Ecosystem Management Report

Bessey Creek

and the

Greater St. Lucie Estuary

Gregory A. Graves

Douglas G. Strom

Florida Department of Environmental Protection

Southeast District

Surface Water Ambient Monitoring Program

Port St. Lucie

December 1992

(5th printing, April 1998)
Mission

“To protect, conserve and manage Florida’s

environment and natural resources.”
Notice

The authors may be contacted directly for additional copies of

this report or to comment on content:

Douglas G. Strom

Internet: Doug.Strom@ dep.state.fl.us

Gregory A. Graves

Internet: Greg.Graves@dep.state.fl.us

Southeast District Branch Office

Florida Department of Environmental Protection

1801 S.E. Hillmoor Drive, Suite C-204

Port St. Lucie FL 34952

Office: (561) 398-2806

Suncom: 222-2806

Fax: (561) 398-2815
Abstract

In response to the Martin County Board of County Commissioners and public concerns about water

quality in the St. Lucie estuary, the Southeast District Florida Department of Environmental Regulation

(FDER) Ambient Water Quality Section collected a series of biological (benthic macroinvertebrate),

water column, and sediment samples from the Bessey Creek - Canal C-23 system. Samples were

taken during the first half of 1992. Due to the influx of stormwater from C-23, the salinity decreased

from 30 ppt (parts per thousand) at the start of sampling in February to less than 1 ppt in July. These

changes in salinity were found to have a greater impact on resident benthic biota than did substrate type,

i.e., muck (“ooze”) versus sand and shell. Samples collected from areas where bottom materials were

more consolidated contained a greater number of taxa and individuals than samples collected from

muck. However, the muck substrate did support an appreciable number of taxa.

Water column and sediment samples were collected for chemical analysis from Bessey Creek and from

the St. Lucie estuary and river system. Water quality data from these samples, in addition to historical

data from United States Environmental Protection Agency’s (EPA) Storet national water quality database, were used to assess water quality. Fluctuating conditions were apparent in several indicator

parameters (salinity, dissolved oxygen, nutrients, and turbidity) and were related to stormwater. Evidence is presented that shows that the documented accelerated rate of sedimentation is also due to

stormwater inflow. Estimates of the amount of nutrients and solids entering the estuary from three major

tributaries to the estuary (canals C-23, C-24 and C-44) were calculated based upon flow data and

average concentration of total suspended solids and nutrients for the period 1980 to 1990. These

estimates indicate that more than eight million pounds of suspended solids, two million pounds of nitrogen, and two hundred thousand pounds of phosphate enter the estuary annually. The actual transport to

the estuary from these sources is believed to be much higher than this estimate.

Data used for this water quality assessment indicate that the amount of substances being transported to

the estuary show no sign of abatement. Stormwater treatment is recommended as a first step toward

improving water quality within the estuary.

i
Acknowledgements

We thank Jeff Christian, Mary Figueira, Jackie Kelly, and Tom White, Department personnel who

aided in sampling for this study; Tom White, for analyses performed, particularly benthic BOD

determinations; Department personnel William Thiel and Jamie Caston for technical advice; Lee

Banks, Tim Fitzpatrick, Marion Hedgepeth, John Meyer, William Thiel, and Mary E.S. Williams, for

review and comments; Doug Farrell (FDER Southwest District) and Harvey Rudolph (Palm Beach

County Department of Environmental Resource Management), for help in identification of

macroinvertebrates; Ernie Gallego and Dan Haunert, of South Florida Water Management District,

and Scott Weber, of Martin County Engineering, for providing reports, data, and sampling assistance.

ii
Table of Contents

 Introduction.................................................................................. 1

 Sampling Locations....................................................................... 4

 Methods....................................................................................... 6

 Biology............................................................................ 6

 Chemistry........................................................................ 6

 Results and Discussion.................................................................. 9

 Biology............................................................................ 9

 Overview of Biological Results......................................... 17

 Chemistry........................................................................ 19

 Bessey Creek Water Quality.................................. 19

 Canal C-23 Water Quality..................................... 22

 Canal C-24 Water Quality..................................... 26

 Canal C-44 Water Quality..................................... 29

 Other Tributaries to the Estuary.............................. 34

 Greater St. Lucie Estuary....................................... 37

 Heavy Metals in Sediment..................................... 43

 Overview of Chemical Results......................................... 46

 Conclusions................................................................................. 48

 Recommendations....................................................................... 52

 References.................................................................................. 54

 Appendix A - Storet Stations...................................................... 56*

 Appendix B - Chemical Data Inventory........................................ 58*

 Appendix C - Biological Data...................................................... 78*

 Appendix D - Flow Data............................................................. 86*

 Appendix E - Rainfall Data.......................................................... 98*

*Notice!

Appendices available only upon request.

iii
List of Tables

Table 1. Sample Station Locations........................................................................... 4

Table 2. Bessey Creek Biological Sampling Physical Data Summary......................... 10

Table 3. Bessey Creek Biology Data Summary........................................................ 11

Table 4. Bessey Creek Number of Taxa in Major Groups........................................ 12

Table 5. Bessey Creek Similarity Indices................................................................. 13

Table 6. Key to Abbreviations, Terms and Units of Measurement............................. 19

Table 7. C-23-influenced Bessey Creek.................................................................. 20

Table 8. “Natural” Bessey Creek............................................................................ 20

Table 9. Total Recoverable Metal Standards for C-23............................................ 23

Table 10. Total Recoverable Metal Standards for C-24........................................... 27

Table 11. Turbidity Violations in C-44...................................................................... 31

Table 12. Total Recoverable Metal Standards for C-44........................................... 32

Table 13. Winters/Blakeslee Creeks........................................................................ 34

Table 14. Frazier Creek.......................................................................................... 35

Table 15. Krueger Creek........................................................................................ 35

Table 16. Poppolton Creek..................................................................................... 35

Table 17. Danforth Creek....................................................................................... 36

Table 18. Howard Creek........................................................................................ 36

Table 19. Warner Creek......................................................................................... 36

Table 20. Mapp Creek........................................................................................... 36

Table 21. Total Recoverable Metal Standards for Marine Waters............................ 42

Table 22. Comparison of Average Parameter Values for the St. Lucie Estuary versus

 Statewide Medians................................................................................. 43

Table 23. Sediment Metal Concentrations for the Bessey Creek - C-23 System..... 44

Table 24. Heavy Metal Concentrations in Bivalve Mollusks.................................... 45

iv
1

Introduction

During most of geologic history, estuaries have been relatively uncommon. The present day estuary

system, which currently comprises 80 to 90% of the Atlantic and Gulf coasts, formed at the end of the

Wisconsin Glaciation which ended 15,000 years ago. At that time, in comparatively recent geological

history, sea level was approximately 100 meters lower than it is today. Global sea level rise continued

more or less unabated from this time until around 3000 to 1000 B.C., when the rate of sea level rise

declined and the estuaries assumed their current configurations. The St. Lucie estuary seen today

(Figure 1) is a result of this sea level rise, being a drowned river valley (versus the Indian River Lagoon,

a bar-built estuary).

Geologically, estuaries are ephemeral formations, typically lasting from a few thousand to a few tenthousands of years. Freshwater, in the process of flowing from the land to the sea, transports materials

that may range in type and size from dissolved organic matter to large grains of sand, dependent upon

the type of terrain the water must transverse and the velocity at which the water moves. The estuary

provides an area of relative quiescence and dynamic chemistry where substances are naturally deposited. Estuaries are a sink for terrigenous (land produced) deposits and as such, are gradually filled in

over time.

Estuaries are classified (Pritchard, 1955) into four basic types dependent upon the saltwater-freshwater

circulation pattern. The St. Lucie estuary is, under normal conditions (when there is not an influx of

stormwater and the estuary becomes fresh) a Type B estuary, that is partially mixed and moderately

stratified. When fresh water overlies a layer of more dense, saltier water, the layers may flow at different

velocities and directions. This two-layer flow pattern is called “estuarine circulation”. Particles being

carried downstream from the freshwater inflow will sink into the lower water layer and be carried back

upstream with the incoming tide. Though the process may be repeated many times for any given set of

particles, the net statistical result of estuarine circulation is that it acts as a “sediment trap”. Particles

heavier than water are retained within the estuary. Estuarine circulation is responsible for regions of high

turbidity commonly observed in the upper and middle reaches of an estuary (Olson and Burgess, 1967).

It is a normal condition for any estuary to be turbid, to experience sedimentation, and to possess deposits of fine silt and clay materials. These materials may be resuspended in the water column through wave

action. However, if the natural process of estuarine sedimentation proceeds at an accelerated rate, as a

result of anthropogenic (man’s) activities, potentially adverse effects on the quality and quantity of these

materials will result.
2

Figure 1. Greater St. Lucie Estuary, Florida
3

“Sediments are a major controlling factor in the ecology of estuaries. Not only do they form

habitats for many benthic plant and animal populations, but they also influence the life processes

of planktonic and nektonic (drifting and swimming) organisms. For example, the high turbidity

commonly encountered in estuaries - due, in part, to fine sediments held in suspension - attenuates

light, thereby limiting primary production. The morphology, feeding and dominance patterns of

benthic species are a function of the substratum type. In addition, ecological relationships among

the benthos hinge on the characteristics of estuarine sediments. The complexity of food webs and

the overall biotic productivity of estuaries are responsive to the nature of the substratum and the

communities of organisms inhabiting the estuarine seafloor and shore.” (Kennish, 1986)

Estuaries are by definition areas where freshwater and saline waters mix, and fluctuations in salinity are

natural for estuaries. Historical records indicate that the St. Lucie River, as well as large portions of the

Indian River Lagoon, became almost entirely fresh during certain periods when major inlets were closed

(Hutchinson, 1975). However, under ordinary conditions, seasonal discharge patterns can be expected

to cause a shifting gradient of interaction between fresh and saline waters with a corresponding gradient

of species of varying tolerances. During the last century, a system of ditches and canals was constructed

that allowed expanded residential and agricultural development of the St. Lucie River area. This increase in drainage basin size resulted in a corresponding increase in the rate at which water is delivered

to the estuary and in the total volume of water delivered.

The Bessey Creek - C-23 complex drains into the southwest corner of the North Fork of the St. Lucie

River estuary (Figures 1 and 2). The system consists of the “natural” Bessey Creek (and its extensive

tributary system) and the artificial drainage canal, C-23, which intercepts Bessey Creek near its mouth.

