Progress Report on Sediment Analyses

at Selected Faunal Monitoring Sites

in North-central and Northeastern Florida Bay

by

Thomas M. Scott1, Guy H. Means1 and G. Lynn Brewster-Wingard2

1

 Florida Geological Survey, Tallahassee, FL

2

 U.S. Geological Survey, Reston, VA

Open-File Report 97-534

Prepared in cooperation with the Florida Geological Survey, Tallahassee, Florida

This report is preliminary and has not been reviewed for conformity with U.S. Geological

Survey editorial standards or with the North American Stratigraphic Code. Any use of

trade, product, or firm names is for descriptive purposes only and does not imply

endorsement by the U.S. Government

1997
TABLE OF CONTENTS

Abstract

Introduction

Acknowledgments

Previous Investigations

Geologic Setting Of Florida Bay

Methods of Investigation

Sample Collection

Sediment Analyses

Discussion of results

Lithology

Insoluble Residues

Organic Content

Grain-Size Analysis

Summary

References Cited

Appendix: Qualitative description of sediment greater than 63 μm

FIGURES

1. Map of sampling localities

2. Photograph of grainstone (lag deposit) from site 6 (Feb C)

3. Photograph of packstone/wackestone from site 6 (Feb A)

4. Photograph of packstone/wackestone from site 12 (Feb B)

5. Photograph of packstone/wackestone from site 12 (Feb C)

6. Photograph of packstone/wackestone from site3 (July B)

7. Photograph of packstone/wackestone from site 10 (July)

8. Photograph of mudstone from site 13 (July D)

9. Histogram of non-carbonate sediment component: northeast basin

10. Histogram of non-carbonate sediment component: basin south of Little

Madeira Bay

11. Histogram of non-carbonate sediment component: southern portion of study

area

12. Histogram of sediment finer than sand

TABLES

1. Localities and sample descriptions

2. Sediment analysis data
Progress Report on Sediment Analyses at Selected Faunal Monitoring

Sites in North-central and Northeastern Florida Bay

by

Thomas M. Scott, Guy H. Means and G. Lynn Brewster-Wingard

ABSTRACT

Florida Bay is a shallow, subtropical lagoon at the southern tip of the Florida

peninsula. The 2200 square kilometer, triangular-shaped area is the site of modern

carbonate sediment formation and deposition. The intricate ecosystem of the bay has

undergone significant changes as the result of natural influences and human intervention.

The purpose of this study is to investigate carbonate sediment characteristics and

distribution in conjunction with faunal and floral to determine the substrate preferences of

associated fauna and flora. The modern data provide the proxy data for down-core

analyses of sediments, fauna and flora in order to document ecosystem changes in the bay.

Selected sediment samples collected during 1996 from 18 sites in the northeastern

and central bay were analyzed for insoluble residues, organic content, total carbonate, and

percent of silt and clay sized particles. Insoluble residues range from 0.8% of the sediment

in a shell lag to 11.5% with an average of 5.1%. Organic content ranged from a minimum

of 1.43% of the sediment to 18.05% with an average of 7.6%. The total carbonate

content ranged from 72.56% to 97.81%, averaging 87.98%. The percent silt and clay

sized particles ranged from 13.75% to 63.62% for the samples analyzed. The insoluble

residue content shows a general trend of decreasing insoluble residues from the

northeastern bay toward the southwest. Organic content is variable throughout the bay

and does not show a regional trend. Several sites show a trend of higher organic content

in the samples collected in February as compared to those collected in July.

Lithologic examination indicated that, in addition to the carbonate mud (less than

63μm), sample components included whole and fragmented mollusks, foraminifers,

bryozoans, ostracods, and organic matter. The insoluble residues consisted of quartz sand

and silt, clays and siliceous fossils. A component of the insoluble residues may be dust

derived from Africa and transported to southern Florida by the prevailing winds.
INTRODUCTION

The south Florida ecosystem is a complex interplay of physical, chemical and

biological components. Recent negative trends in the biological components of the

system, such as declining numbers of wading birds, decreases in the shell fish populations,

and seagrass dieoffs, have caused a great deal of scientific attention to be focused on the

region. The emphasis, however, has been on examining the biological trends over the last

ten to forty years. Attempts to restore the ecosystem to its natural state, as mandated by

the Everglades Forever Act, passed in 1994, should be based on a knowledge of the

history of the system, and how the physical, chemical and biological components

interacted prior to significant human intervention in the region.

The U. S. Geological Survey (USGS) and the Florida Geological Survey (FGS), in

cooperation with the National Oceanic and Atmospheric Administration (NOAA), the

National Park Service (NPS), the Army Corps of Engineers (ACOE), and the South

Florida Water Management District (SFWMD), among others, are conducting research to

provide data on the historical trends in the physical, chemical and biological components

of the ecosystem. The time scales examined are the last 150-200 years and the last few

millennia. The primary goal of this work is to understand what are the natural patterns of

change in the ecosystem, and to what extent has human alteration of the environment

overprinted these natural patterns. In order to understand the natural variation in the

biological components of the system, we must understand how the organisms interact with

the physical and chemical parameters of their environment.

Florida Bay is an integral part of the Everglades ecosystem, constituting 2200 km2

of shallow water, and providing habitat for birds, and a nursery for many forms of marine

life. It has been profoundly affected by alteration of the natural flow of water across the

terrestrial Everglades environment, and by the alteration of the Florida Keys. The

sediments of Florida Bay preserve a record of the physical, chemical and biological

changes that have occurred in the environment. Sediments, fauna, and flora preserved in

shallow cores from the Bay are used to interpret the changes that have occurred in the

environment over the last 150-200 years (Wingard et al., 1995; Ishman et al., 1996;

Brewster-Wingard et al., 1997). In order to interpret the significance of the down-core

changes more accurately, it is important to understand the distribution of sediments, fauna

and flora in the present-day Florida Bay, and it is essential to determine the substrate and

salinity preferences and tolerances of the living fauna and flora (Brewster-Wingard et al.,

1996). Thus, we have established 26 monitoring sites within Florida Bay that are sampled

twice per year, in February and July, to examine the modern distribution, and the

frequency of change on a seasonal scale. This report includes data from 18 sites, sampled

in 1996, in the north-central and northeastern Florida Bay (Figure 1; Table 1).
20

JOHN PENNEKAMP

CORAL REEF

STATE PARK

ONAL

1

8

1

3

4 5 9

11

2
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

1

Shell creek 

- mouth Feb A - SW 

channel W 80 29.200' N 25 12.426' ± 168' 18.4 18.3 19.1 19 26.37 26.28 26.69 29.41 2 ' Thalassia, Halodule, algae 

on firm mud. 

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

1

Shell creek 

- mouth Feb B - channel W 80 29.200' N 25 12.426' ± 168' 18.4 18.3 19.1 19 26.37 26.28 26.69 29.41 3' Shell lag deposit.

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

1

Shell creek 

- mouth Feb C - NE 

channel W 80 29.200' N 25 12.426' ± 168' 18.4 18.3 19.1 19 26.37 26.28 26.69 29.41 2'

Mix of Thalassia and 

Halodule. Soft, soupy, mud 

bottom. Patchy. 

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

1

Shell creek 

- mouth July A - SW of 

Channel W 80 28.78' N 25 11.17' N/A 10.1 14.1 29.8 30.4 17.03 23.54 18.75 25.99 2.5' Soft mud, ~ 80% Thalassia 

cover. 

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

1

Shell creek 

- mouth July B -channel W 80 28.78' N 25 11.17' N/A 10.1 14.1 29.8 30.4 17.03 23.54 18.75 25.99 3.5 Shell lag.

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

1

Shell creek 

- mouth July C - NE of 

channel W 80 28.78' N 25 11.17' N/A 10.1 14.1 29.8 30.4 17.03 23.54 18.75 25.99 2.5

~ 90% Thalassia cover, ~ 

5% Halodule grass. 

Halodule grass patch noted 

in past is gone, replaced by 

Thalassia. 

Mouth of creek flowing 

from Long Sound; 

surrounded by 

Mangroves.

2

Trout 

creek H2O 

station

Feb A - 10 yrds 

offshore W 80 32.018' N 25 12.742' ± 391' 12.8 13 19.7 19.7 19.1 21.1 21.24 23.8 2.5 Soft mud, sparse Halodule 

grass; scattered Ruppia?.

Off mangrove island near 

mouth of Trout Creek at 

water monitoring station.

2

Trout 

creek H2O 

station

Feb B - 2 yrds 

offshore W 80 32.018' N 25 12.742' ± 391' 12.8 13 19.7 19.7 19.1 21.1 21.24 23.8 1

Firm mud with coarse 

organics (Oyster and 

wood); Halodule present. 

No Thalassia seen.

Off mangrove island near 

mouth of Trout Creek at 

water monitoring station.

2

Trout 

Creek 

H2O 

station

July

A - 10 

yards off 

island 

W 80 31.62' N 25 11.43' N/A 2.6 2.7 30.8 30.8 4.94 5.05 5.48 5.6 2'

~ 2 - 3' mud over 

limestone. Mud is fairly 

soft. Little Thalassia; ~ 

10%; Halodule cover. 

Off mangrove island near 

mouth of Trout Creek at 

water monitoring station.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

2

Trout 

Creek 

H2O 

station

July B - 1 yrd. 

off island W 80 31.62' N 25 11.43' N/A 2.6 2.7 30.8 30.8 4.94 5.05 5.48 5.6 2'

~ 2 - 3' mud over 

limestone. Mud is fairly 

soft. Little Thalassia; ~ 

10%; Halodule cover. 

