, and the island had an offshore trend (see 1940

photo).

3. Oyster deposit interpretation.

a. Sea level has risen approximately 20cm in the last century. Combined sea

level rise and hurricane erosion was responsible for 25m of coastline retreat

and the submergence of the oyster facies seaward of present coastline because

of transgression and overstep.

b. Frequency of high energy events also redistributed oyster shells from the reef

facies. Three major hurricanes have passed over this part of the Biscayne Bay

shoreline in the last century.

c. Fossil oysters were found as 1) transported debris characterized by thin,

discontinuous lenses of disarticulated shells not in life position, 2) sparse

individual oysters or small clumps in growth position randomly scattered, 3)

wedge shaped oyster shell deposits along the creek banks (predominantly

comprised of coon oyster debris), and 4) thick lensoidal deposits including

skeletal debris and small clusters, some of which were in life position. This

latter was the mangrove covered island. The oyster deposits were covered by

red mangrove peat and the oysters were exposed only at low tide. The island

has undergone modifications from high energy events (Figure 3).

B. Oyster paleoecology.

Oysters are one of the most studied marine animals with a literature dating back to at

least 1665 (Joyce, 1972). This is no doubt because of the economic significance of the

oyster as a foodstuff, a nursery ground for numerous other estuarine organisms, and the

navigation hazard oyster reefs, or bioherms, pose to nearshore craft. The earliest studies

of oyster distribution documented that their preferred location, especially true for

bioherms, was between the freshwater and marine environments. Presently, this zone is

usually referred to as an estuarine or brackish water regime. Numerous studies document

the specific conditions that oysters live in from New England to Mexico. The generally

agreed to environment is one of brackish salinities, near river mouths or other sources of

organic particulate matter, the presence of water currents sufficient enough to prevent

siltation of the bioherms or individual oysters, and generally within the depth range of

one foot above mean low tide to 60 ft. Intertidal oysters differ from subtidal bioherms by

the greater stress of exposure (temperature extremes and desiccation).

The oyster of concern, Crassostrea virginica, is found from the Gulf of St. Lawrence

to Biscayne Bay, Florida along the Atlantic coast continuing along the Gulf of Mexico to

the Yucatan Peninsula, Mexico (Gunter, 1951). Southeastern U.S. oysters, Crassostrea

virginica, are well-studied commercial shellfish, which also are well preserved in the

geological record. C. virginica is a euryhaline species found singly in conditions ranging

from near freshwater to normal marine salinities. Oyster reefs, or more properly
19

bioherms, are much more restricted in their distributions. Temperature, predation, water

circulation, larval period and settlement requirements, and tidal range also greatly affect

oyster reef growth and distribution.

The factors controlling oyster development and distribution include:

1. Salinity. Although euryhaline in nature, C. virginica bioherm development

usually occurs either in intertidal areas or subtidal areas of reduced salinities.

Neither eggs nor functioning spermatozoa develop unless salinities exceed 7.5ppt

whereas larvae and young adults find optimal conditions at 17.5ppt, although

tolerating 10 to 40ppt (Stenzel, 1971).

The relationship between oysters and the low salinity estuarine habitat was

recognized very early in South Carolina (Dean, 1892), Georgia (Oemier, 1894),

Mississippi and Alabama (Ritter, 1896), North Carolina (Grave, 1905), and

Florida (Pearse and Wharton, 1938). The significance of the salinity range to

oyster presence and development is believed to be related to the paucity of oyster

parasites and predators in low salinities (Grave, 1905, Gunter, 1955).

Oyster spat successfully develop in waters of greater than 5ppt. Young

and adult oysters can maintain freshwater for up to 10 days by closing their

mantles tightly and storing water. The length of time for successful exposure to

freshwater appears to be the amount of energy stored in the oyster tissue.

2. Temperature. C. virginica can tolerate a temperature range from –2 to 30o

C.

Subtidal oysters can withstand the extremes better than intertidal individuals.

Spawning is reduced or eliminated as temperature decreases. Mature oysters can

live in freezing conditions for long periods of time but in the colder portion of

their range oyster occurrence is dependent upon larval recruitment. Southern

oysters grow faster than northern ones but are more subject to death in sudden

freezes (Menzel, 1951).

3. Predation. Grave (1905) documented that oysters are subject to higher rates of

predation and parasitism with increased salinity. Gunter (1950) suggests that this

is a response to his documentation of a general increase in marine diversity with

increase salinity. This is particularly true when considering that the brackish

water fauna is derived almost exclusively from marine stock. In our area, there is

frequently one exception, the estuarine hydrobiid. However, this may be

considered incorrect because the hydrobiids are a group of mesogastropods that

have secondarily become adapted to freshwater conditions. Wells (1961) studied

the relationships of oyster fauna along a salinity gradient in Beaufort, North

Carolina. He found the biggest break in species diversity between stations at

Galliant Point (28ppt) and Cross Rock (19ppt). In addition, numerous predators

and parasites were excluded between Write Rock (24ppt) and Cross Rock. Many

predators and parasites while not excluded at 19ppt were found in very reduced

numbers or only during periods of elevated salinity.
20

4. Feeding. Oysters are passive, sessile, filter feeding organisms which capture

particulate organic detritus and algae. Loosaneff (1962) determined that feeding

activity is highest at low food concentrations.

5. Water circulation (siltation and suspended food supply). Oysters are suspension

feeders and require water current to both 1) carry and retain in suspension organic

detritus as the primary food source and 2) to prevent siltation and burial of the

oyster. Therefore, oysters tend to form positive relief features at or near river

mouths and on the high-energy side of tidal creeks.

Siltation of oyster ecosystems occurs frequently after both large flood and

hurricane storm tides. Both events cause considerable bottom erosion and

redeposition of vast amounts of sediment. These events happen episodically and

the reef system usually responds to burial by permanent death, shifting laterally,

or by recolonization of the new surface. These events have been recorded in

Texas, Mississippi, Louisiana, Apalachicola, Florida and other areas.

6. Larval period and settlement requirements. The larval life stage ranges from 7

to 10 days, but some larvae remain planktonic for up to two months in cooler

periods or when food is not abundant (Bahr, 1981). Oyster larvae are usually

present from April through October. This period coincides with the rainy season

in South Florida, which is the period of highest daily and spring tides. The free

swimming larval stage is reduced in warmer climates. South Florida oysters are

25o

C spawners (Yonge, 1960).

7. Tidal range. Most well developed oyster bioherms occur in areas that

characteristically have a tidal range exceeding 1 M. In areas of intertidal oyster

bioherms, exposure increases stress from temperature at both extremes but also

offers protection from many predators that do not tolerate exposure. The height

of intertidal oyster bioherms decreases with decreasing tidal amplitude. In South

Florida, the development of intertidal oyster bioherms is impeded by the

microtidal range, as well as the presence of more carnivores.

