WATER QUALITY, BIOLOGICAL AND
HYDROGRAPHIC STUDY
B. K. ROBERTS CANAL
ALLIGATOR HARBOR, FLORIDA
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TABLE OF CONTENTS
Page
LIST OF FIGURES ii
LIST OF TABLES iii
PROJECT PERSONNEL 1
INTRODUCTION 1
FINDINGS 1
OBJECTIVES 3
STUDY AREA AND STATION LOCATIONS 3
METHODS 3
RESULTS 4
Project Depth 4
Water Levels 4
Flow Through Culverts 4
Dye Tracer Study 4
Groundwater Dynamics 5
Dissolved Oxygen and Water Quality Standards ... 8
PHYTOPLANKTON-CHLOROPHYLL a 9
Water Column Metabolism 9
Light Transmission . 9
WATER CHEMISTRY 9
SEDIMENT CHEMISTRY AND PARTICLE SIZE 10
BENTHIC MACROINVERTEBRATES 11
DISCUSSION 12
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LIST OF FIGURES
Page
1. General Study Location, B. K. Roberts Canal,
July 1983 15
2. Station Location and Canal Configuration,
B. K. Roberts Canal, July 1983 16
3. Fathometer Transects, B. K. Roberts 17
4. Surface Water Level Record, B. K. Roberts,
July 1983 18
5. Flow Direction at Culverts Indicated,
B. K. Roberts 19
6. Tracer Response, B. K. Roberts 20
7. Water Exchange Rate, B. K. Roberts 21
8. Ground and Surface Water Level Record,
B. K. Roberts . . . 22
9. Mid Depth Diel Dissolved Oxygen Concentration,
B. K. Roberts Canal, July 1983 23
10. Location Map of Project Area Showing Extent of
Tidal Marshes and Submerged Vegetation (From
NMFS, Circ. 368) 24
11. Sediment Composition (%) of Bottom Sediments,
B. K. Roberts Canal Study 25
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LIST OF TABLES
Pa9e
1. Summarization of Dissolved Oxygen, Salinity
and Temperature Profiles, B. K. Roberts Canal
and Alligator Harbor, July 1983 26
2. Phytoplankton - Chlorophyll a Concentrations
(mg/m3) from B. K. Roberts Canal and Alligator
Harbor. July 1983 28
3. Water Column Metabolism, B. K. Roberts Project,
Alligator Harbor, Florida, July 1983 29
4. Light Transmission, B. K. Roberts Canal Study,
July 1983 30
5. Water Chemistry Data, B. K. Roberts Canal
Study, July 1983 31
6. Sediment Chemistry Data, B. K. Roberts Canal
Study, July 1983 32
7. Benthic Macroinvertebrates Collected by
Qualitative Sampling, B. K. Roberts Canal
and Alligator Harbor, Panacea Florida,
July 1983 33
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PROJECT PERSONNEL
Thomas Cavinder - Engineer
Delbert Hicks - Aquatic Biologist
Hoke Howard - Aquatic Biologist
Philip Murphy - Aquatic Biologist
Ted Vaughan - Engineer Technician
INTRODUCTION
During the period July 11-16, 1983, personnel of the En-
vironmental Services Division (ESD), EPA, Region IV, conducted
a water quality, biological and hydrographic study of the B. K.
Roberts Canal adjoining Alligator Harbor near Panacea, Florida.
The subject project is a relatively old (early 1970's) Section
10, River and Harbor Act, violation being handled by the Jack-
sonville District, Corps of Engineers (COE) and the U.S. Attor-
ney's office. For a number of years, the Roberts Canal remained
plugged and isolated from Alligator Harbor. However, the earther
plug was breached at some time in the past and presently the cane
is open to Alligator Harbor through a shallow connector channel.
Resistance by the developer to reconstruct the plug resulted in
initiation of legal action by the COE and Department of Justice.
At their request, ESD personnel conducted the subject study to
determine existing environmental conditions of the canal.
FINDINGS
1. B. K. Roberts Canal is separated from Alligator Harbor by a
shoaled connector canal less than 1 foot deep at mean tidal
stage. Shoaling at the mouth of the canal is expected to be
a continuing problem due to prevailing seasonal winds and
littoral drift.
2. Except for the shoaled areas of the connector canal, project
depths ranged from about 4 to 7-1/2 feet at mean tide.
3. During the course of the study, water level fluctuations due
to tide ranged from 4 feet to 2 feet. In general, tide level
in the loop canal tracked closely with those of Alligator Har
bor with inequities of only approximately a quarter (1/4) a
foot at extreme low tide.
4. Due to positioning and elevation of the culverts relative to
the canal loop, flood tides pass westerly through the culvert
and ebb tides move easterly. Elevation of the culverts above
the low water mark creates a no flow condition when water
levels fall below -0.5 feet.
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5. Release of a dye tracer to monitor canal flushing showed
dispersal not to be uniform throughout the system. Four
days after release, tracer concentrations in the western
loop were 3 times greater than the concentration in the
eastern loop. Overall, 50 percent of the tracer was re-
leased to Alligator Harbor within 44 hours, and 90 percent
exchange was projected to occur in 140 hours.
6. Groundwater response to tides was rapid and its range was
approximately 2/3 of the tidal range. Such rapid communi-
cate between tidal and groundwater makes the use of septic
tanks along the canal inadvisable.
