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CARIBBEAN RESEARCH INSTITUTE
WATER POLLUTION REPORT NO. 10
WATiER QUALITY AND ENVIRONMENTAL STATUS
OF MBENNER BAV-MANGROV LAGOON, ST. THOMAS
David I. Grigg, Robert P. vanEepool and Robert W. Brody
(April, 1971)
GOVERNMENT OF THE VIRGIN ISLANDS
DEPARTMENT OF HEALTH, DIVISION OF ENVIRONMENTAL HEALTH
WATER POLLUTION REPORT NO. 10
CONTRACTED by:
CARIBBEAN RESEARCH INSTITUTE
COLLEGE OF THE VIRGIN ISLANDS
WATER QUALITY AND ENVIRONMENTAL STATUS
OF
BENNER BAY MANGROVE LAGOON
ST. THOMAS
David I. Grigg, Robert P. vanEepoel
Robert W. Brody
April, 1971
TABLE OF CONTENTS
Page
INTRODUCTION . . . . . . . . . 1
Statement and Purpose . . . . .. 1
Previous Work . . . . . . . 5
Description of the Study Area . . . .. 6
RESULTS . . . . 10
Temperature * * * * * * 10
Salinity . 11
Dissolved Oxygen .. 14
Water Clarity ............. 15
Diurnal Studies . . . . . . . .21
SUMMARY . . . . . . 28
RECOMMENDATIONS . . . . . . . .. 31
Recommendation I .. . .. 36:
Reoammendation II . . .. .. 36
Reeomaendation III . . . . . . 37
Recommendation IV . . . . . . 37
Reco-mendation V .. . . . . .. 38
LITERATURE CITED . .. .* . . . . . 39
APPENDIX . .. . . . . . . . 41
List of Figures . . . . . ..... .41
List of Tables . * * .......... 41
INTROD UCT 1ON
General Statement and Purpose
Development on the east end of St. Thomas is increas-
ingly geared toward water oriented facilities. The need
for boat anchorage and related service facilities on this
end of the island is being met in two places -- Red Hook/
Vessup Bay and, to a greater extent, Benner Bay (Figure 1)
where, within the past year the number of boats at anchor
or piered has more than doubled, due mainly to the opening
of a new facility (Antilles Yacht Services). There are
presently three bare-boat charter concerns operating out
of Benner Bay and plans for their expansion and for addi-
tional facilities will result in even higher boat densities
and traffic in the future. Construction has begun for the
Compass Point Club, a shoreline support facility for "Aqua-
miniums" -- ownership-lease properties similar to condoai-
niums but involving 46' powered houseboats as the property
unit; they are presently operating out of leased space on
the channel between Mangrove Lagoon and Banner Bay. Antilles
and a second charter sailboat facility, West Indies Yachts,
have docks on Benner Bay. Lagoon Fishing Center and Toby
Mann Mrine operate the remaining "public" dockage on
Benner Bay.
Benner Bay is relatively shallow, maximum depth is
about 2.5 meters, and deep draft or deep keeled boats
Paqe 1
regularly run aground, especially in the narrow passage
into the bay between Bovoni and Bird Cays (Figure 2).
Several requests have been made by boat owners and area
businessmen to dredge and deepen the channel.
Marinas and other good anchorages. which are used by
large numbers of boats are inevitably sites of extremely
poor water quality and an impoverished biota. Motor ves-
sels contribute appreciable quantities of various pollu-
tants to the water, especially when engines are running
slowly or at idle as they usually are within the anchorage.
Exhaust gases and unburned hydrocarbons are continuously
injected into the water at higher than ambient temperatures
and pressures. This material dissolves or is finely dis-
persed in the water and kills living things. In addition
to combustion products there is sewage (none of the marinas
on the island have pump-off facilities and very few craft
have holding tanks, in any case), other refuse and some un-
avoidable fuel and oil spillage. The significance of these
additions to the water can really be appreciated only if
other attendant facts are considered. The first is the
number, and, more important, the density of boats in most
anchorages where their combined effects are concentrated in
a relatively small area. The second factor is that places
best suited for docking and anchoring are usually least
capable of tolerating the ensuing stresses placed upon them.
P ae 2
Quiet, protected waters are often so because of very low
currents resulting in poor water exchange or flushing.
Pollutants added to such systems are not quickly removed
and their concentrations build up to very high levels.
These facts must be recognized and taken into account
whenever one is assessing the possible impact of boats and
boat traffic. This is not to say that marine oriented
coamsroe is undesirable -- without a doubt it is desirable,
and necessary, in an island setting -- but its consequences
must be recognized and admitted so that its proliferation
and development can be kept in proper perspective to other
requirements. One of the cardinal guidelines for insular
development should be to preserve as many varied natural
systems as possible. The tendency to convert natural
systems toward the economic end to which they can most
easily be converted cannot always be justified when weighed
against the rapidly deteriorating quality of man's environment.
During the past few years considerable controversy has
cantered around a proposal to fill most of the Mangrove Lagoon
for construction of a jet airport. Engineering proposals
for the airport provide for waterways under the runway de-
signed to maintain the present flow of water from the open
sea into the Lagoon. Such flow is essential to the proper
circulation and flushing of the Lagoon, but certainly is not
the only requirement for its preservation. Conservationists
Page 3
generally agree that, such structures notwithstanding, con-
struction of the jetport would destroy the Lagoon. Physi-
cally, it would occupy about two-thirds of the area, leaving
only the central shallow turtle grass area and part of one
mangrove islet. Additionally, it is anticipated that run-
off and siltation and other forms of pollution, during con-
struction and after development of the airport complex and
its satellite commercial facilities, will rapidly obliterate
these remaining portions of the Lagoon.
The Lagoon area now remains as the only extensive repre-
sentative of its kind in the U. S. Virgin Islands. Similar
areas on St. Croix have already been destroyed in the course
of industrial, tourist accommodating and housing developments.
While conservationists urge the protection of the St. Thomas
site, they are hard put to offer tangible evidence of its
value. It presently has no assessable economic value beyond
the price of the real estate. Its worth as a natural area
and recreation site and its potential for research and ar'aa-
culture have been described by conservationists and biologists
but have not been translated into terms most people can appre-
ciate, i.e. dollars and cents, or even been publicly acknowl-
edged by local agencies responsible for its disposition.
The purpose of this study was to describe the Benner Bay-
Lagoon environment, primarily the water quality. Field work
Pane 4
was conducted from February to July, 1970 by the authors
with the assistance of Lyn Slocum (Virgin Islands Ecologi-
cal Research Station) and several marine technology students
from Cape Fear Technical Institute. Other students who
assisted in the field and the laboratory were David Morris
(Fairleigh Dickenson University) and Laverne Ragater (Uni-
versity of Miami). Eileen Shatrosky, assisted by Sonya
Nelthropp of the College of the Virgin Islands, did most
of the laboratory analyses and Roosevelt Bryant and Lawrence
Lewie of the College of the Virgin Islands prepared the
figures. Jackie Thomas of the Caribbean Research Institute
and Paula Bailey deserve special thanks for the laborious
job of typing the report.
Previous Work
Several previous reports have covered various aspects
of the Lagoon biology and hydrography. All have acknowl-
edged the uniqueness and the natural value of the area. In
a survey of the biological aspects of water quality in the
three Virgin Islands, a Department of Interior, FWPCA, report
(1967) includes some data on sediment nutrients in the Lagoon.
McNulty, et al, (1968), in the most comprehensive study of
the Lagoon to date, divided the area into nine ecological
zones, presented data on its hydrography and wildlife and
called for several safeguards to be observed for the pro-
tection of the area if the airport is constructed. At the
Page 5
request of local government agencies, studies on biological
and engineering aspects of the proposed airport were made
(Tabb and Michel, 19689 Michel, 1970). These reports con-
tain information on the distribution of the major organism
in the area and on the importance of the existing unique
tidal and current regimes to the sustenance of the Lagoon.
Michel (1970) presents data on salinity distributions, tidal
cycles, and flushing rates of the Lagoon and proposes engi-
neering structures to be incorporated into the proposed runway
designs to maintain the critical water flow. Additional hydro-
graphic data are contained in Dammann (1970).
Description of the Study Area
The study was conducted in Benner Bay and Mangrove
Lagoon to the west. The area is on the southeast coast of
St. Thomas (Figure 1) and is open to the Caribbean Sea on
the south. Field work was confined to the area bounded by
Patricia and Cas Cays on the south and Coculus Rocks on the
east. Sampling stations are shown in Figure 3. Bovoni and
Patricia Cays, as well as the low land to the north and west
of the Lagoon are alluvial material (Donnelly & Whetten, 1968)
deposited by the Turpentine Run gut. This stream is pre-
sently the largest surface water producer remaining on
St. Thomas. Although it now runs into the Lagoon only after
very heavy rains, that portion of it below Mt. Zion, and
Pace 6
spots farther southeast, contain water the year round and
harbors an interesting but little known faunal assemblage
which includes at least two species of shrimp, several
species of fish, and an eel. The gut drains the entire
Tutu Valley plateau, about four square miles, which lies at
about 200 feet elevation and is fed by four tributary branches.
Much smaller guts drain the hills around Estate Nulliberg,
northwest of the Lagoon and Langmath and Benner on the north
and the northeast. The latter drains into a salt pond be-
hind the northeast shore of Banner Bay. The pond has been
partially filled as part of the area development already
mentioned.