Off mangrove island near 

mouth of Trout Creek at 

water monitoring station.

3

Duck key 

H2O 

station, S 

side of 

island

Feb A - 

offshore W 80 29.363' N 25 10.784' ± 493' 18.5 18.5 17.2 17.2 25.38 25.42 29.79 29.84 2.5 '

Very sparse grass, patches 

of Thalassia, some algae. 

Substrate fairly firm.

Southern end of mangrove 

island in center of basin 

away from any mud banks 

or other islands.

3

Duck key 

H2O 

station, S 

side of 

island

Feb B - inlet W 80 29.363' N 25 10.784' ± 493' 18.5 18.5 17.2 17.2 25.38 25.42 29.79 29.84 0.5' Substrate firm mud. No 

vegetative cover.

Southern end of mangrove 

island in center of basin 

away from any mud banks 

or other islands.

3

Duck Key 

H2O 

station

July A - 

offshore W 80 28.97' N 25 09.61' N/A 19.3 19.6 31 31.4 31.12 31.66 34.71 35.54 2.5'

Mud with high shell content, 

~ 75% algae, and some 

Thalassia. 

Southern end of mangrove 

island in center of basin 

away from any mud banks 

or other islands.

3

Duck Key 

H2O 

station

July B - inlet W 80 28.97' N 25 09.61' N/A 19.3 19.6 31 31.4 31.12 31.66 34.71 35.54 1'

Very fine-grained mix of 

crushed shell and firm 

mud, sparse Halodule 

grass. 

Southern end of mangrove 

island in center of basin 

away from any mud banks 

or other islands.

4

Northern 

Nest key Feb

B - side of 

bank, 

grass

W 80 30.561' N 25 08.692' ± 92' 17.7 17.5 21.1 19.8 26.21 25.48 28.5 28.31 2'

Soft sediment. Sparse, 

patchy coverage (70-80%) 

of Thalassia and algae in 

deeper H2O. 

Mud Bank at southern end 

of northern mangrove 

island in center of basin.

4

Northern 

Nest key Feb

C - top of 

bank, 

grasses

W 80 30.561' N 25 08.692' ± 92' 17.7 17.5 21.1 19.8 26.21 25.48 28.5 28.31 0.5'

Soft sediment; mix of 

Thalassia and Halodule 

grass. 

Mud Bank at southern end 

of northern mangrove 

island in center of basin.

4

 Northern 

Nest Key July A - top of Bank W 80 30.558' N 25 08.679' ± 89' 13.8 17.4 30.6 31.2 23.28 29.14 25.82 32.58 1'

Very soft soupy mud. ~80-

90% Thalassia. Scattered 

algae .

Mud Bank at southern end 

of northern mangrove 

island in center of basin.

4

Northern 

Nest Key July B - side of bank W 80 30.558' N 25 08.679' ± 89' 13.8 17.4 30.6 31.2 23.28 29.14 25.82 32.58 2'

Very soft soupy mud. 

Thalassia, patchy. 

Scattered algae .

Mud Bank at southern end 

of northern mangrove 

island in center of basin.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

4

Northern 

Nest Key July C - beach W 80 30.558' N 25 08.679' ± 89' 13.8 17.4 30.6 31.2 23.28 29.14 25.82 32.58 0

Shell lag from beach off 

main island, east side.

Mud Bank at southern end 

of northern mangrove 

island in center of basin.

5

Porjoe key - 

S mud 

bank

Feb A - edge of 

bank W 80 28.342' N 25 08.084' N/A 20.3 20.3 16.6 16.5 27.28 27.22 32.45 32.45 2'

Patchy - Thalassia, 

abundant algae, sparse 

Halodule. Variable firmness 

of substrate. 

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.

5

Porjoe key - 

S mud 

bank

Feb B - side of 

bank W 80 28.342' N 25 08.084' N/A 20.3 20.3 16.6 16.5 27.28 27.22 32.45 32.45 1'

Patchy - abundant algae, 

Halodule grass increasing 

in density on bank. 

Variable firmness of 

substrate. 

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.

5

Porjoe key - 

S mud 

bank

Feb C - top of 

bank W 80 28.342' N 25 08.084' N/A 20.3 20.3 16.6 16.5 27.28 27.22 32.45 32.45 0.5'

Patchy - Halodule dominant 

grass type, mangroves 1-2' 

high. Variable firmness of 

substrate. 

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.

5

Porjoe key - 

S mud 

bank

July A - edge of 

bank W 80 27.87' N 45 06.81' N/A 21.8 21.8 31.5 31.6 34.9 34.98 39.26 39.41 3.5'

Thalassia density variable, 

but very healthy. Deeper 

water off bank: 80 - 90% 

Thalassia, scattered 

Halodule, disk algae, 

halimeda and penicillus 

present. Abundant live 

molluscs.

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.

5

Porjoe key - 

S mud 

bank

July B - side of 

bank W 80 27.87' N 45 06.81' N/A 21.8 21.8 31.5 31.6 34.9 34.98 39.26 39.41 1'

Decreasing amount of 

Thalassia compared to 

deeper water.

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

5

Porjoe key - 

S mud 

bank

July C - top of 

bank W 80 27.87' N 45 06.81' N/A 21.8 21.8 31.5 31.6 34.9 34.98 39.26 39.41 0.5' Halodule predominant 

grass type.

To west of Little 

Buttonwood Sound on 

eastern edge of basin. 

Well developed mud bank 

on southern end of keys.

6

Butternut 

key H2O 

station

Feb A - 

nearshore W 80 31.132' N 25 05.200' N/A 18.6 18.5 20.4 19.7 27.3 26.9 30 29.89 0.5'

Sandy shell deposit and 

shell lag just below water 

line at beach.

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

key H2O 

station

Feb

B - 

offshore ~ 

10m

W 80 31.132' N 25 05.200' N/A 18.6 18.5 20.4 19.7 27.3 26.9 30 29.89 2'

Peat deposits overlain with 

CaCO3 sand. Very sparse 

Thalassia (<5%)

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

key H2O 

station

Feb C - beach W 80 31.132' N 25 05.200' N/A 18.6 18.5 20.4 19.7 27.3 26.9 30 29.89 0' Shell lag on beach, above 

water. 

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

key H2O 

station

July A - 

nearshore W 80 31.15' N 25 05.212' ± 98' 26.5 26.6 29.7 29.6 41.48 41.65 45.17 45.31 0.5'

Very firm coarse substrate, 

with a few patches of 

Thalassia. Surface covered 

with live Batillaria , and shell 

debris. 

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

6

Butternut 

key H2O 

station

July

B - 

offshore ~ 

10m

W 80 31.15' N 25 05.212' ± 98' 26.5 26.6 29.7 29.6 41.48 41.65 45.17 45.31 3.5'

Firm substrate; peats with 

very thin layer of coarse 

calcareous material 

overlying the peats. 10-

15% Thalassia. 

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

Key July C - beach W 80 31.15' N 25 05.212' ± 98' 26.5 26.6 29.7 29.6 41.48 41.65 45.17 45.31 0' Shell lag on beach. 

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

Key July D - 

onshore W 80 31.15' N 25 05.212' ± 98' 26.5 26.6 29.7 29.6 41.48 41.65 45.17 45.31 0'

Large blocky calcareous 

mud/marl eroded out of 

island, sitting on peat above 

water level.

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

6

Butternut 

Key July E - 

onshore W 80 31.15' N 25 05.212' ± 98' 26.5 26.6 29.7 29.6 41.48 41.65 45.17 45.31 0"

Shell lag trapped in 

mangrove roots above 

water level.

Mangrove island; samples 

from ne side of western tip 

of island on east side of 

basin. A long mud bank is 

present to the east of the 

island.

7

Bottle Key: 

SE mud 

banks

Feb A - top of 

bank W 80 33.519' N 25 03.686' N/A 21.7 22.1 21.5 19.4 32.1 31.35 34..48 35.1 0.5'

Very soft mud. Dense mix 

of Thalassia, Halodule and 

algae (~ 70%). 

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.

7

Bottle Key: 

SE mud 

banks

Feb B - side of 

bank W 80 33.519' N 25 03.686' N/A 21.7 22.1 21.5 19.4 32.1 31.35 34..48 35.1 2' Very soft mud. Mostly Thalassia.

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

7

Bottle Key: 

SE mud 

banks

July A - top of 

bank W 80 33.044' N 25 03.901' ± 99' 28.3 26.4 31.2 30.8 44.2 41.43 49,39 46.02 0.5'

Very soft, soupy mud with 

10 - 30% unhealthy 

Halodule. 

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.

7

Bottle Key: 

SE mud 

banks

July B - side of 

bank W 80 33.044' N 25 03.901' ± 99' 28.3 26.4 31.2 30.8 44.2 41.43 49,39 46.02 1.5' Thalassia bed, firm mud 

with lots of shell material.

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.

7

Bottle Key: 

SE mud 

banks

July C - off 

bank W 80 33.044' N 25 03.901' ± 99' 28.3 26.4 31.2 30.8 44.2 41.43 49,39 46.02 3.5' Very soft gelatinous mud; 

no vegetation.

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.

7

Bottle Key: 

SE mud 

banks

July D - Beach W 80 33.044' N 25 03.901' ± 99' 28.3 26.4 31.2 30.8 44.2 41.43 49,39 46.02 0' Coarse shell lag collected 

on beach of main island.

String of mangrove 

islands. Very shallow flats 

with lots of juvenile 

mangroves.

8

Little 

Madeira 

Bay mouth

Feb A - N side 

of bar W 80 37.913' N 25 10.564' ± 97' 15.7 15.8 19.7 19.2 23.08 22.98 25.65 25.76 1' Soft mud; ~ 70% Thalassia.

