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Monitoring cruise at the Western Long Island Sound Disposal Site, July 1988 online

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estimated by comparing pre- and post-disposal bathymetric surveys.
Applying this factor to the present data results in a corrected scow
log volume estimate of approximately 31,300 m 3 of dredged material.

A comparison of the corrected scow log estimate of 31,300
m 3 with the depth difference calculation of 23,370 m 3 showed a
difference of approximately 8,000 m 3 of dredged material which could
not be accounted for on the bottom. Examination of the scow logs
from 1987 confirmed that some disposal took place up to 360 meters
away from the buoy, but scow log positions can be subject to a
number of reporting errors and are difficult to verify with
certainty. Disposal at such distances from the buoy would have
resulted in dredged material being beyond the area used to compare
the November 1987 and July 1988 bathymetric surveys (a 350 x 350 m
area around the center of the "B" mound) and therefore not
represented in the depth difference volume estimate. At WLIS in
1987 and at other DAMOS disposal sites surveyed in recent years, the
corrected scow log volume estimate consistently has been higher than
the depth difference volume estimate. This suggests that the scow
log volume estimate correction factor (40.7%) may require
re-evaluation based on a comprehensive mass balance study.

4.2 REMOTS® Sediment-Profile Photography

One objective of the REMOTS® survey at WLIS was to
delineate, in conjunction with the precision bathymetric survey,
the extent of dredged material deposited during the past year at
the "B" disposal mound. The results indicate that



recently-deposited (i.e., since November 1987) dredged material
occurred at two stations in the immediate vicinity of the "B" mound.
This correlates well with the acoustically-determined changes in
depth noted in this location. Likewise, relict dredged material was
noted at stations at and in the vicinity of the "C" and "A" mounds,
consistent with the results of both the 1988 bathymetric and 1987
REMOTS® surveys. The indistinct, low-reflectance horizons noted at
some stations away from the three mounds (Figure 3-9) serve as
indirect evidence of disposal which might have occurred anytime in
the past, probably well before the 87-88 disposal season.
Apparently these errant disposal events were not all that common,
because the resulting relict dredged material layers present at
these locations appeared relatively thin and are widely-spaced.

A second objective of the REMOTS® survey at WLIS was to
assess environmental impacts related to dredged material disposal.
The lack of significant differences between reference and disposal
site stations in such REMOTS® parameters as RPD depths, percentage
of Stage III organisms, and OSI values indicated a rapid recovery
by the ambient benthic community; the seafloor disturbance caused
by dredged material disposal was apparently rather transient as
detected at the benthic population level. This disturbance
primarily was physical in nature and limited to the immediate
vicinity of the active "B" disposal mound, where stations 3-C and
5-E exhibited OSI values +6. The low OSI values at a small number
of stations elsewhere at the site were caused by variable RPD layers
or within-station patchiness in the distribution of Stage III
infauna. At each reference site, apparent between-station
variability in such parameters as the RPD, OSI and infaunal
successional stage was most likely due to the fact that only one
REMOTS® image was obtained at the individual stations. Because of
the patchy distribution of benthic organisms, and in some cases RPD
depths, it is recommended that additional replicate photographs be
obtained at each individual reference site station in future
surveys. This would match the level of replication employed at the
disposal site and would allow a better assessment of any apparent
variability or sampling artifact caused by using the cross-shaped
station pattern at the reference sites.

In November 1987, significantly greater RPD depths coupled
with a slight increase in the number of Stage III organisms at both
reference and disposal site stations lead to the conclusion that
overall benthic habitat quality at WLIS had improved relative to the
stressed conditions noted during a period of near-bottom hypoxia in
August 1986. This was reflected in the significantly higher OSI
values in 1987 compared to 1986. The 1988 results suggested a
continuation of this trend. While RPD depths and OSI values were
not significantly different in 1988 compared to 1987, there was an
increase in the percentage of replicate photos showing evidence of
head-down, deposit-feeding Stage III organisms. This serves as one
indication that relatively healthy benthic conditions continued to
exist both at the site and in the general area outside the site

8



between the November 1987 and July 1988 surveys. The patchy RPD
layers which existed at many stations may have been a direct
consequence of the sediment-reworking activities of Stage III
organisms. It appears that the reduced sediments which typically
extended to the surface in many of the photos (see Figure 3-13) were
transported from deeper zones as a result of burrowing and/ or
"conveyor-belt" feeding by the larger infauna.