The dominant terrestrial organism in the study area is
hiophor mangle (red mangrove). The entire shoreline of
the Lagoon and of Benner Bay was formerly fringed with red
mangrove, but much of the Benner Bay shoreline has been cut
and piers and bulkheads constructed. The remaining mangroves
along Benner Bay are in a belt usually one plant wide. Ex-
tensive growth of mangroves is responsible for the formation
of the many cays in the area.
The dominant marine feature of the area is an extensive
pasture of turtle grass, Thalassia testudintum the distribu-
tion of which has been mapped by Tabb and Michel (1968) and
McNulty, et al, (1968). Its density is sparser as one pro-
grasses into Benner Bay where all benthic plant growth
Paqe 7
disappears below 0.5 meter. Due to the dense boat anchor-
age, heavy traffic, increased runoff due to land clearing
and construction, great shoreline alteration and attendant
pollution, water quality in Benner Bay is extremely poor.
Although better, the water quality in the northern part of
the Lagoon is also reduced. The major part of the Lagoon,
however, contains clear water as does the outer portions
of Benner Bay and west Jersey Bay.
Other zones in the Laoon are characterized by various
algae, grass and coral assemblages (McNulty, 1968}) and con-
tribute to the habitat diversity which makes Mangrove Lagoon
possibly the most complex and varied natural system in the
islands. Not as obvious, but just as important to this eco-
system, is the reef on the south, dominated by Acropora
palate (elkhorn coral) which has been shown to be vitally
important to the Lagoon ecology (Tabb and Michel, 1968;
McNulty, 19609 Michel, 1970) by virtue of its effect on the
local water circulation. The present distribution of bottom
types is shown in Figure 16.
Benner Bay and the Lagoon are well protected from
strong seas by the reef and cays on the south and by the
eastern tip of St. Thomas and Great and Little St. James
islands to the east and southeast (Figure 1). Water moving
into the area northwesterly looses most of its energy where
the bottom shallows up rapidly between Potto and Cas Cays.
Page 8
Most waves are dissipated after moving across the shallows
of south Banner Day.
The north shore of Benner Bay is heavily developed.
Except for marinas along the northeast corner, most buildings
are private dwellings. North of the Lagoon in the Bovoni-
Nadir area, a fair-sized community is developing. Sewage
from this community is treated in a 70,000 gpd.plant (Figure 15)
located on the northwest shore of the Lagoon and the effluent
drained to the shore.
Long Point is undeveloped, although a small salt pond
on its west shore, south of Stalley Bay, has been dredged
open to the sea and a small beach area has been created by
dredging on the lee side of the southeast point. These
modifications are shown on Figure 2. The Cays and Compass
Point are also undeveloped, although the latter is soon to
be the site of extensive construction for another marina
facility. Land clearing, shoreline alteration and extensive
filling have already been accomplished.
Presently, most of the Lagoon's north shore is unde-
veloped. A horse racing track has been proposed for the flat,
formerly swampy, area west of the highway and some filling
and grading has been accomplished on that project.
Page 9
RESULTS
The raw data collected in this study is presented in
thirteen tables. Table 14 gives some mathematical qualities
for the data from two diurnal studies. Table 15 is a sum-
mary of the monthly averages of the raw data. Locations of
sampling stations are given in Figure 3; the mean depth at
each station can be found in Table 4.
Temperature
Temperature measurements were made from February to May
and are shown in Table 1 with the calculated monthly aver-
ages in Table 15.
Minimum and maximum temperatures were measured at
Station 10i 24.01C and 33.0*C. Temperatures of 24-C were
also encountered once each at Stations 6 and B. The aver-
age monthly temperatures for the period of study also exhi-
bits a wider range (4.7*C) at Station 10 than elsewhere.
The ranges of the monthly means are shown in Figure 4, and
give an indication of the relative thermal stability at
various points in the area. The shallow waters along the
north shore are not as well mixed and have higher and more
variable temperatures.
Temperatures are lower and exhibit less fluctuations
in the deeper and more exposed east and south parts of the
Page 10
area where good mixing with open sea water occurs. Aver-
age temperatures were lowest and very constant at Stations
1 and 2. The depth at these stations, 6.9 and 10.7 meters,
respectively, is, however, considerably greater than that
at other sample sites. The shallower more protected parts
of the area tend to be more sensitive to variations in air
temperature than are the deeper better flushed locations.
Thus, during cooler periods and at night, water temperatures
in the shallows fall below those at the deeper, exposed
stations; while during warmer weather or in the daytime,
water temperature in the shallows are higher than those at
deeper stations.
Salinity
Salinity varied widely, both spatially and temporally
(Table 1). Generally the shallow, more protected reaches
of Banner Bay and the Lagoon maintain a higher salinity than
do the more mobile waters to the south. However, during
Hay and June, 1970 unusually heavy rains caused considerable
flooding throughout the island. In May the study area and
its watershed received sone eight inches of rain, almost
half of it between May 9 and 10. Seven inches of rain fell
in June, about four inches from June 14 to 16.
In Benner Bay and especially the Lagoon, salinities
were depressed considerably; most notably at Station 10
Page 21
where a minimum salinity of 4.9 ppt. was recorded on
June 19. All stations showed some effects of the run-
off and the results are somewhat revealing of water circu-
lation in the area.
Before flooding, the highest salinity levels were at
Station 10; average for February and March were 37.5 and
37.8 ppt. During these months the average salinity at
individual stations ranged from 36.3 to 37.8 (Stations
11 and 10 respectively); a range of 1.5 ppt. During the
same period the range on any given day was from 0.7 ppt.
to 1.8 ppt. (mean, 1.2 ppt.). As might be expected, sali-
nity was most regular at Station 1, where the range of daily
values was 34.8 to 37.0 ppt. and of monthly averages from
February to June 35.2 to 37.0 ppt.
After flooding,the range increased to as much as 31.0
ppt. when, on June 19, 1970 salinities of 4.9 ppt. and 35.9 ppt.
were measured at Stations 10 and 4. Figure 5 shows the effects
of flooding in May and June on the average salinity based on
eleven sampling stations. The rank of stations in order of
increasing salinity reduction was, in May: 1, 3, 6, (2,7) 5,
8, 9, (4, 11) 10. In June the relative rank was the same,
with the exception that salinity was least affected at Sta-
tions 4 and 11. The relative ranking is as follows (4, 11) 1,
3, 6, (2, 7) 5, (8, 9) 10. The degree of salinity changes
Page 12
at various stations can be appreciated from the ranges of
the monthly averages shown in Figure 4 and Table 15.
The spatial distribution of salinity and its reduction
and recovery at each station following flooding can be seen
in Figure 6. The monthly salinity averages have been rounded
to the nearest 0.5 ppt. to facilitate comparisons. By the
beginning of July salinity at most stations was still below
normal and the range throughout Benner Bay and the Lagoon
was still 5 to 6 ppt.
Since Stations 4 and 11 are at the southern end of the
Lagoon and since the prevailing predominant water movement
is south to north and tends to oppose the southward spread
of flood water, these data indicated that very large amounts
of fresh water from Turpentine Run may reach as far south as
Patricia Cay. This may be aided if flooding occurs during
calm seas or very low tides at which times wave indicted
transport from south to north through the Lagoon is at a
minimum. (McNulty, at al, 1968; Michel, 1970).
Pace 13
Dissolved Oxygen
In general, waters throughout the area are well-
oxygenated (Table 2). Daytime levels below 5.0 mg./L
were measured only at Station 10. Mean oxygen content
for the study period was highest at Stations 3 and 4.
This is perhaps not surprising since both are located in
lush growths of Thalassia and other algae and, in addition,
have superb water clarity and good circulation due to their
positions near the periphery of the study area. The high-
est and the lowest levels of D.O. encountered were measured
on March 21; 8.2 no./L at Station 2 and 4, and 4.6 mg./L
at Station In (Table 9). Dissolved oxygen levels seemed
to be unaffected by flood run-off following the May rain-
storms. The data (Table 2) does not indicate any correla-
tive changes. Monthly averages for eaci station are given
in Table 15.
EH
The pH at all stations was usually between 8.2 and 8.4.
Of all the measurements made the lowest was 7.8 taken early
on the nornine of April 21 at Station 10. It will he shown
later, during analysis of the diurnal studies, that night-
time pH values can fall below 9.0. However, the lowest mid-
day value was 8.0. Like other variables measured, pl was
more chanaeable at shallower or more polluted spots. The
Pace 14
range of values measured was 8.2 8.4 at all stations
except Stations 6 10. At Stations 6 and 8 the range
was from 8.1 to 8.4; at Station 9, 8.1 to 8.5 and at
Station 10, 8.0 to 8.4.
Water Clarity
Water clarity is the single most variable water quality
indicator in the Benner Ray-Lagoon area. Basically, all of
Benner Bay, and to a lesser extent the channels from Benner
Bay weRt to the Lagoon and southeast to Jersey Bay, have
poor water clarity and color. In these areas the bottom is
typically not visible. Secchi depth is as little as 0.25
meters, the water contains dispersed fine particulate matter.
and the color is brown, greyish brown or greenish brown.
Quantitative data for water clarity and color are in
Tables 4, 5, 6, 7 and 14.