7. Violation of water quality standards (4.0 mg/L minimum) was
evident even at mid depth at interior canal Stations 3, 6
and 7 for a considerable part of the day. Under conditions
where low tide coincides with much of the night time hours,
more pronounced and extended violations are expected.
8. The canal was enriched with ammonia nitrogen concentrations
ranging up to 0.35 mg/L. Ammonia concentrations in Alligator
Harbor were 0.20 - 0.24 mg/L. Hydrogen sulfide (H2S), an in-
dicator of anaerobic metabolism, was present in bottom water
(lower one foot) at all canal stations. Potentially toxic
concentrations of H2S were detected at several locations.
9. Chlorophyll a_ concentrations ranged from 10.64 to 34.83 mg/m^
in the canal while the bay concentrations ranged from 19.03
to 26.45 mg/m^.
10. Light-dark bottle experiments yielded a P:R ratio ranging
from 1.2 to 3.0, indicating an autotrophic water column in
both the canal and bay.
11. Dissolved oxygen concentration at mid-depth monitoring sta-
tions were above State water quality standards during day-
light hours reflecting photoynthetic oxygen production by
the abundant phytoplankton community. Bottom water. DO con-
centrations, however, were below the 4.0 mg/L minimum through-
out the day at interior canal stations.
12. Benthic macroinvertebrate communities were sparce in the
canal, limited in species richness, and confined primarily
to shallow side slopes of the canal system. Conversely, the
Alligator Harbor station exhibited a diverse and abundant
assemblage of benthic macroinvertebrates.
13. Canal sediments featured an accumulation of finely divided
organic material ranging from 10.5 to 14.5%of the total
composition. Organic component of bay sediment was only
0.6% of total composition. Excessive amounts of finely
divided matter such as in the canal are not conducive to
development of diverse benthic macroinvertebrate communities.
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OBJECTIVES
The primary task of the study was to characterize water
quality, hydrology and biology of the B. K. Roberts Canal and
adjacent waters (Alligator Harbor). To accomplish this task,
specific objectives were as follows:
o assess water quality of the B. K. Roberts Canal and
adjacent waters through dissolved oxygen, temperature
and salinity profiles and water chemistry sampling;
identifying any water quality violations
o characterize the surface and groundwater hydrology of
the B. K. Roberts Canal
o determine the flora and fauna of the B. K. Roberts Canal
and Alligator Harbor
o determine phytoplankton-chlorophyll a levels of the
B. K. Roberts Canal and Alligator Harbor
o characterize sediment structure and chemistry of the
B. K. Roberts Canal and Alligator Harbor.
o assess water column metabolism via light/dark bottle
experiments.
STUDY AREA AND STATION LOCATIONS
The B. K. Roberts Canal is located on the north side of
highway 370 between the shoreline of Alligator Harbor and the
highway (Figure 1). The canal, constructed in a loop config-
uration, is approximately 4500 feet long but is interrupted by
a causeway with culverts near the eastern end of the looped
waterway (Figure 2). A 400 feet long access channel perpendic-
ular to the Alligator Harbor shoreline connects the canal to
open water. Presently, only minimal residential development
is directly associated with the canal although it does receive
some use by local boats and water skiers. Five sampling stations
were located in the loop canal with additional stations in the
access channel and offshore in Alligator Harbor (Figure 2).
METHODS
For reasons of clarity, a brief discussion of methods used
in the accomplishment of each task is included in the results
section for each study task.
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RESULTS
Project Depth
Project depths were determined by longitudinal and cross-
sectional traces using a recording fathometer. Depths in the
canal system varied from 7 1/2 feet to less than 1 foot at mean
tidal stage (Figure 3). Considerable shoaling existed in the
entrance channel and radiated into the loop system near its
junction with the entrance channel. The junction as depicted
in Figure 3 provides for a longitudinal division of the canal.
The western leg of the canal between the junction and culverts
measures approximately 3000 feet with the eastern leg approxi-
mating 1500 feet.
Water Levels
Water level recorders were placed in Alligator Harbor near
the entrance of the canal from Alligator Bay and in the canal
loop at the culverts. Water level range was approximately 4 feet
on the first two days of the study and decreased to approximately
2 feet on the last day of the study (Figure 4).
In general, tide levels in the canal loop tracked closely
those of Alligator Harbor. Inequities of approximately 0.25 feet
were experienced during extreme low tides. As shown during these
low water extremes, the loop canal system was not allowed to drain
thoroughly due to shoaling in the entrance canal.
Flow Through Culverts
A current meter equipped with a recording strip chart was
used to monitor flow through the culverts. Figure 5 depicts the
flow direction through the culverts superimposed upon the water
level record at the culverts. Notation "0" represents no flow,
"W" represents flow to the west and "E" represents flow to the
east. Due to the skewed configuration in respect to the place-
ment of the culverts in the loop (Figure 2), flood waters passed
westerly through the culverts and ebb waters passed easterly
through the culverts. The culvert inverts were placed well above
the low waters experience during the survey period, consequently
no flow passed through the culverts when water levels fell below
-0.5 feet (Figure 5).
