United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis OR 97333
Research and Development
EPA-600/S3-83-010 May 1983
SEPA Project Summary
Lake Restoration: A Five-Year
Evaluation of the Mirror and
Shadow Lakes Project
Waupaca, Wisconsin
Paul J. Garrison and Douglas R. Knauer
The objectives for the Mirror and
Shadow Lakes study were to determine:
(1) the response of both lakes to storm
sewer diversion; (2) the effectiveness of
an aluminum hydroxide layer in preven-
ting phosphorus migration from the
sediments; (3) if the nutrient control
measures would effectively reduce the
pelagial productivity and standing crop;
(4) the response of the pelagial zoo-
plankton and benthic invertebrate com-
munities to the restorative measures.
Important physical, chemical, and
biological data were collected before,
during, and after the various restorative
procedures. The data collection began
October 1976 and continued until Sep-
tem ber 1981. The first restorative tech-
nique was storm sewer diversion. The
diversion, which was completed in
December 1976, reduced the water-
shed size by 60 percent for Mirror Lake
and 26 percent for Shadow Lake. Exter-
nal phosphorus loading rates were re-
duced by 58 to 65 percent. In May
1978, both lakes were treated with
aluminum sulfate, reducing intake P
concentrations from 0.09 mg/l in
Mirror Lake and 0.055 mg/l in Shadow
Lake to between 0,02-0.03 mg/l. These
lower concentrations were still present
at the end of the study. Artificial circula-
tion of Mirror Lake in the fall prevented
fish winter kill by increasing oxygen
concentrations, while spring circulation
increased the period of oxidation above
the sediments.
Following restorative measures, algal
primary productivity was reduced 40
percent in Mirror Lake and consequently
sedimentation rates of C, P, and N also
declined. The vernal phytoplankton
standing crop was reduced in Mirror
Lake and the community composition
changed from one dominated by blue-
green algae to a more diverse assem-
blage. In response to a decrease in the
trophic status of Mirror Lake, the zoo-
plankton community declined. In re-
sponse to the spring and fall artificial
circulation periods in Mirror Lake, the
size of the benthic invertebrate com-
munity greatly increased.
This Project 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 order-
ing information at back).
Introduction
In the last century, cultural eutrophica-
tion of some lakes has become a problem.
With an increasing population, greater
impact has been placed on our waters.
With increasing nutrient loads due to
perturbation of the watershed, the lakes
have become less desirable, owing to
large standing crops of algae and macro-
phytes. With the increase in population
and leisure time activities has come
greater awareness of lake water quality
conditions and a desire to promote im-
provements.
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The strategies and schemes for correc-
tive action include both those which
control the problem sources and meas-
ures which treat only the symptoms.
Perhaps one of the most frequently
applied solutions is diverting the major
source of incoming nutrients away from a
lake. The results of such diversion can be
very spectacular as in the case of Lake
Washington (Edmondson, 1977), or very
disappointing as in the case of Lake
Norrviken (Ahlgren, 1977). In cases where
nutrient diversion is not successful, the
problem can be traced to continued
nutrient input from the sediments.
The restoration plan for Mirror and
Shadow Lakes included elimination of
the major external nutrient source by
diversion of the storm sewers, reduction
of internal phosphorus loading by adding
aluminum sulfate after the storm sewers
were diverted, and artificial circulation in
Mirror Lake to prevent winter fish kills.
Storm sewer diversion was completed by
December 1976, the aluminum sulfate
was applied in May 1978, and mixing
began in November 1977.
Study Area
The study lakes (Figure 1) are kettle
lakes that were formed during the last
glaciation period about 12,000-13,000
years ago in the pitted margin of the Gary
outwash plain. The lakes are located in
central Wisconsin in the City of Waupaca.
The current watershed of Mirror Lake
consists of 13.1 ha of residential lawns
and rooftops. The present watershed of
Shadow Lake, 56.7 ha, is more diverse
containing residential areas, undeveloped
lowlands, and some paved streets Mirror
Lake has a maximum depth of 13.1 m,
mean depth of 7.8 m and a surface area of
5.1 ha. The maximum depth of Shadow
Lake is 11.6 m while the mean depth is
5.3 m and the surface area is 17.1 ha.
Results
By the late 1 960s, residents surround-
ing Mirror Lake complained of winter fish
kills and offensive algal odors. Subse-
quent studies indicated that storm sewers
were adversely impacting Mirror and
Shadow Lakes. A paleolimnological study
confirmed that in Mirror Lake following
the introduction of storm sewers in the
1930s, the eutrophication process was-
accelerated as demonstrated by an in-
creased sedimentation rate, occurrence
of diatoms that indicate eutrophic condi-
tions, increased organic matter and pig-
ment degradation products including the
blue-green algal pigment oscillaxanthin.
N
Figure 1. Mirror and Shadow Lakes study area in the city of Waupaca, Wisconsin.
Nutrient Diversion
The diversion of the storm sewers was
completed in December 1976. This re-
duced the Mirror Lake watershed size
from 32.2 ha to 13.1 ha and Shadow
Lake's from 76.9 ha to 56.7 ha. More
importantly, the phosphorus loading rate
was greatly reduced from 0.341 /g/mVyr
to 0.120 g/mVyr for Mirror Lake. The
phosphorus loading rate to Shadow Lake
was reduced from 0.236 g/mVyr to
0.099 g/mVyr. In Mirror Lake, epilim-
netic concentrations of P and N were
reduced 50 percent and 34 percent
respectively the first summer following
storm sewer diversion. Unlike years prior
to storm sewer diversion (Knauer 1975),
algal biomass and primary productivity
were unresponsive to occasions of majc
rainfall events.