The bottom is never visible at Stations 6, 7, 0 and
9 in Denner Bay even though the depth at all these points
is less than 2.5 meters. In contrast, the bottom could
always be seen at Stations 3 and 5 and it was (except
following mud-laden flood run-off) always visible at
Stations 1, 4, 10 and 11 (Figure 4).
Following flooding on May 9th to 10th, Secchi depths
were first reduced at those stations nearest the sites of
Page 15
input: the northern Lagoon and the heavily developed Benner
Bay Marine basin. Secchi depth reduction was not noted at
Station 11 until five to seven days later and the bottom
was again visible here after another three or four days.
At Stations 1 and 2 more than a week passed before turbidity
reached levels high enough to obscure the bottom. At Sta-
tions 3, 4 and 5 turbidity, while increased, was usually not
severe enough to obscure the bottom.
The relative transparency of water at various points
is shown in Table 5. These data do not indicate optimum
or usual water clarity because the area was still suffer-
ing some effects of the early May flooding when the measure-
ments were made. In particular, the data from Station 11
greatly underrated the clarity of this water which, under
normal conditions, is probably the best in the whole area.
It will be noted that the extinction rates given in
Table 5 relate well to the Secchi Depth measured on the
same day (Table 4). If one divides the amount of available
light (surface light) in Table 5 by the extinction rate at
each station, it will be seen that this theoretical limit
of visibility approximates very closely the Secchi Depth
actually recorded. At Stations 2 and 9 these calculated
depths of visibility are greater than the depth to the bottom
(which is visible from the surface at these locations),
NPa- 16
indicating that the water is of a clarity sufficient to allow
greater visibility; that is, the Secchi Depths at these
stations are limited by the bottom and not by the clarity
of the water. This close correlation between Secchi Depths
and light transmittance in coastal waters has also been re-
cently reported by Holmes (1970).
The amount of suspended matter (Table 7) in the water
varies throughout the study area, as is obvious on visual
inspection. Further, those sites which routinely have high
turbidity are also most heavily affected during periodic
flooding. of interest is the observation that, following
the initial drop in concentration of suspended solids, con-
tributed by flooding on May 9th to 10th, there was a second
slighter increase about a week later (Figure 7). This in-
crease is attributed to organic debris from organisms dam-
aged or killed by the suddenly lowered salinity. Beginning
on May 18th, when enough mud had cleared from the water to
make a noticeable improvement in clarity, large amounts of
floating material was noted throughout the Lagoon. Most ot
it was recognized as fragments of Thalassia, various fila-
mentous algae, and hydroids which are abundant on the mangrove
roots.
On Hay 11, after the storm, the entire area was heavily
silted and visibility was poor everywhere. The plume of muddy
Page 17
water extended as far south as the reef and, at that time,
as far east as Bird Cay and out to a line running to the
eastern tip of Cas Cay. The area around Station 3, south of
Compass Point, was not noticeably affected at that time. The
turbidity was highest, of course, in the northern reaches of
the Lagoon proper and throughout the channel north of Bovoni
Cay. The bottom was visible at Stations 2 and 3 and points
southeast and the surf cresting over the reef to the south
presented an effective barrier to the further southward spread
of the plume. Besides the considerable amounts of mud still
in suspension, quite a lot had already settled and was dis-
turbed by the boat's prop. At approximately 4:30 p.m. on
May 11, with the tide at or near low slac; there was good
flow of very turbid water from at least two points on the
north shore, one adjacent to Station 10, the other farther
west.
On May 13 little improvement was noted. A traverse
from Station 10 to 11 stirred up large amounts of brown mud.
By May 18 there was improvement in some areas, most notably
at Station 11 and southward, where clean, sandy bottom with
open worm holes was visible. Clearing to a lesser extent
was noted north of Station 11 with increasing amounts of
settled clay and turbidity toward the shore where there was
still no evidence of improvement. By May 20, however, the
Paae 10
bottom was again visible where it usually was, except still
along the north shore of the north shore of the Lagoon.
From October 3 to 11 rainstorms again produced consider-
able run-off, but the effects this time were confined to
Benner Bay and the north shore of the Lagoon.
As far as we can tell the water quality and the bottom
biota have not yet returned to normal everywhere. Along the
north shore of the Mangrove Lagoon and throughout the channel
from Benner Bay into Jersey Bay, turbidity has remained higher
than it was before flooding. A distinct brown plume extend-
ing from Henner Bay into Jersey nay well southeast of Cas Cay
is visible from the air. The shallows over the grass flats
northwest of Cas Cay to Bovoni Cay are not noticeably affected,
however. This continued turbidity is believed to be maintained
by periodic clay contributions caused by rain showers and, in
Benner Bay, aided by boat traffic which keeps silt suspended.
Water color also, because of increased turbidity in these
quarters, is poor.
Estimates of shallow water color are greatly subject to
the character of the bottom. The color estimate may, barring
large amounts of suspended matter, be the color of the bottom.
The apparent color of the waters in the study area falls into
four broad categories:
1. Brown, opaque water of Benner Bay and the north
shores of the Mangrove Lagoon (Forel-Ule colors ranging from
Pa,.,, 1
XVIII-XXI) contains large amounts of suspended and dissolved
materials.
2. Green or bluish-green water is relatively clear,
low in suspended matter and transmits light reflected from
plant cover on the bottom. In deeper water the blue com-
ponent is heightened as the longer wave lengths are selec-
tively absorbed by the water, giving colors from bluish
green (IV), tending toward blue (I), which is characteristic
of clear, deep offshore water.
3. Apparently green water (VI-XII) contains some sus-
pended matter, but it primarily reflects the color of the
grass and algal cover of the bottom. The largest portion
of the area falls into this range, including the grass beds
between Bovoni and Cas Cays and most of the Mangrove Lagoon
proper west of Bovoni Cay.
4. Clear, essentially colorless water which is not
really embraced by the Forel-Ule scale, is found over clean,
current-swept sand in the channels and northof Patricia Cay.
I'ae 20
Diurnal Studies
This section presents the results of two twenty-four hour
studies of the fluctuations of temperature, salinity, pH, and
dissolved oxygen at six sites in Benner Bay and the Lagoon.
Measurements and water samples were taken at each station at
three hour intervals. Data were also taken periodically on
sunlight intensity, air temperature, wind, sea and tide state.
Diurnal fluctuations of water quality parameters in
Banner Bay and the Lagoon are the result of physical and bio-
logical dynamics which are extremely variable from site to
site. Tidal effects on salinity, temperature, etc. vary de-
pending on the site, because of the peculiar combination of
wave and tidal forces throughout the area and fluctuations
of these parameters follow an unusual spatial sequence dic-
tated by the local bathymetry and shoreline irregularities.
Besides the familiar pumping effect of tidal action on
water movement, the state of the tide is also critical to
water movement induced by wind and waves offshore of the
Lagoon. The offshore currents south of the cays have a
westerly set with velocities, varying with the tide, from
2.4 to 28.8 ft./min. (McNulty, 1960; Michel, 1970).
McNulty's group found that at slack tides the drift was in-
terupted and either no current was measured or there was a
weak easterly current.
Page 21
North of the reefs, inside the Lagoon, Michel and
Tabb (1968) found that water movement was always northerly.
Their measurements were made north of Bovoni Cay, between
Long Point and Patricia Cay and between Patricia and
Cas Cays.
Tidal Variation along the southern coast of St. Thomas
is of mixed character (both diurnal and semidiurnal) although
it is primarily diurnal, i.e. one high and one low per day
(McNulty, at al, 19608 Michel, 19701 U. S. Dept. of Commerce,
ESSA, 1970). The average tidal range is about 0.8 feet.
McNulty (1968) and Michel (1970) both found that the
amount of water entering over the reefs to the south of the
Lagoon depends on the height of the tide and is modified by
the state of the offshore seas. This circulation, which is
generally quite good, tends to increase on the high tide and
is enhanced by strong wind and wave activity. According to
McNulty, et al, (1968) the general wind and surf induced
circulation through the Lagoon is north, northwest into the
Lagoon from the reefs which run from Long Point to Cas Cay;
water then moves easterly from the Lagoon into Benner Bay
via the channel north of Bovoni Cay, and then south, southeast
into Jersey Bay. Circulation in the northwestern Lagoon and
in the head of Benner Bay is usually somewhat retarded. Our
observations support this description.
Page 22
During times of extremely low tides, however, we have
observed the tops of the Acropora reef protruding from the
water, exposure of the Porites-Penicillus back-reef flats,
and apparent cessation of water movement in the Lagoon.
Both McNulty (1968) and Michel (1970) also observed simi-
lar periodic loss of circulation. At such times, with calm
weather, the southerly movement of Lagoon water is unopposed
by the usual wind driven waves from the reefs, and hyper-
saline or storm water may move south from the northwest
Lagoon into the channels around Patricia and Bovoni Cays.
This rather unique interaction of waves and tides and
its effects on circulation and flushing of the Lagoon is
crucial to the hydrography and ecology of the area. One
of the most obvious of these effects is that increased
circulation causes the water in Benner Bay and the Lagoon
to become more homogenous, generally reflected by a reduc-
tion of the usually higher salinities in northeast Benner
Bay and northwest Lagoon to levels closer to those of the open
sea to the south. This effect is less marked at deeper more
exposed stations (2, 4, 11) which normally maintain salini-
ties close to open sea values, and, as a consequence, the
range of salinity throughout the area is compressed.
