740
Notes
An analysis of salinity
variations
within
Abstract-A
series of correlation
coefficients comparing
stream flows with Great
South Bay salinities
indicates
that changes
in salinity observed within the bay were statistically
associated with variations in stream
flow. No significant
correlation
between salinity and rainfall was observed.
The results
may have significance
to outfall sewering on
Long Island.
Great South Bay is a tidal lagoon along
the south shore of Long Island (Fig. 1).
The bay, whose salinities are about 20%
lower than that of the coastal ocean, has experienced large-scale variations in its salinity regime over the past 50 years. The most
dramatic changes occurred in 1931 following the breaching of the barrier beach and
the opening of Moriches Inlet. As the exchange rate with the ocean increased, bay
salinities rose from ~13%~ to ~26%, ( Hair
and Buckner 1973). Since this event, salinities have shown smaller fluctuations in
response to variations in inlet stability,
ocean salinity, and freshwater discharges.
It has been speculated that the planned
use of sewage ocean outfalls on Long Island may affect the salinities within the
NEW
JERSEY
Fig.
ATLANTIC
1.
Study
area and sampling
OCEAN
locations.
Great South Bay, New York
bay when groundwater tables of the underground aquifers are lowered and the flow
of the 95% aquifer-fed surface streams (Pluhowski and Kantrowitz 1964) and subsurface outflows which discharge into the bay
are reduced (EPA 1972; Franke 1973).
Here I present evidence that the salinities
are correlated with stream flows and will
therefore be affected by any project which
alters these discharges.
I thank S. Lane for providing the salinity
data (collected by J. Foehrenbach).
I also
thank M. J. Bowman, R. W. Wilson, and
C. D. Hardy for their criticism of this
manuscript and E. R. Baylor for his discussions on this topic. Figure 1 was drafted by
M. Eisel; The Marine Sciences Research
Center (Stony Brook) provided computing
facilities.
Spearman rank correlation coefficients
( r, ) ( Sokal and Rohlf 1969) were computed to quantify the relationships between
bay salinities, stream flows, and rainfall. A
correlation
between groundwater
table
levels and rainfall
( Cohen et al. 1968)
showed no direct relationship
between
these variables.
Salinity data came from l-4 samples randomly collected each month from June
through September from the three stations
shown in Fig. 1 between 1967 and 1973.
Salinity
was measured by the Harvey
(1955) titration technique with an estimated accuracy *O.lsO.
Mean monthly stream discharges from
he Connetquot River (U.S. Geol. Surv.
1954-1973), the major tributary of the region, were used. Monthly
precipitation
records came from a rain gauge located at
Patchogue, New York (Fig. 1). Monthly
averaged bay salinities were correlated
with mean monthly stream discharges and
the total monthly precipitation.
Higher
order frequency variations were not analyzed because of inadequate data. There
were 27 data points from each station.
The computed correlation
coefficients
are shown on the scatter diagrams of Fig.
2. All are statistically significant at the
Notes
.
-.*.* .
. .* .
.
l
741
.
.
1
I
.
*
.
-1
.
.
.
.
I_
600
1
I,000
BOO
MEAN
MONTHLY
,
1,200
DISCHARGE:
1,400
ILITER%
30
-1
1;
1,600
1
t
.
.*
8
-a- 27 t
.
*
,
l.
0.75*
.
,
.
.
-
.
*
.
.
L
600
1
rs =
29
MEAN
MONTHLY
MONTHLY
4
6
8
10
12
IChl / MONTH
14
16
18
20
1
Fig. 3. Rainfall
versus salinity
at station 1.
The analysis utilizes salinity data taken during the
months of June through September, 1967 to 1973.
NS-Nonsignificant
correlation
at the 95% confidence limit.
.
.
*.
.
5
~.ooo
800
MEAN
2
RAINFALL
,
28
0
DISCHARGE
DISCHARGE
1
.
.
,
1,400
I.*co
(LITERS
2
a.600
,S )
(LITERS/S)
Fig. 2. Connetquot
River discharge versus salinity at stations 1, 2, and 3. The analysis utilizes
salinity
data taken during the months of June
through September, 1967 to 1973. Asterisk-statistically
significant
correlation
at the 95% confidence limit.
95% confidence limit (rcrit = 0.381) (Rohlf
and Sokal 1969). In comparison, the correlation of salinity with precipitation was not
statistically significant (rs = 0.11) (Fig. 3).
A review of the scatter diagrams and correlation coefficients suggests that salinity at
each station varies most during periods of
low flow and that the correlation decreases
with increasing distance from the mouth of
the Connetquot River.
To verify the relationships between salinity, stream flow, and rainfall, I used the
published data of Hair and Buckner (1973)
who analyzed the average salinity values
in the bay from 1954-1972 (the years 1955,
1957, 1966, 1967, and 1971, when salinity
data were not available or Moriches Inlet
was only partially open, were not included).
I computed a correlation coefficient comparing the yearly averaged Great South Bay
and Moriches Bay salinities with total annual rainfall and mean annual stream flow
from the Carlls River (Fig. 1) ( U.S. Geol.
Surv. 1954-1973 ) , selected because of its
close correlation with groundwater levels
(Franke 1973). The results gave an rs
value of -0.74 for stream flows compared
with bay salinity. There was no significant
correlation (rcrit = 0.553) (Rohlf and SokaI
1969) between bay salinity and precipitation ( rs = -0.40) (Figs. 4 and 5).
The computed correlation
coefficients
indicated that the changes observed within
bay salinities were associated with variations in stream flows. The remaining unexplained variations in salinity are probably
controlled by a combination of factors including changes in the salinity regime offshore, fluctuating
tidal cycles causing
742
30
Notes
I
/
29
28
. .
eIj 27
L 26
.
3
..
“,252
.
a2 2411
i
,,L-L’.,.
400
600
/
/
These calculations confirm the hypothesis that bay salinities are associated with
stream discharges and indicate that altering
the dicharges will alter the bay’s salinity.
The data of Cohen et al. (1968) suggest
that the same will hold true for the relationship between subsurface outflows and bay
salinities.
Paul D. Moskowitx
i
rs = -0.74*
. ..
800
MEAN ANNUAL
I,OW
1
1,200
(LITERS/S)
DISCHARGE
I*400
I
l.6c.c
Fig. 4. Carlls River discharge versus average
bay salinity ( 1954-1972 ) . The analysis excludes
1955, 1957, 1966, 1967, and 1971 (see text). Asterisk-statistically
significant
correlation
at the
95% confidence
limit.
changes in the flushing time of the bay, and
the sizes of the inlets: Fire Island Inlet is
in fact quite variable and requires annual
maintenance dredging. Single large storms
may also influence Great South Bay salinities by introducing unusually large quantities of freshwater (Mar. Sci. Res. Center
1973) *
Although
direct
rainfall
contributes
about 15 to 30% of the freshwater discharged into the bay on an annual basis,
my analysis did not show any significant
correlation between salinity and rainfall.
The reason for this is not clear, but may be
related to the simplified analysis which did
not allow for specific storm events.
rs = -0.35
NS
i
[I
.
.
.
.
.
.
I
100
RAINFALL
[CM/
I
I
I25
150
175
YEAR)
Fig. 5. Rainfall
versus average bay salinity
( 1954-1972).
The analysis excludes 1955, 1957,
1966, 1967, and 1971 (see text). NS-Nonsignificant correlation
at the 95% confidence limit.
Environmental
Defense Fund
162 Old Town Road
East Setauket, New York 11733
References
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Submitted:
Accepted:
14 April 197’5
11 March 1976