In summary, the two most important factors controlling oyster development are a

proper salinity regime and steady food bearing water currents.

C. Oyster bioherms.

1. Structure . Previously discussion revealed that oyster bioherm distribution and

structure are related to physical parameters and the supply of suspended organic

detritus. Butler (1954b) reports types of subtidal oyster accumulations based upon

their location in an estuary (Table 1). He found that location of the oyster in the

estuary was most influenced by salinity regime. As salinity increases towards

open water species diversity increases and with increased diversity, parasitism,

predation, and fouling increase which influences the survivorship of oyster spat

and oyster growth morphology.
21

Table 1. Characteristics of four categories of oyster reefs.

Location Shell

characters

Salinity

Range

(ppt)

Salinity

Mean

(ppt)

Diversity Oyster

abundance

Spatfall Fouling

and

predation

1 Estuary

Head

Small, round,

smooth, little

clumping

0-15 10 Low Sparse Low Low

2 MidestuarySmooth, narrow,

dense, w/small

clusters

10-20 15 Moderate Max High Low

3 Near

estuary

mouth

Massive, eroded

w/ heavy,

concentric

ridges

10-30 25 High Dense Highest High

4 Junction

of estuary

with bay

Large, highly

eroded and

ridged

20-35 30 high sparse Low Highest

Bahr and Lanier (1981) report the distribution and characteristics of

intertidal oyster reefs in a tidal creek system and discussed reef development.

Oyster reef development has four stages; 1) colonization, 2) clustering phase, 3)

accretionary and 4) maturation and senescence. Briefly, the colonization stage

occurs as spar find successful places to settle and form an area of single live

oysters and a few small clumps. The clustering phase occurs when several

successful generations of spat create clusters with two to eight generations of

oysters with the base of clusters mostly dead shells. The oyster accumulation still

expresses very little relief. The accretionary stage occurs after additional spat fall

closes the gap between clusters and the reef begins to expand vertically and

laterally. At this stage most reef are approximately one meter in thickness (where

tidal range permits). A mature or senescent stage is reached when the reef grows

to the surface where exposure limits vertical growth.

Within the tidal creek system oysters colonize where water currents

provide a clean substrate for spat settlement with low sediment deposition rates.

Locations favored for reef development include: 1) along the concave outer banks

of meander loops, 2) in areas immediately adjacent to smaller tidal tributaries, and

3) at points of tidal creek confluence (Bahr and Lanier, 1981).

2. Oyster Bioherm Distribution. The southernmost oyster bioherm in the United

States is in Oyster Bay, Everglades National Park (Tabb et al., 1962).

Distribution of dead oyster shells and buried shell deposits suggest that the

bioherm was much larger than present in the recent past. The oyster bioherm is

exposed during low spring and most neap tides (Tabb et al., 1962). Recovery of

the bioherm has been rapid after severe impacts by hard freezes and hurricane

impacts. The oyster community was species poor. During winter dry periods as

water salinities increased, the bioherm was overgrown by the algal species;

Gracilaria, Laurencia, and Acanthophora spicifera. The nearest salinity stations
22

are approximately one mile northwest of Oyster Bay (low salinity of 12, high of

37.6 and a mean of 28.1ppt) in Whitewater Bay XII near the mouth of the bay and

approximately two miles southeast (low salinity of 2.2, high of 38.7 and a mean

of 17.9) at White water Bay VII. Oyster Bay salinities should be closer to Station

VII than XII because of different geography and freshwater discharge patterns.

Turney and Perkins (1972) report that C. viriginica was abundant in 25%

of their benthic sites in northern Florida Bay. They did not sample oyster

bioherms or tidal creeks. This region they referred to as the Northern Sub

environment which they characterized: salinity range 13-48ppt, Temperature

range 15-38oC, restricted circulation with little tidal activity, and subject to severe

freshwater runoff events. The characteristic species in this sub environment is

Anomalocardia cuniemeris followed by the following common species:

Parastarte triquetra, Melongena corona, Retusa cacaliculata, Rissoina

browniana (probably R. fisheri). Other species were also common but more

abundant in the interior subenvironment (also with low salinities) are

Brachidontes exustus, Pinctada radiata, Cerithium muscarum, Bittium varium,

Modulus modulus, Lucina multilineata, Olivella sp. Most of these species are

associated with the present oyster fossil assemblage.

Generally, the oyster habitat in southern Florida /Florida Bay region is

located below low water in the intertidal mangrove zone along creek bank prop

roots and less frequently along high energy tidal creek banks and as bars in tidal

creeks. Tabb et al. (1962) report that the abundance of oysters decreases away

from Oyster Bay both to the west towards the mouth of the estuary with the

increase in salinity, and to the eastward where salinities range from 0 to 15 ppt.

This delineates a range of 5 to 20 ppt that may be the optimal for C. virginica in

South Florida. This range is supported by studies in Applicacola Bay, Texas,

Georgia and the Carolinas as previously cited.

Oyster bioherm have been reported permanently killed by increases in

salinity associated with levee construction that prevented freshwater from

reaching estuaries in the lower Mississippi River (Gunter, 1952). Construction of

deep water navigable channels usually results in saltwater intrusion and increased

salinities, for example Calcasieu Lake and Atchafalaya Basins, Louisiana (Van

Sickle, 1972).

D. Biscayne Bay and study site oysters. Harlem (1979) reported extensive oyster shell

beds in Northern Biscayne Bay. Little literature reports oysters in central and

southern Biscayne Bay. However, oyster bioherm strata were mapped in 9 of 48 tidal

creeks along western Biscayne Bay (Meeder et al., 1999). Most tidal creeks where

oysters were present were located at tidal creeks that began as freshwater sloughs.

None of these historic oyster beds were active. At our present study site oysters were

distributed over most of the Bay bottom as a thin lens, as a large single reef, and

along some creek banks. Throughout the study area the oysters appeared to have died

off within a short period of time, and were subsequently buried by marine sediments.
23

They overlaid fresh to brackish water sediments. The die off was associated with the

loss of freshwater discharge via transverse glades-tidal creek systems. The loss of

freshwater discharge produced three major changes in the system responsible for the

loss of living oysters; 1) rise in salinity, 2) decreased particulate organic carbon load

and 3) increased siltation rates. The loss of freshwater discharge probably started

after the turn of the century associated with dewatering of the Everglades. All sheet

flow to the Bay was lost by the construction of the L31E system in the 1960’s. In

addition to increased salinity (and associated increase in parasitism and predation)

and decreased food supply, water quality has decreased with the addition of

anthropogenic sources of nutrients. The increased nutrient loading to the Bay has

resulted in the nearshore zone frequently being overgrown with filamentous algae.