Due to the system’s manageable size and its semi-natural drainage basin in close association with discharge from a major stormwater canal, Bessey Creek was considered an appropriate starting point to

assess possible problems in the estuary. Bessey Creek represented a microcosm of the Greater St.

Lucie Estuary, its water quality problems being representative of the estuary at large. In addition,

Bessey Creek - C-23 has been a major contributor of sediments to the estuary (Schrader, 1984).

This study is part of an intended analysis of the ambient biological and physico-chemical conditions of all

major waterbodies of the FDER’s Southeast District. This report is based upon original research conducted by the District Ambient Water Quality Section, as well as relying upon all available historical

water quality data from FDER, South Florida Water Management District (SFWMD) and the United

States Geologic Survey (USGS). The intention was to minimize inter-governmental redundancy. The

goal of this report is to present a general overview of water quality in the Bessey Creek - C-23 system

and the Greater St. Lucie Estuary.
Locations of sampling stations in the Bessey Creek - C-23 area are given on Table 1

and shown on Figure 2. For locations of other stations refer to Appendix A.

Table 1. Sample Station Locations

Station Storet # Location

 1 28010031 at mouth of C-23 canal opposite seawall to north

 2 28010016 mid-channel of C-23 at Murphy Rd. bridge

 3 28010098 just east of C-23 spillway west of Murphy Rd.

 5 28010176 west side of the bend of natural Bessey Creek just south of confluence with C-23

 6 28010212 northwest bend of Hidden River west of confluence with

 Bessey Creek

 7 28010047 at Murphy Rd. bridge over non-channelized “natural” Bessey Creek

 8 28010213 11⁄2 mile west (further upstream) of Station 7

 9 28010214 in the estuary, 100 yds east of RGA/Cutter Sound docks, 100 yds west of Jenkins Point

 10 28010051 in the estuary, 100 yds north of Dyer Point

Sampling Locations

4

Figure 2. Bessey Creek - C-23 Stations
Methods

Biology

Macroinvertebrate sampling was conducted February 11, April 22, and July 16th, 1992. Three replicate grab samples were taken at each station with a petite ponar grab sampler. The organisms were

relaxed with clove oil for at least fifteen minutes. Samples were preserved with a ten percent buffered

formalin solution containing rose-bengal dye. Temperature, dissolved oxygen, conductivity, and pH

measurements were taken at top, mid and bottom depths at the time of sampling with a Hydrolab® unit.

Time of sampling, secchi depth, substrate type, and the nature of bottom substrate was also recorded

(see Tables 2 & 3).

In the laboratory the samples were passed through a number 30 (0.6 mm aperture) sieve. Coarser

materials were retained in a 2.0 aperture sieve and examined in a white enamel pan for organisms. Finer

material was examined under a dissecting scope until all macroinvertebrates were removed. The specimens were preserved in 70 % isopropanol containing glycerin until they could be identified. The organisms

collected were identified using standard marine identification handbooks to the lowest practicable taxon.

All identified species were retained as labeled voucher specimens, and all organisms were saved.

Chemistry

All field sampling and analyses were taken according to FDER standard procedures (Graves, 1988)

and FDER Southeast District and FDER Central Laboratory Quality Assurance Plans. On January 21,

1992, water column and sediment samples were collected at 7 sites (Figure 1) within the Bessey Creek

- C-23 basin. On April 23 and May 14, 1992, mollusks were collected for heavy metal analysis. On

May 26, 1992, water column samples were collected from a network of 42 stations (Figure 3) located

throughout the Greater St. Lucie River system. On June 30 through July 1, 1992, a diurnal Hydrolab®

survey was executed in conjunction with collection of fish for heavy metal analysis in the Bessey Creek

C-23 system.

EPA’s Storet water quality database was used extensively as a source of historical water quality information. Data produced by USGS, SFWMD, as well as FDER’s own data was employed in the

preparation of this report. Lists of Storet stations used for data analysis are given in Appendix A.

Summary raw data inventories for groups of stations as shown in Appendix A are given in Appendix B.

Flow data used in the computation of loadings are given in Appendix D. Rainfall data is given in

Appendix E.

The North and South Forks of the St. Lucie River system were considered outside the scope of this

report and were not included in its preparation. Future water quality assessments will be forthcoming as

a result of FDER’s bioassessment program.

5
6

Figure 3. St. Lucie River Sampling Network
7

Results and Discussion

Biology

Because of the harsh conditions inherent to estuaries, few macroinvertebrate species can thrive in them.

As a result, the production and numbers of individuals are often dominated by a few tolerant species

(Kennish, 1986). This numerical dominance of one or a few species makes traditional benthic statistics

such as the Shannon-Weaver diversity index difficult to use in a meaningful way; this index gives higher

values for stations which have few individuals in many taxa than for stations with many individuals in few

taxa. Since this latter case is the rule for most estuarine communities, the diversity indices calculated

may be misleading if used to compare stations. Hence, this discussion will concentrate on numbers of

taxa, numbers of individuals, and dominant organisms because this information is more germane to the

conditions at each station at the time of sampling.

The identities and numbers of each taxa are listed in Appendix C for each station. The numbers of

organisms and taxa, the Shannon-Weaver Diversity Index, and the Equitability Index were calculated

(Table 3). The number of taxa in major taxonomic groupings was listed (Table 4). Sorenson’s Index of

Similarity was calculated (Table 5).

STATION 1

Station 1 (located at the mouth of the Bessey Creek - C-23 system) was sampled during all sampling

events. The substrate at this station was muck. The numbers of organisms collected were always lower

at this station compared to other concurrently sampled stations. The number of taxa collected was also

low except in the July collection when several opportunistic insects (Chironomidae) were found. Diversity index values were moderate at this station, because no one species occurred in large enough numbers

to depress the index value.

Since Station 1 was the closest of stations within Bessey Creek to the ocean, it had the highest conductivity/salinity sampled on February 11, 1992. Conductivity was 38,100 μmhos/cm at the bottom (about

24 ppt salinity or 69% seawater) and 34,700 μmhos/cm at the surface (about 22 ppt salinity or 63%

seawater). The conductivity of seawater is approximately 53,000 μmhos/cm.
8

Table 2. Bessey Creek Biological Sampling Physical Data Summary

FEBRUARY 11, 1992

STA DEPTH TEMP. DIS. O2 COND. pH

 (FEET) (DEG C) (PPM) (UMHOS) (UNITS)

1 10 18.3 6.5 38100 8.1

5 18.2 8.1 35300 7.3

1 18.7 8.3 34700 7.2

 5 8 18.8 6.9 37900 8.0

4 19.6 7.5 34800 7.7

1 19.8 7.8 27600 7.6

 8 3 20.2 2.2 31500 7.9

1.5 19.3 1.5 19200 7.8

0.5 18.2 3.7 7000 7.7

 9 4 18.4 8.8 35200 8.2

2 18.5 8.6 35200 7.7

1 18.5 8.5 35200 7.6

APRIL 22, 1992

 1 9 23.8 3.8 36000 7.6

4.5 24.2 6.9 35100 7.8

1 26.1 7.3 29600 7.8

 10 6 24.8 7.0 35000 7.7

4 25.3 7.2 34400 7.8

1 25.7 7.4 33300 7.9

JUNE 30 - JULY 1, 1992 (AVERAGES)

 1 NA 27.6 4.0 503 7.1

 5 NA 27.3 3.3 376 7.1

 7 27.8 3.5 188 6.9

JULY 16, 1992

 1 9 29.8 2.2 2810 6.9

4.5 29.6 3.7 1550 6.7

0.5 31.1 5.9 1370 6.6

 10 7 30.1 3.4 4330 6.8

3.5 30.0 3.7 3910 6.8

0.5 30.4 3.8 3270 6.9
Table 3. Bessey Creek Biology Data Summary

 FEBRUARY 11, 1992

PARAMETER STA 1 STA 5 STA 8 STA 9

# OF ORGANISMS 135 915 312 651

# ORG./SQUARE METER 1,875 12,708 4,333 9,042

# TAXA 14 22 8 28

DIVERSITY INDEX 2.73 1.82 1.84 1.77

DI CONFIDENCE INTERVAL 0.26 0.13 0.13 0.19

EQUITABILITY 0.65 0.21 0.58 0.16

SUBSTRATE MUCK MUCK, SAND SAND,

 CLAY, SHELL

SAND

 APRIL 22, 1992 JULY 16, 1992

 STA 1 STA 10 STA 1 STA 10

# OF ORGANISMS 155 722 239 487

# ORG./SQUARE METER 2,153 10,028 3,319 6,764

# TAXA 19 33 25 20

DIVERSITY INDEX 2.65 2.73 2.14 2.35

DI CONFIDENCE INTERVAL 0.30 0.16 0.31 0.16

EQUITABILITY 0.46 0.28 0.23 0.34

SUBSTRATE MUCK MUCK, MUCK MUCK,

 SHELL SHELL

9
Table 4. Bessey Creek Number of Taxa in Major Groups

FEBRUARY 11, 1992

MAJOR TAXA STA 1 STA 5 STA 8 STA 9

MOLLUSCA:

GASTROPODS 3 4 0 1

BIVALVES 2 4 1 10

ANNELIDS 5 5 5 8

CRUSTACEANS 3 4 1 5

INSECTS 1 4 1 3

APRIL 22, 1992

MAJOR TAXA STA 1 STA 10

MOLLUSCA:

GASTROPODS 4 4

BIVALVES 3 7

ANNELIDS 8 10

CRUSTACEANS 4 7

INSECTS 0 0

FISH 2 0

JULY 16, 1992

MAJOR TAXA STA 1 STA 10

MOLLUSCA:

GASTROPODS 2 2

BIVALVES 1 1

ANNELIDS 6 3

CRUSTACEANS 3 9

INSECTS 12 5

10
ST 1 5 8 9

 1 0.33 0.18 0.38

 5 0.2 0.4

 8 0.28

 9

FEBRUARY 11, 1992

 STA/DT 1 10 1 10

 4/22 4/22 7/16 7/16

 1

 4/22 0.52 0.13 0.2

 10

 4/22 0.14 0.35

 1

 7/16 0.44

 10

 7/16

APRIL 22 AND JULY 16, 1992

Table 5. Bessey Creek Similarity Indices

11
12

Although somewhat lower, April conductivities were similar. In the latter part of June this area experienced a period of ten days of heavy rains. These rains caused large quantities of freshwater to flow into

the St. Lucie Estuary, making it fresh. A diurnal study of water quality in the Bessey Creek system

conducted June 31 through July 1, 1992 found the C-23 canal flowing heavily. The average conductivity for this sampling event was 503 μmhos/cm (see Table 1). This conductivity corresponds to a salinity

of 0.33 ppt or 1% the salinity of seawater. This low salinity event was further investigated with more

benthic sampling July 16, 1992 at Station 1 and Station 10 (which was also sampled concurrently with

Station 1 in April). The conductivity on this date was 1,370-2,810 μmhos/cm (top to bottom), which is

roughly 1-2 ppt salinity or 3-5% of seawater.