Mouth of Bay which Taylor 

Creek feeds into. 2 small 

mangrove islands on 

either side of mouth. 

8

Little 

Madeira 

Bay mouth

Feb B - S side 

of bar W 80 37.913' N 25 10.564' ± 97' 15.7 15.8 19.7 19.2 23.08 22.98 25.65 25.76 2.5' Firm mud; ~ 35% Thalassia 

and algae.

Mouth of Bay which Taylor 

Creek feeds into. 2 small 

mangrove islands on 

either side of mouth. 

8

Little 

Madeira 

Bay mouth

July A - N side 

of bar W 80 37.889' N 25 10.546' ± 123' 8.3 10.2 31.2 31.3 14.49 14.6 16.22 16.28 1'

Soft mud with shell 

material, forams and 

mollusks abundant. Sparse 

but healthy Thalassia. 

Mouth of Bay which Taylor 

Creek feeds into. 2 small 

mangrove islands on 

either side of mouth. 

8

Little 

Madeira 

Bay mouth

July B - S side 

of bar W 80 37.889' N 25 10.546' ± 123' 8.3 10.2 31.2 31.3 14.49 14.6 16.22 16.28 2.5' Soft mud and lots of shell 

material, ~ 15% Thalassia. 

Mouth of Bay which Taylor 

Creek feeds into. 2 small 

mangrove islands on 

either side of mouth. 

9

Middle of 

basin s. of 

Little 

Madeira 

Bay 

Feb W 80 37.048' N 25 08.436' ± 142' 16.9 18.1 19.3 17.9 24.45 25.18 27.4 29.17 5'

Cover of 3 - 6" of sediment 

over hard rock substrate. 

Substrate exposed in some 

places. <2% coverage of 

Halodule grass. Burrows 

present.

Center of basin; fair 

distance from any islands.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

9

Middle of 

basin S of 

Little 

Madeira 

Bay

July W 80 37.088' N 25 08.460' ± 103' 21.2 21.1 30.8 31 34.02 33.9 37.8 37.7 5'

Sparse sediment cover over 

hard rock. Scattered 

Thalassia, Halodule, 

Acetabularia. Green 

sponges, black sponges, 

and burrows present.

Center of basin; fair 

distance from any islands.

10

Middle of 

basin 

between 

Park and 

Russell

Feb W 80 36.017' N 25 05.817' N/A 17.6 18.1 19.6 17.5 25.4 25.03 28.46 29.2 5'

Varied from exposed rocks 

to holes with ~ 4" of 

sediment. Plant material 

present (0 visibility 

prevented identification).

Center of basin between 

Park Key and Russell Key; 

fair distance from any 

islands; deeper water with 

little sediment cover.

10

Center of 

basin 

between 

Park and 

Russell 

Key

July W 80 34.991' N 25 05.842' ± 100' 24.6 24.6 31.4 31.4 43.69 43.76 38.95 38.97 5'

Hard bottom with little 

substrate. Some algae and 

burrows. 

Center of basin between 

Park Key and Russell Key; 

fair distance from any 

islands; deeper water with 

little sediment cover.

11 Park Key 

SW bank Feb A - top of 

bank W 80 34.010' N 25 06.274' N/A 18.9 18.7 22.1 19.8 28.2 27.05 30.56 30 0.5' Soft gelatinous mud. 

Sparse Halodule.

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

11 Park Key 

SW bank Feb B - side of 

bank W 80 34.010' N 25 06.274' N/A 18.9 18.7 22.1 19.8 28.2 27.05 30.56 30 1' Thalassia present but not 

healthy. Soft mud.

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

11 Park Key 

SW bank Feb

C - side of 

bank, 

deeper 

water

W 80 34.010' N 25 06.274' N/A 18.9 18.7 22.1 19.8 28.2 27.05 30.56 30 2' Firm mud with dense 

Thalassia cover.

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

11 Park Key 

SW bank July A - top of 

bank W 80 34.134' N 25 06.485' ± 92' 24.1 24 30.6 30.5 42.15 41.85 38.06 37.96 0.5' Thalassia, soft, gelatinous 

mud. 

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

11 Park Key 

SW bank July B - side of 

bank W 80 34.134' N 25 06.485' ± 92' 24.1 24 30.6 30.5 42.15 41.85 38.06 37.96 2' Firm mud, with shell lag 

below. Thalassia present.

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

11 Park Key 

SW bank July

C - side of 

bank, 

deeper 

water

W 80 34.134' N 25 06.485' ± 92' 24.1 24 30.6 30.5 42.15 41.85 38.06 37.96 3.5' Sparse Thalassia, soft 

mud. 

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

11 Park Key 

SW bank July D - Very 

top of bank W 80 34.134' N 25 06.485' ± 92' 24.1 24 30.6 30.5 42.15 41.85 38.06 37.96 0.5-0"

Firm mud cap (algal mat?), 

burrowed with flat laminae, 

mud cracks where 

exposed.

Samples on mud bank 

100 yrds to SW of key to 

south of Park Key. Key is 

sparsely developed 

mangrove island.

12

Russell 

Key SE 

bank

Feb A - top of 

bank W 80 37.782' N 25 04.044' N/A 19 18.9 18.7 18.5 27.02 26.6 30.7 30.25 0.5' Very soft mud with dense 

unhealthy Thalassia.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

12

Russell 

Key SE 

bank

Feb B - sides of 

bank W 80 37.782' N 25 04.044' N/A 19 18.9 18.7 18.5 27.02 26.6 30.7 30.25 1' Firm shelly substrate; ~ 

70% Thalassia.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

12

Russell 

Key SE 

bank

Feb

C - side of 

bank, 

deeper 

water

W 80 37.782' N 25 04.044' N/A 19 18.9 18.7 18.5 27.02 26.6 30.7 30.25 2.5' Firm sticky mud with 

moderate Thalassia cover.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

12

Russell 

Key SE 

bank

July A - top of 

Bank W 80 36.402' N 25 03.309' ± 88' 26.9 23.4 31.4 31.5 42.1 37.21 47.19 41.89 0.5' Shell lag with unhealthy 

Thalassia (~80% cover).

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

12

Russell 

Key SE 

bank

July B - side of 

Bank W 80 36.402' N 25 03.309' ± 88' 26.9 23.4 31.4 31.5 42.1 37.21 47.19 41.89 1.5' Firm mud with large shell 

hash component; shell lag.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

12

Russell 

Key SE 

bank

July

C - side of 

bank, 

deeper 

water

W 80 36.402' N 25 03.309' ± 88' 26.9 23.4 31.4 31.5 42.1 37.21 47.19 41.89 3.5' Firm, gelatinous mud; some 

Thalassia present.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

12

Russell 

Key SE 

bank

July D - top of 

the Bank W 80 36.402' N 25 03.309' ± 88' 26.9 23.4 31.4 31.5 42.1 37.21 47.19 41.89 0.5'

Shell lag deposit; sparse 

Halodule and live Batillaria 

present.

Taken about 200 yrds off 

Mangrove Island on top of 

mud bank and erosional 

side of bank.

13 Bob Allen 

mud bank Feb

A - top of 

bank, 

grass

W 80 39.553' N 25 01.390' ± 111' 26.8 27.2 25.2 19.8 42.18 37.9 41.9 42.15 0.5'

Soft mud with dense 

Thalassia. No transitional 

area between grass and 

mud areas.

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

13 Bob Allen 

mud bank Feb B - side of 

bank, mud W 80 39.553' N 25 01.390' ± 111' 26.8 27.2 25.2 19.8 42.18 37.9 41.9 42.15 1'

Very soft gelatinous mud, 

no Thalassia. No 

transitional area between 

grass and mud areas.

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

13 Bob Allen 

mud bank Feb

C - side of 

bank, 

grass

W 80 39.553' N 25 01.390' ± 111' 26.8 27.2 25.2 19.8 42.18 37.9 41.9 42.15 2.5'

Relatively firm mud with 

some shell debris and 

dense Thalassia. 

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

13 Bob Allen 

mud bank July

A - top of 

bank, 

grass

W 80 39.398' N 25 01.358' ± 184' 32.9 32.9 31.3 31.3 50.5 50.5 56.6 56.6 0.75'

Thalassia bed over soupy 

mud. Sharp patchiness as 

before - no transition 

between thick grass beds 

and gelatinous mud. 

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

13 Bob Allen 

mud bank July B - top of 

bank, mud W 80 39.398' N 25 01.358' ± 184' 32.9 32.9 31.3 31.3 50.5 50.5 56.6 56.6 0.75'

Gelatinous mud; 0.75' of 

mud covers old Thalassia 

bed. No lateral transition 

between thick grass beds 

and gelatinous mud. 

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

13 Bob Allen 

mud bank July

C - side of 

bank, 

grass

W 80 39.398' N 25 01.358' ± 184' 32.9 32.9 31.3 31.3 50.5 50.5 56.6 56.6 2.5'

Shelly soupy mud under 

dense Thalassia bed. No 

lateral transition between 

thick grass beds and 

gelatinous mud. 

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

13 Bob Allen 

mud bank July D - off 

bank W 80 39.398' N 25 01.358' ± 184' 32.9 32.9 31.3 31.3 50.5 50.5 56.6 56.6 3.5'

Gelatinous mud. No 

transition between thick 

grass beds and gelatinous 

mud. 

~ 1/4 mile s. of Mangrove 

Island. Shallow mud flats 

& grassy areas extend out 

for quite some distance.