On the other hand, during periods of poor circulation
evaporation increases salinity in the more remote areas and
distinct spatial heterogeneity develops.
Page 23
Air and water temperatures were higher in April than in
March but at most stations dissolved oxygen reached higher
levels in March. In March pH was lower, especially at night,
possibly the result of higher metabolic activity associated
with the higher water temperatures. Diurnal oxygen curves,
although markedly different among stations, were similar
at each site on both occasions.
These pictures of the diurnal changes in dissolved
oxygen are useful in assessing the health and productivity
of an area.
Under purely physical forces, dissolved oxygen in sur-
face waters tends to equilibrate at 100 per cent of satura-
tion. The analysis of diurnal oxygen curves for their fluc-
tuation around the saturation point can be used to assess
the metabolic activity of an area and to estimate changes
in photosynthesis and respiration and the relative balance
between the two. Dissolved oxygen levels beyond saturation
indicate net photosynthetic activity while concentrations
below saturation reflect relatively greater respiration than
photosynthesis and, therefore, a net consumption of oxygen.
Station 2 (Figure 9) was the deepest of the diurnal
stations and on both occasions maintained supersaturated oxy-
gen levels well into the night. Dissolved oxygen never fell
far below saturation. The surface water here is well mixed,
Page 24
not heavily taxed by the benthos and probably equilibrates
to near the saturation point at night more as a result of
diffusion across a concentration gradient at the air-sea
interface than as a result if respiratory depletion which
would be expected to cause a continued fall in the dissolved
oxygen curve to levels further Below the saturation point
than were actually encountered. In fact, the curves show
a definite leveling off just at or below the saturation
levels.
A similar situation is indicated at Station 11
(Figure 14) where, however, daytime levels do not reach as
high and there is a greater depletion at night. The depth
here is only one-fifth that at Station 2, the bottom is clear
white sand with a rich infauna, but practically no grass or
algae.
Oxygen curves from Station 4 (Figure 10) are closest
to a simple diurnal pattern and indicate an extremely pro-
ductive area where photosynthesis rapidly builds up dissolved
oxygen during the daytime, where this production ceases and
a net respiratory depletion begins in the evening and where
nighttime demands continue to reduce dissolved oxygen levels.
Station 4 is characterized by an extremely rich algal-
grass community, very good water clarity and almost continuous
water movement from the reef northward. In such clear waters
over Thalassia beds we have observed thousands of small oxy-
gen bubbles rising to the surface from the grass leaves.
Page 25
Diurnal oxygen changes at Station 7 (Figure 11) are
similar to those at Station 9 and indicate maintenance of
nocturnal oxygen concentrations by transport associated
with the tides. Oxygen concentrations were least dynamic
that is, showed the least degree of change, at Station 9
(Figure 12). Changes in concentration follow gentle slopes
and the dissolved oxygen is, except for a few hours during
the day, near or below saturation. The maximum concentra-
tion attained during the day was the lowest for all stations
studied. On the other hand, nighttime minima were not as
low as at Station 10, probably because of the greater volume
of water and apparently lower benthic biomass at Station 9
(the bottom here is patchy Thalassia, as opposed to a dense
cover at Station 10). Oxygen curves at Station 9 are very
similar to the salinity curves which may indicate that oxy-
gen changes here are due mainly to transport. This interpre-
tation is supported by the fact that nighttime concentrations,
on both occasions, did not fall steadily, but were supported
during the flood and high tide (2000-2400 hours). In fact,
there is bulge or "knee" in both curves during this period.
The greatest diurnal oxygen consumption is indicated at
Station 10 (Figure 13) where dissolved oxygen is far below
saturation for all but six hours during the day.. In addi-
tion, there is a considerable lag in oxygen buildup in the
Page 26
early morning following very low levels (4.6 mg./L) to which
it falls at night. The nighttime depletion of dissolved
oxygen is extremely rapid, due most likely to the respiratory
demands of the bottom fauna. It should also be remembered
that the water is very shallow here (average O.Sm.) and so
the volume overlying a given area of bottom and the total
amounted oxygen it carried is not great. The result is that
the small oxygen reserve produced during daylight is rapidly
used up at night. The dominant benthic organism here is
dense Thalassia, so that the aereal potential for oxygen
production is great and once production commences the con-
centration raises quickly to high levels (7.8 to 8.0 mg./L).
However, because of the shallow water column and the generally
higher temperatures and salinity, there is little storage
capacity for oxygen and on both occasions levels fell rapidly
after about 3 p.m. Recovery from nocturnal low begins only
after an early morning lag, but is relatively rapid.
Page 27
SUMMARY
This study and the available literature reveals that
the Benner Bay-Mangrove Lagoon area is one of diversity;
diversity not only of habitat types but in the degree of
anthropogenic destruction throughout the area. Benner Bay,
as a result of concentrated development for marine faci-
lities, is biologically devastated. Water color and clarity
are extremely poor because of an extremely high loading of
various dissolved and suspended pollutants, including clay,
organic matter and hydrocarbons. The visibility is so poor
that the bottom cannot be seen anywhere in the Bay even
though the maximum depth is only about 2.5 meters. Diur-
nal oxygen balance indicates an excess of respiration over
photosynthesis. In addition, the Bay is well protected
and, while perhaps desirable for marina facilities, is
incapable of handling the present pollution load because
the rate of addition is greater than the rate of removal.
It is expected that the Benner Bay environment and water
quality will continue to deteriorate, although further
changes will, relatively speaking, be of no great import.
Water quality and natural systems are less affected to
the west along the northern fringe of the study area and
improve rapidly toward the south. There is an obvious plume
Page 28
of turbid water which extends from a focus in Benner Day south
into Jersey Bay along the navigable channel east of Bird Cay.
Environmental stresses on the Lagoon are increasing from ex-
panding development in Nadir and Bovoni and as far away as
Tutu which contribute increasing amounts of silt and fresh
water during storms. Sewage eutrophication and pollution
from the Nadir plant will increase and there are signs that
the ability of the receiving water to absorb these wastes is
waning. Foam from the plant is frequently piled up along the
northwest shore.
In addition, previous studies (Michel and Tabb, 1968;
Michel 1970; McNulty, 1970) have shown that this corner of the
Lagoon is one of the most poorly flushed reaches of the area.
It is, therefore, probably the least suitable to receive sew-
age effluent. The ability of the system to absorb this waste
in the past is testimony to the healthy and productive nature
of this environment. However, this ability to assimilate
organic and inorganic nutrients is not infinite and with the
increasing pressures of other ecological modifications (silta-
tion, fresh water, turbidity), the productivity and assimila-
tion potential of the Lagoon nay be declining. At any rate,
conditions are presently less normal in this quarter than they
are elsewhere in the Lagoon. All of the lagoon, however,
still appears highly productive even though siltation on
Thalassia, resulting from floods a year ago, still persists.
Pace 2"
The southern section of the Lagoon, the reefs and the
grass flats northeast of Cas Cay remain superb examples of
shallow tropical reef and marine pasture systems. They re-
main so because of the unique northerly flow of clean water
from the open sea, because they are not subject to heavy
boat usage and because Long Point and the cays are undeveloped.
The data collected in this study indicate this area is one
of very high net productivity.
Page 30
RECOMMENDATIONS
We strongly urge that the local government come to a
decision on the use to which the Mangrove Lagoon is to be
put. The present course of development in and around the
area increases pressures daily on this unique ecosystem.
Because of the lack of a stated objective for the area,
continuing development and shoreline alteration is destroy-
ing this area as a basic production, prime recreational and
as a research site. Its value for these purposes is being
lost by default.
The uniqueness of this environment on the island,with
its presently healthy and varied complex of habitats,pro-
vides a site of significant natural value for which esti-
mates of the esthetic and economic worth have not yet been
constructed. Its destruction, however, can have decisive
and far-reaching effects, many of which cannot be predicted
and some of which are likely unimagined.
In recent years detailed productivity studies and va. te
analyses have been accomplished for particular open coastal
submerged lands, mangrove swamps, and river swamps, and for
the first time a total resource worth has been described
for some of the coastal zones of the states of Florida and
Georgia. These value estimates range from $300 per acre
Page 31
per year for fish production alone on the coastal sub-
merged lands, to over $3,000 per acre per year total value
for the highly productive protected marshes. The present
worth of an asset yielding $3,000 per year over a long term
at nominal interest rates would be listed at a surprising
figure in the hundreds of thousands of dollars; thus, if the
worth of protected lagoons and marshlands is computed in
terms of the 100-year asset value, a not worth in the range
of $200,000 to $300,0n0 per acre would be realized.
The island has several marine facilities and other bays
which could be used for additional anchorage. There is no
other good representative of the mangrove ecosystem in the
Virgin Islands. Sube (19F8), in a survey of island resources,
said:
"The beach vegetation, mangrove and rain forest
areas are important vegetation types because of
their relative scarcity compared to other types.
They are also important as. natural features which
contribute to the diversity of the scenery. There
is only one remaining mangrove lagoon of size in
the U. S. Virgin Islands. It is located on the
southeast shore of St. Thomas. . Decisions on
the allocation of this resource should be withheld
until comprehensive scientific investigations have
Page 32
been completed and its intrinsic natural values
have been more clearly delineated."
