Physical
and Ecological
Effects
of Waste Heat
on
Lake Michigan
U. S. DEPARTMENT OF THE INTERIOR
FISH AND WILD LIFE SERVICE
SEPTEMBER 19 7O
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PHYSICAL AND ECOLOGICAL EFFECTS
OF WASTE HEAT ON LAKE MICHIGAN
Prepared by
Great Lakes Fishery Laboratory
Bureau of Commercial Fisheries
Ann Arbor, Michigan
in cooperation with
Bureau of Sport Fisheries and Wildlife
Federal Water Quality Administration
UNITED STATES DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
September 1970
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CONTENTS
I. INTRODUCTION 1
II. DESCRIPTION OF LAKE MICHIGAN 2
A. Overview 2
B. Inshore Waters 7
1. Importance of inshore zone 7
2. Extent of inshore water 10
3. Thermal trends in inshore waters IQ
4. Inshore currents 13
5. Inshore water chemistry 13
6. Fishery resources 15
C. Open Lake 21
1. Definition and extent 21
2. Thermal trends in the open lake 21
3. Currents in the open lake 22
4. Open lake chemistry • 24
5. Fishery resources 25
III. THERMAL LOADING 27
A. Present Loading 27
B. Future Loading (Through Year 2000) 34
C. Waste Heat Dissipation 35
1. Non-technical overview 35
2. Studies of model plumes 41
3. Magnitude of projected waste heat addition 45
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IV. EFFECTS OF TEMPERATURE FLUCTUATIONS ON LAKE MICHIGAN FISH 49
A. Introduction 49
B. Effects on Adults and Juveniles 51
C. Effects on Maturation and Spawning Requirements 59
1. Maturation 59
2. Spawning 60
D. Effects on Incubation Requirements 63
E. Effects on Fry Requirements 68
F. Other Effects 71
1. Effects on fish 71
2. Mortality of water birds 74
3. Intake damage 74
4. Discharge damage 75
V. EUTROPHICATION 77
VI. ECOLOGICAL RAMIFICATIONS OF THE ADDITION OF WASTE HEAT
TO LAKE MICHIGAN 82
A. Introduction 82
B. Generalized Plume Impact 82
C. Potential Impact of Cumulative Waste Heat 86
VII. CONCLUSIONS 88
VIII. LITERATURE CITED 92
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I. INTRODUCTION
There is reason for concern about potential serious ecological
damage to Lake Michigan as a result of the discharge of industrial
and municipal warte heat. At the predicted rate of increase, the
waste heat load "ejected to Lake Michigan by year 2000 would be
more than 10 times the present load. The source of most of the waste
heat will be the power industry. Required power capacity has been
doubling each decade and there is no sign that this rate will diminish.
Everyone concerned with the problem agrees that not enough is
known about the ecological effects of massive heated effluents and
that a great deal of research is needed on this problem. Unfortunately,
the information is needed now; since it is not available, however,
interim standards must be set for Lake Michigan on the basis of existing
knowledge.
The purpose of the present report is to present the available
evidence that substantiates this concern. The evidence reasonably
demonstrates that heat addition, as presently proposed, is an essentially
cumulative problem that would contribute to inshore eutrophication and
be intolerable from the fish and wildlife standpoint by year 2000.
Therefore, it is in the public interest to stop this process now,
rather than attempt the difficult task of correcting or reversing it
after it has occurred. On the basis of the evidence presented herein,
this Department supports stringent standards for Lake Michigan, and
concludes that no significant amounts of waste heat should be dis-
charged into Lake Michigan.
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II. DESCRIPTION OF LAKE MICHIGAN
A. OVERVIEW
The following general information is largely from Beeton and
Chandler (1963) and United States Department of the Interior (1966).
Lake Michigan, the sixth largest freshwater lake in the world,
has an area of 22,400 square miles and a shoreline of 1,661 miles
(including Green Bay) (Figure 1). It is bordered by Michigan,
Indiana, Illinois, and Wisconsin; most of the 67,860 square-mile
drainage area is in Michigan and Wisconsin. Maximum length of the
lake is 307 miles, and maximum width is 118 miles in the northern
basin (from Little Traverse Bay to Little Bay de Noc) and 75 miles
in the southern basin (from Grand Haven to Milwaukee). Maximum
depth is 923 feet and mean depth is 276 feet. Lake volume is estimated
at 173 trillion cubic feet or 1,170 cubic miles.
The southern two-thirds of the lake is an open water area free of
islands. The shoreline is regular and the bottom contours are gentle.
The northern one-third of the lake is characterized by more rugged
bottom relief and shoreline. Islands and bays are common.
No large tributaries (over 5,000 cfs) flow into Lake Michigan, and
it has the smallest discharge of the five Great Lakes--55,000 cfs at
the Straits of Mackinac. Lake level is subject to an annual fluctuation
of slightly more than 1 foot. Water levels are highest in summer and
lowest in late winter or early spring. The average surface elevation
of the lake is 578.77 feet above the mean sea level (International
Great Lakes 1955 datum).
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GRAND
TRAVERSE
BAY
1.38
6.47
GREEN
BAY
13.75
185.55
CAPACITY (H U )
Lscanaba
Pull lam
Kewaunee
Point Beach
Mam towoc
Edgewater
Pt Washington
Valley («il«.)
Commerce St (HiIn.)
Lake Side
Oak Creek
Racine
Zion
Haukegan
South Works
State Line
Mitchell
Bailly
Michigan City
(Mo name yet)
D C Cook
Palisades
So Haven
DeYoung
Campbel 1
Grand Haven
B C Cobb
Traverse City
Big Rock
23
392
527
2«497
52
129(
411
280
35
311
1619
23
2«1100
1066
105
923
390 (
590
203
400
2x1100
811
17.5
53 5
650
23
510
15
75
NU 1972 -
NU 197U72 -
330 in 1969)
in 1969
NU 1972«73 -
115 1970) -
1973
1973
NU 1972173 -
NU 1970 -
CHICAGO
GARY
12.13
148.10
Figure l.--Lake Michigan map showing four shoreline sectors described
by Acres (1970), and estimate of total waste heat production (billions
of BTU's/hr) for 1968 (upper number) and 2000 (lower number). The
sites of existing power installations (numbers 1 to 29) are from
Krezoski (1969).
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Ice is common along the shores of Lake Michigan in winter but
the open lake remains ice-free during all but the most severe winters.
The open lake surface waters range in temperature from a low of 32
to 35°F in March to a peak of 75°F or greater in August. The lake is
stratified in summer and deep waters remain near 39°F throughout the
year (Figure 2). A graphic generalized annual temperature cycle, by
lake sector, is shown in Figure 3.
Winds over Lake Michigan are primarily westerly; at least 60
percent of all observations at Grand Rapids, Michigan, and Chicago,
Illinois, recorded wind from the western half of a north-south line.
The chemical environment of Lake Michigan has changed and is
changing at a significant rate. The concentrations of total dissolved
solids in Lake Michigan are increasing at a rate of about 2 percent
per decade. Typical values were 128 mg per liter in 1880, 142 in 1920,
155 in 1960, and about 158 in 1969. Concentrations of phosphate and
nitrate are also presumably increasing, although this increase cannot
be demonstrated because measurements in past decades were not reliable.
Dissolved oxygen in Lake Michigan, except in southern Green Bay,
is usually above 90 percent of saturation at all depths. A few isolated
measurements of 65 to 90 percent of saturation have been reported for
the hypolimnion of the southern basin. No values below 90 percent
were detected, however, in studies by the Bureau of Commercial Fisheries
Great Lakes Fishery Laboratory in 1968.
Although Lake Michigan in 1970, by generally accepted standards
(and excluding pesticides), has high water quality and most of the
characteristics of an oligotrophic lake, a measurable loss of water
quality is taking place and the rate of change has not been altered.