An algal cover on the substrate may reduce successful larval recruitment and interfere

with oyster filtration processes (Redfield, 1952; Lund, 1957). A salinity increase

could be associated with decreased groundwater discharge because of a loss of

between 4 to 6 ft of hydraulic head due to drainage (Parker, 1975). This scenario has

been reported for the Duplin River, SC (Kjerfve in Bahr, 1981). The failure of oyster

reefs because of increased salinity has been reported from numerous locations and is

quite likely the major problem at this site. Bahr (1981) suggested that in most regions,

an increase in salinity has more serious implications for oyster reefs than moderate

levels of nutrient loading.

Oysters at the historic creek site developed through the clustering phase and

probably no further because of the microtidal range. Because the tidal creeks emptied

directly into Biscayne Bay without an embayment or restricted exchange, oyster

distribution and development was somewhat different than in most places. Oysters

were most abundant at the mouth of the tidal creek which has since been stranded by

shoreline erosion.

In conclusion, the presence of oysters was indicative of salinities ranging between

5-20ppt, and continuous water current, which brought particulate organic carbon and

prevented siltation. Small-scale oyster structures were indicative of the microtidal

range, occasional freezes, and hurricane energies, which limited growth and

maintained early successional stages of oyster reef development. The loss of oysters

in this situation was the likely the result of the loss of freshwater discharge, which

permitted salinities to rise. With increased salinities, increased predation, parasitism,

and fowling organisms reduced oyster survival. In addition, the loss of freshwater

flow reduced particulate organic carbon available and allowed siltation to occur.

When oysters were lost, nutrient loading probably was not a causative factor,

however with today’s high nutrient loading rates oyster recolonization and bioherm

development may be retarded.
24

PART 2: FRESHWATER DISCHARGE (Q) MODEL

The major objective of this model was to estimate the volume of water required to

meet nearshore Biscayne Bay salinity targets. The water to be discharged via the L-31E

canal into a historic creek watershed empties into Biscayne Bay, just south of a

prominent point, approximately 400 M north of Military Canal (Figure 9). Historically,

freshwater discharge was sufficient to provide a salinity regime that supported

accumulations of the bay oyster, Crassostrea viriginia (Meeder et al., 1999) and

numerous estuarine fish species (Serafy et al., 1997). The salinity regime determined to

be adequate for the establishment of an estuarine zone was: Wet season (5 to 15ppt) and

dry season (10 to 19ppt). The following model was based upon estimates of numerous

parameters, including biological, climatological, physical, bay water circulation, and

others, and was summarized in Table 2. More detailed sections on each parameter

follow the table.

Figure 9. Schematic model of study areas illustrating the major processes.
25

Table 2. Summary of model parameters. Volumes were calculated under normal spring tide

conditions unless otherwise noted. Sources and calculations follow.

Parameter Dry

Season

Wet

Season

Units Comments

A. Target salinity 10 to 19,

mean of

15

5 to 15,

 mean of

7

ppt Max of 20

B. Bay Salinity 25 15 ppt Max 36

C. Marsh area M2 551,700

D. Wetland basin

volume

9,557 53,702 M3

E. Estuarine

basin area

65,500 81,700 M2

F. Estuarine

Basin volume

20,445 42,525 M3

G. Tidal volume 14,445 29,302 M3

H.Wind:direction

 speed

340

 9.3-10.1

120

7.9-10.6

Compass

degrees

mph

2.26

5.74

7.18

18.23

in/mo.

cm/mo.

Annual=56.1in over

29 yrs

I. Rainfall:

Miami

Tavernier 1.93

4.9

5.6

14.22

in/mo.

cm/mo.

MW= Annual = 44.8in

over 29 yrs

J. PE 6

5.5

2.5

2.3

Mm/d

L/M2

/d

MW=1268.9M3

/

d

MD=3034.3M3

/d

BW=187.9M3

/d

BD=449.4M3

/d

Duever et al., 1979

1.74-2.05 L/M2/d 2,758.5M3 K. Transpiration /d

Dwarf mangroves

Fringe mangrove 8.6-11.8 L/M2

/d

Ross et al.,1999 (p.

38)

L. Groundwater

discharge: 50M

200M

0.03

0.105

M3

/M2/d

M3

/M2/d

For study area

2084M3/d

19,850M2

 rock

bottom

M. Water table

elev.

1’7” 2’1” SFWMD schedule

N. Military to

Mowry Bay vol.

503,125 568,750 M3

O. Military to

Mowry bay tidal

volume

M3 131,250

P. Estimated

renewal time

2.5 1.5 d

Q. Estimated

required

freshwater

discharge

10 15

M3/d

Acre-ft.
26

A. Target salinity. Seasonal target salinity ranges and means were determined in

Part 2. In summary, target salinities were based upon oyster paleoecology. Wet

season nearshore salinities should range between 5 and 15 ppt with a desirable

mean of 7 ppt, whereas dry season salinities should range between 10 and 19 with

a mean of 15 ppt. Maximum salinity target should be 20ppt.

B. Bay Salinity. The nearshore area of western Biscayne Bay was subjected to

seasonal salinity changes. The nearshore area was defined as the area within

100M of the shoreline and usually less than 1.3M in depth. Salinity was measured

every month at two sites between the Military and Mowry Canals for five years

(Figure 10). This water was a mixture of Mowry Canal discharge and open

Biscayne Bay waters (approaching normal marine salinities). This mixture,

ranging from near fresh to 30 ppt, formed a plume that traveled northward along

the coastline most of the year, and was the source of bay water reaching the

present historic creek site. Therefore, in modeling for target salinity, we used

these seasonal values rather than 35ppt for normal seawater. There was no

significant difference in salinity between the two bay stations (CBB and TBB),

which are about 1km apart. However, there was an obvious difference between

the dry season salinity mean (approximately 25ppt) and the wet season salinity

mean (15ppt). The strong break between the end of the dry season and the

beginning of the wet season (June) was also very apparent (Figure 10).

0

5

10

15

20

25

30

35

40

Jan Feb March April May June July August Sept Oct Nov Dec

Salinity (ppt)

Year 1 CBB (1996)

Year 2 CBB (1997)

Year 3 CBB (1998)

Year 4 CBB (1999)

Year 5 CBB (2000)

Year 1 TBB (1996)

Year 2 TBB (1997)

Year 3 TBB (1998)

Year 4 TBB (1999)

Year 5 TBB (2000)

Figure 10. Nearshore salinity from two stations just south of the Historic Creek site.