14

Bob Allen 

Key H2O 

mon. 

station

Feb A - ~20m 

offshore W 80 40.872' N 25 01.577' ± 149' 28 28 19.9 19.4 39.1 38.72 43.37 43.43 1' Soft sticky mud, Halodule predominant.

South side of Mangrove 

island near water 

monitoring station at 

western most Bob Allen 

Key.

14

Bob Allen 

Key H2O 

mon. 

station

Feb B - ~ 40 m 

offshore W 80 40.872' N 25 01.577' ± 149' 28 28 19.9 19.4 39.1 38.72 43.37 43.43 3'

Very firm bottom with 

"crunchy" shell layer; ~ 

20% Thalassia cover; 

abundant shell material 

present.

South side of Mangrove 

island near water 

monitoring station at 

western most Bob Allen 

Key.

14

Bob Allen 

Key H2O 

mon. 

station

July A - ~20 m 

offshore W 80 40.9' N 25 01.59' ± 93' 33.5 33.4 31.3 31.3 51.2 51.1 57.4 57.2 1'

Very soft, soupy mud with ~ 

30 % Halodule; surface 

covered with live Batillaria . 

South side of Mangrove 

island near water 

monitoring station at 

western most Bob Allen 

Key.

14

Bob Allen 

Key H2O 

mon. 

station

July B - ~40 m 

offshore W 80 40.9' N 25 01.59' ± 93' 33.5 33.4 31.3 31.3 51.2 51.1 57.4 57.2 2'

Firm mud with shell hash 

layer; scattered (~10-20%) 

Thalassia.

South side of Mangrove 

island near water 

monitoring station at 

western most Bob Allen 

Key.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

15

Gopher 

Pass - 

south side 

of channel 

cut

Feb A - top of 

mudbank W 80 43.630' N 24 58.730' ± 88' 31.3 same 17.4 same 40.87 same 47.93 same 0.5'

Mud and shell lag on bank 

with unhealthy Thalassia 

covering surface.

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

15 Gopher 

Pass Feb

B - top of 

bank, 

deeper 

water

W 80 43.630' N 24 58.730' ± 88' 31.3 same 17.4 same 40.87 same 47.93 same 1' Shelly substrate, with 

healthy Thalassia. 

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

15 Gopher 

Pass Feb

C - top of 

bank, next 

to channel

W 80 43.630' N 24 58.730' ± 88' 31.3 same 17.4 same 40.87 same 47.93 same 2.5' Firm shell lag.

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

15 Gopher 

Pass July

A - top of 

bank, shell 

lag

W 80 44.212' N 24 58.859' N/A 37.1 same 28.8 same N/A N/A N/A N/A 1' Shell lag on top of bank.

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

15 Gopher 

Pass July B - top of 

bank W 80 44.212' N 24 58.859' N/A 37.1 same 28.8 same N/A N/A N/A N/A 1.5' Dense Thalassia bed.

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

15 Gopher 

Pass July C - sides 

of bank W 80 44.212' N 24 58.859' N/A 37.1 same 28.8 same N/A N/A N/A N/A 2.5 Thalassia overlying shell 

lag.

Cut through n-s trending 

mud banks. Mangrove 

island just N ~ 200 yrds

16

Mud Bank 

SW of Sid 

Key SE of 

Corinne 

Key

Feb A - top of 

bank W 80 45.889' N 25 00.724' ± 115' 31.5 31.4 17.7 17.6 41.4 41.33 48.26 48.1 0.5'

Very soft, soupy mud. 

~75% Thalassia coverage 

(unhealthy) with scattered 

Penicillus.

E-W trending mud bank, 

W of N-S trending islands 

and banks.

16

Mud Bank 

SW of Sid 

Key SE of 

Corinne 

Key

Feb B - side of 

bank W 80 45.889' N 25 00.724' ± 115' 31.5 31.4 17.7 17.6 41.4 41.33 48.26 48.1 1.5'

Firm substrate, mud with 

shell lag. Thalassia 

unhealthy.

E-W trending mud bank, 

W of N-S trending islands 

and banks.

16

Mud Bank 

SW of Sid 

Key SE of 

Corinne 

Key

July

A - top of 

bank, 

grass

W 80 45.889' N 25 00.75' N/A 34.5 34.5 30.3 30.4 52.7 52.6 58 58 1'

~ 90% Thalassia beds on 

bank top covering soupy 

mud, w/ open areas of 

gelatinous mud.

E-W trending mud bank, 

W of N-S trending islands 

and banks.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

16

Mud Bank 

SW of Sid 

Key SE of 

Corinne 

Key

July B - side of 

bank W 80 45.889' N 25 00.75' N/A 34.5 34.5 30.3 30.4 52.7 52.6 58 58 2.5'

Firm mud with shell debris 

and ~20% Thalassia. 

Bottom patchy with ~1m 

depressions with shell lag 

on bottom. No grass.

E-W trending mud bank, 

W of N-S trending islands 

and banks.

16

Mud Bank 

SW of Sid 

Key SE of 

Corinne 

Key

July C - top of 

Bank, mud W 80 45.889' N 25 00.75' N/A 34.5 34.5 30.3 30.4 52.7 52.6 58 58 1' Open area of gelatinous 

mud over buried grass bed.

E-W trending mud bank, 

W of N-S trending islands 

and banks.

17

Rabbit Key 

H2O 

station

Feb

A - top of 

mudbank, 

shell lag

W 80 49.451' N 44 58.895' ± 97' 30.7 same 17.6 same 40.4 same 47.05 same 1'

Shell lag from scour 

through Thalassia bed on 

top of mudbank.

Mud flats to east of 

mangrove island, 

separated from island by 

channel. Island used for 

overnight camping.

17

Rabbit Key 

H2O 

station

July

A - top of 

bank, shell 

lag

W 80 49.535' N 24 58.894' ± 91' 34.6 34.4 32.5 32.3 52.8 52.6 60.4 59.8 1'

Shell lag from scour 

through Thalassia bed on 

top of mudbank.

Mud flats to east of 

mangrove island, 

separated from island by 

channel. Island used for 

overnight camping.

17

Rabbit Key 

H2O 

station

July

B - top of 

bank, 

grass

W 80 49.535' N 24 58.894' ± 91' 34.6 34.4 32.5 32.3 52.8 52.6 60.4 59.8 1'

Soft sticky mud, with 

varying amounts of shell 

material; ~80% patchy 

Thalassia, some Halodule 

present where Thalassia 

sparse. 

Mud flats to east of 

mangrove island, 

separated from island by 

channel. Island used for 

overnight camping.

17

Rabbit Key 

H2O 

station

July C - Sides 

of bank W 80 49.535' N 24 58.894' ± 91' 34.6 34.4 32.5 32.3 52.8 52.6 60.4 59.8 3' Soft marl with Thalassia.

Mud flats to east of 

mangrove island, 

separated from island by 

channel. Island used for 

overnight camping.

18

Peterson 

Key H2O 

station

Feb A - near 

island W 80 44.829 N 24 55.100' ± 369' 31.3 same 17.7 same 41.31 same 48.1 same 0.5'

Soft mud with Halodule, 

sparse Thalassia; ~ 3m 

from mangrove roots.

NW side of mangrove 

island on mud flats just S 

of station. Channel 

separates mudflats from 

island.
Table 1: Field data from 18 monitoring sites sampled in February and July 1996 and discussed within this report.

GPS Data Salinity (ppt)

Temperature 

(C)

Conductivity 

(MS)

Specific 

Concuctance 

(ms)

SITE #

Location

Month Sampled

Sample Longitude Latitude

GPS Error ± FT.

Top

Bottom TopBottom TopBottom TopBottom

Depth (ft.)

 Bottom Conditions General Area Description

Mouth of creek flowing 

18

Peterson 

Key H2O 

station

Feb B - top of 

grass flat W 80 44.830 N 24 55.100' ± 369' 31.3 same 17.7 same 41.31 same 48.1 same 0.5'

Soft, sticky mud, fairly high 

shell content, with 

Thalassia (unhealthy) 

cover.

NW side of mangrove 

island on mud flats just S 

of station. Channel 

separates mudflats from 

island.

18

Peterson 

Key H2O 

station

July A - near 

island W 89 44.829' N 24 55.117' ± 238' 35.7 35 32.5 32.5 54.3 53.5 62.1 61.2 1' Soft, soupy mud with 

Halodule. 

NW side of mangrove 

island on mud flats just S 

of station. Channel 

separates mudflats from 

island.

18

Peterson 

Key H2O 

station

July B - top of 

grass flat W 89 44.829' N 24 55.117' ± 238' 35.7 35 32.5 32.5 54.3 53.5 62.1 61.2 1' Soft soupy mud; ~ 90% 

Thalassia with Halimeda. 

NW side of mangrove 

island on mud flats just S 

of station. Channel 

separates mudflats from 

island.

18

Peterson 

Key H2O 

station

July

C - off 

north end 

of bank

W 89 44.829' N 24 55.117' ± 238' 35.7 35 32.5 32.5 54.3 53.5 62.1 61.2 3.5' Soupy, gelatinous mud.

NW side of mangrove 

island on mud flats just S 

of station. Channel 

separates mudflats from 

island.
Acknowledgments

We would like to thank our colleagues at the South Florida Water Management

District, National Oceanic and Atmospheric Administration, and Everglades National

Park for their cooperation and assistance in this investigation. The Keys Marine Lab,

Florida Institute of Oceanography and Florida Department of Environmental Protection,

Long Key, FL provided facilities, boats and personnel to assist us in the sample

collection. We have benefited from discussions with Robert Halley, Charles Holmes,

Ellen Prager and Gene Shinn, USGS, St. Petersburg, FL. Our reviewers, Bruce Wardlaw, 

USGS, Reston, VA, and Ken C. Campbell, FGS, Tallahassee, FL, improved this report 

with theirsuggestions and comments. Steve Wandrei and Carey Costello, USGS, Reston, 

VA, assisted during the field sampling. Rob Stamm assisted us with figure preparation.