4.3 CTD and Dissolved Oxygen Sampling

The objective of the CTD/DO sampling at WLIS was to assess
near-bottom dissolved oxygen concentrations in relation to benthic
habitat conditions at and in the vicinity of the site. As
indicated, the REMOTS® results suggested that relatively healthy
benthic conditions existed at the time of sampling, although
near-bottom dissolved oxygen concentrations at both the disposal
and reference sites were near the hypoxic range (Table 4-1) . The
strong thermal stratification of the water column apparent in the
CTD profiles most likely contributed to the observed vertical
distribution of DO. Past experience has shown that in Long Island
Sound, the lack of mixing associated with a strong and persistent
pycnocline during the warmer summer months can exacerbate oxygen
depletion in near-bottom waters. Furthermore, the solubility of
oxygen in seawater declines as water temperature and salinity
increase (Weiss, 1970) . Dissolved oxygen concentrations remained
at or close to saturation in the surface waters and were slightly
higher at reference stations 2000W and 2000S. This reflected the
normal spatial and temporal variability in near-surface DO which
might be expected in any estuarine area over a 6 to 8 hour sampling
period.

The relatively healthy benthic conditions at WLIS as seen
in the REMOTS® photos suggest a general absence of stress which
might otherwise be attributed to near-bottom hypoxia in the weeks
and months preceding the survey. On a larger time scale, it was
found that seasonal hypoxia was not as severe or widespread in Long
Island Sound in the summer of 1987 compared to the preceding year
(SAIC, 1988) . This might help to explain the continued improvement
in benthic conditions noted at WLIS in 1987 and 1988, as well as the
generally healthy conditions noted at the other Long Island Sound
disposal sites (CLIS and NLON) in 1987. Conditions observed at WLIS
in July 1988 may still have represented the "pre-hypoxic" condition
in this region of the Sound, with the possibility that hypoxia
developed later in the summer with attendant adverse sediment
effects. However, the dramatic change in both the high reflectance
of the oxidized sediment layers in the REMOTS® photos and the
increased region-wide appearance of Stage III infauna as compared
with results from 2-4 years ago lend increasing support to our
conclusions from earlier studies that the stressed conditions noted
earlier were unrelated to disposal but resulted from region-wide
hypoxia or, in 1985, physical seafloor disturbance due to the

9



passage of Hurricane Gloria. Apparently, seasonal hypoxic effects
in 1987 and the first half of 1988 (up until the July 1988 survey)
were not as severe as they were in the past, and the benthic
communities in and around the disposal site were not showing as much
evidence of stress as they had in previous years.

5 . CONCLUSIONS

Both the precision bathymetric and REMOTS® surveys at WLIS
indicated an accumulation of recently-deposited dredged material at
the "B" mound. The deposited material occurred around the buoy in
a broad, circular mound up to 2.0 m thick having a radius of about
100 m. The minimum depths of the "C" and "A" disposal mounds
remained unchanged since the previous bathymetric survey in November
1987. Relict dredged material was visible in the REMOTS® photos
from stations at and in the vicinity of these two mounds, consistent
with the results of the November 1987 REMOTS® survey.

The lack of significant differences between reference and
on-site stations in such REMOTS® parameters as RPD depths,
percentage of Stage III organisms, and OSI values suggested that
any seafloor disturbance related to dredged material disposal at
the site was minimal. This disturbance primarily was physical in
nature and limited to the immediate vicinity of the active "B"
disposal mound. The July 1988 results further suggested a
continuation of the trend of improving benthic habitat conditions
at the site since it was severely stressed by the passage of
Hurricane Gloria in September 1985 and by region-wide near-bottom
hypoxia in August 1986. This trend was marked by continued
colonization of the site by Stage III taxa.