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LUDINGTON LT
4 = 39.2
8 = 46.4
12 = 53.6
16 = 60.8
20 • 68.0
24 - 75.2
-500
26
25
24
,0 23
22
21
20
SURFACE TEMPERATURE °C
II i
J L
26
25
24
23 O
22°
21
20
B T CAST NO.
Figure 2.—Typical summer vertical temperature structure of Lake
Michigan. Warm waters of 20° to 24°C (68.0-75°F) are in upper
10-20 meters, thermocline or zone of rapid temperature change is
at 15-25 meters, and cold water of 4° to 8°C (39-46°F) at greater
depths.
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For later consideration in this report, it is desirable to dis-
cuss the lake as two distinct, major zones, the inshore zone and the
open lake. The inshore zone is defined as that volume of water
which lies between the shoreline and the 100-foot depth contour.
Within the inshore zone is the beach water zone, a sub-area that ex-
tends from the shoreline out to the 30-foot depth contour. The open
lake zone lies beyond the 100-foot contour. Tables 1 and 2 present
certain characteristics of these zones.
B. INSHORE WATERS
1. Importance of Inshore Zone
The inshore zone of Lake Michigan is probably the most
important portion of the lake from the standpoint of man. Not only
is it the zone that is most used by man (for example, as a source of
water supply for domestic, industrial, and cooling water and as an
area for fishing, boating, and swimming), but it is also the most
biologically productive portion of the lake. The fishery productivity
of the shallow and inshore waters of Lake Michigan has traditionally
been the highest of any area in the lake. For example, within the
State of Michigan waters of Lake Michigan, Green Bay constitutes less
than 10 percent of the area but has contributed as much as 65 percent
of the total annual commercial catch (Mile et al.,1953). Probably one
of the basic reasons for the high productivity of the shallow water is
the presence there of a substrate within the lighted surface zone where
photosynthesis can take place. Also, nutrients are continually recycled
from the bottom back into the water column due to strong vertical mixing
processes.
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Table 1 .--Depth and volume characteristics of the major zones of
Lake Michigan
Zone
Open Lake
Inshore Water
Beach water
(subzone)
Depth range
(ft)
>100
0 to 100
0 to 30
Area
(sq mi)
17,360
5,040
1,677
Percentage
of total
area
77.5
22.5
7.5
Volume
(cu mi)
1,122.0
47.6
4.8
Percentage
of total
volume
95.5
4.1
.4
Entire Lake
22,400
1,174.36
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10
The inshore and surface waters of Lake Michigan also are occupied
by all species of fish (except chubs and sculpins) at one time or
another during their life cycles. Some species such as yellow perch
and catfish spend much of their life in shallow water; other species
are present in the shallows only when immature or during migrations.
2. Extent of Inshore Hater
The average width of the inshore water zone is 3 miles. The
area is 5,040 square miles, or about 22 percent of the total area of
the lake and three times the area of the beach water zone. The volume
of water is 48 cubic miles--10 times that of the beach water zone but
only 4.1 percent of the volume of the entire lake.
In contrast, the beach water zone has an average width of
only 0.96 mile although the average is 2.05 miles for the Chicago-Gary
sector. Its surface area is 1,677 square miles, or about 7 percent
of the lake surface, including Green Bay. The volume is 4.5 cubic
miles, or about 0.5 percent of that of the entire lake.
The approach of Acres (1970) has been followed in dividing
the inshore zone of Lake Michigan into four sections (Figure l).
The physical dimensions of these segments are described in Table 2.
3. Thermal Trends in Inshore Maters
Seasonally, inshore water temperatures range from 32°F to
as high as 82°F. They are lowest from January to mid-March, when the
water is usually covered with ice. The initial period of warming
generally begins in late March. Because of the high surface-to-
volume ratio, the inshore areas warm more rapidly than the open lake.
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11
By mid-April the beach waters are warmed to about 48°F, while the
waters of the open lake remain below 38°F. This situation creates
a strong temperature gradient between the inshore and open lake
waters, and is an effective horizontal mixing barrier, which may
persist as long as 6 weeks. During this time, pollutants introduced
into inshore waters pose a potentially serious problem, because they
are trapped there and progressively increase in concentration.
Inshore surface waters reach maximum temperatures in mid-
August; bottom water temperatures are variable, however, due to
vertical movements of the thermocline. During the summer, such move-
ments are caused by wind-induced internal waves or seiches and cause
bottom temperature changes as much as +_ 18°F in less than 24 hours.
Changes in the wind direction over the lake induce large
changes in the temperature of the entire inshore zone, at least several
times each season. Wind shifts cause surface waters to be blown away
from shore and deep, colder waters to upwell into the inshore zone.
Figure 4 shows the vertical temperature structure of the lake during such
event, including the very cold water along the eastern shore.
The net natural warming causes the top of the thermocline to
descend below the 100-foot depth contour during September to mid-
October. Cooling is rapid in the fall and is complete by late
December.
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12
Figure 4.--Lake Michigan vertical temperature profile in mid-August,
showing thermocline and a seiche-induced upwelling of cold water
along the east shore.
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13
4. Inshore Currents
The currents of the inshore waters are to some extent inde-
pendent of the general system of lake-wide currents (which are dis-
cussed later). Inshore currents move parallel to the shoreline and
with the prevailing winds, especially within the 30-foot depth con-
tour (that is, a wind blowing from the north will cause the inshore
waters to flow south).
Average current speeds at the 60-foot contour tend to be
slower on the western shore of the lake (0.16 to 0.32 ft/sec) than
on the eastern shore (0.38 to 0.45 ft/sec). Since winds throughout
the region average 11 to 13 miles per hour (17 to 20 ft/sec), the
currents average 1 to 3 percent of the wind speed.
5. Inshore Water Chemistry
Generally chemical concentrations are higher and the variation
is greater in inshore waters than in the open waters of Lake Michigan
(Table 3). The inshore waters receive municipal and industrial dis-
charges and have in many locations been classified as being polluted
(FWPCA, 1968).
Ammonia concentrations up to 1.4 mg per liter have been found
near Calumet City, Illinois, and soluble phosphorus concentrations up
to 1.5 mg per liter near Milwaukee, Wisconsin. Phenols and chlorides,
both originating from industrial wastes, have been detected in high
concentrations in inshore waters of the lake.
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14
Table 3.--Chemical characteristics measured in inshore waters of
Lake Michigan in 1962-63
[Values for average and range are in milligrams per liter unless
otherwise indicated; ND - not detectable at sensitivity of test.]
Characteristic
Number of
samples
Average
Range
Dissolved oxygen
Saturation (percent)
BOD
NH3-N
NO^-N
Organic-N
Total P(L
SiOo
Na
K
Dissolved solids
Specific conductance (micromhos
per centimeter)
pH (pH units)
Alkalinity
Ca
Mg
Cl
SO
Ph
.
enols (micrograms per liter)
2,541
1,701
730
1,751
1,654
529
1,382
645
400
453
976
2,452
2,113
2,169
616
898
1,611
1,547
1,033
10
102
1.4
0.13
0.14
0.21
0.04
1.7
4.0
1.2
175
285
105
35
12
7.1
20
2
3.7-16
43-148
ND-8.6
ND-1.4
ND-0.90
0.01-0.70
ND-5.0
0.4-4.4
1.8-7.5
0.5-3.8
86-810
33-1130
6.4-9.3
70-210
17-40
7-14
1.5-94
10-76
ND-32
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15
Dissolved oxygen is sometimes more depleted in the inshore
waters than in deeper areas of the lake. Concentrations as low as
3.7 mg per liter (43 percent saturation) have been detected. Measured
biochemical oxygen demands (BOD) have been as great as 6.7 mg per liter
outside Milwaukee Harbor and 8.6 mg per liter near the mouth of the
Grand River (off Grand Haven, Michigan).