Previous Investigations

Numerous investigators have focused their efforts on the Florida Bay ecosystem.

Florida Bay sediments were first mentioned by Agassiz (1888) when he noted that

carbonate sedimentation was occurring within the bay. Dall (1892) stated “...much of the

limy deposit of the area behind the reefs and defended by them is probably the result of

the deposition of lime originally held in solution and precipitated by chemical action

rather than of mechanically transported sediment.” Sanford (1909) briefly mentioned the

“marls” in Florida Bay and referred to the development of the banks and islands.

Vaughan (1910) provided the first descriptions of the carbonates of Florida Bay. Matson

(1910) gave detailed descriptions of textural and microscopic examinations of these

sediments including grain size and composition.

Trask (1932, 1939) discussed the occurrence of organic matter in the bay

sediments and provided the first estimates of its abundance. Thorp (1935, 1939)

investigated the organisms that contributed to the accumulation of bottom sediments. He

cited coralline algae, mollusks and foraminifers as major sediment producers. A note

authored by Parker Trask in Thorp (1939) briefly described the bay sediments and

environmental conditions. Thorp (1939) believed that the quartz grains found in the bay

sediments came from the weathering and erosion of the Pleistocene Miami Limestone.

Ginsburg (1956), in a pivotal investigation of southern Florida carbonate sediments,

studied the effects of depositional environments on grain sizes and constituent particle

composition in Florida Bay and the reef tract. Ginsburg (1957) observed the organic and

physical processes affecting the carbonate sediments during early diagenesis. He

determined the organic processes observed were mainly a result of the effects of marine

organisms on the sediment, including aggregation, particle size reduction and

bioturbation. The physical processes mentioned included compaction, desiccation

shrinkage, and penecontemporaneous deformation. Ginsburg and Lowenstam (1958)
investigated the role of marine flora and fauna on the depositional environment of

southern Florida carbonate sediments.

Stehli and Hower (1961) determined the mineralogy of carbonate sediments from

southern Florida. They state “Carbonate sediments produced in warm shallow water,

either by biochemical activity or a combination of biochemical and physiochemical

processes, show a well defined composition in which aragonite predominates and in which

high-magnesium calcite is dominant over low-magnesium calcite. About 70 % of the

average shallow water carbonate sediment consists of unstable forms of CaCO3.”

Fleece (1962) studied the carbonate geochemistry and sedimentology of Florida

Bay sediments from cores taken on and near keys off Islamorada and Tavernier. Fleece

provides an excellent review of the pre-1962 literature on the bay sediments. Eighty-five

percent of the samples he examined contained more than 70 percent silt and clay sized

carbonate and approximately 70 percent of the finer-than-sand-sized sediment occurred in

the medium silt size range. He discussed the tendency for increasing organic matter

content with decreasing grain size. Organic content reached as high as 36 percent of the

sediment.

Taft and Harbaugh (1964) recognized a bimodal distribution of sediment particle

sizes within the carbonate sediments of Florida Bay. They attributed the size distribution

to several causes including 1) inorganic precipitation of very fine particles, 2) secretion of

finer particles by organisms or by the interaction of particles with organic matter, 3)

breakdown of skeletal material. They found little size variation with depth in the

sediment. Dolomite was not found in the eastern half of Florida Bay.

The origin of the fine carbonate muds in southern Florida was dealt with by

Stockman et al. (1967). They determined that the major contributor of fine aragonite mud

was Penicillus, a calcareous algae. Ginsburg (1972) presented a compilation of textural

and compositional data of the Florida Bay sediments showing the silt-clay-sized

component of the sediments ranged from 10-92 percent with an average of 6.2 percent

organic matter. Multer (1977) also provided a compilation of data on the Florida Keys

carbonate sediments.

Analyses of the sediments from Peterson Key Bank (Kick, 1981) provide an

accurate picture of the sediments present in this portion of the bay. Sand accounted for

10-80 percent of the sediment with an average of 38 percent. Silt and clay comprised 20-

80 percent of the sediment with the clay fraction usually making up less than 30 percent of

the total. The banks are composed primarily of silt in the 31-5.9 μ range. An

investigation of the sediments of Florida Bay’s grass-covered mud banks (Holmquist et al.,

1989) indicated that for the entire bay the silt-clay content averaged 56.3 percent, sand

content 36.6 percent and gravel content 7.1 percent. Organic content was determined to

range from 5.8 percent to 11.1 percent in the combined northeastern and east central

portions of the bay.
Holmquist et al. (1989) recognized distinct exposed and sheltered zones at most of

the sampling stations as had other investigations (Ginsburg, 1956; Ginsburg and

Lowenstam, 1958; Turney and Perkins, 1972; Enos, 1977; Enos and Perkins, 1979;

Bosence, 1989a). Enos and Perkins (1979) and Bosence (1989a) suggested that the

exposed sides of the banks (the northeast-facing sides) were most subject to winnowing

and erosion with the finer sediments deposited on the lee side and a lag deposit remaining

on the windward side. Wanless et al. (1994) discussed the Holocene environmental

history of the carbonate mudbanks of Florida Bay. The evolution of the islands has been

investigated by Enos and Perkins (1979) and Wanless and Tagett (1989). Enos (1977)

produced a Florida Bay surface sediment facies map showing the distribution of skeletal

grainstones and packstones and peloidal skeletal wackestones. Note that Enos (1977)

utilized a 63 μm break between grains and mud rather than the 20 μm Dunham (1962)

used and did not recognize significant areas of mudstone (>90 % mud).

Bosence (1989b) determined that carbonate sediments in Florida Bay were

produced by, in decreasing importance, Thalassia epibionts, mollusks, Penicillus, soritid

foraminfera and Halimeda. The banks produced twice as much skeletal carbonate per unit

area as the basins. However, the basins cover much more area than the banks and

generate approximately four times more sediment than the banks. The sediment textures

on the banks vary from mud-pebble conglomerates, packstones and grainstones on the

windward side to wackestones and mudstones with basin-floor packstones on the leeward

side and basin (Bosence, 1989a). Bosence (1989a) and Wanless and Tagett (1989)

modified Dunham’s (1962) mudstone definition to include more coarser material.1

Steinen and Tennet (1990) examined the origin of the fine-grained sediments of

Florida Bay, the reef tract and the Great Bahama Bank. They state that the Florida Bay

muds were primarily composed of equant one micron grains with less than 20 percent

aragonite needles. Three main processes were responsible for the sediment production: 1)

disintegration of skeletal encrustations, mainly red algae and spirorbid worm tubes, on

Thalassia grass blades; 2) postmortem desegregation of aragonite needles from

calcareous green algae; and 3) direct precipitation of aragonite and Mg-calcite from

supersaturated marine waters.

The role of epibionts living on Thalassia in carbonate production was determined

by Nelson and Ginsburg (1986) and Frankovich and Zieman (1994). The distribution of

calcifying epibionts and the distribution of epiphyte production in Florida Bay appear to

reflect salinity variations (Frankovich and Zieman, 1994). The variability of carbonate

production by epibionts is great across the bay and regional variation exceeds seasonal

variations at most sites (Frankovich and Zieman, 1994).

The occurrence of siliciclastics in the Florida Bay sediments has been briefly

mentioned in many papers but very few focused on this sediment component. The origin

and distribution of clay-sized silicate minerals in Florida Bay was investigated by Manker

 

1

 In Dunham’s (1962) definition of a mudstone, material coarser than 20μm cannot exceed 10%.
(1969). His results indicated two clay mineral assemblages - 1) an eastern Florida Bay

chlorite dominated assemblage, and 2) a western Florida Bay montmorillonite dominated

assemblage. The distribution of the clay minerals was thought to be controlled by source

area influences. The occurrence and abundance of quartz grains in the sediments is

mentioned in many of the papers cited here. Ginsburg (1956) found that greater than 125

μm quartz grains constitute up to 20 percent of the sediment. Fleece (1962) found up to

4.3 weight percent clear, subrounded, 0.5 mm to 0.125 mm quartz grains. Layman (1977)

reported an easterly decrease in the abundance of quartz grains from the Gulf of Mexico

toward the inner portions of Florida Bay.

Peat deposits are often found interbedded with marine carbonate sediments. The

occurrence of peats is mentioned in a number of the Florida Bay investigations, most

notably Enos and Perkins (1979) and Quinn and Merriam (1988). The most complete

description and discussion of the Florida Bay peats is presented by Davies (1980).

Recent investigations of the lithology and variability of the Florida Bay sediments

have been conducted in relation to the south Florida ecosystem restoration efforts. The

sediments have been studied as a means of documenting the link between the sediments,

sea level and onshore water management practices (Halley et al., 1995), recognizing

natural and anthropogenic changes (Nelsen et al., 1996), sediment transport (Prager et al.,

1996, 1997) and the age of the sediments (Halley et al., 1997). Wanless et al. (1995)

presented data on sedimentation styles found in Florida Bay.