C. Wetland area and relief. The area of marsh involved in this project was

determined by planimetry based upon a 10M2 grid (Figure 11). Topographic
27

relief was mapped by the use of several survey lines and field observations

(Meeder et al., 2000).

Figure 11. Displays the marsh topography (contour interval 2.5cm) and the estuarine zone

bathymetry (depth contour intervals 0.3M). The bathymetry is based upon normal spring tide

water depths that flood the marsh by 20cm near the coast.

D. Wetland basin volume. The volume of water required to flood the coastal

mangrove wetland east of the L-31E canal with up to 15 cm of water (a normal

wet season spring tide flood depth) is 53,702 M3

. This was based upon

planimetry of areas of similar elevation using a 5cm contour interval and

assuming a uniform slope (Figure 11). The assumption of a uniform slope

permitted the volume calculation using one half of the contour interval. This

approximated conditions at the site in most areas, except around tidal creeks,

shoreline, and just behind the coastal levee. A normal summer spring tide

inundated most, but not all, the wetland surface. A water depth greater than 20cm

was unusual except in local areas around old abandoned tidal creeks and near the

coast behind the coastal levee. A normal dry season spring tide rarely flooded

more that half of the wetland surface (0.425cm). Therefore, flood volume was

equal to III + IV in Table 3 on 9,557M3

.
28

Figure 12. A schematic model that illustrates the method used in calculation of

wetland inundation volume. The critical data used in the calculation are summarized in

Table 3.

Table 3. Summary of area and volume of wetland by elevation increments.

Depth increment (M) Units Area (M2)=units x 100 Volume (M3)

0.525 to 0.475 445 44,500 26,473

0.475 to 0.425 3075 307,500 17,672

0.425 to 0.375 1084 108,400 7,275

0.375 to 0.325 93 9,300 2,282

TOTAL 469,700 53,702

E. Estuarine basin area and bathymetry. The estuarine area was calculated in the

same manner as the wetland. A 10M grid was overlaid on the aerial image,

bathymetry lines drawn for typical depths at spring high tide, and squares counted

using standard methods. The bathymetry was originally taken from USCGS chart
29

for Biscayne Bay but lacked detailed inshore data. Several wading transects were

made at high tide (Figure 5). These same transects were used for soil probing

and core sampling.

The predicted nearshore area to be impacted by this rehydration of a tidal

creek was 81,700M2

. A bathymetry map, at normal high tides that inundates an

extensive mangrove swamp by up to 15 cm, was produced (Figure 7). The area

flooded during the dry season was approximately 65,500M2

. This calculation was

based upon the average dry season spring tide elevation which was approximately

0.3M lower than during the wet season.

F. Estuarine basin volume. The volume of the estuarine zone was calculated in the

same manner as for the wetland flood volume (Figure 13). The only difference

was that the bathymetry contours were in 30cm increments. Data used in

calculation of wet season spring basin volume by water depth increment were

summarized (Table 4).

Table 4. Summary of basin data used in volumetric calculations by depth increment.

Depth increment (M) Map units Area (A=map units x

100M2)

Volume (M3)

0 to 0.3 162 16,200 22,080

0.3 to 0.6 347 34,700 14,445

0.6 to 0.9 262 26,200 5,310

0.9 to 1.2 46 4,600 690

TOTAL 81,700 42,525

Wet season spring tide volume was 42,525M3. Dry season volume was

calculated in the same manner, however, dry season spring tides were

approximately 30cm lower than in the wet season. Therefore, dry season volume

was equal to II + III + IV or 20,445M3.
30

Figure 13. A schematic model that illustrates the method used in calculation of estuarine basin

volume.

G. Tidal volume. Tidal volume for the nearshore basin was determined using a wet

season spring tide range of 45cm and dry season tidal range of 30cm. The wet

season tidal volume was equal to the sum of depth increment one (I) and one-half

depth increment two (II) (Figure 13). Not only were dry season spring tides

lower than wet season spring tides, but also the height of the high tide in the dry

season was approximately 30 cm lower than the maximum normal spring tide

during the wet season. Therefore, dry season tidal volume approximated the

volume for the depth increment two (II) (Tide tables for South Florida, USCGS

and short term water level recorders (Ross et al., 2000)).

H. Wind direction. Wind data were provided by The National Climatic Data

Center. The following data was collected at Miami International Airport (MIA)

for a period of 44 years for wind speed and 28 years for wind direction. Data

provided were monthly means (Table 5).
31

Table 5. Summary of wind data at Miami International Airport.

Record Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Yr.

Wind 44 9.5 10.1 10.6 10/6 9.5 8.2 8.1 7.9 8.3 9.3 9.7 9.3 9.3

Dir. 28 340 340 120 120 120 120 120 120 90 70 90 340 120

Wind =mean monthly wind speed (mph); Dir. = Prevailing wind direction.

I. Rainfall and temperature. Rainfall was hard to estimate along the coastal zone

from inland rainfall stations. This was due to the fact that daily convection

rainfall usually did not drop until clouds reach a temperature change over land.

This usually occurred several miles inland. Rainfall was almost always less per

event than inland records indicate unless rainfall was associated with large fronts

or depressions. Therefore, we chose to utilize the Tavernier rainfall data over the

Miami Airport data set (Table 6). A visual comparison between the two stations

suggested that dry month rainfall varied less than wet season rainfall, which was

mostly convection and depression rainfall.

Table 6. Monthly means of temperature (o

F) and rainfall (in.) for Miami and Tavernier, Florida.

29 yr. record.

Month Miami Tavernier

Ave temp. Rainfall Ave. temp. Rainfall

Jan 67.3 2.01 69.5 2.18

Feb 68.3 2.08 70.1 1.96

Mar 71.8 2.39 73.7 1.7

Apr 75.2 3.03 76.7 2.0

May 78.6 6.21 79.8 4.54

Jun 81.3 9.33 82.2 8

Jul 82.8 5.7 84.1 3.28

Aug 83 7.58 84.2 4.5

Sep 81.9 7.63 82.9 6.25

Oct 78.3 5.64 79.4 6.01

Nov 73.4 2.66 75.1 2.6

Dec 69.1 1.83 71.1 1.79

Annual 75.9 56.1 77.4 44.82

J. Evaporation. Data on evaporation came from the Big Cypress Swamp, SW

Florida (Duever et al., 1979) and for Hialeah and Tamiami Trail Stations (Florida

Climate Center).
32

Table 7. Evaporation rate data summary.