Although levels of most chemical substances in the inshore
waters are not now high enough to be considered critical for most water
uses, they do show evidence of water quality degradation due to the
large amounts of pollutants being discharged to Lake Michigan.
Control of these pollutants has been clearly recognized as a
matter of great public concern; to date more than $1 billion has been
spent by government (at all levels) and industry for sewage treatment
facilities along the shore of Lake Michigan. It is estimated that
several billion more dollars will be required to complete the job.
6. Fishery Resources
Nearly all of the most valuable and abundant native species of
Lake Michigan live in the inshore region, but all of the important
native species that lived in this zone have been greatly reduced or
are now rare (Tables 4 and 5). All of these native species once migrated
into tributary streams and rivers, usually to spawn; except for the runs
of common suckers, these migrations have virtually vanished. The white-
fish was once the most valuable fish of the lake, and whitefish and
lake herring were extremely abundant in shore and tributary areas. Both
species vanished from these areas, however, soon after mill dams,
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18
industrialization, and deforestation blocked movement or caused trib-
utaries and shore areas to become warmer and more turbid. These
factors may also have contributed to early elimination or reduction
of runs of sturgeon, yellow perch, and walleye in many tributaries
or shallow areas.
Populations of the larger native inshore species less affect-
ed by warming and turbidity (suckers and walleye) or that persisted
at intermediate depths of the inshore region (lake herring and white-
fish), were reduced greatly in the late 1940's and the 1950"s by
sea lamprey predation. The lake herring and remaining abundant in-
shore species (emerald shiner and yellow perch) were adversely in-
fluenced by competition during the explosive increase in dominance of
the ale'wife during the late 1950's and 1960's. Before the alewife
invasion, the lake herring was the most abundant species of the lake,
and the emerald shiner was extremely abundant in rivers and harbors,
where it often clogged water intakes. Both were major forage species
for inshore predators such as yellow perch and walleyes.
All exotic species, including coho salmon, are very abundant
in inshore areas during part of the year. Carp became abundant in
shallow areas in the late 1800's and were particularly favored by the
warmer and more turbid tributaries that resulted from forest removal
and settlement. Smelt became abundant at the shallower depths during
1930-60 but were reduced substantially when the alewife became extremely
abundant. The alewife has become the most conspicuously abundant inshore
species because of spring dieoffs, but there is no evidence that its
-------
19
abundance equals the total of the previously very abundant species
that it has replaced. The alewife is now the primary forage species
for all major predators of the lake, but its objectionable charac-
teristics have fostered management objectives aimed at reducing its
abundance.
Other new inshore species which are not abundant, but which
are important features of the present fishery restoration efforts on
the Great Lakes, are the steel head trout, brown trout, kokanee salmon
and splake (lake trout-brook trout hybrid). Plantings of steelhead
trout and brown trout have been started in Lake Michigan, and early
results are promising.
Substantial amounts of money have been and are being spent
on Lake Michigan fishery programs. Since 1967 the sea lamprey control
program on Lake Michigan has involved an expenditure of $6 million
(69 percent U.S., 31 percent Canadian), and the current annual lamprey
control budget is $500,000. In addition, 11 million lake trout have
been planted since 1965 by Federal and State governments at a cost of
about $1 million. The States of Illinois, Indiana, Michigan, and
Wisconsin all maintain fishery management programs on their Lake
Michigan waters and place very substantial monetary values on the
sport fishery, boating, and other recreational uses. Michigan, for
example, is carrying a $90,000 management budget in fiscal year 1971
to conduct Lake Michigan fishery sampling and maintain a research
station. The cost of the State's 1970 Lake Michigan stocking program--
involving principally coho salmon—was $270,000. Michigan
fishery statistics indicate that in 1969, 557,000 angler days were
-------
20
spent fishing for trout and salmon on Michigan waters of the lake,
at an estimated expenditure of $16 per day, for a total angler
expenditure of $9.5 million (Fish Division, Michigan Department of
Natural Resources, personal communication).
-------
21
C. OPEN LAKE
1. Definition and Extent
The maximum length of the open lake area is 307 miles;
the average width is 118 miles. The surface area is 17,360 square
miles—approximately 77 percent of the entire lake surface. The
vo-lume is 1,122 cubic miles--96 percent of the entire lake volume.
2. Thermal Trends in the Open Lake
Despite its great depth, Lake Michigan undergoes seasonal
temperature changes similar to those in most inland lakes of temperate
North America. The deep waters of the open lake remain close to 39°F,
the temperature of maximum density, throughout the year, whereas sur-
face (and shallow) waters undergo considerable thermal changes seasonally
ranging from 32°F to as high as 82°F. (See Figure 3 for a generalized
treatment of the temperature cycle in the open lake.)
The open lake remains ice-free except during extremely
cold winters. During this period the water cools very slowly to the
seasonal minimum in mid-March. Highest temperatures (35-39°F) at
this time are in deep offshore waters.
Initial warming begins in late March. Thermal stratifica-
tion is evident in the open lake by early June, but is not persistent
and well established until late June. Depth of the upper limit of the
thermae!ine is then about 50 feet. Surface temperatures rise rapidly
over the entire lake until mid-July. Between mid-July and mid-September,
surface temperatures remain nearly constant. Maximum lake temperatures
usually are in mid-August. The upper limit of the thermocline descends
-------
22
from a depth of about 50 feet to about 100 feet during September to
mid-October; it continues descent in the open lake during November
and may reach 250 feet before it disintegrates. By late December,
rapid cooling is complete and the lake is again nearly homothermous.
3. Currents in the Open Lake
Winds, water temperatures, bottom shape, rotation of the
earth, and other factors all influence the currents of Lake Michigan.
Seasonal temperature changes may be the predominant driving forces of
net circulation (Huang, 1969). This recent theory contradicts an
earlier one that winds are the primary driving force (Ayers et al ., 1958)
Huang's mathematical evidence demonstrated that net circulation can be
maintained in southern Lake Michigan by thermal factors alone. Winds
modify net circulation by causing surface-driven movements and by
rocking the entire lake back and forth. Huang (1969) distinguished
several different types of thermally induced circulations in Lake
Michigan. All are based on the fact that fresh water is most dense
at about 39°F. Water of higher or lower temperature is lighter and
floats on 39°F water. Figure 5 summarizes Huang's theory and shows
the annual cycle of water temperature in the lake.
During January to March the entire lake mixes together
but as heating begins in April the inshore water heats most rapidly.
A "thermal bar" develops and effectively isolates the inshore waters
from the rest of the lake. As heating continues the "thermal bar"
moves out into the lake and by June the lake becomes thermally strat-
ified into a warm upper layer and a cold deep layer.
-------
23
JANUARY
34
FEBUARY-EARLY MARCH
32 37 32
LATE MARCH
37 35
APRIL
"Thermal Bar"
4J
MAY
"Thermal Bar"
JUNE
44
AUGUST
75
SEPTEMBER
62
NOVEMBER
42 48
DECEMBER
"Thermal Bar"
37 39
Figure 5.--Seasonal water temperatures and thermally induced circula-
tions in southern Lake Michigan. (Numbers indicate approximate water
temperature in °F. Circulation in July through October is primarily
wind driven, and seiches are common. Figure adapted from Huang
[1969], Rondy [1969], and others.)
-------
24
After fall cooling, a second but weaker "thermal bar"
occurs in December. Normally it is not observed, however, because
of the weak temperature differences and the mixing of the strong
winter winds.