The numbers of organisms and taxa were low during the February and April collection, while in July the

number of taxa increased. Annelids were the most diverse major taxonomic group collected at this

station during February and April, while insects were the most taxa-rich group in July. Two species of

benthic fish were collected at this station in April. The dominant species collected in February and April

were the mollusc, Mulinia lateralis, and the amphipod, Grandidierella bonnieriodes. The July samples

were dominated by the polychaete worm, Streblospio benedicti, and a variety of Chironomid midges

(Insecta). Many freshly dead shells of Mulinia lateralis were found in the samples taken at Station 1

during July; these appear to have been killed by the influx of fresh water. Several chironomid species

were represented by single individuals which inflated the taxa total for this collection. Streblospio is an

opportunistic species (one which is present in low or moderate numbers during normal conditions, when

it can be out-competed by other species, but “blooms” when conditions become inimical to the other

species). Streblospio can tolerate low salinities to about 1 ppt (personal communication, Doug Farrell,

Tampa FDER). Chironomids are also opportunistic and are generally found in freshwater.

In July aquatic weeds were common (having floated down with the fresh water). About one centimeter

of fresh detritus was noted in the samples taken at this station in July. Two species of worms collected

(Aulodrilus pigueti and Bratislavia unidentata) may have been associated with this detritus. The substrate at this station was composed of black organic muck and was presumed to be poor

macroinvertebrate habitat. However, the persistent presence of macroinvertebrates (and the collection

of the two fish, Gobionellus hastatus and Myrophis punctatus, in one sample) shows that this muck is not

a “sterile” habitat.

STATION 5

Station 5 (located just inside the natural Bessey Creek from the C-23 Canal) was sampled only on

February 11, 1992. The substrate was composed of muck mixed with small amounts of sand and clay.

The number of organisms collected at this station was the highest of all collections made for this study.

The number of taxa collected was also high. The diversity index calculated for this station was low due

to high numbers of individuals in a few species. The most abundant taxa were the mollusca, Mulinia

lateralis and Mytilopsis leucophaeata, and Hydrobiid snails, with Grandidierella bonnieriodes also being

common.
13

Station 5 was the second most freshwater influenced station sampled on February 11, 1992. It is

located in an area of transition between the “natural” Bessey Creek and the altered Bessey-Creek/C-23

junction. The numbers of organisms were high, and the number of taxa was moderate to high. The

variation in conductivity at this station was less than at Station 8 (the bottom conductivity value was

37,900 μmhos/cm, roughly 24 ppt salinity or 69% seawater; the surface conductivity was 27,600 μmhos/

cm, roughly 17 ppt or 49% of seawater).

The taxa found at this station were evenly dispersed among five major groups. Dominant organisms

collected at this station included the bivalves Mulinia lateralis and Mytilopsis leucophaeata and the

gastropod family Hydrobiidae. The amphipod Grandidierella bonnieriodes was also common. Mytilopsis

and the Hydrobiids are considered freshwater tolerant, while Mulinia and Grandidierella are tolerant of

somewhat lowered salinities, but not to the extent of the former two taxa (Doug Farrell, Tampa FDER,

personal communication). Thus this station appears to have experienced moderate salinity stress in the

period preceding sampling.

STATION 8

Station 8 (located one and one half mile upstream of the Murphy Road bridge in “natural” Bessey

Creek) was sampled once on February 11, 1992. The substrate was composed of fine white sand. The

number of organisms collected was low, with only Station 1 having fewer. The number of taxa collected

was the lowest of all collections made for this study. The diversity index was also low. The most

abundant taxa collected were Mytilopsis leucophaeata and the Spionid polychaete worms Streblospio

benedicti and Polydora ligni.

Station 8 was the most freshwater influenced station of the stations sampled on February 11, 1992,

being located in the “natural” part of Bessey Creek which receives a fairly steady flow of semi-natural

runoff. The number of organisms collected at this station was moderate to low, while the number of taxa

collected was very low. These numbers indicate that the benthic community at this station was stressed.

The most obvious stress appears to be salinity variation; the conductivity measured at the bottom at the

time of sampling was 31,500 μmhos/cm, while the surface conductivity was 7,000 μmhos/cm. These

values correspond roughly to salinities of 19 ppt (parts per thousand) and 3 ppt respectively, or 54%

and 9% of seawater. Thus, the macrobenthic community at this station could be presumed to experience considerable variation in salinity during a tidal cycle, limiting the species to those with wide tolerances

of salinity variation. This would be expected at this station due to drainage from the extensive basin

which flows to and through this site.

Annelids were the only well represented major group at this station; this lack of balance among major

taxa is an indicator of stress. The dominant organisms collected, the bivalve Mytilopsis leucophaeata

and the Spionid polychaetes Streblospio benedicti and Polydora ligni prefer lower salinities. Polydora

and other Spionids will compete with Streblospio in salinities of this range. The absence of the bivalve

Mulinia lateralis may show that this station was subject to even lower salinities that those measured.

Mulinia lateralis is tolerant of conductivities as low as 6,000 μmhos/cm or salinities of 5 ppt (Doug

Farrell, Tampa FDER, personal communication).
13

STATION 9

Station 9 (located in the estuary, 100 yards west of Jenkins Point) was sampled once on February 11,

1992. The substrate was composed of coarse sand mixed with a small amount of shell fragments. The

number of organisms collected was high, as was the number of taxa collected. The diversity index was

low, due to many individuals of one species collected (Mulinia lateralis).

Other than Station 1, Station 9 had the highest conductivity of stations sampled on February 11, 1992.

Conductivity was 35,200 μmhos/cm from top to bottom, indicating that the water was well mixed and

that a salt wedge was lacking at this station. This conductivity corresponds to a salinity of about 22 ppt

or 66% of that of seawater.

Numbers of taxa and organisms collected at Station 9 in February were high, perhaps reflecting the

relative stability of conditions at this station. Bivalves and Annelids were the best represented major

groups, with Crustaceans also being well represented. The highest number of bivalves was collected at

this station, and the presence of many Annelids and Crustaceans may further reflect stability. Mulinia

lateralis was the dominant species at this station.

STATION 10

Station 10 (located in the estuary, 100 yards north of Dyer Point) was sampled on April 22, and July 16,

1992. The substrate was composed of muck and shell in an approximate 3:1 ratio. The number of

organisms and taxa collected was high, although both were lower in the July samples. The diversity

index was moderate for this station, though it was also lower for the July sampling period. In April

Mulinia lateralis and Mytilopsis leucophaeata were the most common macroinvertebrates collected. In

July Streblospio benedicti, Mytilopsis leucophaeata, and Grandidierella bonnieroides were most abundant.

Station 10 was sampled before and after the rain event. In April conductivity was 33,300-35,000

μmhos/cm (top to bottom), about 21-23 ppt salinity or 60-66% of seawater. The conductivities recorded for July were 3,270-4,330 μmhos (top to bottom), or about 2.2-2.8 ppt salinity or 6-8% of

seawater. This station was doubtless subjected to the freshwater pulse from the rain event (conductivities ~500 μmhos/cm or about 1% salinity of seawater).

All major groups (Gastropoda, Bivalvia, Annelids, and Crustaceans) were well represented at Station

10 during the April sampling, indicating a relatively stable and balanced macroinvertebrate community.

By contrast, in July numbers of Gastropods, Bivalves, and Annelids decreased substantially. Numbers

of Crustaceans increased somewhat, and five species of insects appeared. These changes reflect the

disruption in the benthic community caused by the rapid change in salinity from the rain event. A fairly

large decline in numbers of taxa and individuals counted can also be attributed to the freshwater influx.

The April collection at Station 10 reflected the most healthy benthic community sampled during this

project; when sampled again in July the macrofauna appeared substantially degraded.
14

Overview of Biological Results

The biological results of this study can be divided into two periods: one corresponding to the time

before the heavy rains at the end of June, 1992, and one after the resultant influx of freshwater to the

estuary. Before the rain event there was a gradient of freshwater influence from the mouth of the

“natural” Bessey Creek (near Station 8 where a semi-natural drainage basin was flowing nearly continuously) out into the estuary proper (Stations 9 and 10). Opportunistic and freshwater tolerant species

(such as Mytilopsis leucophaeata and Streblospio benedicti) dominated only at further upstream locations (especially Station 8). More typically brackish adapted species (such as Mulinia lateralis) dominated

at the stations in the estuary proper (Stations 9 and 10). Similar upper estuary communities were

sampled by Rudolph (1990) and Haunert and Startzman (1985). At the stations between these two

extremes (Stations 1 and 5) a mixture of species was found, with the amphipod Grandidierella bonnieriodes

being typical of the intermediate condition.

After the rain event there was a dramatic shift in the communities at Stations 1 and 10 to dominance of

tolerant or opportunistic species typified by Streblospio benedicti and freshwater insect larvae (especially Chironomidae). A South Florida Water Management District study of the effects of a large

freshwater discharge documented a similar faunal shift (Haunert and Startzman, 1985). Large populations of the bivalve Mulinia lateralis appeared to have been extirpated by the rapid change in salinity

caused by the freshwater inflow. Haunert and Startzman (1985) also found Mulinia lateralis to be

eliminated at several stations in the upper estuary by the large flow of freshwater they studied.