Geologic Setting Of Florida Bay

Florida Bay, a shallow, subtropical lagoon, lies at the southern tip of the Florida

peninsula, east of the axis of the Florida Platform. The bay, a generally triangular-shaped

area, covers nearly 2200 square kilometers. It is bounded to the north by the Everglades,

to the south and east by the Florida Keys (a Pleistocene reef, Key Largo Limestone), and

to the west by the Gulf of Mexico (Figure 1). The western boundary with the Gulf of

Mexico is arbitrarily placed at the westernmost mudbanks extending south from Cape

Sable to the Florida Keys (Wanless and Tagett, 1989). The most striking feature of

Florida Bay is the “anastomosing array of shallow mudbanks composed of shelly

calcareous silts that cordon the bay into a lacework of interconnected shallow

basins...”(Scholl, 1966). Water depths in this important estuary reach a maximum of

approximately 3 meters immediately behind the Keys and along the southwestern margin

of the bay (Enos and Perkins, 1979). While the mudbanks may be exposed at low tide, the

average depth of the basins is about 1.5 meters (Scholl, 1966.) Scholl (1966) estimated

that approximately 1.5 X 109

 cubic meters of calcareous sediment have accumulated in the

bay.

The Holocene sediments of Florida Bay lie disconformably upon the late

Pleistocene Miami Limestone. The Pleistocene limestone surface is generally planar,

gently dipping (approximately 0.1 meter per kilometer to the southwest [Enos and
Perkins, 1979]) and microkarstic. The Miami Limestone is closest to sea level under the

northeastern portion of the bay where it lies 1.5 meters below mean sea level (msl) and

dips southwestward to -3.7 meters msl at the southwestern edge of the bay (Davies, 1980;

Wanless and Tagett, 1989). Subtle irregularities occur on the bedrock surface. These

include 1) larger, subcircular depressions up to more than 1.6 kilometers in diameter and

up to 2.1 meters below the surrounding limestone surface, common beneath the broader

banks and islands of western Florida Bay; 2) long, narrow, anastomosing depressions, up

to one meter below surrounding bedrock, criss-cross larger circular depressions and are

commonly associated with narrower mudbanks in the central and eastern bay; 3) deeper

channel depressions exist in the bay adjacent to and paralleling the exposed Florida Keys

(Davies, 1980).

The Holocene calcareous sediments have been deposited in Florida Bay during the

last 4,000 years as rising sea level encroached upon the southern tip of the peninsula. The

sediments are thinnest under the basins where the Miami Limestone is often exposed or

buried by only a few centimeters. The thickest accumulations occur under the banks. An

average of one meter of sediment occurs beneath the banks (Enos and Perkins, 1979) but

may exceed 1.5 meters in some areas. Scholl (1966) estimated that mudbanks covered

approximately 32 percent of Florida Bay. The banks are not equally distributed across the

bay. In the eastern portion of the bay, small, narrow, discontinuous banks cover about 13

percent of the area while the broad, irregularly shaped banks in western Florida Bay

occupy nearly 75 percent of the area (Scholl, 1966). Islands, irregularly distributed in the

bay, evolved from the mudbanks (Enos and Perkins, 1979; Enos, 1989). The islands are

least numerous in the western bay (0.76% of area), most common in the central bay

(2.89% of area) and intermediate in the northeastern bay (1.88% of area) (Enos, 1989).

The mudbanks of Florida Bay have been classified in to four categories: 1) inner

destructional zone in the eastern bay; 2) central migrational zone in the central part of the

bay; 3) western constructional zone in western Florida Bay; and 4) outer destructional

zone along the exposed western margin (Wanless and Tagett, 1989). Sampling for this

report occurred in zones one and two. Zone one consists of smaller, more discontinuous,

erosional mudbanks while zone two is a maze of narrow, more continuous mudbanks

(Wanless and Tagett, 1989).

METHODS

Sample Collection:

Sediment samples were collected from 18 sites in Florida Bay during February and

July 1996 (Figure 1; Table 1). Samples were collected by wading and snorkeling in water

depths ranging from a few centimeters to two meters. Sampling via this method allowed

us to make detailed observations of the substrate, the condition of flora and fauna, and

microhabitats that existed at each site. Representative samples were obtained from the
subenvironments recognized at each location. For each location, the environmental

conditions including surface and bottom salinity and temperature, water depth, and

substrate were recorded (Table 1). Salinity, temperature, and conductivity measurements

were taken with a YSI Model 30 hand-held instrument.

At each site, at least one push core (4 cm diameter clear plastic tube) and one bag

sample (approximately four liters) were collected. When a number of subenvironments

occurred at a site, each subenvironment was sampled. Push cores were obtained by

pushing the plastic tubing into the substrate as deep as possible. The tubes were capped to

maintain a vacuum and extracted from the substrate. Push cores were cut at the sedimentwater interface and sealed to prevent sediment disruption. Bag samples were taken by

scooping the upper ten centimeters of sediment into a one gallon plastic bag. The samples

analyzed and discussed in this report represent a subset of the total number of samples

taken.

Sediment Analyses:

The sediment samples analyzed for this investigation were taken from the one

gallon bag samples collected at each site. Samples taken in both February and July were

analyzed. Analyses performed on the samples include visual examination under a

binocular microscope, wet sieving, acid dissolution of the carbonate fraction and organic

matter digestion.

Samples examined visually utilizing a binocular microscope were classified based

upon Dunham (1962) and subsequent modifications by Enos (1977) and others. The

break between grains and mud in Dunham’s (1962) classification was at 20 μm; Enos

(1977) used a 63 μm break. Bosence (1989a) used mudstone to denote sediments with

greater than 50 % sediment finer than 63 μm. In this analysis, we used the 63 μm break

between grains and mud and a sample was referred to as a mudstone if it contained more

than 90 % mud by visual estimate.

Subsamples of sediments collected at selected sites were prepared for grain size

analysis utilizing a modification of Ginsburg’s (1956) method. Approximately 50 grams of

dried sediment were weighed on a Metler Toledo PG 803 balance and placed in a ten

percent H2O2 solution for up to 48 hours. Some samples dissaggregated completely under

this treatment. However, other samples did not thoroughly disaggregate, resulting in an

abundance of sediment clumps. Sediments that did not disaggregate completely were

placed in a Calgon solution and submerged in an ultrasonic bath for 10 minutes to one

hour. Despite these efforts, a number of samples continued to contain varying amounts of

sediment clumps. As a result, the recorded percentage of sediment finer than 63 μm from

these samples can be considered as a minimum only. Efforts are continuing to develop a

method to totally disaggregate the sediments.

Prepared samples were wet sieved at .5 phi intervals from -1.0 to 4.0 phi (2.0 mm

to 63 μm). The sediments retained on each screen were dried, weighed and visually
examined for grain-type identification. A grain-size distribution was determined for the

selected samples.

Approximately 20 grams of sediment were taken from each sample for acid

dissolution and organic digestion to examine the amount and types of insoluble residues.

Samples were weighed on a Metler Toledo PG 803 balance and submerged in a 10 percent

HCl solution. Each sample remained in the HCl until the sediment no longer reacted to a

fresh HCl solution. The acid-insoluble residue was washed to remove residual HCl, dried

and weighed to determine percent total insoluble plus organics.

Following acidulation, the acid-insoluble residues were treated with an

approximately 20 to 30 percent warm H2O2 solution to remove organics. The samples

remained in the H2O2until all evidence of the reaction ceased. The remaining sediment

was washed to remove residual H2O2, dried and weighed to determine total insoluble

content and calculate the organic content. The remaining sediment was visually examined.

DISCUSSION OF RESULTS

Lithology

The lithologies of the sediments collected from the 18 sites in Florida Bay during

1996 ranged from mudstones (gelatinous muds) to grainstones (lag deposits) (Figures 2 to

8). Most commonly, the sediments were wackestones to packstones containing varying

percentages of mollusks, foraminifers, ostracodes, bryozoans, other faunal elements and

organic matter, usually seagrass. Quartz grains were coated with carbonate and were not

recognizable upon examination of the bulk sediment.

The condition of the mollusks contained in the sediment varied from well

preserved to having a leached, weathered appearance. In general, the mollusks were well

preserved at the majority of sites. Weathered shell was most common at Site 1 in a shell

lag found in the channel.

There was little evidence of seasonal variation in the samples analyzed from these

sites. A possible seasonally-controlled variation in organic content was observed in a

comparison of February and July samples from a few sites. This limited data suggested a

higher organic component in the February samples.
cessed sample). This sample is from a lag deposit above the water line

nt mollusc present. Also present is Diodora sp. and a serpulid worm
 (dried unprocessed sample). This sample is from a Thalassia bed

e bank at site 12. Most molluscs present are fragmented.
 (dried unprocessed sample). This sample is a mix of finely crushed

 foot of water.
ocessed sample). This sample is from 3.5 feet of water off the bank at
Insoluble Residues

Samples from all 18 sites collected during 1996 were analyzed for insoluble

residues. At selected sites, samples from the top and side of the mudbank were analyzed

while only a single sample from the remaining sites was treated. Percent insolubles ranged

from a minimum of 0.8 % in a shell lag at Site 6 (July E) (see Table 2 and Figures 9 - 11)

to a maximum of 11.5 % at Site 5 (Feb B) averaging 5.1 %. These results fall within the

range of percentage insoluble cited by Ginsburg (1956) and Fleece (1962).

Visual examination of the insoluble residues revealed the presence of rounded to

subangular quartz grains in the medium sand to silt size range (350 to 31 μm). Clay

minerals appeared to be present in all samples. Visual comparison indicated a high degree

of variability in the concentration of clay-sized insoluble components. Siliceous spicules

and diatom frustules were present in widely varying amounts in virtually all samples.

A trend in the proportions of the insoluble constituents moving from the northeast

to the southwest was recognized during the visual examination. There was more quartz

sand and silt in the samples from the northernmost portion of the bay closer to the

mainland than in the southwest portion. The clay sized proportion increased in comparison

to the silt and sand sized component toward the southwest. Grains of coarse and medium

sand-sized quartz occurred in samples from Site 1 (July A, C). In most samples, the first

appearance of quartz grains occurred in the fine to very fine grain size.