4. Open Lake Chemistry
The open-lake waters of Lake Michigan are generally
typical of oligotrophic lakes. Oxygen is always near saturation and
the concentrations of nitrogen and phosphorus are low. Total dissolved
solids average 158 mg per liter and the alkalinity is 110 mg per liter
(Table 6).
5. Fishery Resources
Few native species have been abundant in the offshore
region of Lake Michigan (Table 5). All of these are now reduced or
very rare. The deepwater sculpin and seven species of chubs were
extremely abundant in deep water where they lived during the entire
year. These were the major forage of the two native deepwater predators-
the lake trout and burbot. Larger chubs were also valuable food species
and the two largest species were heavily exploited by the early fishery
and became rare in the early 1900's. All other species of chubs have
recently been reduced greatly by the combination of continued heavy
exploitation, sea lamprey predation, and alewife competition.
Lake trout and burbot once lived in all depth zones of the
lake. The adults were most abundant in deep water, and the young in
shallower areas. Reports of the early fishery indicate, however, that
adult lake trout were common in inshore areas and the larger rivers,
as they were taken by fishermen in shore seines during the mid-1800's.
-------
25
Table 6.-- Chemical characteristics measured in the open-lake portion
of Lake Michigan in 1962-63
[Values for average and range are in milligrams per liter unless
otherwise indicated; NS = not sampled; ND = not detectable at
sensitivity of test.]
Characteristic Number of Average Range
samples
Dissolved oxygen
Saturation (percent)
BOD
NH3-N
N03-N
1,080
497
NS
429
595
12
102
-
0.06
0.13
8.4-17
73-152
-
ND-0.50
ND-0.65
Organic-N 0 313 0.19 ND-0.52
Total Solids P 4 388 0.02 ND-0.14
Si02 299 2.5 0.6-5.5
Na 321 3.9 2.7-6.5
K 325 1.1 0.4-2.0
Dissolved solids 417 155 100-240
Specific conductance (micromhos 918 260 185-345
per centimeter)
pH (pH units) 1,040 7.5-8.9
Alkalinity 858 110 75-130
Ca 395 33 25-40
Mg 318 12 8-16
Cl 607 6.5 3.3-11
SO^ 561 20 12-30
Phenols (micrograms per liter) NS - -
-------
26
Large burbot may also have been taken in the early inshore fishery
but not mentioned because of their low value as food fish. Lake
trout and burbot were reduced to near extinction by sea lamprey pre-
dation in the late 1940's and early 1950's. Sea lamprey control
measures and intensive lake trout stocking in the late 1960's have
increased lake trout abundance substantially.
Of the exotic species that have been introduced into or have
invaded Lake Michigan, the alewife and coho salmon live in the off-
shore region of the lake. Chinook salmon are also being stocked in
Lake Michigan; their distribution is not clearly understood, although
they appear to live in the offshore areas. Young coho salmon and
alewives live throughout the lake most of the year and adults of both
species live in the offshore area during the winter and much of the
summer. Adult alewives concentrate to spawn near shore and in
tributary streams in late spring and early summer; in some years they
clog water intakes and die in large numbers, causing a major public
nuisance. Coho salmon move to shore areas, and into streams to spawn
during the fall and early winter. Alewives have become the most
abundant fish in the lake and constitute the major forage supply for
open-lake predators; all native forage species have been reduced
greatly by various factors—including alewife competition.
-------
27
III. THERMAL LOADING
A. PRESENT LOADING
Projections on thermal loading have been developed primarily
from a recent Canadian publication here referred to as the "Acres
Report" (Acres, 1970). These projections have the advantage of also
providing data on heat discharges from the steel industry and
municipalities. Current, but unpublished, Federal Power Commission
projections are also available, and do not differ significantly from
those in the Acres Report. The FPC projections have been inserted
for decades not represented in the Acres Report. Tables 7 to 12
summarize the projections for megawatt capacity of power plants,
waste heat from power plants and from other sources, cooling water
requirements of power plants, and a breakdown of waste heat input by
shoreline sector.
The primary source of Lake Michigan waste heat effluents is the
power industry. In 1968 once-through cooling requirements for all
Lake Michigan power installations were 6,643 cfs, which introduced an
estimated 29.85 billion Btu's/hour of waste heat to the lake. As of
early 1970, one nuclear and 23 fossil fuel power plants were operating
on the lake, with a total capacity of 8,278 mw. Seven additional plants
(five nuclear and two fossil fuel) were under construction and scheduled
for operation by 1974, bringing the total on the lake to 31. In aggre-
gate these plants will have a power capacity of 15,626 mw.
-------
28
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Table 9.--Projected heat addition (billions of Btu's/hr) from the
steel industry and municipal effluents to different sectors of
Lake Michigan. 1_/
Source and sector Year
1968 2000
Steel industry
Grand Traverse 0.00
Holland 0.00
Chicago-Gary 6.13 10.95
Green Bay 0.25 0.45
Subtotal 6.38 11.40
Sewage effluents
Grand Traverse 0.60
Holland 1.00 1.00
Chicago-Gary 1.00 1.40
Green Bay 1.60 2.30
Subtotal 4.20 4.70
Combined steel and sewage
effluent inputs 10.58 16.10
I/ Adapted from Acres (1970).
-------
31
Table 10.--Principal present and projected waste heat addition
(billions of Btu's/hr) to Lake Michigan.]_/
Source Year
1968 2000
Power industry
Fossil fuel plants
Nuclear plants
Steel industry
Municipal effluents
29.35
.50
6.38
4.20
115.31
299.36
11.40
4.70
Total heat input 40.43 430.77
]_/ Although based on power capacity projections from Acres (1970),
the Btu figures were derived by assuming 100 percent capacity
operation and a 20°F effluent rise. Btu/hr estimates were
obtained by multiplying megawatts of capacity by 0.0039 x 109
for fossil fuel and 0.0067 x 109 for nuclear fuel. Acres assumed
average capacity operation.
-------
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34
Although the power industry is the primary source of man-made
heat addition to Lake Michigan, it should not be regarded as the
only one. Certain industrial and municipal sources are also signifi-
cant contributors of waste heat. The Acres Report projections indi-
cate, for example, that in 1968 the steel industry contributed 16
percent of the man-made thermal input to Lake Michigan, or 6.38
billion Btu's/hour.
The combined power,steel industry, and municipal waste heat input
to Lake Michigan in 1968 is estimated at some 40 billion Btu's/hour.
B. FUTURE LOADING (THROUGH YEAR 2000)
For the past 30 years, the Nation's electric power loads have
grown at an average rate of 7 percent per year; consequently a doubling
of electric power facilities has been required each decade. Forecasted
load growth is the same through 1990 (Anonymous, 1968) and 2000 (Acres,
1970). More nuclear units will be installed in the Northeast and
Midwest than in any other section of the United States. Nowhere are
these plans for expansion more apparent that on Lake Michigan. Table 7
summarizes projections of growth in capacity.
The doubling of power capacity each decade shows the estimate
of Lake Michigan megawatt capacity increasing at a geometric rate.
Cooling water requirements will also increase at a similar rate (almost
fourteenfold) from 6,643 cfs in 1968 to 91,179 cfs in 2000 (Table 11).
Heat addition from steel and municipal sources is expected to increase
to 17.30 billion Btu's/hour by 2000 (a 63 percent increase over that
-------
35
in 1968). In aggregate, it is estimated that waste heat addition
to Lake Michigan from these sources will increase from 40 billion
Btu's/hour in 1968 to about 431 billion in 2000.
C. WASTE HEAT DISSIPATION
1. Non-technical Overview
To consider both the immediate and eventual fates of
waste heat in Lake Michigan, it is necessary to understand the
process of addition of effluent heat to the water mass and its
dissipation to the air. Recent findings tend to substantiate the
theory that under normal conditions the principal amount of waste
heat is passed to the water mass, and only a relatively small pro-
portion is dissipated directly from the plume to the atmosphere.