Except Station 1 (where it is unclear whether poor substrate, depth, low dissolved oxygen, or contaminants from the C-23 Canal reduced numbers of taxa and individuals), substrate appears to have played

a secondary role in determining the composition of the benthic macroinvertebrate communities. For

instance, the invertebrates found at Station 9 were more similar to those collected at Station 1 than those

collected at Station 8 (see Table 5), though the substrates at Stations 8 and 9 were both primarily sand

while that at Station 1 was muck. Stations 1 and 10 were more similar to each other for a particular date

than they were to themselves for a different date. Stations 1 and 10 were much more similar to each

other in April than was Station 1 to itself for the April and July sampling events, during which interval the

salinity changed drastically (see Table 4). The effect of salinity (whether due to rain events or to normal

estuarine longitudinal salinity gradient) appears more important than substrate in determining which species could dominate at a particular station.

The bivalves Mulinia lateralis and Mytilopsis leucophaeata were dominant at Station 10 in April. In July

Streblospio benedicti, Mytilopsis leucophaeata, and Grandidierella bonnieriodes dominated. Many freshly

dead shells of Mulinia lateralis were collected at Station 10 in July. As with Station 1, there was a clear

shift in the benthic community at this station from species that tolerate moderate salinities (such as

Mulinia) to opportunistic species which tolerate very low salinities (Streblospio and Chironomidae).
15

Chemistry

Bessey Creek Water Quality

Existing data on Bessey Creek consists of the results of sporadic, unrelated sampling efforts carried out

by FDER in 1978, 1987, and 1992. For comparison, the Bessey Creek - C-23 system can be divided

into three sections: “natural” Bessey Creek, C-23-influenced Bessey Creek, and Hidden River. The

Storet stations used for this analysis are listed in Appendix A. “Natural” Bessey Creek is considered to

be that portion of Bessey Creek not immediately contiguous with C-23. Tables 7 and 8 summarize

selected water quality parameter averages for the “natural” and C-23-influenced sections of Bessey

Creek. Hidden River was only sampled once in 1992.

As the variability within any system increases, the number of samples (data points) that are required to

determine a meaningful average for that parameter increase. Thus the ranges (LCL to UCL) for each

parameter represent the range of values within which the average for that particular parameter might be

statistically expected to fall with a confidence of 95% (95% confidence interval for the mean). A wide

range should be interpreted as meaning that the historical data is too scant to account for the variation

observed. Units and terms are explained in Table 6.

Table 6. Key to Abbreviations, Terms and Units of Measurement

LCL - Lower 95% Confidence Limit of Mean

UCL - Upper 95% Confidence Limit of Mean (midpoint between LCL and UCL

 lies the mean or average value)

Nobs - Number of Observations

Maximum - maximum value reported

Minimum - minimum value reported

ppm - parts per million

 ppb - parts per billion

 mg/l - milligrams per liter; ppm

 μg/l - micrograms per liter; ppb

mg/Kg - milligram per kilogram; ppm

 μg/Kg - microgram per kilogram; ppb

DO - Dissolved Oxygen, mg/l

Cond. - Conductivity, Tmhos/cm

TKN - Total Kjeldahl Nitrogen, mg/l (total nitrogen minus nitrate/nitrite nitrogen)

TP - Total Phosphate, mg/l

F.Coli - Fecal Coliform, # colonies /100ml

NTU - nephelometric turbidity units

TSS - nonfilterable residue or total suspended solids

r

2

 - sample correlation coefficient (statistic: how well a calculated trend actually fits

 the data; 1.0 indicates a perfect fit)
16

Table 7. C-23-influenced Bessey Creek

Parameter Nobs LCL UCL Minimum Maximum

DO 101 4.45 5.27 0.1 11.8

pH 95 7.10 7.24 6.0 8.1

Cond. 95 9580 16300 299 47100

TKN 11 0.703 0.904 0.62 1.23

TP 11 0.105 0.160 0.08 0.201

F.Coli 9 19.8 73 <5 127

Table 8. “Natural” Bessey Creek

Parameter Nobs LCL UCL Minimum Maximum

DO 44 3.05 3.75 1.4 8.3

pH 45 6.88 7.11 6.4 7.9

Cond. 44 3330 11000 162 43300

TKN 7 0.619 3.17 0.230 4.60

TP 7 -0.32 1.90 0.099 4.17

F.Coli 6 99.6 456 40 650

C-23-influenced Bessey Creek typically meets dissolved oxygen standards while the “natural” stream

area does not. All of Bessey Creek is subject to periodic low dissolved oxygen concentrations, particularly near the bottom. The C-23-influenced area is subject to more strongly anoxic bottom conditions,

presumably due to the greater depths in concert with greater benthic oxygen demand. Both areas

experience stable pH, with the “natural” area being slightly more acidic. Both areas are subject to

conditions that range from almost entirely salty, with respect to ocean water, to completely fresh. The

“natural” area, which is more removed from the estuary, was somewhat fresher.
17

The nutrient regime in C-23-influenced Bessey Creek appears more stable than that in the “natural”

area, where wide swings of nutrient content are documented. However, wide swings in nutrient content

have been documented upstream of the spillway (see C-23 Water Quality section), thus it is reasonable

to surmise that the appearance of stability is due to lack of data. There is insufficient data to assess

bacteriological water quality in Bessey Creek, though it appears that the “natural” area may be more

prone to elevated levels of fecal coliform bacteria. The majority of residences in this area are on septic

tanks which have a history of frequent failure due to high water table levels and soil conditions.

A diurnal (24 hour) survey was executed from June 30 through July 1, 1992, in an attempt to assess the

variation in dissolved oxygen regime. During daylight hours, photosynthesis, and the concurrent production of oxygen, may make it appear that dissolved oxygen content is acceptable. However, once the

sun goes down and photosynthesis ceases, oxygen concentrations may plummet. The intended purpose

of the diurnal survey was thwarted by the influx of large quantities of fresh water from C-23; the resulting

turbulence and aeration served to keep dissolved oxygen concentrations fairly constant throughout the

course of sampling. Only the station located in Hidden River (somewhat removed from the effects of the

rapid flow down C-23) showed a diurnal oxygen depression (Figure 4).

Figure 4
18

A series of nine biochemical oxygen demand (BOD) measurements were carried out during the diurnal

survey in “natural” Bessey Creek. These samples averaged 5.0 mg/l with a maximum of 6.1 mg/l. Two

additional samples taken in May, 1992, from “C-23-influenced Bessey” reported a BOD of 7.2 mg/l.

Though none of the BOD measurements were from Hidden River, it may be arguably stated that the

observed water column BOD’s were insufficient to account for the dissolved oxygen sag depicted in

Figure 4. This observed sag was probably due to the oxygen demand of the sediment. Experiments

conducted by the FDER Southeast District laboratory showed that the average BOD of six samples of

unconsolidated bottom material collected from within the estuary was around 550 mg/l.

Canal C-23 Water Quality

Canal C-23 is a significant source of freshwater to the estuary. To assess the quality of water being

discharged, Storet data from stations located in C-23 upstream of the Bessey Creek basin were analyzed. The Storet stations involved are given in Appendix A.

Figure 5 shows the concentration of total nitrogen in samples collected from C-23 during the period

1976 to 1992. Total nitrogen is defined as the sum of organic nitrogen (nitrogen bound up in organically

derived molecules) and inorganic nitrogen forms of ammonia nitrogen (NH3 / NH4

+

), nitrite nitrogen

(NO2

-

) and nitrate (NO3

-

) nitrogen. The average concentration of the 214 total nitrogen samples collected was 1.49 mg/l with no detectable trend over time.

Figure 6 depicts the concentration of total phosphate in samples collected from C-23 during the same

period. Total phosphate is defined as the sum of organic and inorganic phosphate (PO4

-3). The average

concentration of the 213 total phosphate samples collected was 0.18 mg/l with no detectable trend over

time.

 Figure 5 Figure 6
19

Figure 7 illustrates the concentration of nonfilterable residue or total suspended solids (TSS) in samples

collected from C-23. The average TSS for the 182 samples collected during this period was 5.1 mg/l

with no detectable trend over time. Figure 8 shows the turbidity in nephelometric units (NTU) in samples

collected from C-23. The average turbidity for the 213 samples collected was 4.1 NTU with no

detectable trend over time. One observation (52 NTU) violated the water quality standard given in

FAC 17-302.510.

Quality standards for heavy metals in freshwater are based upon total hardness. Using the standard

equations given in FAC 17-302, and the average total hardness found in C-23 of 313 mg/l, it was

possible to estimate applicable standards. These standards, in Tg/l for “total recoverable metals”, are

shown in Table 9.

 Figure 7 Figure 8

 Table 9. Total Recoverable Metal Standards for C-23, Tg/l

Cu Cd Cr Pb Ni Hg As

 31.3 2.78 23.2 13.6 40.3 ≤0.012 ≤50

Twenty-three water samples were analyzed for copper during the period 1984 - 1991. The average

concentration was 3.8 μg/l with a high value of 13 μg/l in March, 1985. Twenty-one water samples

were analyzed for cadmium during the same period, with an average of 0.52 μg/l and a maximum of 3

μg/l, which may represent a violation of FDER standards. Of the seven water samples analyzed in 1981

for chromium, four had detectable concentrations (0.2 - 0.7 μg/l) of chromium. Twenty-three samples

were collected 1984-1991 for lead, which averaged 0.84 μg/l, with a maximum of 2 μg/l. Of the two

water samples collected for nickel analysis, detectable levels of 5 and 11 μg/l were reported in February,

1979, and August, 1981 respectively. Of the 21 water samples analyzed, two samples had detectable

levels of 0.2 and 0.4 μg/l of mercury, which may represent a violation of water quality standards. Twentythree samples for arsenic averaged 1.4 μg/l.
20

Of the five sediment samples analyzed by USGS 1976 - 1977, two exhibited detectable concentrations

(0.01 μg/Kg) of the DDT decomposition products, DDD and DDE, and one showed detectable concentrations (1.00 μg/Kg) of Ethion. Of the five water samples analyzed by USGS 1976 - 1977, three

of these had detectable concentrations (0.01, 0.04, 0.04 μg/l) of Ethion, two indicated detectable concentrations (0.01 μg/l) of Diazinon and (0.14 μg/l) of the herbicide 2,4-D, and one with detectable

concentration (0.07 μg/l) of Silvex. No recent (post 1980) data for pesticides or herbicides was available.