The generally healthy benthic conditions observed in the
REMOTS® photos suggested an absence of stress related to near-bottom
hypoxia in the weeks and months preceding the survey. At the time
of sampling, dissolved oxygen levels in near-bottom waters were near
the hypoxic range at both disposal and reference stations. This
might have signaled the beginning of seasonal near-bottom hypoxia
in this region of the Sound, as it developed in response to thermal
stratification of the water column. No evidence of extreme adverse
effects of the low dissolved oxygen levels were apparent in the
sediments. The low DO levels measured near the bottom at both the
disposal site and reference stations support earlier studies which
showed this was a region-wide phenomenon unrelated to disposal.

Overall, the results of the July 1988 survey indicate a
continuation of the trend of improved benthic conditions noted at
WLIS after the November 1987 REMOTS® survey (SAIC, 1990) . Similar
to conclusions reached from the November 1987 survey, it appears
that this trend represents a return to relatively "normal"
conditions at the site. Such conditions were noted after the August
1985 REMOTS® survey, prior to both Hurricane Gloria in September

10



1985 and the severe hypoxia which occurred in western Long Island
Sound in the summer of 1986. The improved conditions at WLIS have
been attributed to the lack of severe hypoxic stress in this region
of the Sound during 1987 and 1988. Several investigations in recent
years conducted by the University of Connecticut and SUNY-Stony
Brook for EPA Region I have concluded that near-bottom hypoxia
observed in western and central Long Island Sound during the summer
months occurred in response to a combination of excessive
anthropogenic organic loading (primarily sewage discharge) and
seasonal water-column stratification. The response of the local
benthic environment to dredged material disposal at the WLIS site
is primarily influenced by these persistent and recurrent regional
phenomena .



11



6 . REFERENCES

Parsons, T. R. , Y. Maita and C. M. Lalli. 1984. A Manual of
Chemical and Biological Methods for Seawater Analysis. New
York, Pergamon Press. 173 p.

Perkin, R.G. and E.L. Lewis. 1980. The practical salinity scale
1978: fitting the data. IEEE J. Oceanic Eng. OE-5: 9-16.

Rhoads, D.C. and J. Morse. 1971. Ecological and evolutionary
significance of oxygen-deficient marine basins. Lethaia 4:
413-428.

SAIC. 1988. REMOTS® Reconnaissance Mapping of Near-bottom
Dissolved Oxygen and Benthic Facies: Long Island Sound, August
1987. SAIC Report # SAIC-88/7502&175, submitted to US EPA
Region I, Boston, MA.

SAIC. 1989. Seasonal Monitoring Cruise at the New London Disposal
Site, July 1986. DAMOS Contribution #60 (SAIC Report #
SAIC-86/7540&C60) . US Army Corps of Engineers, New England
Division, Waltham, MA.

SAIC. 1990. Monitoring Cruise at the Western Long Island Sound
Disposal Site, November 1987. DAMOS Contribution #74 (SAIC
Report # SAIC-88/7532&C72) . US Army Corps of Engineers, New
England Division, Waltham, MA.

SAIC. In prep.. Standard Operating Procedure Manual for DAMOS
Monitoring Activities. Draft DAMOS Contribution (SAIC Report
# SAIC-89/7561&C81) . US Army Corps of Engineers, New England
Division, Waltham, MA.

Strickland, J.D.H. and T.R. Parsons. 1972. A Practical Handbook
of Seawater Analysis. Fish. Res. Board Can. Bull. 167.

Tavolaro, J.F. 1984. Sediment budget study for clamshell dredging
and ocean disposal activities in the New York Bight. Environ.
Geol. Water Sci. 6 (3): 133-140.

Weiss, R. F. 1970. The solubility of nitrogen, oxygen and argon
in water and seawater. Deep-Sea Res. 17: 721-735.



12



Table 3-1



Near-bottom and Near-surface Dissolved Oxygen Concentrations at
Selected Disposal Site and Reference Stations at WLIS, July 1988



Station

7-M

7-K

7-1

7-Y

2000W

2000S

WLIS-REF



Near-Bottom


Near-Surface


DO (ma/£)


DO (ma/ 2)


4.1


7.8


4.1


7.2


4.1


7.4


3.5


7.6


3.5


10.2


3.9


8.1


4.2


7.6



Table 4-1



Ecologically Important Dissolved Oxygen Ranges as
Determined from Permanently Stratified Low-Oxygen Marine
Basins (from Rhoads and Morse, 1971)



Dissolved Oxygen Range (mg/2) Facies



> 3.0 Aerobic

3.0 to 0.41 Hypoxic*

0.4 to 0.14 Dysaerobic

< 0.14 Anaerobic



The hypoxic facies has been added to the Rhoads
and Morse (1971) basin model by Dr. Barbara Welsh,
University of Connecticut, to include responses of
high metabolic rate demersal or benthic megafauna.