Dye Tracer Study
A tracer dye was released into the water column at Station
7 (see Figure 2) and monitored by means of automatic samplers
and a fluorometer for a period of 4 days. The samplers were
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placed at Stations 2, 4, and 6 and were programmed to collect
samples at hourly intervals. Results of the tracer study are
given in Figures 6 and 7. As shown in Figure 6, the dye re-
leased into the western loop at Station 7 dispersed into the
eastern loop and into Alligator Harbor by way of the culverts
and entrance channel respectively. The spread of the dye cloud
through the western leg of the loop, however, was not as effec-
tive. On 7/16/83, 4 days after the tracer release, tracer con-
centrations in the western loop remained 3 times those of the
eastern loop (Figure 6).
A measure of the exchange rate between the loop canal and
Alligator Harbor is shown in Figure 7. As shown, 50 percent of
the tracer had been released to Alligator Harbor in 44 hours
and 90 percent exchange was projected to occur at 140 hours.
Groundwater Dynamics
Dynamics of the groundwater levels in response to the tides
were measured by means of an auger hole and a water level re-
corder. As shown in Figure 8, the groundwater response to the
tides was rapid and its range was approximately 2/3 of the tidal
range. Calculations on the following pages relate the dynamics
of the groundwater response:
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GROUNDWATER RESPONSE TO TIDE
— groundwater record
1 (32 feet to canal)
mean tide level
tide range
= 2 x Amplitude
Groundwater Response to tide
-x
hx = hQ e
where hx = groundwater amplitude at distance x from shore
h0 = tidal amplitude (ft)
x = distance from shore (ft)
s = aquifer storage coefficient
T = aquifer transmissibility gal/day/foot
for period of 1700 on 7/15/83 to 0300 on 7/16/83
groundwater range = 1.25 ft.
thus hx = 0.63 ft.
tide range = 1.95 ft.
thus h0 = 0.98 ft.
and x = 32 ft. and t0 = 0.25 days
solving for S/T
0.63 = 0.98 e
-5
S/T = 1.52 x 10
Equates to a clean sand with a transmissibility
of — 500 and a storage coef of 0.005
time lag (tT) = x J t„. s/4 * T
I 0?25
- 32 >1 4 tj 1.52
1.52 x 10
=» 0.018 days
25 min. (ck's with record)
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COMPUTE GROUNDWATER RESPONSE AT 100' FROM CANAL
Period of Record > tide range = 2.5 ft.
thus hQ = 1.25 ft.
-100 >| ( tt /0.25 (1.52 x 10~5
hx = 1.25 e
= 0.31 ft.
Groundwater range = 2 hx ® 0.62 ft.
time lag
tL - 100 N
0.25
h tt (1.52 x 10"5)
0.055 days
= 80 minutes
Ground Surface
High tide
Mean Water Surface
—- — Low tide
Distance from Canal (ft.)
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Dissolved Oxygen and Water Quality Standards
Continuous monitoring of dissolved oxygen concentrations
and temperature was conducted over a 24-hour period at all canal
and open water stations. Self-stirred dissolved oxygen probes
connected- to YSI Model 56 DO/temperature monitors were calibrated
by the modified Winkler method immediately before and after each
monitoring period and suspended near mid-depth throughout the
diel period.
State of Florida water quality standards for Alligator Harbor
and attendant waters require a minimum DO concentration from sur-
face to bottom of 4.0 mg/L throughout the day (24-hour). Figure
9 depicts the daily record of EX) concentrations at all stations
for mid-depth except Station 2 where equipment problems negated
accurate measurement. As revealed by these records, dissolved
oxygen concentrations decreased with progression toward the in-
terior of the canal and exhibited a pronounced decline during
darkness. At Stations 3, 6 and 7 these trends resulted in vio-
lation of dissolved oxygen standards for a considerable time
period. Review of surface to bottom profiles (Table 1) conducted
at each station during high and low tide revealed the severely
depressed dissolved oxygen concentrations in canal bottom waters
near the culverts (Station 7).
Evident on all of the diel curves is the decline in DO con-
centrations with the onset of darkness (Figure 9). This is an
expected response related to the respiration of phytoplankton
and other biota resident in the water column and substrate in
the absence of photosynthesis which does not occur at night.
At Stations 3, 6, and 7, the diel curves show a night time
increase in dissolved oxygen during the period from about 2400 to
0600 hours (Figure 9). Such increases obviously cannot be related
to photosynthetic oxygen production since darkness still prevails.
Instead, explanation for such increases in this case is best de-
fined through observation of the tidal traces (Figure 5) in con-
junction with the diel DO curves. In short, as the dissolved
oxygen was being metabolized during night-time of the specific
study period, its decline was mediated by and temporarily elevated
by oxygenated water from the harbor and surface layer being trans-
ferred to the probe zone by flood tide currents. On July 14-16,
and between 2400 and 0600 hours, a flooding tide was in progress.
Should the study be conducted during a period of the lunar tidal
cycle when high tide does not directly correspond to darkness,
(i.e. ebbing tide occurring during the maximum respiration period
of 2400 to 0600 hours) then this "boost" or supplement of DO to
the night-time DO regimen would not be available and concentra-
tions at such a time would likely be even more suppressed and for
a longer period of time than observed during the study period.
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PHYTOPLANKTON-CHLOROPHYLL a
Water samples were collected from the B. K. Roberts canal
and Alligator Harbor (Station 1) for chlorophyll a analysis.