SFWMD provided flow data which is measured at the S-97 spillway on C-23 near the turnpike (see

Appendix D). In those instances where a sample was collected on a particular date and there was flow

data for that day, it was possible to calculate the amount of materials being transported. From review of

this data it could be seen that during periods of high flow samples were rarely taken. Thus Figures 9, 10,

and 11 rarely depict instances when most of the transport is occurring. For reasons of scale on Figure

11, the total suspended solids transport on May 31, 1984 is not shown. Flow on this date was 948 cfs

and TSS measured 30 mg/l in a sample collected by SFWMD at the S-97 spillway. The calculated

amount of suspended solids being transported was estimated at 153,000 pounds for that particular day.

 Figure 9 Figure 10
21

 Figure 11 Figure 12

Using flow information from 1980 through 1985 and the average concentrations of total nitrogen (TN),

total phosphorus (TP) and total suspended solids (TSS) as given above (1.49 mg/l, 0.18 mg/l and 5.1

mg/l), it was possible to estimate the amount of substances being transported (Figures 12, 13 and 14).

During this six year period approximately 2.63 million pounds of nitrogen, 318 thousand pounds of

phosphorus and 9 million pounds of suspended solids were transported to the estuary. Note that the

amount of suspended solids reported is as dry weight. Based upon annual averages for this period, each

year brings about 438 thousand pounds of nitrogen, 53 thousand pounds of phosphorus and 1.5 million

pounds of suspended solids to the estuary.

 Figure 13 Figure 14
22

Canal C-24 Water Quality

Canal C-24 is also a significant source of freshwater to the estuary. To assess the quality of the waters

being discharged, Storet stations located in C-24 were selected. The Storet stations involved in this

analysis are given in Appendix A.

Figure 15 shows the concentration of total nitrogen in C-24 from 1970 to 1992. The average concentration of the 159 total nitrogen samples collected was 1.61 mg/l with no detectable trend over time.

Figure 16 depicts the concentration of total phosphate during the same time. The average concentration

of the 184 total phosphate samples collected was 0.25 mg/l (95% confidence interval: 0.23 to 0.27 mg/

l) with no detectable trend over time. Figure 17 illustrates the concentration of nonfilterable residue or

total suspended solids (TSS) during the same period. The average TSS for the 113 samples collected

was 5.1 mg/l with no detectable trend over time.

Figure 18 displays the turbidity in nephelometric units (NTU) in samples collected from C-24 during the

same time. The average turbidity for the 187 samples collected was 3.0 NTU with no detectable trend

over time. Based upon an average total hardness of 289 mg/l, the Class III fresh water standards for C24 water-column metals are given in Table 10. Nineteen water samples analyzed for copper during the

period 1984-1991 averaged 3.2 μg/l with a maximum of 7 μg/l. Seventeen samples analyzed during this

period for cadmium averaged 0.15 μg/l with a maximum of 0.4 μg/l.

 Figure 15 Figure 16
23

Two samples for chromium were analyzed in 1984; both were 0.9 μg/l. Nineteen samples for lead

analyzed 1984-1991 averaged 3.5 μg/l with a maximum of 9 μg/l (75% of the standard). No reliable

data was available for either nickel or mercury. The maximum value for dissolved arsenic was 17 μg/l.

Table 10. Total Recoverable Metal Standards for C-24, μg/l

Cu Cd Cr Pb Ni Hg As

29.3 2.61 21.8 12.3 37.7 ≤0.012 ≤50

 Figure 17 Figure 18

The average fecal coliform count from forty-three samples taken 1978-1990 was 304/100ml, which

may be a violation of the FDER bacteriological water quality standard. However the 95% confidence

interval for this mean is -54 to 662 fecal coliform per 100ml. Thus the mean being used to substantiate

a violation is the result of considerable variation. However, FAC 17-302 further stipulates that no one

sample may contain more than 800/100ml. On two occasions, February, 1986, and October, 1989,

bacteriological water quality violations of 6680 and 4400/100 ml, respectively, were reported. In

samples taken 1976-1979, USGS reported DDE, DDT and ethion in sediments collected from C-24.

Also reported were detectable concentrations of ethion, diazinon, 2,4-D and silvex in water column

samples. No recent pesticide or herbicide data was available for sediments in C-24.
 24

SFWMD provided flow data which is measured at the S-49 spillway on C-24 near the turnpike (see

Appendix D). In those instances when a sample was collected on a particular date and there was valid

flow data for that day, it was possible to calculate the amount of materials being transported as shown in

Figures 19, 20 and 21.

 Figure 19 Figure 20

 Figure 21 Figure 22
 25

Using flow information from 1980 through 1987 and the average concentrations of total nitrogen, total

phosphorus and total suspended solids as given above (1.61 mg/l, 0.25 mg/l and 5.1 mg/l), it was

possible to estimate the amount of nutrients and suspended solids being transported annually (Figures

22, 23 and 24). During these eight years at least 3.58 million pounds of nitrogen, 555 thousand pounds

of phosphorus, and 11.3 million pounds of suspended solids were transported to the estuary. Estimated

annual transport averages are 448 thousand pounds of nitrogen, 69 thousand pounds of phosphorus,

and 1.4 million pounds of suspended solids.

 Figure 23 Figure 24

Canal C-44 Water Quality

The St. Lucie Canal (SFWMD Canal C-44) is another significant source of freshwater to the estuary.

To assess the quality of the waters being discharged, Storet stations located in C-44 were selected (see

Appendix A).

Figure 25 illustrates the concentration of total nitrogen in samples collected from C-44 during the period

1973 to 1992. The average concentration of the 228 total nitrogen samples collected was 1.48 mg/l

with no detectable trend over time. Figure 26 shows the concentration of total phosphate in samples

collected from C-44 during 1968 to 1992. The average concentration of the 356 total phosphate

samples collected was 0.13 mg/l (95% confidence interval for the calculated mean is 0.118 to 0.136

mg/l) with no detectable trend over time.
26

 Figure 25 Figure 26

Figure 27 displays the concentration of nonfilterable residue or total suspended solids (TSS) in samples

collected from C-44 during 1972-1992. The average TSS for the 245 samples collected during this

period was 7.4 mg/l with no detectable trend over time (95% confidence interval for this mean is 4.7 -

10.0 mg/l). Five of the samples show TSS values greater than 50 mg/l. Figure 28 depicts the turbidity

in nephelometric units (NTU) in samples collected from C-44 during 1972-1992. The average turbidity

for the 323 samples collected was 5.7 NTU with no detectable trend over time. The 95% confidence

interval for this calculated mean is 4.7 to 6.8 NTU. Water quality violations for turbidity are defined in

FDER rules as samples that measure greater than 29 NTU “above natural background”. Using 6.8

NTU, the upper 95% confidence interval, as “natural background”, there are seven instances when

turbidity in C-44 violated the state water quality standard (see Table 11).

 Table 11. Turbidity Violations in C-44

Agency Date Turbidity

USGS 78/03/15 40

USGS 83/03/22 55

FDER 83/03/03 72

FDER 83/03/03 83

SFWMD 83/02/24 77

SFWMD 83/03/24 37

SFWMD 83/04/21 55
 27

Based upon an average total hardness of 199 mg/l, the Class III fresh water standards for C-44 watercolumn metals are given in Table 12. Sixty-seven water samples analyzed for copper during the period

1972-1991 averaged 3.2 μg/l with a maximum of 12 μg/l. Forty-four samples analyzed during the same

period for cadmium averaged 0.67 μg/l with three possible violations reported (4 μg/l in 1978 by USGS,

and 5 μg/l in 1976 and again in 1987 by FDER). Sixty-eight samples for lead analyzed 1984-1991

averaged 3.5 μg/l with high values of 15 and 10 μg/l reported by USGS in 1978 and 1979 respectively;

recent data fails to confirm these values. No reliable data is present for nickel. Of the thirty-six water

samples analyzed for mercury from 1971-1991, several had detectable concentrations of 0.1 to 0.2 μgl.

These values are near the detection limit of the instrumentation, and may be unreliable. Higher, perhaps

more reliable, values of 0.7 μg/l were reported by USGS in 1985 and 0.4 μg/l by SFWMD in 1989.

Maximum value reported for dissolved arsenic was 17 μg/l.

 Figure 27 Figure 28

 Table 12. Total Recoverable Metal Standards for C-44, μg/l

 Cu Cd Cr Pb Ni Hg As

 21.3 1.95 16.0 7.64 27.5 ≤0.012 ≤50
 29

The average of fecal coliform data from the ninety-nine samples taken in the period 1978-1990 was

158/100ml. On February 2, 1978 a single bacteriological water quality violation of 12,500/100 ml was

reported. During 1978-1979, USGS reported by-products of DDT (DDE & DDD), PCB’s and dieldrin in sediments collected from C-44. No organic contaminant data was available after 1979.

The 148 determinations of dissolved solids transport by USGS from 1957-1980 indicate that C-44

transported an average of 798 tons/day of dissolved solids. Of these figures, nine measurements showed

dissolved solids transports of greater than 2000 tons/day, the most recent figure being 3120 tons/day

reported June 23, 1978. On October 15, 1979, USGS determined that the total suspended solids

transport was 105 tons/day (210,000 pounds/day). SFWMD provided USGS flow data measured at

the S-80 spillway located on C-44 west of the turnpike (see Appendix D). In those instances where a

sample was collected on a particular date and there was valid flow data for that day, it was possible to

calculate the amount of nutrients and suspended solids being transported annually (Figures 29, 30 and

31).

 Figure 29 Figure 30

 Figure 31
 30

Using flow information from 1980 through 1990 and the average concentrations of total nitrogen, total

phosphorus and total suspended solids as given above (1.48 mg/l, 0.13 mg/l and 7.4 mg/l), it was

possible to estimate the annual transport (Figures 32, 33 and 34). During this eleven year period at least

11.9 million pounds of nitrogen, 1.04 million pounds of phosphorus, and 59.3 million pounds of suspended solids were transported to the estuary. Estimated annual transport averages are 1.1 million

pounds of nitrogen, 95 thousand pounds of phosphorus, and 5.4 million pounds of suspended solids.

 Figure 32 Figure 33

Figure 34
 31

Other Tributaries to the Estuary

Tables 13 through 20 summarize available data from minor tributaries to the estuary. Refer to Appendix

A for a list of the Storet stations used in this analysis. There was no flow data available to assess the

quantity of water, and consequently the stream load of pollutants each tributary may be transporting is

unknown.