Housing, horseracing and commercial establishments
could be planned in the Bovoni-Nadir area in a manner con-
sistent with the continued healthy existence of the Mangrove
Lagoon -- if its preservation were deemed desirable govern-
ment policy. Me cannot justify destruction of the Mangrove
Lagoon by over-developnment deemed necessary to accomplish
alternate critical land or water user and with the possible
exception of the proposed jetport, none of the existing or
proposed land use schemes is absolutely essential at the
site. Whether the jetport is built or not, the Mangrove
Lagoon will be lost -- is presently being lost -- by de-
fault because the appropriate policies and priorities have
not been yet assigned.
If there is a decision to preserve the area in a state
close to the natural, then immediate action is needed to
develop a management plan to ensure proper protection and
preservation. In some instances, remedial action may he
necessary. It cannot be too strongly emphasized that the
present course of development in the Nadir and Bovoni area
is inconsistent with the maintenance of the Mangrove Lagoon
in the natural state.
Decisive planning for use of the Lagoon itself is just
as important, although less pressing, or the area,too, will
Page 33
be committed to further marina and other shoreline develop-
ment. Because of its predominantly shallow depth and rela-
tively small water volume, the Lagoon is unsuited for sewage
outfall or navigation. If development and pollution pressures
continue to increasethe natural cleansing abilities of the
system will be overloaded and the Lagoon will succumb and
eutrophy to a much less desirable state.
Several recommendations are here offered to serve as
a basis for action in Benner Bay and the Lagoon as well as
to indicate some of the problems which we feel require atten-
tion. These recommendations are built around the following
assumptions:
1. The proposed airport will not be built.
2. The Mangrove Lagoon is a valuable resource
and should be so treated.
3. Banner Bay has been committed to use as a
commercial marina area.
4. Planning for the beast use of the territory's
resources requires the maintenance of a diver-
sity of ecosystems, particularly those which
are unique because of their rarity or because
they are representative segments of local resources.
The recommendations build the framework for planning
and establishing a Virgin Islands Coastal Zone Preserve
which, besides its aesthetic worth, will continue to be
of value as a recreation site for fishing, sightseeing
and swimming; an educational resource for use as a living
laboratory; a research asset which can play a significant
Page 34
part in the development of the Islands' economic future
and a nursery for the fishery of the northern Virgin Islands.
The suggested houndries of the preserve in minimum area
form and references to the recommendations are shown in
Figure 15.
In May, 1970, by letter to the Department of Conser-
vation and Cultural Affairs, Caribbean Research Institute
recommended designation of the area as a territorial natural
preserve, protected by legislation and warden policing. Areal
extent recommended was "all of the peninsula west of the la-
goon, Patricia Cay, Cas Cay, Bovoni Cay and all of the smaller
mangrove islands; all of the enclosed submerged lands and
enclosed waters, the grass/sand flats east of Bovoni Cay and
north of Cas Cay, and the marine waters and submerged lands
offshore to the south to a water depth of ten fathoms."
The area outlined in the 1970 recommendation included
more land area on the peninsula west of the Lagoon (the
western slopes), but did not include Bird and Rotto Caya.
This investigation does not support need for inclusion of
the western slopes for adequate protection of the Mangrove
Lagoon itself, but does suggest need to isolate the flats
east of Dovoni Cay from heavy boat traffic hence, relo-
cation of the channel into Renner Ray if the traffic to the
existing commercial marinas is allowed at the present level.
The land on the western slope of the Long Point peninsula
Page 35
should still be considered for inclusion in a Coastal Zone
Preserve to be set up in more than minimum area form.
Recommendation I:
Marina development should be confined to Benner Bay
and any extension should be east rather than westward. No
further development should be allowed on the shoreline north
of Bovoni Cay. Additional commercial marine activity should
be shifted to the Red Hook area (see Grigg, et al, 1970).
All activity allowed under an area use and development
plan must be closely monitored and strictly controlled. Sub-
merged land permits, zoning exceptions and building plans
must be complete in detail and exact in scope. All applica-
tions need to be reviewed with consideration of possible
leechings and discharges and direct disposal of effluents
prohibited.
Recommendation II:
No dredging should he allowed outside of Benner Bays
except if channel deepening is allowed in the development
plan, it should not be allowed in the present channel west
of Bird Cay. Necessary access channel improvement should
be made around Compass Point north of Bird and Rotto Cays
(as shown in Figure 15).
Page 36
Recommendation IIIs
The government should acquire the necessary land on
Long Point (or institute restrictive zoning to ensure its
use in a compatible manner), to include at least all of
the eastern slopes and designate the area generally within
the suggested boundaries shown on Figure 15 as a Virgin
Islands Coastal Zone Preserve.
Well planned, limited access to scenic and recreation
points would allow public use of swimming and fishing areas.
General motor boat traffic within the preserve should be
prohibited or strictly regulated. The area would be made
available for educational use by local and visiting students
and teachers and could be used for a wide variety of research
and development programs.
As such, it could become an outstanding example of
multiple resource use, which is particularly suited to small
island settings which have limited resources.
Recommendation IV,
The Nadir sewage treatment plant should be made to
operate closer to optimal. Eventually, the effluent should
be piped to an outfall point which is better situated to
provide rapid diffusion and dilution of the effluent.
There is need for buffering the Lagoon from the pre-
sent effects of the effluent now discharged; thus,
Page 37
construction of a polishing pond for further reduction of
the effluent strength is recommended. Additionally, eco-
nomic feasibility of reuse of the polishing pond effluent
should be studied -- as in flushing/irrigation systems in
the new housing development constructions.
Recommendation Vi
The proposed horse race track should not be placed
close to the shore, but should be located far enough west
to allow for a green belt between it and the shore to act
as an ecological buffer zone. Design proposals for this
facility should include features necessary to minimize
runoff and other pollution of the Lagoon. Use of a race
track-park area here will have to he continually regulated
and policed as are the other sections of the preserve.
Page 36
LITERATURE CITED
Dammann, A. E. 1969. Study of the fisheries potential of
the Virgin Islands. Contrib. #1, Virgin Islands
Ecological Research Station, College of the Virgin
Islands.
Donnelly, T. 01. and J. Whetten 1968. Field guides to the
geology of St. Thomas, St. John and St. Croix,
Virgin Islands, Fifth Caribbean Geol. Conference.
Grigg, D. I., R. P. vanEepoel and R. W. Brody 1970. Water
quality and marine environment of Vessup Bay,
St. Thomas. Water Pollution Report No. 8,
Caribbean Research Institute.
Holmes, R. W. 1970. The Secchi disk in turbid coastal
waters. Limnol. and Oceanogr. 15(5):688-694.
McNulty, J. K., W. B. Robertson and B. F. Horton 1968.
Departmental study team report and recommendations
on proposed now jet airport, St. Thomas, Virgin
Islands, U. S. Dept. of Interior.
Michel, J. F. and D. C. Tabb 1968. A study of the biolo-
gical and coastal engineering aspects of the pro-
posed jet airstrip at Jersey Bay, St. Thomas,
II. S. Virgin Islands; Part II, Coastal engineering
considerations, Institute of Marine Sci., University
of 'aTi.a.
Page 39
Michel, J. F. 1970. A study of the hydrodynamic effects
of the proposed airport at Long Beach Point,
St. Thomas, Virgin Islands. Univ. of Miami,
School of Marine and Atmospheric Sciences. Rpt.
to the Virgin Islands Port Authority.
Tabb, D. C. and J. F. Michel 1968. A study of the biolo-
gical and coastal engineering aspects of the pro-
posed jet airstrip at Jersey Bay, St. Thomas,
U. S. Virgin Islands, Part I. Biological considera-
tions. Institute of Marine Sciences, University of
Miami.
U. S. Dept. of Commerce, E.S.S.A. 1970. Tide tables.
East coast North and South America. U. S. Govt.
Printing Office, Washington, D. C.
U. S. Dept. of Interior, F.W.P.C.A. 1967. Biological
aspects of marine water quality, St. Thomas,
St. Croix and St. John, U. S. Virgin Islands.
F.W.P.C.A., Tech. Advisory and Investigations
Branch, U. S. Dept. of Interior.
Zube, E. H. 1968. The islands. Selected resources of the
U. S. Virgin Islands. U. S. Dept. of Interior.
Page 40
APPENDIX
Figure;
1. Location Map
2. Study area and watershed
3. Sampling stations
4. Panges of monthly averages of temperature
and salinity
5. Salinity changes during study period
6. Monthly averages of salinity to nearest
0.5 ppt.
7. Suspended solids changes during study period
8. Air temperature and sunlight during diurnal
studies
9. Diurnal variables at Station 2
10. Diurnal variables at Station 4
11. Diurnal variables at Station 7
12. Diurnal variables at Station 9
13. Diurnal variables at Station 10
14. Diurnal variables at Station 11
15. Suggested land usage
16. Distribution of benthic communities
Table:
1. Temperature and salinity
2. Dissolved oxygen
3. pH
Page 41
4. Secchi depth and average water depth
5. Submarine illumination
6. Water color
7. Suspended solids
8. March diurnal temperature and salinity
9. March diurnal dissolved oxygen
10. March diurnal pH
11. April diurnal temperature and salinity
12. April diurnal dissolved oxygen
13. April diurnal pH
14. Means, maxima, minima and ranges of
diurnal data
15. Monthly averages for water quality
parameters
Pace 42
TABLE I
BENNER BAY MANGROVE LAGOON
TEMPERATURE (C) AND SALINITY (PPT.)
