United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis OR 97333
Research and Development
EPA-600/S3-81-017 August 1982
Project Summary
The Monitoring of the
Restorational Dredging of
Collins Lake, Scotia, New York
C. J. George, P. L. Tobiessen, Phillip D. Snow and T. K. Jewell
This report describes a study carried
out to evaluate the impact of hydraulic
dredging on the restoration of Collins
Lake in the Village of Scotia, Schenectady
County, New York. The principal purpose
of the dredging was to remove nutrient-
rich sediments. The extent of the dredg-
ing operation covered approximately 10
percent (2.6 hectares) of the lake bottom
with the removal of 52,000 m3 of or-
ganic enriched sediment. The dredging
took place from August to November in
1977 and June to August in 1978. The
dredged material was placed in a sedi-
mentation basin constructed 100 m
southeast of the lake.
Important physical, chemical, and bio-
logical data were collected before, during,
and after the dredging operation. The
field survey work began in July of 1976
and was completed in August of 1979.
Sampling was carried out every two
weeks at several depths for four stations.
Additional studies on macrophytes,
fishes, and sediments were conducted
at other locations within the lake.
Interpretation of the results was com-
plicated in several ways. During the
study, there was a decline in the lake
level brought about by a lowering of the
outlet level. Also, extremes in weather
occurred along with backf looding of the
lake by the adjacent Mohawk River.
The curly leaf pondweed, Potamogeton
crispus, which had previously grown at
problem densities over most of the lake,
did not recolonize in the dredged areas
during the study period. Other biological.
chemical, and physical features of the
lake remained relatively unchanged.
While this report contains some interest-
ing and useful data, only a continued
evaluation would document the long-
term effectiveness of hydraulic dredging
to retard recolonization of the dredged
area by P. crispus.
This Profect Summary was developed
by EPA's Environmental Research Lab-
oratory, Corvallis, OR, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report ordering
information at back).
Introduction
This report describes a study to eval-
uate the impact of hydraulic dredging on
the restoration of Collins Lake in the
Village of Scotia, New York. Collins Lake
and its adjacent park is a major recrea-
tional center of the village and the region
within approximately a 50 km radius. It
is one of the few public waters in the
vicinity suitable for swimming and often
attracts over 500 users per day during
the summer. Collins Lake has a surface
area of 24.3 ha, mean depth of 3.8 m,
and is a hard water, well-buffered system.
The lake has been severely impaired by
earlier uses and activities such as adja-
cent landfilling with domestic wastes,
concrete debris, and sediments from the
Mohawk River; stormwater runoff; and
the introduction of the water chestnut,
Trapa natans, and the curly-leafed pond-
weed, Potamogeton crispus. This resulted
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in at least 60 percent of the lake surface
being covered predominantly with P.
crispus along with the production of
large amounts of organic matter with the
deeper waters becoming anaerobic dur-
ing the summer months.
The principal purpose of the dredging
was to remove nutrient-rich sediments
which contribute about 60% of the P in
the water column as shown by the lake
nutrient budget. The extent of the dredg-
ing operation covered approximately 10
percent (2.6 hectares) of the lake bottom.
The dredging took place from August to
November in 1977 and from June to
August in 1978. Dredged material
(52,000 m3) was placed in a sedimenta-
tion basin constructed by building dikes
at the southeast section of the lake
(Figure 1). Supernatant waters were re-
turned to the lake through 200 m of
marsh.
Important data were collected before,
during, and after the dredging operation.
The data included physical, chemical,
and biological characteristics of the lake.
The field survey work for the study begaVi
in July of 1976 and was completed in
August of 1979. Sampling was carried
out every two weeks at several depths
at four stations. One station, established
at the deepest point (9 m), was used to
monitor stratification and whole-lake
effects. The other three were used to
describe dredging influences by compari-
son of dredged with non-dredged stations.
Additional studies on macrophytes,
fishes, and sediments were conducted
at other locations in the lake.
Results
Interpretation of the results of this
study was complicated in several ways.
A modification of the outlet was made
by village personnel, resulting in a drop in
the lake level of 0.5 m during the study.