Csanady .(1970) advanced theoretical conclusions which indicate that
heat dissipation is "diffusion-controlled." He concluded (though he
did not fully discuss the important topic of atmospheric loss through
back radiation) that excess temperature diffuses into the lake, if
shoreline currents are normal and the water is moderately deep. He
believed that his findings are supported by an empirical study by
Palmer (1969). Hoops et al. (1968) concluded, on the basis of work
at a Lake Monona (Wisconsin) power plant, that surface heat losses
were about 5 percent of the heat discharged by the power plant; the
remaining 95 percent was dissipated by dilution with lake water.
Sundaram et al. (1969) concluded that the heated discharge of the pro-
posed Bell Nuclear Station on Cayuga Lake (New York) would increase
the average surface temperature of this 66.4-square mile lake about 0.7°F.
-------
36
The size of the area affected by heat addition often can
be predicted with some degree of confidence. However, the state of
the art is not such that forecasts are completely accurate for any
given heat source. The reasons for this deficiency are several,
and they must be understood if an appreciation for the prediction is
to be gained. It is also necessary to gain insight into the
mechanics of heat dissipation in general. An attempt is made here
to outline the theory, presupposing no special background in fluid
mechanics or thermodynamics.
Heat, like mass, must be accounted for—and it can be
accounted for through the idea of its conservation with time. Heat
contained in a given parcel of water can be lost in several ways:
(1) by absorption at the (lake) bottom, (2) by radiation back to
the atmosphere when in contact or near-contact with the air, or
(3) by evaporation and conduction to a colder air mass. If a mass
of heated water is discharged to a lake and does not decrease in
temperature as a result of these processes, it will naturally add its
heat to the heat already in the lake. This process cannot, of course,
continue indefinitely; it can, however, increase the temperature of
the lake receiving water to that of the immediate discharge area if the
lake is small enough. After a certain time, the entire lake comes to
equilibrium and this equilibrium is maintained by exchange at the air-
water interface.
-------
37
A second process can be envisioned: Instead of following
a body of water, consider a volume fixed in space in such a way that
movement of water through the volume is allowed. Water of a certain
temperature may then entirely displace a colder body of water
mechanically. Such a process is due simply to the physical movement,
or advection, of water into the volume.
A final process can be envisioned: Assume that half the
water in the fixed volume is displaced by water of a different tempera-
ture. If the two bodies of water are allowed to mix completely, t;he
result is a temperature midway between the two initial temperatures.
This process can be roughly described as turbulent diffusion.
Thus, there are essentially four means by which a body of
water can lose (or gain) heat: (1) by exchange at the air-water
interface, (2) by advection, (3) by diffusion, and (4) by any com-
bination of these three means. Analyses that are currently employed
to evaluate temperature effects are based on these processes, although
some of the mathematical tools that are employed are exceedingly
sophisticated and the analyses are sometimes intractable. The intracta-
bility results from our lack of knowledge about such matters as lateral
and vertical exchange processes (advection and turbulent diffusion),
evaluation of background temperatures (or what the temperature would be
if no heat sources were present), and hydrodynamics under the influence
of bouyant jets.
-------
38
If a dyed, heated, body of water is steadily discharged
from a small orifice at a given velocity into a shallow, non-moving,
clear, very large body of water, the dye decreases in intensity with
increasing distance from the source and gradually becomes indistin-
guishable at a certain distance from the source. If the intensity
of color down the midstream of the resultant plume could be measured,
the intensity could be plotted on graph paper in the form of a simple
curve that would describe the intensity-distance relationships. If
the shallow receiving water body is replaced by a deep one, the plotted
points will not fall on the same line. This simplified description
differentiates between two-dimensional situations (i.e., in shallow
water, where the dye is uniformly distributed with depth and the two
dimensions are in the horizontal direction) and three-dimensional cases
(i.e., in deeper water, where the dye distribution drops to zero at
depth and has a different vertical distribution with distance from the
source). The three-dimensional situation is extremely difficult to
analyze theoretically; under field conditions it is even difficult to
sample properly. Most engineering evaluations proceed from the two-
dimensional case (in technical jargon the 'vertically integrated'
assumption is made) to calculate the area which is of a higher tem-
perature because of the heated water discharge.
In the three-dimensional situation, there is a region
immediately near the discharge point (which is usually in shallow water)
where the dye intensity remains essentially the same as that at the
-------
39
point of discharge. The surface area of this region may be rather
small (a point to remember when considering loss of heat to the
atmosphere). Adjacent to this region, "clear" water is brought into
the dyed area in conjunction with a certain decrease in velocity;
this clear water is said to be "entrained" and its magnitude is
described by an "entrainment coefficient." In the entrainment region
mixing occurs at the edges of the plume; little mixing takes place very
near the source. This process is similar to the perhaps more
familiar process of the building up of towering storm clouds. Here
the vertical growth is effected by air being brought in from below
(entrained) and moving upward. In the entrainment region, mixing
occurs at the edge of the plume, whereas little mixing takes place
very near the source. Another region can be described where the dye
concentration is diminished by diffusion at the edges and loss in a
vertical direction; the surface area traced by the edges of this
region is relatively large (analogously with the heat loss phenomenon
this is the region where loss to the atmosphere by evaporation, con-
duction and back radiation, accounts for a considerable amount. But,
as it is in proportion to its differences in temperature above natural
or "ambient," the total loss is actually rather small.)
Three main points evolve from the preceding description:
(1) Although heat is lost to the atmosphere near the source because
the temperature may substantially exceed the ambient temperature, the
total amount lost is small because the surface area of this region
-------
40
(where losses take place in the absence of mixing) is small. (2) The
bulk of the heat in the region near the source is simply added to the
receiving water for a longer time. Further losses will occur in the
next region, and the magnitude of loss to the atmosphere will depend
on the surface area (greater than in the latter region) and the
temperature difference between the regions and the ambient (smaller
than in the latter regions). (3) In the final dissipative stages,
heat is diffused and lost by surface cooling, but here the temperature
does not greatly exceed the ambient temperature.
In total, therefore, most of the heat is retained in the
volume of water near the discharge site and a rather large area can be
expected to become heated.
Ayers et al. (1970), who made field observations near
power plants in Michigan City, Indiana, and Waukegan, Illinois, did
not list the condenser flows or discharge temperatures, nor give
auxiliary data which could be used to make a 'jet release1 analysis.
They ascribed most of the temperature decrease with distance from the
outfall to surface cooling. This explanation can hold, however, only
if the discharge volume is small or the width of the discharge orifice
is so great as to reduce the velocity of the jet to a small valve. To
evaluate properly the heat buildup near an outfall, results from one
survey cannot be extrapolated directly to another. Rather, a case-by-
case evaluation is required and, at this stage of our knowledge, nothing
less will suffice. Information required for the evaluation has been
given in earlier paragraphs and includes such data as the dimensions
-------
of the outfall, volume of flow, and background or ambient temperatures.
When the ambient temperature is not uniform in relation to distance
from the shore, evaluation of what constitutes an "excess" temperature
is doubtful at best; such conditions are likely to result periodically
and, of course, during "thermal bar" conditions. The analysis by
Ayers et al . (1970) is open to criticism because of their choice of
ambient temperature; in fact, it is not clear from their illustrations
whether an ambient temperature was indeed measured at all.