Samples were collected from the one-half (0.5) foot depth in
Alligator Harbor, due to its shallow depths, and from one-half
(0.5) foot and 3 foot depths in the B. K. Roberts canal. Fil-
tering of the collected samples was accomplished in the field,
and filter pads were stored in aluminum foil and placed on ice
for return to the EPA lab for analysis. Chlorophyll a concen-
trations (Table 2) were similar at the B. K. Roberts canal and
Alligator Harbor. Canal chlorophyll a concentrations ranged
from 10.64 to 34.83 mg/m3, while concentrations in Alligator
Harbor were 19.03 and 26.45 mg/m^. Chlorophyll a concentrations
for the canal and Alligator Harbor samples were, with a couple of
exceptions, higher than average concentrations of 17 mg/m^ ob-
served in Gulf inshore waters (Steidinger, 1973).
Water Column Metabolism
Assessment of the oxygen metabolism in the water column
was accomplished through the deployment and incubation of light
and dark bottles at depths totally integrating the water column.
Associated with bottle deployment was the determination of light
extinction (transmission) profiles with a marine photometer.
The oxygen metabolism of the phytoplankton community was
reflected in gross primary production (GPP) and respiration (R)
rates for the water column (Table 3) which translate into P:R
ratios exceeding 2.0 at all stations except Station 7. Water
column respiration at Stations 3 and 7 was substantially greater
than other stations (Table 3). Stations 3 and 7 were associated
with the culvert area of the canal.
Light Transmission
A submarine photometer was used to determine percent light
transmission at all stations except 2 and 4. Light transmission
data was utilized in determination of depths for light/dark bot-
tle experiments and phytoplankton chlorophyll a sampling.
Light transmission was similar at all stations (Table 4)
with the exception of Station 7, a canal dead-end site.
WATER CHEMISTRY
Water chemistry sampling was accomplished in conjunction
with monitoring of dissolved oxygen, temperature and salinity
(DST). Samples for water chemistry analyses (NH3, NO2-NO3, TKN
and T-P) were taken as close as possible to corresponding low
and high slack tide. Samples were taken at mid-depth with a
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horizontal Van Dorn sampler umess uisauiv^ J(
temperature (DST) profiles indicated stratification, in which
case, stratified sampling of the water column was initiated.
In addition, samples were collected near the water/mud inter-
face for hydrogen sulfide analysis. Preservation and storage
of samples followed the ESD SOP (standard operating procedures)
manual protocol and chain-of-custody was maintained.
Results of water chemistry analyses show concentrations
of NH3, NO2-NO3, TKN and T-P in the canal water to be similar
to the background station (BK-1) in Alligator Harbor (Table 5).
The most prevalent form of nitrogen was ammonia (NH3-N)
which ranged from 0.07 - 0.35 mg/L in canal waters and 0.20 to
0.24 mg/L in Alligator Harbor. Sources of ammonia for Alligator
Harbor and the B. K. Roberts canal system can include surface
drainage, domestic wastewater, recruitment from marine sediments,
and export from submerged vegetation and tidal marshes which are
prominent in the study area (Figure 10). Studies conducted on
nitrogen, phosphorus and carbon flux in undisturbed Chesapeake
Bay marshes (Axlerad, Moore and Bender, 1976) revealed that am-
monia was exported from the marsh system in the spring and summer.
Other studies by EPA personnel measured net fluxes of ammonia
from marine sediments in Tampa Bay (Murphy, 1983). Similar sedi-
ment exchanges of ammonia have been reported by Boyten/ Kempler .
Total phosphorus (T-P) concentrations ranged from 0.06 to
0.08 mg/L at canal and Alligator Harbor waters, with the exception
of a single concentration of 0.16 mg/L at Station BK-7.
The most salient chemical characteristic of the B. K. Roberts
canal waters, other than DO dynamics is found in hydrogen sulfide
(H2S) concentrations which are a product of a reducing environment
(Table 5). Undissociated H2S at concentrations of 0.02 mg/L are
toxic to aquatic life. At pH's common to the estuarine environment
(7 to 8 units), the reported H2S values of 1.2 and 4.6 mg/L would
be considered toxic concentrations.
SEDIMENT CHEMISTRY AND PARTICLE SIZE
Replicate cores were collected with a 2-inch acrylic tube
from the upper 10 cm of the bottom sediments at stations shown in
Figure 2. Samples were labeled, placed in plastic storage bottles
and kept on ice for return to the EPA lab in Athens, Georgia for
processing. Analyses included chemical determination of TKN, NH3,
T-P and COD plus particle size assessment. Processing of the
samples were in accordance with Divisional SOP's and QA protocol.
Sediment chemical analyses results reveal greater concentra-
tions of NH3, TKN, T-P, and COD in canal stations than in the
background station (Station BK-1) (Table 6). For example, TKN
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values for the canal stations ranged rrom it»zu to oilu my/js.y;
whereas, the background station (BK-1) in Alligator Harbor
yielded a TKN value of 126 mg/kg. Ammonia values were 6 to
26 times greater in the canal; total phosphorus values were
18 to 40 times greater in the canal, and COD values were 17
to 24 times greater in the canal. Past studies by EPA (1975)
reported similar findings in regard to build-up of nutrients
in canal sediments.