A component of Florida Bay’s insoluble residues may be dust particles originating

in Africa and transported into this area by the prevailing winds (Shinn, personal

communication, 1997). Shinn (personal communication, 1997) hypothesized that the

influx of African dust may play an important role in ecosystem changes, and may explain

some of the negative trends seen in recent years. Further analyses may document the

presence of the dust incorporated in the carbonate sediments of Florida Bay.

Organic Content

Sediments from all 18 sites collected during 1996 were analyzed for percent

organic matter. Organic matter present in the samples ranged from 1.43 % at Site 9 (July)

to 18.05 % at Site 13 (Feb B) with an average of 7.6 % for the entire area sampled (Table

2 and Figures 9-11). The two sites with the lowest percentage of organic matter in the

sediments occurred in the middle of basins, Site 9 (July) in Little Maderia Bay and Site 10

(Feb) in the middle of the basin south of Little Maderia Bay.

Peat was encountered at a few sites sampled for this investigation. These organic

sediments are reddish brown, presumably mangrove peats.
Table 2: Sediment analysis data for Florida Bay samples collected in February and July 1996.

Site number 

(Sample)

Percent 

organics

Percent 

insolubles

Percent 

carbonate

Percent 

total 

sediment 

finer than 

sand

Description of the insoluble 

residues.1

1 (Feb A) 5.52 7.63 86.85

1 (Feb C) 7.37 8.78 83.85 Sand, silt, clay, spicules.

1 (July A) 9.94 7.89 82.17 37.6 Abundant fine-medium sand, 

some silt, clay, spicules.

1 (July C) 43.5

2 (Feb A) 4.89 7.54 87.57 Mostly silt; clay, sand rounded 

to sub-angular, spicules, 

charcoal.

2 (Feb B) 11.31 8.33 80.36 30.6 Silt and clay, sand, spicules.

2 (July A) 8.04 7.51 84.45 30.1 Mostly clay; silt, vf sand, 

spicules.

2 (July B) 14.21 4.89 80.9 Abundant silt, vf sand, clay, 

spicules abundant.

3 (Feb A) 11.13 7.8 81.07 Abundant fine-medium sand, 

silt clay, spicules.

3 (July A) 10.33 6.96 82.71

3 (July B) 2.15 6.93 90.92

4 (Feb B) 9.63 5.25 85.12 Silt, sand, clay, spicules.

4 (Feb C) 8.89 6.7 84.41 Silt, sand, clay, spicules.

4 (July A) 2.9 4.06 93.04

5 (Feb A) 9.51 5.63 84.86 Abundant silt, sand, clay, 

abundant spicules.

5 (Feb B) 15.94 11.5 72.56 Abundant silt, sand, clay, 

abundant spicules.

5 (July B) 3.2 3.03 93.77

6 (Feb B) 13.8 Clay, very little silt and sand.

6 (July A) 0.6 1.59 97.81 16.5

6 (July E) 7.78 0.8 91.42

7 (Feb A) 7.35 3.96 88.69 Silt, clay, sand, spicules.

7 (Feb B) 6.33 3.87 89.8 Silt, clay, sand, spicules.

7 (July A) 3.13 2.77 94.1

7 (July B) 8.53 1.47 90

8 (Feb A) 3.15 4.62 92.23 26.9 Abundant clay and silt, some 

sand, spicules, fish scales.

8 (Feb B) 4.32 8.95 86.73 Gray clay, little silt/sand, 

spicules.

8 (July A) 2.44 2.67 94.89 Clay, silt, some vf sand, few 

spicules.

8 (July B) 1.72 5.99 92.29 Abundant clay, silt, some vf 

sand, few spicules.

9 (Feb) 6.6 4.37 89.03 20.6

9 (July) 1.43 4.31 94.26 Abundant silt to vf sand, some 

clay, few spicules.

10 (Feb) 2.46 4.54 93 17.8 Clay, lot of sand, silt, few 

spicules.
Table 2: Sediment analysis data for Florida Bay samples collected in February and July 1996.

Site number 

(Sample)

Percent 

organics

Percent 

insolubles

Percent 

carbonate

Percent 

total 

sediment 

finer than 

sand

Description of the insoluble 

residues.1

10 (July) 0.85 3.18 95.97

11 (Feb A) 4.32 6.68 89 Abundant clay, silt, some vf 

sand, few spicules.

11 (Feb B) 5.91 5.57 88.52 Abundant clay, silt, some vf 

sand, few spicules.

11 (Feb C) 5.5 6.69 87.81 Abundant clay, silt, finemedium sand, abundant 

spicules.

11 (July A) 5.28 5.89 88.83

11 (July A) 2.2 6.14 91.66

11 (July B) 5.09 3.25 91.66

12 (Feb A) 11.88 6.45 81.67 33.8 Abundant clay, silt to vf sand, 

few spicules.

12 (Feb C) 13.66 6.2 80.14 Abundant clay, silt to vf sand, 

spicules.

12 (July A) 3.26 2.04 94.7 Silt and clay, little sand, 

spicules.

12 (July B) 2.54 3.19 94.27 Abundant medium-fine sand, 

silt, clay, spicules.

12 (July C) 4.45 4.81 90.74 Clay, silt, sand, spicules.

12 (July D) 7.31 2.47 90.22 Clay, silt, sand, spicules.

13 (Feb A) 8.61 4.75 86.64

13 (Feb B) 18.05 6.13 75.82

13 (Feb C) 11.6 5.17 83.23

14 (Feb A) 12.07 4.99 82.94

14 (Feb B) 3.07 1.81 95.12 Sand, silt, clay.

15 (Feb A) 6.09 4.51 89.4 Clay, silt, and little sand, 

spicules.

16 (Feb A) 7.11 4.69 88.2

16 (Feb B) 5.72 3.51 90.77 Gray clay, silt, minor sand, 

spicules.

17 (Feb A) 11.81 4.77 83.42 Abundant clay, silty, little sand, 

few spicules.

17 (July B) 37.2

17 (July C) 37.5

18 (Feb B) 9.99 4.74 85.27

1

 Description based on cursory examination of residue samples under binocular microscope.
 (organics and insolubles) from 

Bay (sites 1-6).
organics and insolubles) from

Florida Bay (sites 8-12).
te sediment component (organics and insolubles) from 

 Bay (sites 7, 13-18).
Grain-Size Analysis

Twelve samples from 1996 were analyzed for grain-size distribution. Despite

difficulties in completely disaggregating some samples, valid results were obtained for

selected sites. The results of wet sieving samples are presented in Table 2. Since the

percentage of mud (<63 μm, 4.0 phi) is important in the determination of the sediment

texture, particular attention was given to obtaining completely disaggregated sediment for

this analysis. In the analyzed samples, the percentage of mud ranged from 13.75 % on the

side of the bank at Site 6 (Feb B) to 63.62% on top of the bank at Site 17 (July B) (Table

2 and Figure 12).

Selected disaggregated samples were wet sieved at 0.5 phi intervals to examine the

types of grains in each size fraction. Whole and large fragments of mollusks occurred in

the 2 mm to 0.5 mm range with the percentage of whole shells decreasing rapidly. In

samples finer than 0.5 mm, most mollusks were fragmented. Large soritid foraminifers

were common in the coarser than 0.5 mm fraction. Smaller miliolid, rotaliid, and elphidiid

foraminifers (Lidz and Rose, 1989) were very common in the 0.71 mm and finer size

range. Micro-gastropods (Caecum sp.) and ostracods are common in the 0.5 mm to

0.0625 mm samples. Spicules and worm tubes were present in many samples.

SUMMARY

Florida Bay’s intricate ecosystem has undergone significant changes due to natural

influences and human intervention. Modern sediment samples have been collected on a

semi-annual basis in order to determine the distribution and characteristics of the

sediments and the associated fauna and flora, and to determine the frequency of change on

a seasonal scale. The distribution of modern fauna and flora collected from 14 sites

collected in 1995 were presented by Brewster-Wingard et al. (1996); a report on the fauna

and flora from the 1996 sites is planned.

Carbonate sediments from 18 sites in Florida Bay were analyzed for lithology,

organic content, insoluble residues, percent of sediment finer than 63m, and percent total

carbonate. The carbonate sediments of Florida Bay vary from mudstones to grainstones

with the majority of the sediments being wackestones to packstones. The sediments

contain mollusks, foraminifers, bryozoans, and other faunal components in varying

concentrations. Organic material occurs as seagrass blades and roots and disseminated

organic matter. The organic content ranges from 1.43% to 18.05% with an average of

5.1%. Insoluble residues consist of quartz sand and silt, clay-sized particles and siliceous

microfossils. The insoluble residue content of the carbonate sediments ranges from 0.8%

to 11.5%, averaging 7.6%. The total carbonate content of the sediments varied from

72.56% to 97.81%. The percentage of the sediment finer than 63μm ranges from 13.75%

to 63.62%.
an sand based on grain-size analysis.
Additional data gathering and a comparison of our data to that of Prager (Prager et

al. 1996, 1997) and Halley (Halley et al., 1997) will be necessary to determine if any

trends in sediment distribution exist. The data presented here, however, suggest a

northeast to southwest trend of decreasing insoluble residue content and a possible

seasonal trend in organic matter. Samples from several sites had higher organic content in

the February samples and lower organic content in the July samples. No geographical

trend in organic matter was recognized.