2. Studies of Model Plumes
Data from two evaluations of model plumes have been
selected to provide some physical dimensions to the foregoing
discussion. In one that was completed by Benedict (1970) specifically
for the present report, the variables used were similar to those that
might be expected for a Lake Michigan thermal plume. The assumed dis-
charge volume (731 cfs) and temperature differential (25°F) are on the
order of a conventional fossil fuel plant on Lake Michigan. The second
evaluation is that of Pritchard-Carpenter Consultants (1970) for the
proposed Davis-Besse Nuclear Power Station on Lake Erie. This study
provides an example of the heat rejection potential of a Great Lakes
nuclear installation of 1,500 cfs. (At least one larger plant is
under construction on Lake Michigan—the Donald C. Cook Plant, near
Benton Harbor, Michigan, at 3,500 cfs.)
a. Lake Michigan Surface Jet Model
Benedict's shoreline discharge model, which simulates
a Lake Michigan discharge on the order of the Campbell Plant (a conven-
tional power plant near Port Sheldon, Michigan), assumes zero lake
-------
42
currents, an ambient temperature of 65°F, once-through cooling, a
25°F rise over the condensers, an effluent of 731 cfs, and a plume
depth of 5 feet. There is no allowance for surface heat loss,
Since the theoretical plume, under conditions of no current, would
generate symmetrically outward from the discharge, it is possible
to examine the thermal characteristics in terms of distance that
waste heat isotherms extend (Table 13).
Evaluation of the isotherms was carried to the
0.5°F limit only for illustrative purposes since under normal condi-
tions natural processes would distort the plume shape and diffuse the
heat to depths greater than 5 feet. However, under the conditions of
the model and at equilibrium, the thermal influence would extend along
the plume center line a substantial distance (4.8 miles to the 1.0°F
isotherm and 20 miles to the 0.5°F isotherm) and thus cover a rather
extensive area.
b. Lake Erie Nuclear Model
Pritchard-Carpenter Consultants (1969, 1970) computed
and analyzed plume distributions for the Toledo Edison Compnay, as
part of that company's evaluation of the proposed Davis-Besse Nuclear
Power Station on Lake Erie.1 Analyses were carried out for two condi-
tions—no lake current and with shoreline current. Only the shoreline-
current condition is discussed here, since it is the more typical in
Lake Michigan. In this situation, the plume is bent in the direction
:The Toledo Edison Company kindly consented to use of these data in
the present report.
-------
43
Table 13.--Distance (miles) from source of excess temperature
isotherms calculated from a Lake Michigan surface jet model.
Waste heat Distance (miles)
isotherm from plume source
(°F) at centerline
20 .052
15 .057
10 .062
5 .234
2.5 . .717
1.0 4.80
0.5 20.17
-------
44
of the current. Although the proposed plant is to be situated on Lake
Erie, the calculations provide interesting summary statistics on plume
dimensions as they apply to the large flows required by nuclear power
plants.
In general, an onshore wind causes currents that are
parallel to the coast in the nearshore region. When the plume is bent
so that it is directed along the coast, entrainment (and thus, dilution)
can be effected only on one side of the plume. The result is that the
rate of decrease of temperature is less than if the plume had been
directed straight out into the lake.
Calculations of the plume dimensions were based on
assumptions of an 18°F temperature rise, 1,526 cfs of cooling water,
70°F ambient temperature, a 10 mph wind, and a longshore current directed
towards the southeast at a rate of 0.67 fps. Estimates were made of the
plume certerline length, width, and area (Table 14).
The 1°F excess temperature isotherms were about 52
and 8 miles from the source for the two conditions of dilution only and
dilution plus cooling, respectively, and the respective areas affected
were about 374 and 13 square miles.
c. Application of results from Model Studies
The Lake Michigan jet and Lake Erie "dilution only"
examples approximate situations in which atmospheric and lake conditions
do not permit rapid dissipation of waste heat to the atmosphere. Under
conditions when such atmospheric losses would occur, the lake volume
-------
45
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46
affected by waste heat would diminish. However, from the earlier
discussion of heat dissipation, it appears that, at best the per-
centage of the total waste heat rapidly lost to the atmosphere is
sufficiently small that the assumption of little or no waste heat
loss to the atmosphere is reasonable, at least during a great deal
of the annual temperature cycle. It follows that the assumption of
moderate or no waste heat loss to the atmosphere is reasonable during
a good deal of the annual temperature cycle—recognizing of course
that short-term loss to the air occurs and that nearly all of the
waste heat will be removed during the fall overturn and winter.
The "dilution plus mixing" example of the Davis-Besse plume evalua-
tion appears to be very conservative in describing the actual area
and volume of thermal influence; and the "dilution only" assumption
of the other two examples is the more applicable. It is concluded
that large percentages (at times virtually 100 percent) of the dis-
charged waste heat will be diluted into the water mass and that the
heating effect of one plume can cover many area! miles of the lake.
3. Magnitude of Projected Waste Heat Addition
It has been advanced that at times most waste heat would
be diffused into the water mass for an ecologically significant time
period. Waste heat production is projected to be 431 billion Btu/hr
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47
on Lake Michigan in year 2000; and to assess the potential ecological
impact of this waste heat addition, it is desirable to place dimensions
on the physical characteristics of waste heat distribution. Existing
information on this topic is very limited; the following discussion
is intended to provide at least a limited amount of insight into the
situation, as projected.
Acres (1970) estimated that 0.52 Btu/ft2/day of waste
heat would be added to Lake Michigan in year 2000--an increase of
0.47 over the 1968 value of 0.05 Btu/ft2/day (based on estimtates of
average power capacity operation and the waste heat additions from
other sources). This estimate applies to the entire lake surface,
however, and does not allow for the likelihood that the waste heat
release would occur in the inshore waters.
Table 12 presents estimates of waste heat inputs to the 1,677
square miles of beachwater zone (0-30 foot depth) by shoreline sector
for the entire lake. The last column of the table presents the pro-
jected waste heat input, expressed as a percentage of the maximum
natural rate of heat input. (The natural input estimate for nearshore
waters of Lake Michigan [based on unpublished data of the Bureau of
Commercial Fisheries] is supported by estimates for Lake Ontario of
1,735 Btu/ft2/day [Rodgers, 1968] and for Lake Cayuga of 2,000 Btu/ft2/day
[Sundaram et al., 1969].) This very general statistic indicates that
the rate of waste heat input would in the year 2000 approximate 13 per-
cent of the natural maximum heat input (For the Chicago-Gary Sector,
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48
this statistic is 51 percent and for the Holland Sector, 34 percent).
The basis of the statistic is subject to criticism, since
some of the waste heat will diffuse beyond the 30-foot contour (average
width, 1 mile), some will be lost to the air, and, of course, the
concentration of waste heat near the discharges will cause great
variability in the actual value of the statistic. However, available
studies indicate that Lake Michigan thermal plumes hug the shoreline,
and it follows that the principal ecological impact would occur in
the shallower waters; and it is this fact that makes the general use
of the statistic valid. Furthermore, during certain periods the
"thermal bar" lies entirely within the inshore zone, preventing transfer
of heat to deeper water.
Substantial refinement of the assumptions is both desira-
ble and needed, and other approaches to the problem can be taken. The
existing calculations are sufficient, however, to permit the conclusion
that projected waste heat production would add to the beach water sector
of Lake Michigan an artificial thermal load that is equal to a signifi-
cant percentage of the natural rate of heat input. This conclusion has
ecological significance in terms of both eutrophication and fishery
effects.
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49
IV. EFFECTS OF TEMPERATURE FLUCTUATIONS ON LAKE MICHIGAN FISH
A. INTRODUCTION
Increased demand in recent years for the use of natural surface
waters for cooling has caused widespread concern that the addition of
artificial heat to these waters will be harmful to aquatic life. As
a consequence the effects of temperature on aquatic life are under
intensive study and some of the results are now being published.