Station Hialeah Tamiami Trail Big Cypress

in cm L/M2 M3

total

in cm L/M2 M 3

total

cm L/M 2

Wet

season

Mn 6.325 16.06 5.05 12.83

D 0.54 5.4 0.43 4.3 0.25 2.5

Dry

season

Mn 5.02 12.75 4.16 10.57

D 0.43 4.3 0.35 3.5 0.6 6.0

High tide bay flooded area = 94,400M2, low tide area = 49,800M2

K. Transpiration. Mangrove transpiration rates were measured just south of this

study site (Ross et al., 2000). As mangrove biomass increases so does

transpiration, consequently, little seasonal difference was determined. Dwarf

mangrove rates varied between 1.74 and 2.05l/M2

/day in contrast to the fringe

mangrove sites, which ranged between 8.6 and 11.8 L/M2

/day. In the historic

creek study area, the scrub mangroves were much higher and denser than at the

previously studied areas. The fringe zone is narrow and located along the

coastline and along the major tidal creeks for a maximum distance of 250M.

Therefore, we selected an average of 5 L/M2/d as a reasonable average for the

entire marsh site. Using that average, we calculated a daily water loss from the

marsh of approximately 2,758.5M3/d by transpiration processes.

L. Groundwater Discharge. Meeder et al. (1997) documented significant

groundwater discharge to nearshore Biscayne Bay. Fifty meters from shore the

average groundwater discharge was 0.03 M3

/M2/d and at 200M from shore

0.105M3/M2/d. This study was completed approximately 1 km south of the

present study site and should be applicable. No significant seasonal differences

were observed in groundwater discharge at the shore or at 200M offshore.

Although the groundwater table was managed seasonally, the head difference

either was not sufficient to produce different discharge rates or, the coincidence

between managed lower groundwater levels and lower tidal heights in the winter

mitigate one another.

Most of the bay bottom was covered by a dense fresh water marl which is

impermeable, or nearly so, and therefore groundwater discharge was negligible.

However, approximately 19,850 M2

 of bay bottom south and southwest of the

island is exposed bedrock. Therefore, we determined groundwater discharge for

the estuary by using the area 19,850 M2 and a discharge rate of 0.105M3/M2/d.

This rate was used (200 M offshore data) for the entire area because of the lack of

overlying sediments which reduced groundwater discharge (Meeder et al., 1999).

This was a conservative figure based upon application of Darcy’s Law that

predicted groundwater discharge decreased exponentially in the offshore

direction. In our previous study of groundwater discharge, the 50M offshore
33

discharge was lower than 200M offshore stations because of sediment overburden

in the inshore area. Therefore, we estimated 2084M3/d.

Figure 14. Relationship between groundwater flow, distance from shore, and season.

M. Water table elevation. The groundwater stage was regulated by schedule using

large water control structures near the mouths of major canals and the coastal

protection levee and canal (L-31E). Between May 15 and Oct 15 (the wet season)

the water table was managed at 2’1” and from Oct 16 to May 14 (the dry season)

N. Military to Mowry Canal near shore Biscayne Bay volume. The volume of

water, at spring high tide during the wet season, from the shoreline to 1.3M depth

(approximately 500M) offshore between the Military and Mowry Canals

(approximately 1750M), was approximately 568,750M3

. Dry season volume was

503,125M3, and was based upon a depth of 1.15M, because winter spring tides

were generally lower than summer and fall spring tides. This calculation assumed

that the bottom gradient was uniform. Tidal volume was approximately

131,250M3/cycle, based upon a 30 cm tidal range.

O. Estimated nearshore water renewal time. Water renewal time is a

measurement of the time required to totally replace the water in a basin. To

obtain target salinity, a balance between freshwater discharge and mixing with

seawater was necessary. The amount of freshwater required was dependent on

how fast the freshwater mixed with seawater, and the rate at which water left the

basin.
34

Estimates of renewal time can be observed by watching the length of time

freshwater remains after a major runoff event or, the reverse, how long the bay

stays saline after a dry spell is broken. The observed rates in Biscayne Bay were

quite fast compared to most estuaries. The small size and volume of the basin, the

shallowness, and the lack of a restricted mouth or inlet to the bay permitted fast

mixing and export. Estuarine zone water renewal time was calculated by

estimating the tidal volume lost to the zone each tidal cycle, multiplied by two

because of our characteristic diurnal tide patterns. This was the volume that must

be replaced each tidal cycle from either freshwater discharge or incoming bay

water. We could, therefore control the estuarine zone salinity by changing the

volume of freshwater discharged.

Wet season tidal flow patterns documented that approximately 33% of the

tidal volume of the estuarine zone moves northward because of prevailing SE

winds and was lost to the estuary (Figure 15A). Approximately 66% of the tidal

volume moved offshore each tidal cycle but returned to the estuarine zone.

Therefore, 33% of the estuarine tidal volume was replaced each tidal cycle by a

combination of bay water and freshwater discharge. Because of wind forcing

processes, more tidal water exited north of the island than came in with rising

tide. During the start of dropping tides with a SE wind, the tidal water mass

separated at the head of the channel south of the island and part moved north from

west of this point. The increased flow during dropping tide north of the island

was proportional to the strength of the SE wind.

Differences between wet season patterns and dry season tidal flow patterns

were slight and related to: The estuarine basin being shallower (less volume) with

less tidal range, and changes in offshore prevailing winds. In addition, most of

the tidal water that moved into the bay returned (80-90%), but bay water salinity

was much higher than during the rainy season.

In summary, the estuarine zone volume was less than during the wet

season because of lower tidal cycles with the prevailing offshore winds. Not only

was the basin volume less, but so was the tidal volume. Tidal range was

approximately 30cm during the dry season in contrast to 45cm during the wet

season. This was due to the limited influence offshore winds had on nearshore

waters. Fetch was limited and the high fringing mangroves produced a wind

shadow for a distance of 100 to 200M from shore. The northwest winds,

however, produced a weak southerly littoral current, and the tide moved out of the

basin into the shallow bay to the east and southeast of the study area.
35

Figure 15. A. Water current patterns for rising wet season spring tide. Current arrow widths are

relative to current strength, the wider the arrow the greater the water current. B. Dry season
36

falling spring tide. These current patterns were determined during numerous field days while

depth and sediment profiling, soil coring, and canoeing across bay for access to coastal wetlands.

P. Estimated freshwater discharge required. The first step to calculate the

volume of freshwater to be released was to determine the volume of water needed

to reach the Bay. The combined effects of transpiration and evaporation minus

marsh rainfall plus the loss of water from the Bay from evaporation minus rainfall

over the Bay was determined. Two conditions were calculated, dry season and

wet season spring tides:

Vwater = [(Tmarsh x Amarsh) + (Emarsh x Amarsh ) – (Rmarsh x Amarsh )] +

[(Eestuarine x Aestuarine ) – (Restuarine x Aestuarine )], where

V = Volume

T = Transpiration rate,

 A = Area,

E = Evaporation, and

R = Rainfall.