Winters/Blakeslee Creek drains a comparatively large area west of the Turnpike including agricultural

lands as well as areas of the Port St. Lucie development. These residential areas are largely served by

septic tank systems. A stormwater detention pond was constructed east of the turnpike, however it was

designed to detain water, not remove stormwater-borne pollutants. The quality of water being contributed to the estuary violates water quality standards for dissolved oxygen and possibly for fecal coliform

bacteria (see Table 13).

 Table 13. Winters/Blakeslee Creeks

 Turbidity DO pH TKN TP F.Coli

 Mean 15.7 3.485 6.95 0.9693 0.145 243.3

 #Obsvtns 81 175 151 75 75 60

 Std.Dev. 23 1.953 0.4245 0.2669 0.0752 399.87

 95%LCL 10.7 3.2 6.88 0.909 0.128 142

 95%UCL 20.7 3.8 7.02 1.030 0.162 344

Frazier Creek drains commercial and sewered residential areas in Stuart. There are no known stormwater controls in place at this time, however, the City of Stuart is currently negotiating contracts. There

is insufficient data available on Frazier Creek (see Table 14). Frazier Creek had frequent bacteriological violations in the period 1987-88 due to infiltration and the resultant system overloading from a leaky

wastewater collection system (FDER data not on Storet).

 Table 14. Frazier Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 9 4.7 7.44 0.885 0.155

 #Obsvtns 1 3 5 2 2 0

 Std.Dev. 0.361 0.207 0.36 0.035

 95%LCL 9.0 4.3 7.26 0.386 0.106

 95%UCL 9.0 5.1 7.62 1.384 0.204
 32

Krueger Creek drains Stuart residential areas partly on septic tanks and partly sewered. There are no

known stormwater controls in place at this time, however the City of Stuart is currently negotiating

contracts. From the small amount of data available, water quality problems are not apparent (see Table

15).

 Table 15. Krueger Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 5.03 7.63 0.53 0.075

 #Obsvtns 0 3 3 1 1 0

 Std.Dev. 1.415 0.058

 95%LCL 3.4 7.56 0.530 0.075

 95%UCL 6.6 7.70 0.530 0.075

Poppolton Creek drains residential areas in Stuart, most of which is on septic tanks. There are no

known stormwater controls in place at this time, however the City of Stuart is currently negotiating

contracts. The water being discharged into the estuary has shown water quality violations for fecal

coliform bacteria on occasions in the past (see Table 16).

Table 16. Poppolton Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 2.83 4.84 7.34 0.848 0.157 720

 #Obsvtns 4 13 13 5 5 4

 Std.Dev. 1.34 0.929 0.45 0.242 0.042 1204

 95%LCL 1.5 4.3 7.10 0.636 0.120 -460

 95%UCL 4.1 5.3 7.58 1.060 0.194 1900

Danforth Creek drains agricultural and residential areas of Palm City. The residential areas are on septic

tanks. Older developments in the watershed lack stormwater controls while newer subdivisions have

them. The water being discharged from Danforth Creek does not meet standards for dissolved oxygen

or fecal coliform bacteria. There were periodic violations of the turbidity standards (see Table 17).
33

 Table 17. Danforth Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 10.92 3.59 7.11 0.838 0.158 583

 #Obsvtns 11 11 14 11 11 9

 Std.Dev. 17.88 1.512 0.4616 0.228 0.08 549.3

 95%LCL 0.4 2.7 6.87 0.703 0.111 224

 95%UCL 21.5 4.5 7.35 0.973 0.205 942

Howard Creek drains residential areas in Port St. Lucie which are partly sewered and partly served by

septic tanks. Older developments in the watershed lack stormwater controls while newer subdivisions

have them. Periodic turbidity violations are apparent (see Table 18).

 Table 18. Howard Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 34.45 7.5 7.2 0.917 0.124 22

 #Obsvtns 4 10 6 3 3 2

 Std.Dev. 63.7 2.1736 0.3578 0.1484 0.0385 14.14

 95%LCL -28.0 6.2 6.91 0.749 0.080 2

 95%UCL 96.9 8.8 7.49 1.085 0.168 42

Warner Creek drains mostly sewered residential areas in Rio and Jensen Beach as well as receiving

runoff from the Savannas during periods of high water. Older developments in the watershed, such as

Pine Lake Village and Leilani Heights, lack stormwater controls, while newer subdivisions, such as Pine

Crest Lakes, have them. There is little data available on Warner Creek (see Table 19).

 Table 19. Warner Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 9.9 5.03 7.14 0.525 0.0445

 #Obsvtns 1 3 5 2 2 0

 Std.Dev. 0.551 0.456 0.092 0.0488

 95%LCL 9.9 4.4 6.74 0.397 -0.023

 95%UCL 9.9 5.7 7.54 0.653 0.112
34

Mapp Creek drains agricultural and residential areas on septic tanks in south Palm City. Older developments in the watershed lack stormwater controls while newer subdivisions have them. There is little

water quality data available for Mapp Creek (see Table 20).

 Table 20. Mapp Creek

 Turbidity DO pH TKN TP F.Coli

 Mean 3.7 5.63 7.38 0.855 0.155

 #Obsvtns 1 3 5 2 2 0

 Std.Dev. 0.473 0.239 0.092 0.035

 95%LCL 3.7 5.1 7.17 0.727 0.106

 95%UCL 3.7 6.2 7.59 0.983 0.204

Greater St. Lucie Estuary

Storet water quality stations located within the open expanse of the estuary were used to assess water

quality (see Appendix A). Figure 35 depicts the concentration of total nitrogen in samples collected

from stations within the estuary during the period 1973-1992. The average concentration of the 184

samples was 0.98 mg/l with no detectable trend over time; the 95% confidence interval for this mean is

0.93 to 1.04 mg/l. The highest total nitrogen values in the estuary were evaluated with respect to inflows

from C-23, C-24, and C-44:

On September 23 and 25, 1981, two samples collected in the estuary measured 2.13 and 2.10

mg/l total nitrogen. On September 17 samples were collected from C-23, C-24 and C-44.

Samples from C-23 measured 4.04 mg/l with low flow, from C-24 measured 3.15 mg/l (with an

estimated transport of 7035 pounds of nitrogen to the estuary), and from C-44 measured 1.72

mg/l with low flow conditions.

On March 3, 1983, two samples were collected in the estuary which showed 2.47 and 2.10

mg/l total nitrogen. A sample collected from C-23 on March 3 measured 1.91 mg/l, or less than

that observed in the estuary. However samples collected from C-24 and C-44 on February 24

measured 2.81 and 2.68 mg/l, with an estimated transport of 6896 and 99,745 pounds nitrogen, all respectively.

Figure 36 illustrates the concentration of total phosphate in samples collected during the same time. The

average concentration of the 229 samples collected was 0.18 mg/l with no detectable trend over time;

95% confidence interval for this mean is 0.17 to 0.19 mg/l. Elevated total phosphate concentrations

observed in the estuary were evaluated with respect to discharges from major canals:

On September 10, 1981, a sample from the estuary showed 0.60 mg/l total phosphate. A sample taken

downstream of the structure on C-44 on this date during low flow conditions measured 0.824 mg/l. On

September 17, samples from C-23 and C-24 measured 0.356 and 0.407 mg/l, respectively.
35

 Figure 35 Figure 36

Figure 37 shows the turbidity in nephelometric units (NTU) in samples collected during 1974-1992.

The average turbidity for the 223 samples collected was 6.1 NTU with no detectable trend over time;

the 95% confidence interval for this mean is 5.1 to 7.2 NTU. Three of the observations violated water

quality standards for turbidity (FAC 17-302.510: 29 NTU above background). Figure 38 shows the

concentration of total suspended solids (TSS) in samples collected during the same time. The average

TSS concentration detected was 14.7 mg/l with no meaningful trend over time; the 95% confidence

interval for this mean is 12.7 to 16.6 mg/l.

 Figure 37 Figure 38
36

Figures 39 and 40 show the extreme range of conductivity within the estuary. Within most years conductivity varied from below 5000 to above 30,000 umhos/cm. Figure 40 contains an approximated

trend line which shows the expected decrease in conductivity during the wet months. Figure 41, from

SFWMD’s HR1 continuous monitoring station located in the North Fork of the estuary, also shows

seasonal swings in conductivity from 1988 to 1992.

 Figure 39 Figure 40

 Figure 41
37

Figures 42 and 43 illustrate dissolved oxygen concentrations from SFWMD’s HR1 continuous monitoring station and data extracted from Storet for the entire estuary. The average DO reported by HR1

is 5.2 mg/l, while that of the Storet data is 6.3 mg/l. The higher average found for the latter may indicate

that the North Fork of the estuary experiences lower overall dissolved oxygen concentrations than the

estuary proper. Both sets of data contain many instances when the dissolved oxygen dropped to 1.0

mg/l or less.

Figures 44 and 45 depict the range of pH and color found in the estuary. Depression of pH to below

water quality standards for Class III marine waters was evident in 1976, 1983, 1988 and 1992. In

1976 and 1983, a few of the samples collected had values over 300 Pt-Co color units. This is indicative

of instances of very intensely colored water.

Figure 46 shows the annual discharge of water from C-23, C-24 and C-44. There appears to be a

relationship between high flow rate, depression of pH, and elevation of color. This was most probably

due to an influx of so-called tannic acid, which is commonly associated with freshwater discharges.

However, a statistical relationship between these variables could not be established due to a lack of

data. Figure 47a illustrates the expected annual curve for water temperature. Figure 47b shows an

apparent widening of the range of observed dissolved oxygen values and an increase in the frequency of

low dissolved oxygen conditions during the warmer periods of the year.

 Figure 42 Figure 43
38

 Figure 44 Figure 45

 Figure 46 Figure 47 a
39

 Figure 47 b

Pertinent standards for Class III marine waters in μg/l for “total recoverable metals” are given in Table

21. Twenty-three water samples were analyzed for copper during the period 1972 - 1991. The

average concentration was 18.1 μg/l with a high value of 58 μg/l. Twenty-one water samples were

analyzed for cadmium during the same period, with an average of 0.7 μg/l. Thirteen water samples were

analyzed for chromium; the average concentration was 31 μg/l with a maximum of 100 μg/l. Thirty-four

samples for lead averaged 11.8 μg/l. Five samples for nickel analysis averaged 10.2 μg/l. Fourteen

samples for mercury analysis averaged 0.35 μg/l. Three samples for arsenic averaged 5.1 μg/l. These

numbers indicate possible water quality violations for copper, cadmium, lead, nickel, and mercury.