Extensive bibliographies by V. S. Kennedy and J. A. Mihursky (1967)
and E. C. Raney and B. W. Menzel (1969) list over 1,200 references
that cover the early literature as well as some of the more recent
publications. Excellent review articles describing the thermal
requirements of fishes were published by J. R. Brett (1956, 1960)
and R. E. Burrows (1963). A book edited by P. A. Krenkel and
F. L. Parker (1969) and the published Proceedings of the Second
Thermal Workshop of the U. S. International Biological Program
(J. A. Mihursky and J. B. Pearce, eds; 1969) deal with the biological
aspects of thermal pollution for major groups of aquatic plants and
animals. Although the present section is limited to a discussion of
the effects of temperature changes on fish and other organisms in
Lake Michigan, references are made to the published literature when
necessary, to describe thermobiological principles and to fill gaps
in the knowledge of the specific thermal requirements of Lake
Michigan aquatic organisms.
The factors that determine the growth, survival, distribution,
and abundance of fishes and other coldblooded aquatic organisms in
nature are complex and incompletely known, but the role of temperature
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50
is firmly established as a major one. All available information
indicates that each organism has specific thermal tolerances or
limits that reflect the thermal requirements for each of the
important metabolic functions in the individual; these functions
and thermal tolerances vary from life stage to life stage. When
the limits are exceeded the organism functions at reduced efficiency,
and may ultimately die. The rate at which individuals, populations,
or species are lost depends on the degree to which the thermal limits
are exceeded, the duration of exposure to thermal stress, and the
indirect effects of these thermal conditions (e.g., effects on the
abundance of organisms suitable as food).
The temperatures that are rapidly lethal have well defined limits
and these,have been thoroughly described for many species, including
some found in Lake Michigan and the other Great Lakes. Less well
known but equally important are the temperature limits for successful
survival in other situations where unfavorable temperatures reduce
the ability of the organisms to move about, escape predation, compete
with other species for food, and otherwise successfully complete all
of the vital life processes and stages (including reproduction).
The use of inshore waters of Lake Michigan for waste heat dis-
posal would have a serious impact on fishes that must complete their
early life stages (especially egg incubation and early growth) in the
inshore and beach water zones. Fishes are least mobile in these life
stages and therefore least able to avoid unfavorable thermal conditions,
Also affected adversely would be the highly mobile adults that require
these shallow-water areas for spawning and the anadromous fishes that
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51
need to pass through the inshore and beach zones to spawn in tributary
streams or to enter Lake Michigan as young from the tributary streams
to complete the growth phase of their life cycle. Shallow-water
organisms other than fishes, many of which are required as food for
fishes or are otherwise important to man, would also be affected by
the use of inshore lake waters for waste heat disposal.
B. EFFECTS ON ADULTS AND JUVENILES
Most organisms cannot live at temperatures much higher or
lower than those to which they are accustomed (Kinne, 1963), and a
general relation can be demonstrated between the temperatures that
are lethal for adult fishes and the temperatures of the natural
environment in which these fishes occur. In natural populations the
temperatures that are lethal for adult fishes usually exceed the
natural temperature extremes by only 9 to 12°F (Brett, 1969).
The lethal limit for juvenile coho salmon is 77°F (Brett,
1952) and adults die in about 60 minutes at 77°F (Coutant, 1969).
Coho salmon must pass through the beach zone waters as juveniles
descending to Lake Michigan and as adults ascending tributary streams
to spawn. When adult coho salmon concentrate off stream mouths in
late summer and early fall before entering these streams to spawn,
average bottom water temperatures in the beach zone range from 69°F
(August) to 58°F (end of September), and one year in three the tem-
peratures can be as much as 10-11°F higher than the average values
(Figure 6). In mid-August of an average year a rise of only 8°F
would increase bottom water temperatures in the beach zone beyond
the lethal limits, and in one year of three an even smaller increase
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52
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would exceed 77°F. By the end of September a rise of 19°F would
exceed the lethal level. Although surface water temperature data
are not available for the beach zone, the surface temperatures
would be higher than those of the bottom waters used to construct
the curve in Figure 6; the migrants must pass through these surface
waters to enter the stream mouths.
In addition to fish mortalities that occur when temperatures
exceed the upper temperature tolerance limit of fishes, mortalities
may also result when fish acclimated to high temperatures are suddenly
exposed to sharply dropping temperatures.
Emery (1970) described a mortality that occurred as a result
of a natural upwelling of cold offshore bottom water in Georgian Bay,
Lake Huron. The upwelling suddenly lowered beach zone bottom water
temperatures from 65.3°F to 44.6°F in about 11 hours; recovery was
rapid, however, and by the 15th hour bottom water temperatures in
the affected area had risen to 64.9°F. The more mobile fishes left
the area when the temperature dropped but crawfish and sculpins could
not; these ceased feeding and many died.
Low temperature mortalities may also occur in Lake Michigan
as a result of the use of lake water for cooling. In a report of a
fish kill on Lake Michigan at the Consumers Power Company Campbell
Plant at Port Sheldon on August 29, 1968, the Michigan Water Resources
Commission concluded that a sharp drop in water temperature (from 71
to 57°F) at the intake of the Port Sheldon installation gave fish in
the discharge water a low temperature shock to which they were unable
to adjust (Robinson, 1969). Species found dying or in distress at the
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54
time of the investigation were channel catfish, carp,
suckers, and gizzard shad--a11 generally considered to be intolerant
of low temperatures or of low temperature shock.
Although the fish kill at Port Sheldon was due in part to
the invasion of the shallow beach zone by cold offshore water, the
high temperature of the effluent water to which the fish had become
acclimated was also a contributing factor. Fish mortalities caused
by low temperature shock are also likely to occur in the absence of
coldwater upwellings when effluent water temperatures fall—as when
a power plant goes "off line" or its level of operation is greatly
reduced. Little information is available on the thermal tolerance
of the alewife but a recently completed manuscript entitled "Effects
of temperature on electrolyte balance and osmoregulation in the alewife
(Alosa pseudoharengus) in fresh and sea water" by J. G. Stanley and
P. 0. Colby, indicates that the alewife is very intolerant of low
temperature shock. When alewives acclimated at 62.6°F were subjected
to an 18°F temperature decrease in 2 hours, 13 of 21 (62 percent) died.
This information suggests that severe mortalities of alewives could
be caused in effluent waters by low temperature shock when a power
plant reduces its level of operation. The effect would be most severe
during the spring when the lake water is cold and alewives concentrate
near shore before spawning.
Sublethal temperature shock has also been shown to affect
adversely the well being and survival of juvenile salmonids. According
to the temperatures of Figure 6 and the lethal temperatures of juvenile
coho salmon (Brett, 1952), a temperature rise of 15 to 35°F in the beach
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55
zone waters at stream mouths would be required to kill young downstream
migrants. Coutant (1969), however, has shown that heat doses only
25 percent as large as those required to cause loss of equilibrium
(the dose required to cause equilibrium loss is less than that required
to cause death) measurably increases the susceptibility of juvenile
chinook salmon and rainbow trout to predation.
The heat doses required to cause harm to juvenile and adult
Lake Michigan fishes are not known but there is little doubt that sub-
lethal temperature shock and increased susceptibility of affected
fishes to predation would be important consequences of discharging
heated effluents into Lake Michigan.
Even more restrictive than the lethal temperature limits are
the limits for the efficient function of the complex of vital life
processes that ensure the continued successful existence of the indi-
vidual, population, and species. The temperature requirements for
these vital processes are known for only a few species, but the avail-
able information indicates that the general form of the relations may
be similar for most fishes native to the temperate waters of North
America. Among these fishes the swimming ability, feeding rate, food
conversion efficiency, and growth rate typically are low at low natural
environmental temperatures, rise with rising temperature to some maximum
(at the "optimum temperature"), and then decline sharply with further
temperature increases as the upper lethal temperature is approached.