Analyses of the sediments collected during the semi-annual monitoring and field

collection in Florida Bay are continuing. Beginning in February 1997, the sediment

sampling procedures were altered. Sediment samples are collected in five centimeter

clear plastic tubes pushed into the sediment. For the 1997 samples, push cores from

selected sites will be analyzed. Analyses of push cores will include overall lithology,

sediment grain size distribution and texture, and sediment structures. These data will be

linked to faunal and floral analyses in order to develop an understanding of the links

between the physical and biological components of the Florida Bay ecosystem.
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APPENDIX

Qualitative Description of Sediment Greater than 63 mm

Following are the qualitative descriptions of sediment greater than 63 μm, retained on

sieves during grain size analysis. Descriptions are listed by site and sample number, at half

phi intervals. Samples were analyzed under a binocular microscope.

PHI Sample Description

SIZE

Site 1 (July A):

-1 Whole and fragmented mollusks, organic matter, encrusting bryozoans,

most shell in excellent shape.

-0.5 Whole and fragmented mollusks, less organic matter, few charcoal pieces,

few large forams most shell in excellent shape.

0 Whole and fragmented mollusks, less organic matter, few large forams.

0.5 Mostly fragmented mollusk shell, some organic matter, few large forams,

Caecum sp.

1.0 Mostly fragmented mollusk shell, ostracodes, few large foraminifer

fragments, abundant fine organic matter, few quartz grains, bryozoan

fragments, Caecum sp.

1.5 Mostly fragmented mollusk shell, abundant ostracodes, abundant organic

fine matter, smaller forams, bryozoan fragments, Caecum sp.

2.0 Abundant smaller forams, organic matter, mollusk fragments with few

whole gastropods, abundant ostracodes, few quartz grains.

2.5 as 2.0 with very few whole mollusks, fewer shell fragments, scattered

quartz grains.

3.0 as 2.5 with no whole shell.

3.5 as 2.5 with spicules present.

4.0 smaller forams, shell fragments, minor organic matter, ostracodes, common

quartz grains.
PHI Sample Description

SIZE

Site 1 (July C):

-1.0 Whole and fragmented mollusks, some weathered shell, organic matter,

encrusting bryozoans.

-0.5 as -1.0 with less coarse organic matter.

0 as -0.5

0.5 Fragmented and whole mollusks, Caecum sp., larger forams, organic

matter, encrusting Bryozoans.

1.0 as 0.5 with abundant bryozoan fragments, smaller forams.

1.5 abundant smaller forams, abundant ostracodes, few whole mollusks, few

Caecum sp., fine organic matter, few quartz grains.

2.0 abundant smaller forams, abundant ostracodes, mollusk fragments,

abundant organic matter, Bryozoan pieces, quartz grains.

2.5 as 2.0, less organic matter, scattered quartz grains.

3.0 abundant smaller forams, fewer ostracodes, mollusk fragments, bryozoan

fragments, less fine organic matter.

3.5 as 3.0

4.0 as 3.0

Site 2 (Feb B):

-1.0 Whole and fragmented mollusks, pieces of wood, abundant organic matter.

-0.5 Whole and fragmented mollusks, larger forams, organic matter.

0 as -0.5 more common gastropods.

0.5 Whole and fragmented mollusks, Caecum sp., larger forams, organic

matter.

1.0 as 0.5 with few large forams
PHI Sample Description

SIZE

1.5 Fragmented and whole mollusks, abundant smaller forams, ostracodes, few

bryozoan pieces, organic matter.

2.0 as 1.5

2.5 few whole mollusks, abundant smaller forams and ostracodes, organic

matter, few quartz grains.

3.0 Mollusk fragments, abundant forams, few ostracodes, little organic matter,

scattered quartz grains.

3.5 Mollusk fragments, abundant forams, , little organic matter, scattered

quartz grains, few spicules.

4.0 as 3.5.

Site 2 (July A):

-1.0 Whole and fragmented mollusks, few wood fragments, organic matter.

-0.5 Whole and fragmented mollusks, few larger forams, organic matter.

0 as -0.5 with abundant larger forams.

0.5 as 0

1.0 abundant whole and fragmented mollusks, abundant smaller forams, few

larger forams, organic matter.

1.5 Mollusk fragments and few whole shells, abundant smaller forams, organic

matter.

2.0 Mollusk fragments, abundant forams, abundant ostracodes, some organic

matter.

2.5 Abundant smaller forams and ostracodes, mollusk fragments, some quartz,

little organic matter

3.0 as 2.5 with fewer ostracodes
PHI Sample Description

SIZE

3.5 Abundant smaller forams, mollusk fragments, quartz grains, spicules, very

little organic matter.

4.0 as 3.5.

Site 6 (Feb B):

-1.0 whole and fragmented mollusks, larger forams, organic matter.

-0.5 as -1.0

0 Whole and fragmented mollusks, common larger forams, Caecum sp.,

organic matter.

0.5 Fragmented mollusks, few whole shells, Caecum sp., worm tubes, organic

matter.

1.0 Fragmented mollusks, few whole shells, Caecum sp., Larger and smaller

forams, few ostracodes, organic matter.

1.5 as 1.0

2.0 as 1.0 with less organic matter.

2.5 as 2.0 with scattered quartz grains, no ostracodes.

3.0 as 2.5 with few spicules.

3.5 as 3.0

4.0 as 3.0

Site 6 (July A):

-1.0 Whole and fragmented mollusks, most in excellent shape, organic matter.

-0.5 Whole and fragmented mollusks, most in excellent shape, Larger forams,

organic matter.

0 as -0.5
PHI Sample Description

SIZE

0.5 Fragmented mollusks with few whole shells, Caecum sp., worm tubes,

larger forams, organic matter.

1.0 Mostly fragmented mollusks, worm tubes, ostracodes, smaller forams,

organic matter.

1.5 as 1.0

2.0 as 1.0, most fragmented.

2.5 as 2.0 with few quartz grains.

3.0 as 2.5

3.5 as 2.5

4.0 as 2.5

Site 8 (Feb A):

-1.0 Whole and fragmented mollusks, larger forams, organic matter

-0.5 as -1.0, mostly larger forams.

0 as -0.5

0.5 Whole and fragmented mollusks, larger forams, some organic matter,

Caecum sp., worm tubes.

1.0 Mostly fragmented mollusks, larger and smaller forams, pieces of worm

tubes and Caecum sp.

1.5 Mollusk fragments, abundant smaller forams, ostracodes

2.0 as 1.5, mostly forams.

2.5 as 2.0

3.0 as 2.0 plus spicules.
PHI Sample Description

SIZE

3.5 as 3.0

4.0 as 3.5 with some quartz grains.

Site 9 (Feb):

-1.0 Whole and fragmented mollusks, larger forams, organic matter.

-0.5 Whole and fragmented mollusks some fresh and others leached, larger

forams, little organic matter.

0 as -0.5

0. fragmented mollusks, Caecum sp., worm tubes, few fragments of larger

forams, few smaller forams, very little organic matter.

1.5 Mostly fragmented mollusks, Caecum sp., worm tubes, abundant smaller

forams, few quartz grains.

2.0 as 1.5 with ostracodes and more quartz grains.

2.5 as 2.0 with more quartz.

3.0 as 2.5 with lots of quartz, some forams filled with pyrite.

3.5 as 3.0 with spicules and less quartz.

4.0 as 3.5

Site 10 (Feb):

-1.0 Whole and fragmented mollusks, organic matter.

-0.5 Whole and fragmented mollusks, few larger forams, less organic matter.

0 as -0.5, some blackened mollusks fragments.
PHI Sample Description

SIZE

0.5 Whole and fragmented mollusks, few larger forams, less organic matter,

blackened shell and black grains, Caecum sp., few smaller forams.

1.0 as 0.5 mostly broken mollusks, some weathered shell.

1.5 fragmented mollusks, abundant smaller forams, ostracodes, quartz grains.

2.0 as 1.5

2.5 as 1.5

3.0 as 1.5, more quartz

3.5 as 3.0

4.0 as 3.0

Site 12 (Feb A):

-1.0 Whole and fragmented mollusks, abundant organic matter.

-0.5 Whole and fragmented mollusks, abundant organic matter, larger forams.

0 as -0.5

0.5 Mostly fragmented mollusks, Caecum sp., larger forams, worm tubes,

organic matter.

1.0 as 0.5 with smaller forams.

1.5 as 1.0 with ostracodes.

2.0 as 1.5, quartz grains.

2.5 as 2.0 with more quartz grains.

3.0 as 2.5 with spicules.

3.5 as 2.5.

4.0 as 2.5.
PHI Sample Description

SIZE

Site 17 (July B):

-1.0 Whole and fragmented mollusks, organic matter.

-0.5 as -1.0.

0 as -0.5 with larger forams.

0.5 Whole and fragmented mollusks, Caecum sp., larger forams, smaller

forams, worm tubes, quartz grains.

1.0 as 0.5.

1.5 as 1.0, ostracodes.

2.0 as 1.5, more abundant ostracodes.

2.5 as 2.0 with abundant forams.

3.0 as 2.5.

3.5 as 2.5.

4.0 as 2.5.

Site 17 (July C):

-1.0 Whole and fragmented mollusks, rock fragments, Bryozoans, organic

matter.

-0.5 Mostly fragmented mollusks, bryozoan fragments, few larger forams, little

organic.

0 as -0.5 with few worm tubes.

0.5 as 0 with few Caecum sp.

1.0 as 0.5 with smaller forams, ostracodes.
PHI Sample Description

SIZE

1.5 as 1.0

2.0 as 1.5 with a trace of quartz grains.

2.5 as 2.0 with more quartz.

3.0 as 2.5 with more abundant smaller forams.

3.5 as 3.0

4.0 as 3.0.