STA T I ON
DATE
1 2 3 4 5 6 8 9 10 11
T S T 6 T 8 T S T 8 T S T T S S T 8 T S
2/12/70 27.1 36.5 27.4 36.9 27.7 36.9 27.9 36.8 28.8 37.0 28.6 37.2 28.5 37.2 28.2 37.2 28.3 36.9 --
2/17/70 28.8 36.8 26.8 37.7 26.9 36.4 28.0 36.6 27.6 38.2 27.5 37.0 27.5 37.0 27,6 37.2 27.2 38.1 ---- -----
2/19/70 26.8 36.6 26.9 37.0 27.3 36.6 27.5 36.5 28.1 36.6 27.9 37.1 27.& 37.1 27.9 37.2 27.7 37.5 -- --
2/24/70 26. 36.5 26.3 36.5 27.0 36.5 26.4 36.3 27.5 36.8 27.3 36.8 27.0 37.1 27.5 36.8 27.0 36.8 27.5 37.5 26.5 36.3
2/26/70 26.7 -- 27.2 -- 27.5 27.7 -- 28.1 28. -- 27.5 -- 28.0 -- 28.0 -- 27.0 26.9 --
)3/4/70 26.3 37.0 25.0 37.0 25.2 36.5 24.8 36.8 24.4 37.0 24.0 37.5 24.2 37.0 24.0 37.3 24.2 37.2 24.0 37.8 24.4 36.6
3/10/70 27.5 -- 28.0 29.5 1 28.0 -- 28.0 -- 29.0 -- 30.0 -- 29.0 -- 29.0 28.0 28.0 --
6/11/70 27.0 36.6 -- 35.7 -- 28.0 30.1 -- 33.2 35.8 -- 353.5 35.7 -- 31.6 29.0 10.8 29.0 22.4
5/13/70 27.0 37.0 27.0 36.9 26.5 36.8 26.2 34.8 28.0 35.8 28.0 36.1 28.0 36.2 28.0 36.1 29.5 33.6 31.2 14.0 27.8 27.3
5/15/70 -- 37.0 -- 36.9 -- 37.3 -- 32.7 -- 35.7 37.1 -- 36.9 -- 36.8 -- 34.4 -- 13.7 31.1
5/18/70 36.5 -- 3.4 -- 36.6 -- 36.3 -- 36.8 -- 36.0 -- 3.3 -- 36.3 -- 36.5-- 32.2 34.0
5/20/70 29.4 -- 27.5 16.6 28.0 29.0 35.5 29.5 35.9 29.5 2 3.6 29.5 36.8 29. -- 30.0 35.5 32.0 34.0 30.0 37.0
5/23/70 28.2 36.9 29.4 37.3 29.5 36.9 30.5 37.1 31.1 36.9 30.6 36.9 31.0 37.0 30.5 37.2 31.0 36.2 33.0 33.1 31.2 35.7
5/25/70 27.2 36.8 27.4 36.9 27.4 36.9 27.6 37.2 28.5 36.7 28.4 37.0 29.2 37.4 29.0 37.1 28.3 36.9 29.6 33.4 28.6 36.A
5/29/70 28.7 -- 28.1 37.5 29.5 -- 28.0 37.4 28.8 37.3 29.0 37.3 29.2 37.4 28.9 37.3 29.2 29.2 36.1 28.8 37.3
6/19/70 35.5 -- 32.4 -- 34.9 -- 39 31.0 34.7 31.9 30.1 -- 24.8 -- 4.9 -- 35.6
6/23/70 34.8 -- 3350 -- 34.6 -- 36.3 -- 33.6 33.4 33.7 -- 33.7 -- 26.7 -- 34.
6/25/70 -- 34.7 -- 35.2 -- 34. -- 34.4 -- 34.6 -- 35.1 -- 4.1 -- 26.3 35.4
6/29/70 35.7 -- 35.9 -- 35.3 -- 35.1 -- 34.7 -- 3 .3 34.3 30.6 -- 35.
7/1/70 -- 32. -- 32J -- 330. .61 3 .0 32.7 -- 32.7 29.8 35.-
TABLE 2
BENNER BAY MANGROVE LAGOON
DISSOLVED OXYGEN (mg/L) AND % SATURATION
__________________________________STATION _______________
1 2 a 4 5 6 7 8 a 9 100
DATE D. % 1Sat. D.O %Sat.D.O. %Sat. D.O. % Sat. D.O. %Sat. D.O. at D.O. 1%Sat D.O. %sat. D.O. J%Sat. D.O.at. D.OSat.
5.2 80 15.4 84 I6.3
5.7 90 S.6
87 I I -
2/12/70
2/17/70
2/19/70
2/24/70
2/26/70
3/04/70
3/10/70
5/11/70
5/13/70
5/20/70
5/23/70
5/25/70
5/29/70
TABLE 3
BENNER BAY MANGROVE LAGOON
PH
STATION
1970 1 2 3 4 5
8.4 8.4 8.3
8.2 8.3 8.2 8.2
8.3 8.4 8.4 8.3
8.4 8.4 8.4 8.4
8.4 8.4 8.4 8.4
8.3 8.3 8.3 8.3
8.2 8.4 8.2 8.2
8.4 8.4 8.3 8.4
8.2 8.2 8.3 8.2
8.4 8.4 8.4 8.4
8.4 8.4 8.4 8.4
U.2 8.3 8.3 -
8.2 8.2 8.2 8.2
8 7 8 9 10 11
8.2 8.2 8.2 8.3 -
8.1 8.1 8.0 8.1 -
8.2 8.2 8.1 8.3 -
8.3 8.4 8.4 8.3 8.4
8.4 8.2 8.2 8.3 8.1 8.2
8.3 8.2 8.2 8.3 8.3 8.2
8.3 8.4 8.3 8.2 8.2 8.2
8.3 8.3 8.3 8.2 8.4 8.3
8.4 8.4 8.2 8.5 8.2 8.3
8.4 8.4 8.3 8.4 -
8.4 8.4 8.4 8.4 8.2 -
- 8.4 8.2 -
8.3 8.2 8.1 8.2 8.0 8.2
TABLE 4
BENNEK BAY MANGROVE LAGOON
SECCHI DEPTH AND AVERAGE WATER DEPTII (METERS)
DATE STATION
1970 1 2 3 4 5 8 7 8 9 10 11
2/12 B 2.8 B B B 1.5 0.8 0.8 1.5 -
2/17 B B B B B 1.3 1.0 1.5 -
2/19 B 4.8 I! B B 1.3 1.0 1.0 1.3 -
2/24 B B B B B 1.0 1.0 1.0 1.0 B B
2/26 B 6.5 B B B 1.5 1.3 1.0 1.3 B B
3/04 B B B B B 1.3 1.0 1.3 B B B
3/10 B 4.5 B B B 1.0 1.0 1.3 1.8 B B
5/13 B D B B B 1.3 0.8 0.8 B 0.5 1.0
5/15 B B B 1.0 B 1.2 1.0 1.0 0.5 0.5
5 18 B B B B B 0.7 0.8 0.6 B 0.4 B
5/20 10.5 5.0 B B B 0.8 0.6 0.6 B 0.4 B
5/23 9.3 0,3 B D B 0.8 0.5 0.8 1.3 0.3 B
5/25 7.0 5.5 B B B 1.3 0.8 0.8 B 0.8 B
5/29 B 2.5 B B B 1.0 0.8 1.0 1.5 0.5 B
Average
Water 10.7 6.9 1.9 2.0 1.0 1.9 1.5 2.3 1.5 0.8 1.3
Depth
B= Visibility to bottom
TABLE 5
BENNER BAY MANGROVE LAGOON
SUBMARINE ILLUMINATION
Noon, May 13, 1970
0. 5 METER 1 METER 4 METERS 9 METERS
Extinction
Surface Rate
Ft. Ft- Pt. t,- Pet. Ft.- Pet. Ft.- Pet. Ft. -Cand.
STATION Cand. Cancd Loss and. Los Cand. Loss Cand. Loss per metel
2 8,700 7,900 9 5,200 40 3,300 62 780
4 11,700 5,700 51 6,000
7 9,500 1,.900 80 7.600
9 8, 700 7,300 16 2.800
10 8,700 1,700 81 14,000
11 8,700 3,300 51 8,800
TABIE 6
BENNEIt RAY MANGROVE LAGOON
WATER COLOR (FOREI. ULE)
DATE
1970 1 7
STATION
d s. K
2/12 IV V VI
2/17 IV VII VI
2/19 IV VI VI
2/24 mI VI VIII
2/26 IV VI VI
3/04 IV V VI
3/10 Iv VIII VI
5/11 m -
5/13 IV VI V
5/15 IV IV V
5/18 mI V V
5/20 m VIII V
5/23 m VI V
5/2b5 m VI IV
5/29 mI VI V
XIV XIV
xny xvi
XV -
XVII XIX
xvn xix
xv xvi
XV XVII
XV XVI
xv xvi
XIV XV
VIII XIX
XVI XIX
XVI XVI
XVI XV
XVI XVmI
XVII XVII -
XVI XIV -
xvI XVIII xv -
XVI XV XVII XII
XIX XX XVII XVII XV
xvi xvi xv] xvn xn
XVII XVm XVI XVII VI
- xx XVII
XVI xVI xvm xx XVII
XV XVI XVIII XVm XVII
XIX XVIII XVI XXT XVI
xvm xvm xix xxi xvi
XVIII XVII XIX XI XVI
XVI XVI XVI XVm XIV
XIX XIX XIV XXI VII
i970 1 2 3 4 5 6 7 8 9 io 11.