Seasonal extremes in the weather oc-
curred along with several floods during
the study period and a break in the dike
of the sediment basin resulted in an
unknown amount of sediment and water
returning to the lake. Indian artifacts
were detected in the northern part of the
lake during the summer of 1978. This
required a north-south bar to be kept in-
tact as an archaeological preserve and
created a second small basin in the lake.
The limited extent of the dredging,
along with the brevity of the study, did
not permit a satisfactory definition of
.Springs
Outlet
Sad/mentation
Basin
Figure 1. Collins Lake showing dredged area, wetland, and sedimentation basin.
Letters indicate sample stations and stippling indicates areas dredged.
any possible long-term effects. However,
some short-term effects were noticeable.
The curly-leaf pondweed, Potagometon
crispus, which had previously grown at
problem densities over most of the lake,
did not recolonize in the dredged areas
during the study period. There was obvi-
ously a removal of considerable amounts
of nutrients (N and P). Table 1 shows the
removal of nutrients and turbidity in the
sedimentation basin. Over 99 percent of
the total phosphorus was removed from
the dredged sediments.
The phytoplankton community re-
mained fairly stable during the study
period, with no definite response to the
dredging. The same can be said of the
zooplankton community. New species
did not appear, and there were no changes
in the percentages of each group present.
Conventional indices of condition for
yellow perch and golden shiner showed
little or no response to the dredging
operation. Ceroid deposits of the spleen,
liver, and kidney were used as an index
of trauma. These data suggest trauma
was increasing for the yellow perch and
decreasing for the golden shiner.
Throughout the dredging period,
recreational use of the lake was not ad-
versely affected, and the response of the
people using the lake and those living
around it was generally favorable. There
was some concern about the* lowered
lake level which resulted in the exposure
of many tree stumps and reduced lake-
shore access due to the proliferation of
shore plants. Swimmers using the beach
100 m away from the working dredge
were apparently not disturbed. There
were no reports of odor problems around
the dredged material disposal basin.
Conclusions and
Recommendations
The limited dredging was quite effective
in suppressing the troublesome curly
leafed pondweed in those areas dredged
However, a more extensive approach
focusing on the removal of the P-ricI
surficial layer over a larger area, wouli
have had more impact on reducing thi
available P in the water. Also, if the dis
posal area volume is limited, as it was ii
this project, surficial dredging may be a
especially valuable alternative approac
to deep dredging.
Evaluation of the chemical and biolog
cal state of the lake should be continuec
although at a less intense level than durin
the actual project. Continued evaluatio
would document the long-term effective
ness of dredging as a lake restoratio
tool.
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Table 1. Removal of Nutrients and Turbidity by Sedimentation Basin
Location
Variable
Turbidity fJTUJ
Suspended Solids (mg/l)
Total Phosphorus** (mg/l)
Soluble Phosphorus (mg/l)
Orthophosphate Phosphorus (mg/l)
Ammonia Nitrogen (mg/l)
Nitrate Nitrogen (mg/l)
Inlet
Pipe
A*
NA
42,285
18.11
NA
NA
NA
NA
Concrete
Barrier
B*
NA
8.758
3.79
0.051
0.036
0.01
0.13
Settling
Area
C*
272
184
1.63
0.084
0.055
0.32
0.28
At
Outlet
D*
388
281
0.206
0.086
0.028
0.16
0.13
Seep
E*
220
153
0.148
0.083
0.037
0.26
0.37
In
Wetlands
F*
100
20
0.074
0.065
0.033
0.20
1.03
Wetlands
Outlet
G*
55
36
0.076
0.061
0.027
0.16
0.80
* Location of sample stations in sedimentation basin. Figure 1.
**Estimated using 0.427 mgp/gm dry weight of solids and adding to soluble phosphorus.
NA = not analyzed.
C. J. George, P. L. Tobiessen, Phillip D. Snow, and T. K. Jewell are with Union
College, Schenectady, NY 12308.
Frank Stay is the EPA Project Officer (see below).
The complete report, entitled "The Monitoring of the Restorational Dredging of
Collins Lake, Scotia. New York," (Order No. PB 82-196 874; Cost: $10.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Corvallis, OR 97333
i US GOVERNMENT POINTING OFFICE. 1982-559-017/0782
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Environmental Protection
Agency
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Information
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