A concern with canal systems is the accumulation or "trap-
ping" of finer sediments (silt, clay and finely divided organic
matter) in the canal trough. Numerous studies by EPA have shown
this to be the case. Liabilities of the trapping nature of the
canals are twofold: (1) finer sediments are not conducive to
establishment of a diverse macroinvertebrate community and (2)
excessive organic matter creates added demands on the oxygen re-
sources of the system.
Results of the sediment analysis from the B. K. Roberts
canal stations clearly show greater percentages of fine sedi-
ments and organic matter present in bottom sediments when com-
pared to the Alligator Harbor station (Figure 11). Silt and clay
fractions constituted from 20% to 30% of the total dry weight of
sediments from all canal stations while sediments from the back-
ground station contained less than 2.5% silt and clay. Organic
content, another parameter indicative of the "trapping" nature of
dead-end canals, ranged from 10.5-14.5% of sediment composition
in the B. K. Roberts canals while organic content at the back-
ground station was only 0.6%.
BENTHIC MACROINVERTEBRATES
In conjunction with water quality studies, qualitative sam-
pling for benthic macroinvertebrates was conducted at Stations
1, 3, 4, 5, 6 and 7. With the exclusion of the Alligator Harbor
station (1), the remaining stations, located within the B. K.
Roberts canal, were sampled at both the littoral area and the
center trough. A variety of methods, including sweeps with a
standard biological dip net, bottom grabs with a core sampler
and visual inspection of available substrates constituted quali-
tative sampling efforts. A one-half (0.5) hour sampling effort
was conducted at each habitat site. Samples were sieved with a
U. S. Standard No. 30 sieve and stored in quart containers with
90% ETOH as the preservative. Chain-of-custody procedures were
followed during sampling and processing as dictated by the Eco-
logical Support Branch SOP (Standard Operating Procedures).
Results of benthic macroinvertebrate sampling were consistent
with the findings of past studies conducted by EPA on man-made
canal systems. The background station in Alligator Harbor (BK-1)
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possessed the greatest species richness with crustaceans, poly-
chaetes and mollusks providing for a total of 11 taxa in the
samples (Table 7). The benthic macroinvertebrate community, in
terms of taxa present in the canal system was much diminished
from that present in Alligator Harbor (Table 7). The littoral
areas (sides) of the canals yielded a few more invertebrate taxa
than did the center trough although still much less than the
background station (Table 7). Three canal stations (3, 6 and
7) had no benthic macroinvertebrates in center trough collections
(Table 7).
- Substrate and water quality are known factors affecting the
benthic macroinvertebrate community. Past studies of hydrologi-
cal and biological characteristics of finger-fill canal systems
(Trent, et. al^, 1973; Taylor and Salomon, 1968; EPA, 1976; and
Yokel, 1979) have indicated the limiting aspect of finely divided
organic substrates on the benthic macroinvertebrate community.
Silt and clay, in addition to organic matter, were much more pre-
valent in the B. K. Roberts canal system sediments than the
background site (Figure 11). An additional liability associated
with accumulation of organics and fine sediments is the excessive
demands placed on the oxygen regime of the system. As can be seen
upon examination of the dissolved oxygen, salinity and temperature
profiles (Figure 9 and Table 1), near bottom concentrations of
dissolved oxygen in the canal were depressed, especially the most
landward stations. Excessive H2S could also add to the impact on
the macroinvertebrate community. Such conditions, coupled with
poor substrate quality, are not conducive to establishment of a
diverse benthic macroinvertebrate community. In a natural system,
such as Alligator Harbor, tidal motion coupled to shallow depths
provides adequate vertical mixing hence reducing the tendency for
the accumulation of fine sediments and organic matter.
DISCUSSION
The B. K. Roberts Canal is a 4500 feet long loop canal, inter
rupted by culverts and a causeway, appended to a shallow bay, Alii
gator Harbor (Figures 1 and 2). Alligator Harbor is a designated
State of Florida aquatic preserve. Aquatic preserve designation
is dependent upon such factors as biological productivity, scien-
tific importance, and aesthetics. Alligator Harbor meets all thes
criteria. Since the B. K. Roberts Canal, in its unplugged status,
is viewed as waters of the United States and, thus, an extension
of Alligator Harbor, then it is reasonable to expect that the cana
should be required to exhibit the same environmentally desirable
qualities as the parent water. However, this is not the case.
Typical of many artificial canals, inhibited flushing of the
B. K. Roberts Canal contributes largely to the decline in water
quality and biological conditions. Shoaling at the entrance to
the loop canal creates a sill effect as illustrated in Figure 3.
The elevation of the culverts at the eastern end of the loop
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canal (Figure 3) creates a second barrier impairing flushing.
The elevation of the culverts are such that at water levels
less than -0.5 feet, no exchange occurs through the culverts.
Dissolved oxygen concentrations at Stations 3, 6 and 7 vio-
late water quality standards (minimum 4.0 mg/L) for a considerable
portion of the day as shown in Figure 9 and Table 1. Such viola-
tions are expected to be more pronounced and extended for longer
periods of the day when low tides and maximum respiration (night-
time) are more coincident. Associated with substandard DO con-
centrations are the respirational demands associated with the
water column in conjunction with organically enriched sediment
(a result of the trapping of finely divided organic material
settling in the quiescent canal waters as well as the organic
substrate through which the canal was constructed). The strati-
fied nature of the water column, as depicted by the DO profiles
(Table 1), illustrate the incomplete vertical mixing of the water
column.