Tmarsh = 551,700M2

 x –5 L/M2/d = -2,758.5 M3/d (for both dry and wet season).

Emarsh = 551,700M2 x –5.5 L/M2/d = -3,034.4 M3/d (dry season)

 = 551,700M2

 x –2.3 L/M2/d = -1,268.9 M3/d (wet season)

Rmarsh = 551,700M2 x 1.6 L/M2/d = 886.7 M3/d (dry season)

 = 551,700M2 x 4.7 L/M2/d = 2,593 M3/d (wet season), therefore:

Eestuary = 65,500M2 x -5.5 L/M2/d = -360.3 M3/d (dry season)

 = 81,700M2 x -2.3 L/M2/d = -187.9 M3/d (wet season)

Restuary = 65,500 M2

 x 1.6 L/M2/d = 106.9 M3/d (dry season)

 = 81,700M2 x 1.6 L/M2/d = 130.7 M3/d (dry season)

 = 81,700 M2 x 4.7 L/M2/d = 383.9 M3/d (wet season)
37

Dry season Wet season

Tm -2,758.5 -2,758.5

Em -3,034.4 -1,268.9

Rm 886.7 2,593.0

Ee -360.3 -187.9

Re 130.7 383.9

Vtotal (M3/d) = -5,135.8 -1,238.4

The volume required for any restoration water to make it to the Bay, because of

ET losses, will decrease with time in the study area. In the beginning, water will be

delivered as sheet flow, maximizing ET. However, over a period of time, delivered water

should begin to channelize, and most water will reach the Bay via the creek channel

minimizing loss due to ET. If additional water is discharged during the first few months

of delivery, perhaps up to a year, the channelization process may take place more

quickly.

Freshwater discharge volumes for different salinity targets, both the dry and rainy

seasons, were calculated based upon flow charts (Figure 9), and listed with other model

parameters (Table 2). The salinity model flow charts, using appropriate data from Table

2, visually present the relationships between the different estuarine basin components.

These components are needed to calculate freshwater discharge required to meet a target

salinity. The first component is the total basin volume (Table 2.F.) and target salinity

(Table 2.A.) at a state of quasi-equilibrium. Two components were derived from the total

basin volume, the tidal volume and the retained estuarine volume, both at target salinities.

The tidal volume component (Table 2.G.) was divided into one outgoing component,

tidal volume lost, and two incoming components, Biscayne Bay replacement water and

freshwater discharge. In order to maintain the target salinity, the combination of

Biscayne replacement water and salinity (Table 2.B.) plus freshwater discharge must

equal the water mass and salinity lost during each tidal cycle. Sea salt was considered a

conservative parameter of seawater, which permitted straightforward mass balance

equations. Data for dry and rainy season spring tides at different estimated tidal volume

losses (10, 20 and 30% for dry season and 23, 33 and 43 % for rainy season) and various

Bay salinities (21.5 and 30 for the dry season and 15.5 and 20.5 ppt for the rainy season)

are presented (Table 8). The midrange value for percent tidal loss is then predicted

(Table 2.O.) and calculations were also made for plus and minus 10%. Mean Bay

salinities for the season were used and a value that represented a typical high, but not

extreme, salinity value.

On a typical dry season spring tide cycle, approximately 825M3

 of freshwater

discharge is required to maintain a estuarine salinity of 15ppt. In contrast, a rainy season

freshwater discharge of approximately 5372M3

 is required to maintain the target salinity

of 7 ppt.
38

The relationship between tidal loss and freshwater discharge volume at various

Bay salinities were expressed for target salinity of 15 ppt for the dry season and 7 ppt for

the rainy season (Figure 16). The relationship between freshwater discharge and Bay

salinity at various tidal volume losses were expressed for both the dry and wet seasons

(Figure 17). These two figures also aided in illustrating the range of freshwater

discharges required to cover small to medium changes in salinity of tidal volume. Tidal

volume was much greater during the rainy season than the dry season with more tidal

volume lost per tidal cycle because of the stronger northern longshore processes.
39

Table 8. Summary data for calculation of freshwater discharge.

Ev Es Tv Ts Tv lost %

lost

Ts

lost

FWQ

vol

FWs Bv Bs Tv

replaced

Ts

dry 20445 15 14445 15 2889 20 15 1445 0 1445 21.5 2889 10.8

2889 20 15 963 0 1926 21.5 2889 14.3

2889 20 15 825 0 2064 21.5 2889 15.4

2889 20 15 722 0 2167 21.5 2889 16.1

4334 30 15 2167 0 2167 21.5 4334 10.8

4334 30 15 1445 0 2889 21.5 4334 14.3

4334 30 15 1239 0 3095 21.5 4334 15.4

4334 30 15 1083 0 3250 21.5 4334 16.1

1445 10 15 723 0 723 21.5 1445 10.8

1445 10 15 482 0 963 21.5 1445 14.3

1445 10 15 413 0 1032 21.5 1445 15.3

1445 10 15 361 0 1084 21.5 1445 16.1

1445 10 15 723 0 723 30 1445 15

2889 20 15 1445 0 1445 30 2889 15

4334 30 15 2167 0 2167 30 4334 15

wet 42525 7 29302 7 6739 23 7 3370 0 3370 15.5 6739 7.8

6739 23 7 3530 0 3209 15.5 6739 7.3

6739 23 7 3744 0 2995 15.5 6739 6.9

6739 23 7 4043 0 2696 15.5 6739 6.2

9670 33 7 4835 0 4835 15.5 9670 7.8

9670 33 7 5065 0 4605 15.5 9670 7.3

9670 33 7 5372 0 4298 15.5 9670 6.9

9670 33 7 5802 0 3868 15.5 9670 6.2

12600 43 7 6300 0 6300 15.5 12600 7.8

12600 43 7 6600 0 6000 15.5 12600 7.3

12600 43 7 7000 0 5600 15.5 12600 6.9

12600 43 7 7560 0 5040 15.5 12600 6.2

9670 33 7 6154 0 3516 20.5 9670 7.4

9670 33 7 6336 0 3334 20.5 9670 7.1

9670 33 7 6447 0 3223 20.5 9670 6.8

12600 43 7 8018 0 4582 20.5 12600 7.4

12600 43 7 8255 0 4345 20.5 12600 7.1

12600 43 7 8400 0 4200 20.5 12600 6.8

6739 23 7 4288 0 2451 20.5 6739 7.5

6739 23 7 4415 0 2324 20.5 6739 7.1

6739 23 7 4493 0 2246 20.5 6739 6.8
40

y = 41.3x - 0.3333

y = 72.2x + 1

y = 162.8x - 0.4

y = 192x - 0.6667

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25 30 35 40 45 50

Tidal Volume Loss (%)

30ppt

21.5ppt

15.5ppt

20.5ppt

WetSeason

Dry Season

Figure 16. Changes in salinity in relationship to freshwater discharge and tidal volume.

y = 36.471x - 371.12

y = 72.941x - 743.24

y = 109.18x - 1108.3

y = 134.2x + 1663.9

y = 192.8x + 2383.6

y = 251x + 3109.5

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 5 10 15 20 25 30 35

Biscayne Bay Salinity (ppt)

Freshwater Discharge (m3)

23% Tidal Loss

33% Tidal Loss

43% Tidal Loss

10% Tidal Loss

20% Tidal Loss

30% Tidal Loss

Wet Season

Dry Season

Figure17. Relationship between freshwater discharge and Biscayne Bay salinity.