TRain1t
TABLE 7
BENNER BAY MANGROVE LAGOON
NON-FILTERABLE SUSPENDED SOLIDS (mg./l)
(greater than 0.45 micron)
DATE STATION
1970 1 2 3 4 5 6 7 8 9 10 11
5/11 102.6 93.2 20.2 68.8 170.0 93.5 31.0 106.0 695.5 26.8
5/13 10.5 13.6 11.7 17.4 12.6 21.7 19.1 15.3 57.9 21.4
5/15 22.7 22.9 20.0 25.1 18.4 29.1 22.4 27.3 24.4 31.3 31.9
5/18 27.1 43.3 48.6 7.9 36.8 83.3 71.8 71.0 39.6
5/20 64.4 14.3 14.2 8.2 16.3 22.9 24.4 77.9 9.7 8.9 12.4
5/23 29.9 22.8 16.5 29.7 22.4 24.4 25.0 30.6 19.5 16.6
5/25 21.2 12.9 20.0 20.4 19.5 5.5 25.1 32.8 32.9 26.2 20.3
5/29 10.6 15.8 14.6 17.7 33.8 32.8 19.6
6/19 20.9 34.8 27.7 29.5 24.7 31.3 25.6 19.5 17.5 107.2 20.8
6/23 6.5 22.2 23.9 21.3 17.6 26.0 19.1 24.4 17.8
6/25 34.5 15.0 20.4 22.5 19.6 15.6 16.2 21.7 13.3
6/29 2.1 13.-4 8.1 28.8 14.3 22.2 22.9 8.8
7/01 21.6 22.9 12.6 22.6 23.5 0.4 25.9 20.9 2.5
TABLE 8
BENNER BAY MANGROVE LAGOON
DIURNAL STUDY, MARCH 21-22, 1970
Temperature (C), Salinity (%o)
8 T A T I O N
TIME 2 4 7 in 11
3T T S T S T 8 T S T S
0630 26.0 37.6 24.8 37.9 26.0 38.6 25.0 38.1 25.5 38.6 25.0 38.2
0930 26.0 38.3 25.8 37.1 26.0 38.5 26.0 38.3 25.5 38.7 25.0 37.1
1230 26.0 38.3 27.0 37.0 27.0 38.9 26.0 38.3 26.0 41.0 25,.7 37.9
1530 26.5 38.3 27.0 37.3 27.0 38.9 27.0 39.1 27.5 39.7 27.0 38.0
1830 28.5 37.9 26.5 37.2 27.0 39.5 26.0 38.1 26.5 39.3 27.0 38.1
2130 26.0 36.6 25.0 36.6 26.0 37.4 26.0 38.3 26.0 37.6 26.0 36.8
0030 26.0 36.5 25.0 36.5 26.0 38.7 26.0 38.5 26.0 40.1 25.5 37.9
0330 26.0 37.9 25.0 37.0 26.0 37.8 26.0 37.2 25.5 38.6 25.0 36.9
0630 2-.5 38.0 25.0 38.3 26.0 39.1 26.0 38.3 25.0 38.0 25.0 41.0
TABLE 9
BENNER BAY MANGROVE LAGOON
DIURNAL STUDY, MARCH 21-22, 1970
Dissolved Oxygen (mg. /1) and' % Saturation
A T A T I n N
%S t DO %Bt
0630 6.3 97 5.3 80 6.1 94 5.6 85 4.7 70 5.4 82
0930 6.3 97 7.0 106 6.5 100 5.9 91 4.6 69 5.6 84
1230 6.3 97 7.9 122 6.8 106 6.7 103 5.5 86 6.1 94
1530 7.8 122 8.1 126 7.5 117 7.3 114 7.8 124 7.6 119
130 8.2 128 7.8 120 7.8 122 6.8 105 7.1 111 7.4 115
2130 7.5 114 5.9 88 7.1 107 6.7 103 6.5 99 7.3 110
0030 6.7 102 5.7 85 6.9 106 5.8 89 5.4 83 6.5 100
0330 6.3 100 5.5 82 6.3 97 6.1 92 4.7 70 5.4 81
0630 6.5 100 5.7 87 5.5 1 85 5.7 88 5.4 82 5.5 85
I tl17 I~0R.y IflAIrLy.,I el
f
L-
TABLE 10
BENNER BAY MANGROVE LAGOON
DIURNAL STUDY, MARCH 21-22, 1970
pH
STATION
'lIME 2 4 7 9 10 1
0630 8.4 8.3 8.2 8.4 8.4 8.4
0930 8.4 8.:; 8.2 8.4 8.1 8.2
1230 8.3 8.4 8.2 8.3 8.2 8.2
1530 8.4 8.4 8.4 8.3 8.2 8.2
1830 8.3 8.5 8.2 8.3 8.4 8.4
2130 8.2 8.2 8.1 8.2 8.2 8.2
0030 8.4 8.4 8.2 8.2 8.2 8.4
0330 8.4 8.4 8.2 8.3 8.3 8.4
0630 8.4 8.4 8.4 8.4 8.4 8.4
TABLE 11
BENNER BAY MANGROVE LAGOON
DIURNAI. STUDY, APRIL 20-21.1970
Temperature (C), Salinity (%o)
TIME
11 S T AT T N
2 4 7 9 10
TI S
T S
T S
T S
0600 26.5 37.1 25.5 37.1 29.5 38.4 28.0 38.4 27.0 Q 9.Z 7.9 38.9
0900 26.5 36.9 26.5 37.9 28.5 38.6 28.0 38.8 27.0 39.6 27.5 37.1
1200 26.5 38.4 28.0 38.9 28.5 37.9 27.5 38.1 27.5 39.6 27.0 37.3
1500 27.0 37.3 29.0 38.6 129.0 38.9 28.5 39.2 28.0 39.5 28.0 38.8
1800 27.4 38.9 28.0 37.3 28.1 38.6 28.0 37.7 28.0 39.9 28.8 -
2100 27.5 36.9 27.0 37.7 28.3 38.4 27.4 37.9 27.5 39.8 28.5 36.9
2400 26.2 37.1 26.5 36.1 28.0 38.4 27.5 37.5 27.5 39.8 27.5 36.3
0300 27.0 16.5 26.3 36.6 28.0 37.9 27.4 38.4 27.0 39.4 26.5 37.9
0600 26.2 .35.5 26.2 36.9 26.0 39.1 27.0 38.6 26.5 39.6 26.0 37.9
TABLE 12
BENNER BAY MANGROVE LAGOON
DIURNAL STUDY, APRIL 20-21, 1970
Dissolved Oxygen (mg. /I) and % Saturation
STATI ON
TIME 2 7 9 10 11
- .O. %Sat. .O. at. D.O. Sat. D.O. %Sat D.O. %Sat D.O. %Sat.
0600 6.5 99 4.9 73 5.7 92 5.1 81 4.5 70 6.0 94
0900 6.5 97 6.2 94 5.6 88 5.8 92 5.2 81 6.4 102
1200 6.6 102 7.3 116 6.6 103 6.1 97 6.7 106 5.2 80
1500 6.5 100 7.5 119 7.1 114 6.9 111 8.0 127 6.8 10B
1800 7.7 117 7.3 116 6.7 106 6.2 98 6.7 108 7.0 113
2100 7.4 112 6.5 102 6.2 98 6.2 97 5.7 92 7.0 113
2400 7.4 112 0.0 91 6.2 98 6.1 97 5.6 90 6.7 105
0300 6.3 97 6.2 93 5.7 90 5.9 92 5.3 83 5.5 86
0600 0.1 92 0.1 92 5.8 89 5.4 84 4.5 70 5.5 85
I I- -I
TABlIJ 13
BIINNI:R BAY MANGROVE [AGOON
DIURNAL STUDY, APRIL 20-21, 1970
pH
8 TA T ION 0
0900 8.4 8.3 8.2 8.2 8.1 8.4
1200 8.4 8.5 8.3 8.2 8.4 8.4
1500 8.2 8.2 8.0 8.1 8.2 8.1
1800 8.3 8.4 8.1 8.2 8.1 8.3
2100 8.3 8.3 8.1 8.1 8.1 8.3
2400 8.2 8.0 8.0 8.0 7.9 8.2
0300 8.1 8.0 7.9 7.9 7.9 8.0
0600 8.0 8.0 7.9 7.9 7.8 8.0
9
4 7 9 10 11
TABLE 14
BENNER BAY-MANGROVE lAGOON
MEANS. MINIMA. MAXIMA. AND RANGES OF VARIABLES
MEASURED DURING DIURNAL STUDIES
Air
Water Tem
o
C
y tinilaS t
STATION STATION
2 4 7 9 10 11 2 4 7 9 10 11
1970
22.0 25.5 24.8 26.0 25.0 25.0 25.0 36.5 36.5 37.4 37.2 37.6 36.8
28.0 26.5 27.0 27.0 27.0 27.5 27.0 38.3 38.5 39.5 39.1 41.0 41.0
24.1 26.1 25.7 26.3 26.0 25.8 25.7 37.7 37.2 38.6 38.2 39.1 38.0
6.0 1.0 2.2 1.0 2.0 2.5 2.0 1.8 2.0 2.1 1.9 3.4 4.2
1970
24.0 26.2 25.5 28.0 27.0 26.5 26.0 35.5 36.1 37.9 37.5 39.2 36.3
29.5 27.5 29.0 29.5 28.5 28.0 28.5 38.4 38.6 39.1 39.2 39.9 38.8
26.4 26.8 27.0 28.2 27.4 27.3 27.6 37.0 37.2 38.5 38.9 39.6 37.9
5.5 1.3 3.5 0.5 1.5 1.5 2.5 2.9 2.5 1.2 1.7 0.7 2.5
D.O. mIg/, p-H
STATION STATION
2 4 7 9 10 11 2 4 7 9 10 11
1970
6.3 5.3 5.5 5.6 4.6 5.4 8.2 8.2 8.1 8.2 8.1 8.2
8.2 8.1 7.8 7.3 7.8 7.8 8.4 8.5 8.4 8.4 8.4 8.4
6.9 6.5 6.7 6.3 5.7 6.3 8.4 8.4 8.2 8.3 8.3 8.3
1.9 2.8 2.3 1.7 3.2 2.2 0.2 0.3 0.3 0.2 0.3 0.2
1970
6.1 4.9 5.0 5.1 4.5 5.2 8.0 8.0 7.9 7.9 7.8 8.0
7.7 7.5 7.1 6.9 8.0 7.0 8.4 8.5 8.3 8.2 8.4 8.4
6.8 6.4 6.2 6.0 5.9 6.2 8.2 8.2 8.1 8.1 8.1 8.2
1.6 2.6 1.5 1.8 3.6 1.8 0.4 0.5 0.4 0.3 0.6 0.4
3/21-2:',
Min.