Initially, the enriched phytoplankton community in the canal
system would appear to exert no liability upon the DO resource of
the canal system since it produces more dissolved oxygen than it
consumes over 24-hour period. However, the night-time respirational
demand for oxygen by this enriched community in conjunction with
such factors as (1) the continuous demand for oxygen by organically
enriched sediments and (2) the inhibited exchange and/or vertical
mixing of oxygen enhanced water from the bay (particularly at in-
terior canal stations) all coincide to produce substandard dissolved
oxygen concentrations for a considerable part of the day.
An indicator that resident conditions in the canal are prob-
ably even more adverse than observed in this short term study is
the high concentrations of hydrogen sulfide (H2S) (Table«5) found
at the water/sediment interface of all canal stations and the
relative absence of benthic macroinvertebrates in the canal bot-
tom (Table 7). Hydrogen sulfide is produced and maintained only
under anaerobic conditions (no oxygen). Concentrations at which
H2S was present in the canal are toxic to animal life, thus im-
pairing the development of a quality macroinvertebrate community.
In contrast to the water quality and biological conditions
in the canal are the conditions observed at Station BK-1, the
background station in Alligator Harbor. No dissolved oxygen stand-
ard violations were encountered and the decline in DO at night-fall
was not nearly as pronounced as at interior canal stations (Figure
9). The organic component of Station BK-1 sediment was only 0.6%
compared to a range of 10.5% to 14.5% at canal stations. Chemical
constituents and chlorophyll a concentrations were not markedly
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,#ferent between canal and bay stations, but the collective
esult to the dissolved oxygen resource are more pronounced
n the canal.
Comparison of hydrographic and chemical features are good
jols for characterization of the B. K. Roberts Canal and the
[ligator Harbor station. As discussed above, in these regards,
,e canal is of inferior quality in comparison to the bay. How-
rer, the most important consideration is how all these water
[ality factors combine to produce value in terms of biological
oductivity which is necessary to sustain important fish and
ldlife. Here lies the most notable distinction between the
nal and Alligator Harbor. Station BK-1, Alligator Harbor, ex-
bited a diverse and balanced community of benthic macroinverte-
ates (Table 7) comprised of 11 taxa. In contrast, the canal
s dominated by worms (Polychaeta) limited primarily to side
opes with three out of five stations being void of benthic
ganisms in the center trough. Accordingly, the contributions
estuarine food chains of the open bay compared to the canal
s quite evident and contrasting. The bay station maximizes
puts from primary production to sustain productivity to the
condary level, producing a numerous and diverse assemblage of
zroinvertebrates to enter the food web. In contrast, the canal's
gh levels of gross primary production in the water column is not
anslated into support of secondary production since bottom water
3 sediment quality is not conducive to development of a diverse
nthic community. The restricted flushing, trapping and accumu-
tion of fine organic material, and resultant anoxic conditions
3 sulfide production associated with the decomposition of this
terial all serve to adversely limit biological productivity. As
ated previously, these adverse conditions exist in the relative
sence of development. With the rapid interaction of tide water
th ground water adjacent to the canal, any insuing development
companied by septic tanks or similar treatment would further com-
und the observed water quality problems through continued enrich-
nt of canal waters.
-14-
-------
FIGURE 1.
GENERAL STuta-^LOCATION, B. K. ROBERTS CANAL, \jUtY 1983.
0 U L 7 OF
vostl Cape
thouso
Point
M S I I C O
r
/3.&. £oai*rs C^n^.
-15-
-------
allig
A T
0. R
H
ARBO
©
-------
Distance (feet)
aAVJH MIOl )HI) HJS
HJUI | Ul 01 KOI wOl Mi
-------
(U
0)
g
«
a
W
n
9
M
ad
+1..
+1.0
+0.5
P.O J
-0.5
¦1,0
•¦2.0
fZ.S
12
7/14/83
DATE - TIME
12 '
7/16/83
-------
u
a)
a>
ss
o
M
h4
W
W
U
c
+ 1.0 .
+0.5
wi -0.5
pi
I
£
-1.0
-1.5
-2.0
-2.5
7/12/83
7/13/83
7/14/83 7/15/83 7/16/83
nATF - TTMF.
-------
FIGURE 6
TRACER RESPONSE
B. K. ROBERTS
7/13/83
7/14/83 7/15/83
Date - Time
-20-
7/16/83
-------
FIGURE 7
WATER EXCHANGE RATE
B. K. ROBERTS
-------
41
01
• g
rvj
M 4J
' (0
~
01
H
W
V
o
m
3
CO
M
0)
¦U
CO
+1.5
+1.0
+0.5
i
00
I
i
j
-0.5
i
I
i-1.0
-1.5
-2.0
j-2.5
-------
1 iVJUi\jj J •
MID DEPTH DIEL DISSOLVED OXYGEN CONCENTRATION,
B. K. ROBERTS CANAL, JULY 1983.
-------
FIGURE 10
LOCATION MAP OF PROJECT AREA SHOWING EXTENT OF TIDAL MARSHES
AND SUBMERGED VEGETATION (FROM NMFS, CIRC. 368)
25' 201
-24-
-------
I
t-o
I
w
H
>
H
M
O
z
r1
o
n
CO
rt
0>
CO
rt
03
CO
rt
Cu
CO
rt
&>
CO
rt
ft)
Coarse - Fine sands
Coarse - Fine sands
Coarse - Fine sands
Medium & Fine gravel
T?