Total freshwater discharge required. Total freshwater discharge required was

calculated by two different methods. The first and simplest was to estimate water

discharged through a channel with a known cross sectional area and flow velocity. This

calculation produced the volume of water discharged and not necessarily the volume of
41

water required to meet salinity targets. The paleochannel that delivered most of the water

in the study area was 35cm deep and 5M wide. We assumed a flow velocity of 1 cm/sec.

This was a very slow rate, which was the average flow rate at a nutrient dosing site in

Shark River Slough. This must be a gross underestimate for use at this site because of the

greater slope at the study site than in Shark Slough. The discharge based upon a flow rate

of 1cm/sec was 0.618cfs (1.2 ac-ft/day), at 5cm/sec (6ac-ft/day) flow rate discharge was

3.1cfs and at 10cm/sec 6.2cfs (12 ac-ft/sec). This was even more of a conservative

estimate than that based upon low flow rates, because more than one creek emptied into

the study area, and during high flow periods considerable sheet flow adjacent to the

channel certainly was present.

The second method was more complicated, and was directed at estimating the

volume of water needed to produce the target salinity regime. The total volume of

freshwater released was the product of the volume of water lost getting to the Bay plus

evaporative losses from the estuarine surface and tidal loss replacement. The sums of

these two products for both the dry and rainy seasons have been tabulated (Table 9).

These figures are to be considered a first approximation because of the difficulty of

quantifying many of the model parameters. The system should be designed to deliver

twice the discharge calculated in order to accompany new discharge values after

monitoring and to handle more extreme climatic events.

Table 9. Estimate for freshwater discharge required to meet salinity targets.

Season Target

salinity

Bay

salinity

Marsh and

surface

estuary loss

Tidal loss

replacement

volume (M3

)

Total

(ppt) (ppt) (M3) (Tide cycle) (Day) (M3) (ac-ft/d)

Dry 15 21.5 5,135.8 825 1,650 6,786 5.5

30 1,445 2,890 8026 6.5

Rainy 7 15.5 1,238.4 5,372 10,744 11,982 9.7

20.5 6,336 12,672 13,910 11.3
42

RECOMMENDATIONS.

1. Water is discharged until initial salinity target is reached.

2. Delivery mechanisms should be able to discharge twice the initial estimated

freshwater volume.

3. Above delivery schedule is utilized while being monitored for two months.

4. After initial monitoring period, adjustment made to parameters.

5. Followed by another monitoring period to make final adjustment.

6. Addition adjustments may also be required, especially if extreme climatic conditions

prevail.

7. As channelization occurs, readjustments will have to be made.

8. The relatively inexpensive addition of oyster shell subtidal bars would aid in retention

of freshwater and provide good substrate for oyster community development. A few

shallow barge loads of shell would suffice.
43

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Appendix 1. Core Descriptions.

GPS

Core # Longitude Latitude Depth (cm) Description

8/7/01-1 25.49186 80.33849 0-27.5 35M south of east end of island.

0-12.5 Tan marine marl with Halodule

roots.

Sample A from 0-4cm

Sample B from 8.5-12 cm

12.5 Erosional unconformity

12.5-27.5 Dark grey, black mottled freshwater

marl with mangrove roots

Sample C from 20.5-22.0 cm

8/7/01-2 25.49187 80.33844 0-28 1M north of 8/7/01-1

0-10 Recent organic muck with Halodule

roots.

10-19 Marine marl with oysters

Sample A from 13-15cm

19-28 Freshwater marl grading downward

to dark black freshwater marl with

mangrove roots and limestone clasts

at base.

Sample B from 23-25cm

8/7/01-3 25.49201 80.33829 0-10 Marine shell debris

Sample A from 4-6cm

10-17.5 Marine marl with oysters

Sample B from 13-15 cm

17.5-46 Freshwater marl with Cladium roots

Sample C from 30-32cm

8/7/01-4 25.49215 80.33811 10 m south of east tip of island

0-10 Skeletal marine muck

10-18 Oysters

Sample A from 13-15cm

18-26 Transitional marine to freshwater

marl

26-61 Freshwater marl with Rhizophora

rhizomes and Cladium rootlets

Sample B from 50-52cm

8/7/01-5 25.4926 80.33785 Same sequence as 8/7/01-4
51

Labeled: Outside Blowout #2

Depth (cm) Description

0-4 Yellowish grey silt. Large rhizomes. Buried Thalassia blades.

4-11 Brownish gray rooted silty mud. Root hairs and rootlets throughout. Rhizomes at

bottom.

11-17.5 Grey silty mud. Fossil fragments slightly larger, some small mollusks. No cams.

17.5-26 Grey silty mud. Very small fossil fragments. No appreciable laminations.

26-29 Light brown grey silt. Small gastropods and fragments of echinoderm spines.

Some black organic blobs, slight lamination.

29-40 Grey yellow shelly mud. Calcareous algae and shell fragments. Distinct

lamination.

40-51 Grey brown mud. Few marine shells. Scattered black flecks, more toward top

layer.

Labeled: long core (channel?)

1-10 Medium grey shelly mud. Numerous rootlets, Thalassia on top. Some large

bivalves, most fragments, all look reworked.

10-13 Medium grey shelly mud. Some whole small gastropods. Most are fragments,

mollusk bits. One large bivalve at top of sequence.

13-46 Long sequence of dark grey-brown mud. Probably carbonate. Many vertical

black rootlets. Fine root hairs in places. At 16 cm is a round shrimp-like burrow

filled with shell hash similar to layer above. At about 29cm the mud changes

color gradually with more yellow below this

Lower half also has red rhizomes 5mm and 10mm diameter. No obvious

mollusks in this area

46-50 White carbonate mud -- looks like decayed ooilite. Few shell fragments

LTS

0-6 Grey brown rooted mar. Root hairs, roots, organic bits. Organic roots. May be

in raint layers.