Max.
MeRan
Range
"/21-22,
Mim.
Max.
Mean
Range
1/20-21,
1 in.
Max.
Mean
lange
TABLE 15
BENNER BAY MANGROVE LAGOON
MONTHLY AVERAGES FOR WATER
QUALITY PARAMETERS
STATION
1 2 1 3 1 4 5 6 7 8 9 10 Ii
2S. 2. 6.9 27.3 1 21.5 28.1 27.5 k 27.7 27.8 27.6 27.3 26.7
.viamcn 1. 26.5 1 2T.4 26.3 .. .e 26.5 1 27.1 1 20.5 1126.6 1 26.0 26.2
May 27.9 27.9 28.2 28.2 29.2 29.1 29.4 29.2 29.6 30.7 29.2
F 2b. 36.6 37.0 36.6 3&.6 37.2 37.0 37.1 37.1 37.3 37.5 36.3
March 37,0 37.0 36.5 36.8 37.0 27.5 37.0 37.3 37.2 37.8 36.8
May 36.8 36.8 36.9 35.1 36.0 36.6 3 36.7 36.6 35.0 25.9 32.6
June 35.2 33.7 35,0 35.8 33.6 34.4 33.7 33.6 31.7 22.1 35.3
July 32.8 32.7 33.0 32.6 33.0 32.7 32.7 29.8 35.9
Ceb. 8.3 6.4 7.2 6.7 6.3 6.1 6.2 5.8 6.3 6.1 6.4
March 6.5 6.4 6.8 6.6 6.6 6.5 6.6 6.0 6.7 6.0 6,3
May 6.3 6.1 6.5 6.5 6.1 6.0 6.0 6.0 6.8 5.8 6.5
Yob. 8.3 8.3 8.4 8.4 8.3 8.2 8.2 8.1 9.3 8.2 8.3
Ma rch .3 _8.4 8. .--8 T3 8.3 3.3 8.2 a. -
May 8.4 8.3 8.3 8.3 8.3 8.4 8.3 8.3 8.4 8.2 8.3
Feb. 10.7 5.6 1.9 2.0 1.0 1.3 1.0 0.9 1.3 0.8 1.3
iMarh 10.7 5.7 1.9 2.0 1.0 12 1.0 1.3 1.7 0.8 1.3
ay a 9.9 5.7 1.9 1. 1.0 1. 0 0. 0.8 1.4 0.5 1.1
Feb. IV I V VIII XIV XVI XVII XV XVI XVIII IV
a .rh .1 ...V. xv i.I
41.9 27.2 21.0 24.0 23.2 39.9 41.2 41.5 39.8 142.1 23.6
13.7 28.5 22.1 19.6 11.7 27.1 119.8 19.1 19.4 50.6 15.2
21.6
22.9
12.6 22.6 1 23.5
0.4 1| 25.9 || 20.9 2.5
-* ____ B ____ ~ ____ ~l ____ 99 ____ 99 ____ 19
Temp.
C
SlBnity
PPt.
D. 0.
mg1 I
PH
Secchl Depth
Meters
Suspended
Solids
mg/1
1970
- ILL -V
A VI XVU I| AX
S T TIO0MAAS
Ha2mLoilik [S
Al.1
lit'.
44
AQ1M Al
FIGURE 3
Sompla "s toti..:,
f+.: .~.5
FIGURE 4
Benner Bay-Mangrove Lagoon
Ranges of monthly averages
for Temp.(Feb.-May) and Sal.
(Feb.-Jul.) rt'c/r y,
I I . I I I I. I I I I I I I I
38
37
36
35
33
32 r
31
30
2/12.17 19 24 26 3/4 10 5/11 15 18 20 23 25 29 6/19 25 29 7/1
13 23
Figure 5. Salinity changes during study period in Benner
Bay Mangrovo Lagoon. Average for 11 stations.
0 *
e-f - -r -e -d o3
meag .... ri''"" FIGURE 6
li.salt pond 4 Benner Bay-Mangrove Lagoon
salt n>d Monthly averages of salinity
s nd luvisum Feb. to July. 1970
SIto nearest 05 esa
r- U
STA.
140 1
2
a
A4
120 .
XA 7
S}* 10
100 *11
gso
60
60 .
IA
S* A
20 A
D I o
5/11 13 15 I8 20 23 25 29 6/19 ?k 25 29 7/1 .9
Figure 7. Suspended solids following flooding, Benner Bay Mangrove
Lagoon. Line is plot of average values. Particle size greater than
0.45 micron.
6 9 12 15 19 21 24 3
Figure 8. Air temperature and sunlight intensity during
diurnal studies. Solid lines March 21-22, broken lines
April 20-21, 1970
9.0 -
7.0 -
0 5.0
4.0 -
41
40
' 39
37 -_.e --
9.0
8.0 - -
29
28-
27
6 9 12 15 10 21 24 3 6h
Figure 9. Sttion 2. Diurnal variables measured at Benner
Bay Mangrove Lagoon. Solid lines March 21-22, 1970, broken
lines April 20-21, 1970. O indicates n.0 saturation points,
8.0 -
Q~ ~ -. -^
7.0 -
4.0 -
41 -
40 -
39
S 38 ..
37
" 5- -
36 -
9.0 -
8.0 -
ou 29
28 40
. 27-
6 9 12 15 18 21 24 3
Figure 10. Station 4. Diurnal variables measured at Benner
Bay Mangrove Lagoon. Solid lines March 21-22, 1970, broken
lines April 20-21, 1970 0 indicates n.0 saturation points.
II I I I I I I
41 -
3S
3. "
31
9. -
8.
23-
S --- --- -- --- | -- 1 --- --- ---- [
6 9 12 15 18 21 24 3 6h
Figure 11. Station 7. Diurnal variables measured at Benner
Bay Mangrove Lagoon. Solid lines March 21-22, 1970, broken
lines April 20-21, 1971. 0 indicates D.0 saturation points.
II i I I i I
78.
6.0 .
N. %
9. 0
- -
-
- --. -
- -
6
6 9 12 15 1B 21 24 3 6h
Pigure 12. Station 9. Diurnal variables measured at Benner
Bay Mangrove Lagoon. Solid lines March 21-22, 1970, broken
lines April 20-21, 1970. O indicates D.0 saturation points
4.d-
7.0-
6.0 -
4.0 -
41
39 -
38-
37-
36-
9.0-
8.0-
29-
2 -
2-
6 9 12 15 18 21 24 3
Figure 13. Station 10. Diurnal variables measured at Benner
Bay Mangrove Ligoon. Solid lines March 21-22, 1970, broken
lines April 20-21, 1970. 0 indicates D.0 saturation points.
S5.0 -
4.0 -
41 -
40 -
39 -
36 -
9.0 -
8.0 -
29 -
S28-
27
S 9 12 15 21 24 3
Figure 14. Station 11. Diurnal variables measured at Benner
Bay Mangrove agoon. Solid lines March 21-22 1970 broken
lines April 20-21, 1970. 0 indicates M .o saturation points.
RACE ~g
*5
M~mangrove .9FIGURE15
Ij.IJJ~t pond B nlhO BaV-Mangrove Lagoon
saiidv allu~ir .-10A Suggested Land Us.
- - rrnr-r -
nreAcyp dom..c
~masngrove !2
IO atpond
sandy alluvium
FIGURE 16
Bonner Bay-Mangrove Lagoon
Distribution of
Benthic Communities
AL
|