O
00
01
3
H«
o
¦i
0>
O
o
a
3
O
*-!
0Q
0)
3
H»
O
o
o
3
Coarse -
Fine sands
Silt & Clay
H«
OQ
C
*
-------
TABLE 1 . Summarization of Dissolved Oxygen, Salinity and
Temperature Profiles, B. K. Roberts Canal and Alligator Harbor,
July 1983.
station
DATE
TIME
DEPTH
SALINITY
TEMP
D.O.
(ft)
(PPt)
(°C)
mg/L
BK-7
7/14/83
1028
1
29.0
29.3
5.0
2
29 .0
29.3
4.9
3
29 .0
29.2
4.7
4
29.0
29.2
4.3
5
29 .2
28.9
2.1
BK-7
7/14/83
1685
1
29.3
32.6
9.0
2
29.4
32.4
8.9
3
29.4
31.3
8.7
4
29.3
30.4
6.7
5
29 .2
29.8
5.5
6
29.3
29.5
4.8
7
29 .3
29.3
4.7
8
29.3
28.8
0.8
BK-6
7/14/83
1040
1
29 .1
29.3
5.8
2
29.1
29.3
5.4
3
29 .4
29.0
3.9
BK-6
7/14/83
1710
1
29 .5
32.5
8.7
2
29.0
31.6
8.8
3
29.7
30.7
8.0
4
29.3
29.7
6.3
5
29.4
29.5
4.2
BK-5
7/14/83
1048
1
29.3
29.1
4.9
2
29.6
28.8
4.4
3
29.6
28.8
3.6
BK-5
7/14/83
1718
1
30 .1
32.0
7.5
2
30.0
32.0'
7.5
3
30.0
32.0
7.5
4
30.0
31.9
6.9
5
29.8
30.6
5.4
6
29.7
30.1
4.5
BK-4
7/14/83
1106
1
29.4
29.7
5.6
2
29.5
29.3
5.0
3
29.5
29.3
4.6
4
29.6
29.2
3.8
-26-
-------
Table i (continued)
AT I ON
DATE
TIME
DEPTH
SALINITY
TEMP
D.O.
(ft)
(PPt)
(°C)
mg/L
K-4
7/14/83
1728
1
30.1
32.5
7.7
2
30.1
32.4
7.8
3
30.0
32.4
7.7
4
29.4
32.2
7.7
5
29.6
30.7
5.9
6
29.6
29.5
4.5
6 1/2
28.6
29.3
3.8
K-3
7/14/83
1113
1
29.2
30.0
5.9
2
29.3
29.7
5.5
3
29.5
29.1
3.3
4
29.6
29.1
2.4
5
29.6
28.9
1.9
(-3
7/14/83
1738
1
29.7
31.8
8.9
2
29.5
31.4
9.1
3
29.7
30.7
8.4
4
29.7
30.4
8.3
5
29.6
30.1
7.7
6
29.8
29.3
4.0
7
29.6
29.2
3.6
7 1/2
29.2
29.1
1.9
;-2
7/14/83
1128
1
29.6
29.8
5.2
,-2
7/144/83
1804
1
30.1
31.4
7.2
2
30.1
31.3
7.2
3
30.0
31.3
7.1
-1
7/14/83
1136
1
29.9
29.3
5.6
2
29.8
29.2
5.6
3
29.8
29.1
5.6
-1
7/14/83
1755
1
30.0
31.2
7.2
2
28.7
31.2
7.2
3
30.0
31.1
7.1
4
29.9
30.9
6.6
-27-
-------
TABLE 2 . PHYTOPLANKTON - CHLOROPHYLL a CONCENTRATIONS (mg/m3)
FROM B. K. ROBERTS CANAL AND ALLIGATOR HARBOR. JULY 1983.
STATION REPLICATE DEPTH CHL. a (mq/m3)
111' 26.45
12 1' 19.03
3 1 1/2' 20.32
3 2 1/2' 10.64
3 13' 24.19
3 2 3' 30.32
4 1 1/2' 20.64
4 2 1/2' 19.67
4 13' 23.87
4 2 3' 29.03
5 1 1/2' 25.48
5 2 1/2' 20.32
5 13' 25.16
5 2 3' 32.25
6 1 1/2' 24.19
6 2 1/2' 26.12
6 13' 25.48
6 2 3' 34.83
7 1 1/2' 17.20
7 2 1/2' 27.41
7 13' 29.03
7 2 3' 23.22
-28-
-------
TABLE 3 . Water Column Metabolism, B. K. Roberts Project, Alligator Harbor, Florida, July 1983.
Station
Net Primary Production
NPP
g 02/m2/hr
Respiration
r
g C^/m^/hr
Gross Primary Production
GPP
g 02/m2/day*
Respiration
R
g C^/mVday**
Production: Respiration
P:R Ration
1
0.42
0.10
6.76
2.40
2.82
3
1.09
0.32
18.33
7.68
2.39
5
0.72
0.16
11.44
3.84
2.98
6
0.58
0.14
9.36
3.36
2.79
7
0.85
0.43
16.64
10.32
1.61
*GPP day = 13 hr photoperiod
**R day = 24 hrs
-------
TABLE 4. LIGHT TRANSMISSION, B. K. ROBERTS CANAL STUDY,
JULY 1983.