Artificial Circulation
Mirror Lake usually did not completel
mix in the spring or fall prior to th
installation of the aeration unit. Becaus
of the relatively large accumulated oxyge
deficit in the bottom 1 meter and failure)
mix in the fall, winter fish kills occasior
ally were experienced. Much of the bo
torn sediments were constantly overlai
with anaerobic waters so the benth
invertebrate community in the deep wati
area was nonexistent.
The Mirror Lake implementation pie
requires the lake to be artificially mix<
for two to three weeks in November ar
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immediately following ice out. As a result
of artificial circulation, dissolved oxygen
concentrations have been maintained at
adequate levels during ice cover even
during the winter of 1978-1979 when
many potential winter kill lakes in the
area were severely stressed with a pro-
longed period of low dissolved oxygen.
Spring mixing has resulted in higher
water temperatures during summer strati-
fication of 2-4°C. The mixing regime
greatly increased benthic invertebrate
population (Chaoborus punctipennis) to a
high of 2200 organisms/m2.
Alum Treatment
Although storm sewer diversion greatly
reduced external phosphorus loadings,
the inlake phosphorus concentrations at
spring mixing remained almost un-
changed. The high phosphorus concentra-
tions were maintained because of inter-
nal loading via phosphorus migration from
the hypolimnetic sediments. In order to
reduce the internal loading, aluminum
sulfate was applied below the epilimnion
in both lakes in May 1978. As shown in
Figures 2 and 3, total phosphorus con-
centrations were greatly reduced in both
lakes In previous years, dissolved reactive
phosphorus (DRP) concentrations ex-
ceeded 0.40 mg/l in the hypolimnion as P
migrated from the bottom sediments.
Following the alum treatment, DRP levels
were generally less than 0.004 mg/l
throughout the lake and never exceeded
0.060 mg/l in the bottom waters. In-situ
measurements of internal loadings from
the lake sediments were measured using
nutrient regeneration chambers before
and after the alum treatment. While
ammonium-N release rates were unaf-
fected, P rates were greatly reduced. Prior
to the alum treatment, the release rate in
both lakes was 1.30 mg P/m2/day
Release rates following the treatment
were 0.07 mg P/mVday in Mirror Lake
and 0 12 mg P/m2/day in Shadow Lake.
The relatively low summer epilimnetic
nutrient concentrations in Mirror Lake
were unchanged following alum treat-
ment The main reason was the develop-
ment of a large population of the blue-
green alga Oscillatoria agardhn The popu-
lation dynamics of this alga involved an
early spring bloom which incorporated
most of the inlake dissolved phosphorus
into an organic form. Since O. agardhii
prefers cool water temperatures it con-
centrates into the lower metalimnion
during the summer, thus displacing most
of the nutrients from the upper waters.
With the reduction of internal P loading,
Mirror Lake
Phosphorus
Alum
10 122 4 68 10 12 24 68 W 12 2468 10 12 246 8 10 12 24 68
1977 1978 1979 1980 1981
Figure 2. Weighted mean phosphorus concentration for Mirror Lake
Shadow Lake
Phosphorus
0 OSt-
Alum
24 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8
1977 1978 1979 1980 1981
Figure 3. Weighted mean phosphorus concentration for Shadow Lake
the biomass of the vernal algal community
was greatly reduced. In Mirror Lake, the
spring chlorophyll a concentrations in
1977 and 1978 were greater than 50
mg/m3. In the spring of 1979, 1980, and
1981, the chlorophyll a concentrations
were reduced to 5-10 mg/m3. In Mirror
Lake the spring phytoplankton community
also exhibited a steady decline in domi-
nance by 0. agardhii from 78% m 1977 to
13% in 1981. The O. agardhii population
was replaced by a diverse algal assem-
blage.
Theannualprimaryproducton in Mirror
Lake was reduced from 210 gC/m2 in
1978 to 130 gC/m2 in 1 981. While pro-
ductivity was lower the summers follow-
ing storm sewer diversion and the alum
treatment, the greatest reduction oc-
curred during spring mixing. With a
reduction in primary productivity, the
sedimentation rates of carbon, nitrogen,
and phosphorus were reduced. Carbon
and nitrogen sedimentation rates de-
clined 27 percent while phosphorus
declined 56 percent. This mdica'tes that
competition for phosphorus increased as
the inlake phosphorus concentration de-
creased. Since 80-85 percent of the
phosphorus produced in the euphotic
zone is mineralized before it is buried in
the sediments, it is very important to
reduce major external nutrient sources,
References
Ahlgren, I 1977. Role of sediments in
the process of recover of a eutrophi-
cated lake. pp. 372-377. In H. L.
Golterman ed. Interactions between
sediments and fresh water. Dr. W. Junk
B. V. Publishers.
Edmondson, W. T. 1977. Trophic equilib-
rium of Lake Washington. EPA-600/
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3-77-087. U.S. Environmental Protec-
tion Agency. Corvallis, OR.
Knauer, D. R. 1975. The effect of urban
runoff on phytoplankton ecology. Verh.
Internal. Verein. Limnol. 19:893-903.
Paul J. Garrison and Douglas R. Knauer are with the Wisconsin Department of
Natural Resources, Madison. Wl 53707.
Spencer A. Peterson is the EPA Project Officer (see below).
The complete report, entitled "Lake Restoration: A Five-Year Evaluation of the
Mirror and Shadow Lakes Project Waupaca, Wisconsin," (Order No. PB83-J76
578; Cost: $13.00, 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 Research Laboratory
U.S. Environmental Protection Agency
200 SW 35th Street
Corvallis. OR 97333
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
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Penalty for Private Use $300
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ASENCY
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