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Figure 3-6. REMOTS® image from station 3-C directly on the
WLIS "B" mound showing "fresh" dredged material
exceeding the depth of penetration of the camera
prism. The streaky appearance at depth is due to
smearing by the REMOTS® prism and the high water
content of this fine-grained (silt-clay) material.
It is notable that a relatively deep RPD has
developed since the material was deposited. Scale
of image = IX.




Figure 3-7. REMOTS® image from station 5-C at the WLIS "B"
mound showing poorly-sorted, "fresh" dredged
material distinguished by its significant sand
component. This material exceeds the depth of
prism penetration in this image. Scale = IX.




Figure 3-8. Discontinuous sand layers at depth (arrow)

distinguish the relict dredged material in this
REMOTS® image from station 3-G. This station was
located at disposal mound "C". Scale of image =
IX.




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WLIS DISPOSAL SITE
JULY 1988




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all replicates at both the reference and onsite
REMOTS® stations at WLIS, July 1988.







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Figure 3-15. REMOTS® image from station 3-K showing a well-
established Stage I assemblage consisting of
small, tubicolous polychaetes at the sediment
surface, as well as the near-surface dwelling,
opportunistic mactrid bivalve Mulinia lateralis
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like structures barely visible within the RPD
layer are probably deposit-feeding errant
polychaetes. Very small, shallow-dwelling
bivalves also occur below the sediment surface,
giving this image a Stage I going to II
designation. Scale = IX.




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ORGANISM-SEDIMENT INDEX



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ORGANISM-SEDIMENT INDEX



Figure 3-17. Frequency distributions of Organ ism- Sediment Index
values for all replicates at both the reference
and disposal site stations at WLIS, July 1988.



16



25



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Figure 3-18. Representative CTD/DO plot obtained at WLIS
station 3-E in July 1988.



APPENDIX



Station 3-Y (1)



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Station 1-G



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— h-



xxxx



20



* +
x +
x +
x



en




X


CD


15-


X
X


en






^E




X
X


r:


?o-


X


+j




X


Q.






CD




X


Q




X




25-


X
X
X
X




30-


X
X
X
X

s



X x



X +

X +

X +

X +

X +

X +

X +

X +

X +

X +

X +

X +

* +
X +
X +
X +
X +
X +
X +
X +

* *



21



Station -3-A



16



17



Sigma-T
18



++++

19



1

Salinity
27



20

— \-



21

—I



25



26



(ppm]



XX**



28

-I-



29



30

—I



16



Temperature (C.)
17 18 19



xxxx



20

— f-



21



en

c

QJ
-P
QJ



+->

Q.
CD
Q



5"



10-



15-



20-



25-



30-



x
x



X
X



X
X



X

X

X

X

X

X

X

X

X

X

X
X



+

X

*



*

*
*
X

X

X
X

X

X

X
X
X
X
X

X
X
X
X
X
X



+
+
+



+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+
+



35 1



Station -3-M



16



17



Sigma-T ++++

18 19
— i 1



20



21

—I



23



Salinity (ppm) xxxx
24 25 26 27

—I 1 1 h-



28



16



Temperature (C.)
17 18 19
—i 1 h-



xxxx



20



21
—I
x



5"



*

*
+ x
x +



10-



en

c

(D

+J

CD



Q.

CD
Q



15-



20 -



25-



30-



x
x

X

X
X
X
X
X
X
X
X
X
X
X
X
X

i

X

*



+ X

+ X

+ X

+ X

+ a
+ x
+ x
+ x

+ X

+ X


2

Online LibraryUnited States. Army. Corps of Engineers. New EnglaMonitoring cruise at the Western Long Island Sound Disposal Site, July 1988 → online text (page 2 of 3)