However it must be noted that low-level atomic absorption analysis in saltwater samples is fraught with

interference; some of the values reported may not be correct. Without further water-column sampling

and analysis, it is not possible to tell which are actual and which may be due to overlooked interference.

However, all of these metals are present in the sediment of the estuary. SFWMD investigations into St.

Lucie estuarine sediments “indicate that arsenic, cadmium, copper, mercury, nickel, and zinc may have

originated from agricultural areas; cadmium, copper, mercury, lead and zinc have been associated with

marinas” (Haunert, 1988).

 Table 21. Total Recoverable Metal Standards for Marine Waters

 Cu Cd Cr+3 Pb Ni Hg As

 2.9 0.3 673 5.6 8.3 ≤0.025 ≤50
40

Storet data shows that several sediment samples collected from the estuary have had detectable concentrations of DDD, DDE and PCB’s. Similar compounds were detected by SFWMD, who reported

detectable levels of PCB’s, DDT, and chlordane (Haunert, 1988).

Median values of selected parameters for Florida estuaries (Friedemann, 1989) and values for the St.

Lucie estuary are compared in Table 22. Using the Estuary Trophic State Index (Hand, 1988) results in

an index of 56.7 for the St. Lucie estuary. For estuaries, 0 to 49 is considered good, 50 to 59 fair, and

60 to 100 poor.

 Table 22. Comparison of Average Parameter Values for the St. Lucie Estuary versus

 Statewide Medians

 Parameter Median St. Lucie

 Total Phosphate, mg/l 0.100 0.178

 Total Nitrogen 0.80 0.98

 TSS, mg/l 17.5 14.7

 Color, PtCo 20 77.3

 Diversity Index 3.0 2.0*

 %DO saturation 82 76

 pH 8.0 7.5

 * NOTE: Old data, 1974 - 1988

Heavy Metals in Sediment

SFWMD reported organic and heavy metal contamination in the sediments of the St. Lucie Estuary.

There was an inverse relationship between quantity of contaminants and particle size (Haunert, 1988).

When freshwater carrying pollutant loads moves seaward it will tend to deposit these loads to the

sediment. This occurs due to flocculation (forming into “tuft-like” masses) of compounds upon contact

with saltier water. Many pollutants such as heavy metals are attracted to these flocculants and settle with

them (Hutzinger, 1980), hence the above noted relationship. In the Bessey Creek sub-basin, fresh

water from C-23 is mixing with brackish water. To investigate what effect flocculation was having on

benthic heavy metal content in the basin, sediments samples were collected at seven sites. At three of

these sites, triplicate samples were collected and analyzed separately to evaluate inter-sample variation.

The results of these analyses are given in Table 23. Employing aluminum:metal ratio nomographs (Schropp,

1988), it appears that copper concentrations may be enriched at Stations 1 and 6. No other metals

show enrichment with respect to aluminum. However, there is substantially more mercury by weight at

Stations 1 and 6 than at the other sites sampled. Stations 1 and 6 are located where flocculation would

be expected to occur.
41

 Table 23. Sediment Metal Concentrations for the Bessey Creek - C-23 System

 Station Rep Al Hg Cd Cr Zn Cu Mn Pb

 1 1 42500 0.17 3U 54 99 51 144 35

 2 53400 0.18 3U 74 117 58 171 51

 3 44000 0.16 3U 60 113 58 164 43

 2 1 17100 0.064 3U 22 36 19 46 14

 2 14400 0.036 3U 19 30 16 43 12

 3 17200 0.045 3U 25 39 20 46 20

 3 1 2850 0.014 3U 5U 7.8 5 8.2 8.9

 2 2500 0.13 3U 5U 8.7 5 7.9 7.6

 3 2030 0.009 3U 5U 6.2 6.5 9.7 7.1

 5 2800 0.019 3U 5U 8.3 5 6.7 7.9

 6 21600 0.11 3U 29 65 37 56 23

 7 2180 0.013 3U 5U 12 5 4 U

 8 9420 0.032 U 13 36 7.3 23 14

 in units of mg/Kg dry weight; bold = enriched with respect to aluminum

Heavy Metals in Aquatic Tissue

Metal biomagnification is the process in which the concentration of heavy metals in each succeeding

trophic (feeding) level increase, with the result that problematic concentrations may develop in the top

carnivores. Small organisms living in the sediment are consumed by small fish, the small fish in turn

consumed by larger fish, etc., with each succeeding population increasing in heavy metal tissue burden.

This is due to the fact that excretion rates are less than consumption rates for the metal involved. Locally, Savannas State Preserve fish mercury content was found to be elevated and a health advisory was

issued in 1990. Elevated concentrations of mercury have also been detected in estuarine game fish from

the Indian River (Strom, 1990).

On June 30, in conjunction with the diurnal Hydrolab® survey, an attempt was made to collect fish

tissue samples for heavy metal analysis. Due to the influx of freshwater and reduced salinities, target

species fled Bessey Creek. The only species that could be collected were gizzard shad and sea catfish.

These were considered unsuitable for analysis. Low conductivities continued in the estuary through the

end of August, therefore it was not possible to collect suitable fish specimens for heavy metal analysis for

this report. A future study is planned for 1993 to address this issue.

A separate effort was made to quantify the extent of heavy metal incorporation in lower level benthic

organisms. Though the biomagnification of heavy metals in top predators was of concern, there is equal

concern that trace quantities of toxic substances might have harmful effects at the bottom of the food

chain. It has been reported that the concentration of metals in the estuarine polychaete worm Nereis

diversicolor was directly proportional to the concentration of the metal in the sediment (Lockwood,

1976). There is a concern that lower level organisms living in the sediment, though not actually high
42

enough up the food chain to experience the effect of biomagnification, could nevertheless be adversely

affected by the substances presence. Such adverse effects could include lower reproduction, lower

growth rates, and avoidance of the contaminated area (van Straalen, 1991). The net effect would be to

reduce the overall primary production of the area involved. In addition, metals enter the food chain at

these lower feeding levels where they may potentially be biomagnified in higher predators. Studying the

levels of metals in lower trophic levels may provide information about biomagnification mechanisms.

Shellfish are considered a priority for monitoring in metal contaminated areas (EPA-600/3-78-103).

On May 14, 1992, samples of Rangia cuneata were collected at Station 1, located at the mouth of

Bessey Creek to the estuary, and samples of Polymesoda caroliniana were collected at Station 6,

located upstream of the juncture of Bessey Creek and C-23. These tissues were analyzed for heavy

metal content (see Table 24).

 Table 24. Heavy Metal Concentrations in Bivalve Mollusks

 Station As Be Sb Cd Cr Cu Pb Ni Se Ag Th Zn Hg

 1 U U U U U 3.48 U 0.3 U U U 6.1 0.088

 6 0.42 U U U U 6.96 U 0.2 U U U 33.3 0.090

 in units of mg/Kg wet weight; “U” denotes below detection

Both samples contained detectable concentrations of mercury and copper. Copper was found in

enriched concentrations in the sediment. Mercury is considered highly bioaccumulative. In similar

experiments, Jensen (1981) found that background concentrations of mercury in the mussel, Mytilus

edulis, were 0.020 mg/Kg and that mussels collected from an estuary near a mercury waste disposal

area contained from 0.040 to 0.138 mg/Kg (wet weight). The concentrations of mercury in mollusc

tissue from Bessey Creek was comparable to the latter range of values.

Overview of Chemical Results

Data has been presented showing high levels of nutrients in the estuary, particularly total phosphate. All

tributaries to the estuary, with the possible exception of Krueger and Warner Creeks, carry an enriched

load of nutrients to the estuary. Flow data was available from canals C-23, C-24 and C-44, thus it was

only possible to calculate loadings from these three major tributaries. Figures have been presented

which show estimated amounts of total nitrogen, total phosphate, and total suspended solids being

delivered to the estuary from the three major canals. Figure 48 illustrates the relative amount of materials entering the estuary from these sources (an incomplete record for canals C-23 and C-24 is presented;

complete flow data was not available for all years within the period 1980-1992).
43

Figure 49 depicts the annual rainfall data for 1980-1990 from two SFWMD rain gauges located in Ft.

Pierce and Jensen Beach. Exact locations and raw rainfall data are given in Appendix E. Figures 50-52

illustrate relationships between average annual rainfall from these two gauges and the quantity of substances being transported to the estuary. Correlation coefficients (r2

) indicate that 81.4% of the variation

in transport of materials for C-23 can be explained by rainfall. Likewise, 83.3% of transport for C-24

and 21.5% of transport for C-44 can be explained by rainfall. r2

 values for C-23, C-24, C-44 are

0.814, 0.833 and 0.215 respectively. The lesser correlation between the transport from C-44 and

rainfall versus that of the C-23 and C-24 canals is the result of a difference in discharge frequency.

Canal C-24 often discharges and C-23 is usually flowing over its simple spillway; both of these canals

respond rapidly to rainfall. On the other hand, canal C-44 is part of a large, complex water storage and

irrigation system linked to Lake Okeechobee and the agricultural areas nearby; management of this

system may temporally uncouple discharges from rain events. Although the relative quantity of materials

transported in Figure 48 appears to have decreased since 1983, this decrease is most probably a

function of decreased rainfall.

 Figure 48 Figure 49

 Figure 50 Figure 51
44

Conclusions

Prior to man-made alterations during the last century, water was delivered to the estuary after flowing

through extensive marsh systems. These marshes slowed the water, allowing it to enter the estuary at a

more continuous rate. The marshes allowed sediments and contaminants associated with the sediments

to settle out within the marsh rather than being delivered to the estuary. In addition, nutrients being borne

in the water column were absorbed by plants and deposited within the marsh when these plants died.

Thus cleaner water reached the estuary at a slower, more constant rate. Under such conditions the

macroinvertebrate community (barring major natural disruptions such as hurricanes) could be expected

to reach a successional stage of “climax community”, the most diverse and productive community for a

particular ecosystem (Whittikar, 1975).