Core B Everglades

0-6.5 Black peat, large roots, elocharis at top.

6.5-13 Black peat, few fine roots.
52

Core 8/11/00 -- 1 Creek channel at 101M mark. 60cm long.

0-2 Leaf litter.

2-7 Black peat with small roots.

7-17 Dark brown-black fibrous peat with small roots.

17-32 Red peat with large roots and root hairs

32-34 Grey brown black marly peat with small roots

34-37 Grey peaty marl

37-43 Grey brown black marly peat with small roots

43-54 Grey brown black peaty marl

54-60 Grey brown marly peat with coarse sand to fine gravel size grains. Several

pebbles <1cm

10-15 M inside mouth of creek

0-2 Dark brown mud (artifact)

2-5.5 Large limestone rock.

5.5-9 Grey rooted mud.

9-11 Mangrove peat

11-13 Grey rooted mud. Numerous small gastropods.

13-20 Light grey mud. Gastropods. Plancrsis common. Rooted.

20-21 Rootup layer

21-42 Light grey mottled mud. Roots (some large). More gastropods toward top. More

bivalve fragments.

42-46 Dark peaty mud. Some "old" bivalve fragments and gastropods at base.

Creek Channel Core 3/20/01

0-8 Brownish grey carbonate mud with Halodule roots and some shell fragments

throughout

8-13 Shelly brown grey mud with bivalve fragments. Dominating the large fractions

these are10-22mm. No ID on small fragments. Abundant. No orientation

13-51 Silty greenish grey dense carbonate mud. Large number of vertical roots more

abundant at top. Shelly filled burrow approximately 2 cm diameter tube. Some

mangrove roots. Scattered quartz silt (fine) in mud. Many small horizontal

rootlets.

3/14/01 1/2 way between island and point in eel grass

0-11 Rooted grey mud, bivalves mostly fragments, mollusks decrease with distance to

bottom. Several whole planorbis.

11-15.5 Lighter grey mud, rooted. Shell fragments. Few sand size particles.

15m S off Turkey Point Transect, W of L-31E Levee
53

0-3 Hydrobid rich brown peaty marl

3-6 Brown-grey mottled fibrous marl, many rootlets

6-13 Light grey carbonate mud, numerous root hairs

13-15 Grey carbonate mud. Few snails.

15-25 White carbonate mud with large plant roots. Sawgrass blades

9/12/01-1

0-4 Dark brown peat, marine shells, many roots

4-7 Dark brown peat and moderate grey peaty marl. Marine shells.

7-9 Dark brown marly peat, many root fibers. A large Gyraulus parvus shell.

9-16 Light grey and white marl.

16-18 Moderate brown peaty marl. Physella cubensis and small Gyraulus parvus shells.

1/2 way between 15 and 81m in eel grass (3/14/01-2)

0-2 Mat of Halodule stems in moderate brown peaty marl

2-7 Brownish-grey marl with Cladium leaves

7-16 Moderate brown peaty marl. Many shells and several Biomphalaria havanensis

shells more Halodule stems.

9/12/01-2

0-8 Dark grey marl with many fine roots. Either Littoridinops monroenis or

Aphaostracon pachynotus shells

9/12/01-3

0-3 Moderate brown peaty marine sediment. Halodule leaves.

3-18 Dark brown peat many roots, some round dark stems/roots.

9/12/01-4

0-11 Small amount of dark brown peat, mostly mangrove debris, leaves, propagules,

and roots

11-34 Dark brown fibrous peat, many fine root hairs, some large woody plant debris.

9/12/01-5 May be reversed

0-19 Moderate grey marl, many woody roots, Thalassia leaves on top.

19-43 Very shelly light grey marl, Thalassia embedded throughout

43-55 Moderate grey marl, Halodule on surface, moderate amount of shells

Oyster Core 1

0-14 Moderate brown peat, many roots and rootlets. Many plant parts, oysters between

12-14
54

14-21 Very shelly moderate brown peat, still many brown plant parts (very round

outside coverings of some kind of plants)

21-40 Moderate brown peaty marl. Moderate amount of shells. Still brown fibrous

material.

40-65 Moderate grey marl. Several Gyraulus parrus shells many fibrous roots.

Still cylindrical plant material

65-72 Dark brown peat with fibrous roots, large particles of limestone.

Labled A-N

0-15 Very fibrous dark brown peat. Many large stems and various sizes of roots.

15-56 Very dark brown peat. Very fibrous. Roots are smaller than layer above.

56-75 Moderate brown peat. Root sizes consistent with layer above. More shell

fragments.

10m N of E end of island (also oyster core 3)

0-18 Very shelly marine marl, dark grey, oysters at bottom of layer.

18-29 Light grey brown marl. Thick woody roots

29-31 Dark brown peat, fibrous and shelly.

31-33 Light grey brown marl.

33-47 Dark brown peaty marl very shelly. Some Sphaostracon pachynotus shells.

Large limestone particles.

9/12/01-6 Dr. Jaffee core?

0-10 Light brown marl mottled with dark brown peat. Many marine shells. Oysters at

bottom of layer

10-12 Very fibrous dark brown peat

12-41 Light brownish grey marl. Several Gyraulus parvus

41-42 Dark brown peat, very fibrous.

42-53 Dark grey marl, several large limestone clasts.

Oyster Core 1 

0-2 Light grey marine sediments. Oyster shells.

2-23 Dark brown peat, very fibrous, many large roots (sawgrass?) Oysters at top

26-57 Light brownish grey marl. Very fibrous and many large roots. Gyraulus parvus

57-82 Dark grey peaty marl. Many large roots or stems.

82-89 Very dark brown peat. Some shells.

9/12/01-7

0-17 Very shelly marine deposits. Dark grey marl.

17-58 Grey green marl with pockets of shells scattered within. Long vertical Cladium

roots. Small limestone clasts at bottom.
55

10m Offshore N end of Island

0-12 Very shelly light grey marine marl.

12-30 Very dark brown peat, sawgrass roots

30-50 Very dark brown peat, many shells including Biomphalaria havanensis

and Physella cubensis

9/12/01-8

0-5 Plant stems

5-21 Moderate brown very fibrous peat

21-61 Very dark brown peat, few roots. Limestone clasts at bottom.

Levy Transect

0-18 Dark brown fibrous peat. Large mangrove stem, leaf litter, root material.

18-33 Dark brown fibrous peat. Much big plant material. Fleshy stems.

33-55 Dark brown fibrous peat. Less big plant material

55-62 Peaty marl with many shell fragments.

9/12/01-9 Core that Pete worked up

0-81 Very dark brown fibrous peat. Many roots and fleshy plant stems.

81-99 White marl, large amount of fibrous root material.