STATION
DATE
TIME
DEPTH (FT)
% TRANSMISSION
1
7/15/83
1112
1
34
1
7/15/83
1112
2
11
3
7/15/83
1155
1
34
3
7/15/83
1155
2
18
3
7/15/83
1155
3
7
3
7/15/83
1155
4
4
3
7/15/83
1155
5
2
3
7/15/83
1155
6
1
5
7/15/83
1132
1
28
5
7/15/83
1132
2
17
5
7/15/83
1132
3
4
5
7/15/83
1132
4
3
6
7/15/83
1040
1
33
6
7/15/83
1040
2
19
6
7/15/83
1040
3
4
6
7/15/83
1040
4
2
7
7/15/83
0958
1
26
7
7/15/83
0958
2
8
7
7/15/83
0958
3
3
7
7/15/83
0958
4
1
7
7/15/83
0958
5
0.5
7
7/15/83
0958
6
0.3
7
7/15/83
0958
7
0.1
-30-
-------
TABLE 5 . WATER CHEMISTRY DATA, B. K. Roberts canal study,
STATION
DATE
TIME
nh3
mg/L
N02-NC>3
mg/L
TKN
mg/L
T-P
mg/L
TOC
mg/L
Sulf ides
mg/L
BK-1 £ 2 '
7/14/83
1137
0.20
0.05U*
0.36
0.07
14.0
BK-1 @ 2 '
7/14/83
1757
0.24
0.05U
0.24
0.06
0.8
BK-2 0 1 '
7/14/83
1129
0.22
0 .05U
0.23
0.07
14 .0
BK-2 (3 2 '
7/14/83
1804
0.20
0 .05U
0.35
0.07
1.2
BK-3 0 2-1/2 '
7/14/83
1115
0.21
0 .05U
0.21
0.08
13.0
BK-3 0 4'
7/14/83
1742
0 .27
0 .05U
0.32
0.07
2.3
BK-3 0 7-1/2 '
7/14/83
1744
0.26
0.05U
0 .26
0.07
14 .0
BK-4 0 2 •
7/14/83
1108
0.11
0.05U
0.28
0.06
15.0
BK-4 0 3 '
7/14/83
1732
0.07
0 .05U
0 .10U
0.06
14 .0
BK-5 0 1-1/2 '
7/14/83
1050
0.07
0.05U
0.15
0.07
15.0
BK-5 0 3 '
7/14/83
1723
0 .07
0.05U
0.15
0.06
1.7
BK-6 0 1-1/2 '
7/14/83
1042
0.23
0 .05U
0.30
0.08
14 .0
BK-6 0 3 1
7/14/83
1710
0.07
0.05U
0 .17
0.06
14 .0
BK-7 0 2-1/2 '
7/14/83
1030
0.25
0.05U
0.25
0.06
14 .0
BK-7 0 3 '
7/14/83
1700
0.22
0 .05U
0.22
0.06
14 .0
BK-7 0 8 •
7/14/83
1700
0.35
0 .05U
0.35
0.16
14.0
BK-3 (bottom)
7/16/83
1415
1.20
BK-4 (bottom)
7/16/83
1355
0.14
BK-5 (bottom)
7/16/83
1345
0.07
BK-6 (bottom)
7/16/83
1325
0.10
BK-7 (bottom)
7/16/83
1450
4.55
*U =
Material was analyzed for but not detected; the nu\jT»bet is the minimum detection limit.
-------
TABLE 6 . SEDIMENT CHEMISTRY DATA, B. K. ROBERTS CANAL STUDY,
JULY 1983.
STATION
DATE
TIME
TKN
nh3
T-P
COD
mq/kq
mg/kg
mg/kq
mg/kq
BK-1
7/16/83
1405
129.0
15.0
10A*
2100
BK-3
7/16/83
1415
1620 .0
183.0
270.0
36000
BK-4
7/16/83
1350
5300.0
400.0
400.0
38000
BK-5
7/16/83
1330
5720 .0
321.0
380.0
38000
BK-6
7/16/83
1325
5495.0
95.0
180.0
51000
BK-7
7/16/83
1305
5378 .0
278.0
300.0
38000
*A = average value
-32-
-------
TABLE 7 . BENTHIC MACROINVERTEBRATES COLLECTED BY QUALITATIVE SAMPLING,
B. K. ROBERTS CANAL AND ALLIGATOR HARBOR, PANACEA, FLORIDA, JULY 1983.*
Station BK-1
(Alligator Harbor)
Station BK-3
Side Center
Station BK-4
Side Center
Station BK-
Side Center
Station BK-6
Side Center
Station BK-7
Side Center
Crustacea
Corophium sp.
Ampellsca sp.
Mysldopsls bahia
Palaemonetes puglo
Penaeus sp.
Tanaidacea
(prob. Leptochelia sp.)
Portunidae
Polychaeta
Glycerldae
Questldae
Paraonldae
Spionidae
Orbiniidae
Terebellidae
Ampharetidae
Nereldae
livalvia
Mullnia lateralis
Parastarte sp."
Periploma sp.
lolothuroidea
'OTAL TAXA
X
X
X
X
X
X
X
X
X
X
X
11
X
X
X
X
X
X
X
1
------- |