Data has been presented that shows conductivity fluctuations within the estuary have been common

during the period 1980-1992. Conductivity has typically ranged from above 30,000 μmhos/cm to

below 5000 μmhos/cm, often undergoing a rapid transformation from very salty to completely fresh.

For example, the June 1992 rain event resulted in an abrupt lowering of the conductivity of the entire

estuary. Drastic changes in salinity and other biologically relevant water quality parameters results in

conditions that some organisms are not able to tolerate (i.e. the periodic extirpation of Mulinia lateralis).

These types of events reduce the productivity of the estuary and may have negative effects on local

fisheries. Thus, the estuary may be undergoing more rapid and pronounced biological change due to

anthropogenic alteration of its basin.

Stations of differing substrates were compared to themselves and to each other using a similarity index.

This comparison indicated that salinity regime was more important than substrate in determining the

composition of benthic macroinvertebrate communities in the vicinity of the Bessey Creek - C-23 complex. Muck sediments dominated at Station 1 (located at the mouth of the C-23 Canal) where numbers

of taxa and individuals were reduced. While it could not be determined whether poor substrate, depth,

low dissolved oxygen, or canal borne contaminants were responsible for this reduction, it is nevertheless

clear that muck sediments do harbor significant numbers of macroinvertebrates and other animals. Since

salinity fluctuations appear to be a major disrupting influence on the benthic macroinvertebrate community, dredging to change the substrate may not enhance productivity.

Data has been presented which estimates the average annual transport of solids and nutrients to the

estuary from three of the major tributaries. Based upon these estimates, it appears that canals C-23, C24 and C-44 deliver to the estuary at least 1.96 million pounds of nitrogen, 217 thousand pounds of

phosphorus, and 8.31 million pounds of total suspended solids each year. The actual amount of materials being transported from these sources is believed to be much higher than these estimates due to the

following:

1> Flowing waterways are known to transport substances as dissolved matter, particulate mat

ter, and as “bed load”. Bed load is that transport which occurs at the bottom of stream or canal

where particles too heavy to be carried in the water column are “rolled along” by water velocity.

Bed load transport can constitute a large percentage of total transport. Both bed load and

dissolved matter transport have been omitted from the calculation of transport.
45

2> It was apparent from a comparison of flow and analytical data that very few samples were

taken during high flow (rain) events. Nearly 50% of the annual sediment and associated contaminant transport of a stream has been shown to occur in but 3.7 days (Meade, 1985). Thus,

periods when transport might reasonably be expected to be highest were not incorporated into

the estimates.

All the tributaries included in this report, save for Warner and Krueger Creeks, were found to carry

excessive quantities of phosphate. These tributaries undoubtedly contribute to the amount of materials

entering the estuary but the extent of their contribution, though doubtless less than the major canals,

could not be quantified. The North Fork of the St. Lucie River, though outside the scope of the this

report, is most likely another major contributor of sediments and nutrients to the estuary. What has not

been determined is the proportion of substances remaining in the estuary versus those continuing out to

sea, i.e., a mass balance for the system. However, the St. Lucie estuary will act as a “sediment trap” due

to the physical phenomenon known as “estuarine circulation”. It is therefore reasonable that a large

percentage of the materials entering the estuary remain there.

It is the normal geologic fate of an estuary to fill in with sedimentary deposits. Reported rates of

sedimentation in the St. Lucie estuary are on the order of 10 to 20 mm/yr (Schrader, 1984). Mean rates

of sedimentation in normal subtidal zones have been reported to vary within the range of 0.7 to 4.0 mm/

yr (Biggs, 1982). Thus the current rate of sedimentation in the St. Lucie estuary may be proceeding at

a rate between 250% to over 1000% faster than normal. Sediment samples collected from deep

quiescent areas consisted of black gelatinous muck. There was no evidence of the distinctive oxidized

surface layer that normal estuarine sediments should possess (Kennish, 1986). The black anoxic layer

(found sub-surface in normal estuaries) appeared to extend to the surface of the sediment. This condition may be a direct consequence of the excessive rate of sedimentation. If sedimentation rates were

decreased, sediments may remain exposed to the overlying waters long enough to become properly

oxidized. Additions of sediment have been shown to affect the biota at all trophic levels. Sediment can

physically damage organisms, increase turbidity (thereby reducing light availability to primary producers

and sight predators), and clog filtering structures in mollusks. These adverse effects have been shown to

propagate throughout the food web (Farnworth, 1979). It is noteworthy that turbidity violations have

been detected in C-23, C-44 and the estuary.

It has been observed that a large quantity of vegetative matter enters the estuary whenever flow rates

become fast enough to dislodge floating plants such as water hyacinth (Eichhornia crassipes). Following the June 1992 rain event, a one centimeter layer of new vegetative debris was apparent in the estuary

immediately adjacent to Bessey Creek. Some of the taxa collected following this event were invertebrates normally associated with freshwater vegetation. This vegetative transport into the estuary adds to

sediment instability and sediment oxygen demand.

Pesticides, herbicides, and heavy metals have been detected in the sediments from the major canals and

also in the sediments of Bessey Creek and the estuary. It may be assumed that at least some of the

contaminants found in estuarine sediments came from the canal basins. Data has been presented to

suggest that heavy metals are being bio-magnified by lower aquatic organisms (mollusks). Bio-magni-
46

fication of heavy metals in higher order predators may also be of concern. Preliminary FDER work in

the Indian River has indicated that mercury accumulation in estuarine fish is occurring. An in-depth

FDER study is underway to address this concern.

Dissolved oxygen concentrations in Bessey Creek and the estuary at large frequently violate water

quality standards. Depressions in dissolved oxygen below 2.0 mg/l appear to occur most frequently

during warmer months and in deeper waters. The warmer months also exhibit instances of high dissolved oxygen content. These high values are evidence of algae blooms taking place in the estuary; such

blooms are known to be related to high nutrient conditions. By day, these blooms produce oxygen

through photosynthesis, while at night, they become oxygen consumers. Since nearly all of the dissolved

oxygen data presented was collected during daylight hours, the number of instances where dissolved

oxygen concentrations violate FDER standards may be much greater than this data may indicate. In

addition, the diurnal dissolved oxygen and benthic biological oxygen demand results presented indicate

that the bottom sediments exert a large oxygen demand upon the water column. Zero concentrations of

dissolved oxygen on the bottom of the estuary are common.

Nutrient concentrations in C-23, C-24, and C-44 often exceed 2.5 mg/l total nitrogen and 0.25 mg/l

total phosphate. These values indicate poor-quality, nutrient-laden water. In comparison with mean

values from other Florida estuaries, levels of nutrients in the St. Lucie estuary are elevated. Figures 22-

24 and 32-34 appear to indicate that the amount of material being transported into the estuary has been

decreasing. However, since overall transport has been shown to be a function of rainfall and no detectable trend is present that would indicate improving water quality in the canals, the apparent decrease is

an artifact of a decrease in rainfall. There is no evidence that loadings to the estuary have improved

during the period 1980-1992.

Adverse conditions currently present in the estuary are directly attributable to unabated and uncontrolled stormwater runoff. Control of runoff would detain deleterious substances and retain excess

freshwater, ameliorating rapid salinity fluxes. If the rate of sedimentation were decreased, the existing

unconsolidated sediments would begin to consolidate through normal processes. The current problem

lies in the inability of these processes to keep pace with an accelerated rate of deposition. If the rate of

freshwater release to the estuary was better controlled, disruption of biological communities would be

reduced.
Recommendations

Anthropogenic problems in estuaries have been well documented:

“In undisturbed watersheds a natural balance is developed between rainfall, runoff, and the materials

which are removed from the watershed through stream channels. This balance, established over a

long time period, allows the ecosystem, which includes organisms and the conditions providing their

food and habitat, to reach a state of relative stability. ...human activities can alter watershed characteristics leading to changes in streams. Urbanization, the concentration of man’s activities in small

areas, fundamentally alters the watershed. The natural balance of the ecosystem will be changed

leading to short-term and long-term instability in the flora and fauna.” (Roesner, 1988)

Possible solutions to these problems are also well documented:

“It is well known that loadings of nutrients, heavy metals and organic micropollutants can accumulate

in (sediments of) lakes. The lake sediments particularly act as a pollutant trap and under proper

conditions in the water phase and in the sediments an essential part of the loadings may be permanently retained. It is important to note that the removal processes taking place in lake systems have

also been found to be effective in wet detention ponds. Therefore, it is obvious to use these pollutant

removal processes as a principle of treatment for urban stormwater runoff by the establishment of wet

detention ponds. It is a fundamental requirement that these ponds should be considered as treatment

facilities and therefore designed and operated based on an optimal function of the removal processes.” (Torno, 1989)

What must be decided is whether sedimentation will continue to occur in the estuary or in properly

constructed upland stormwater treatment facilities. New developments in the region are required to

have adequate stormwater treatment. However the major stormwater sources to the estuary consist of

older residential and agricultural developments dating back to the turn of the century. The decision must

be made whether to individually retrofit all of these older sources or to treat stormwater on a regional

basis. Either of these options will be expensive. Regional stormwater detention, as a possible stormwater treatment choice, is more likely to prevent pollution to the estuary by intercepting all upstream flows,

would mediate the effects of sudden inflows of freshwater, provide water storage, add recreational

value, and provide a mechanism for maintenance. Small-scale stormwater facilities are seldom maintained properly; a regional facility would be maintained by public agencies.

There are currently no vegetative traps on any of the major canals. These traps would stop floating

debris from entering the estuary. In June, 1992 numerous complaints of rafts of floating plants were

received and the estuary floor was covered with oxygen consumptive vegetation. This large amount of

material entering the estuary contains substantial quantities of nutrients and sediments which contribute

to estuarine loading.

47
To summarize, additional stormwater treatment is necessary to prevent the introduction of pollutants and

large quantities of freshwater from entering the estuary. A variety of alternatives have the potential for

accomplishing this goal. Alternatives that should be considered include:

(1) the construction of large regional detention basins

(2) incorporation of floating vegetation and debris traps on major canals

(3) control structure alteration on discharge canals

(4) construction of wetland treatment areas

(5) re-engineering and maintenance of older stormwater facilities

A regional approach which concentrates on the major discharge canals appears to have the most promise for effective treatment.

48
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