Figure 7 shows the effect of temperature on the food intake, growth,
and conversion efficiency of coho salmon. The curve of Figure 7 marked
"ration" describes the voluntary rate of food intake at the various
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56
temperatures. Intake was low at low temperatures, rose with tem-
perature to a maximum at about 59-64°F, and then declined sharply
at higher temperatures. Growth followed a trend similar to that of
intake. Growth rate was most rapid at 59°F and fell off at higher
and lower temperatures. Extension of the ends of the growth curve
indicates that growth rate was nil at about 39 and 70°F.
Conversion efficiency which is defined as,
growth in weight
100 x
weight of food eaten
gives the percentage of the food eaten that is converted into growth.
When no growth occurs the conversion efficiency cannot exceed zero
percent; according to Figure 7 this occurs at about 39°F and at
69-70°F.
Where the problem has been studied intensively (for sockeye
salmon; Brett, 1969), the evidence indicated that the successful
natural range of the species coincides with areas in which water tem-
peratures do not exceed the "optimum" for food conversion efficiency
by more than a few degrees and where food conversion efficiency is
not reduced to less than 80 percent of the maximum. According to
Figure 7, the food conversion efficiency of coho salmon--a close
relative of the sockeye--reached a maximum at about 54.5°F and fell
below 80 percent of maximum at 62°F. Temperatures higher than 62°F
during the growth phase of the coho salmon can be expected to reduce
the population success of this species.
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57
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and conversion efficiency of juvenile (0.5-pound) coho salmon
held in fresh water and fed unrestricted amounts of alewives
from Lake Michgian (T. Edsall, unpublished data).
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58
In addition to its effect on the growth, survival, and
general well being of fishes, temperature is also important because
it directly affects the availability of coho salmon (and other-
fishes) to the angler. The temperature range for optimum feeding
rate of juvenile coho salmon fed unlimited amounts of alewives is
59-64°F; elevation of temperature above 64°F reduces feeding rate
(Figure 7). An even lower optimum temperature for feeding in nature
(where food availability is restricted) is predicted from data on
optimum temperature for growth and conversion efficiency of coho
salmon whose food intake was restricted to levels approaching those
in nature (T. Edsall, unpublished data)--and indeed the optimum
feeding temperature for adult coho salmon in Lake Michigan is about
50-55°F (Borgeson, 1970). When adult coho salmon in Lake Michigan
concentrate off stream mouths before ascending the streams to spawn,
lake water temperatures average 69 to 56 (August to end of September)
and one year in three range from 69 to 79°F in mid-August and from
58 to 69°F at the end of September (Figure 6). According to Figure 7
elevation of inshore water temperatures at this time, when the major
portion of the catch of coho salmon is usually made in Michigan waters
of Lake Michigan, will sharply lower the feeding rate and consequently
reduce angler success.
Elevation of beach zone water temperature may also delay the
start of the upstream migration, thereby shortening the duration of
the stream fishery for salmon. In 1969 about one-half of the Lake
Michigan salmon caught by anglers were taken in tributary streams.
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59
Although temperature data for the beach zone waters at the
time of the salmon runs are not available for Lake Michigan, the
1968 run of coho salmon "jacks" (precocious males) in the Chagrin
River, a tributary of Lake Erie, did not begin until beach zone
water temperatures fell below 65°F, and in 1969 the first run of
adult coho salmon seen in Lake Erie entered the Chagrin River on
September 13, after the beach zone water temperatures had dropped
to 66°F; furthermore, the peak of the 1969 run did not occur until
October 24-26 when temperatures were 58-62°F (Russel Scholle, Ohio
Division of Wildlife, personal communication).
C. EFFECTS ON MATURATION AND SPAWNING REQUIREMENTS
1. Maturation
The environmental requirements for normal maturation of
the sex products within the gonads of adult fishes have been studied
for only a few species (see Welch and Wojtalik, 1968, for a review).
Most studies show that both temperature and light cycles are important.
Recently the FWQA Laboratory, Duluth, Minnesota, has shown that water
temperatures must be 43°F or lower for 5 months to ensure normal
maturation of the eggs of yellow perch; higher temperatures upset the
natural temperature and photoperiod cycles and significantly reduce
both the number and viability of the eggs that are spawned. The
average water temperature in Lake Michigan drops below 43°F on about
November 20 and rises above 43°F again on about April 20--a period of
5 months; any delay in cooling in the fall or acceleration of warming
in the spring will shorten the time available for maturation to a
period less than that required. Although water colder than 43°F will
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60
still be available to perch, there is evidence that they may not
avoid, or may be attracted to, the warmer waters when they are
available (Weatherly, 1963; Ferguson, 1958).
2. Spawning
In general, the discharge of heated effluents in shallow
water can be expected to have its most serious effects on Lake
Michigan fishes during spawning and egg incubation. The available
information suggests that most Great Lakes fishes that spawn in
shallow water have preferred spawning sites, and that in years of
low population abundance these areas are used to the exclusion of
other areas. During years of high abundance, however, spawning is
much more widespread. Spawning areas of most shallow-water spawners
in Lake Michigan are not precisely known, but the distribution of
the whitefish fishery during the spawning season, as indicated by
past records, indicates that whitefish spawned in the shallow shore-
line waters of the entire lake in times of high abundance (S. H. Smith,
Bureau of Commercial Fisheries, personal communication). Although
populations of whitefish in Lake Michigan are now at an all-time low,
and their spawning may be restricted to a few local areas, population
increases that should result from current fishery management programs
will increase the number of spawning areas used; consequently, all
potential spawning sites must be protected. Similar protection may
also be required for the inshore spawning areas of yellow perch, smelt,
lake herring, and lake trout.
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61
There is mounting evidence supporting the hypothesis that
coregonid fishes have narrow temperature limits for spawning. Monti
(1929) found that whitefish did not spawn in Italian lakes where
winter temperatures remained above 45-46°F. Whitefish in the Great
Lake£ spawn in November and December when the lake is cooling, and a
drop to 42°F is required to stimulate spawning (Louella E. Cable,
Bureau of Commercial Fisheries, manuscript in preparation). Tempera-
tures above 42°F will presumably exclude whitefish from their
preferred spawning grounds. Lake herring spawn later than whitefish--
from mid-November to mid-December, when the temperature drops from
39 to 37°F (Smith, 1956). Several other investigators (Stone, 1938;
Washburn, 1944; Brown and Moffett, 1942; P. J. Colby and L. T. Brooke,
manuscript in preparation) observed that lake herring spawn when the
temperature falls below 39°F. Cahn (1927) found that ripe female
lake herring in laboratory tanks would not spawn at 40°F, but would
do so only after the temperature had dropped to 38.5°F or lower.
John (1956) reported that lake herring will spawn—later than usual--
when temperatures are above 39°F during late autumn, but suggested
that the delay may reduce egg survival. Pokrovskii (1960), as cited
by Lawler (1965), wrote that the temperature of the water at the time
of spawning exercises an influence on the abundance of year-classes of
certain whitefishes and on their yield; in some years the quantity of
fertile eggs reached 80-100 percent, in others it decreased to 30-50
percent, and in one instance only 10 percent of the eggs deposited
were fertile. Such low fertility was attributed to long drawn-out
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62
autumns in which the males leave the spawning grounds before the
optimum spawning temperature for females is reached.
Yellow perch spawn in the spring during rising tem-
peratures. Optimum spawning temperatures are 46-54°F; at 61 °F
spawning is reduced and at temperatures above 62°F eggs are aborted
without being fertilized (unpublished data, FWQA, Duluth). The
spawning season for perch in Lake Michigan begins about May 15 and
ends about July 1 (L. Wells, Bureau of Commercial Fisheries,
personal communication). Water temperatures average 49°F on May 15
(one year in three this average may be as high as 53°F) and 62°F on
July 1 (in one year in three this average may be as high as 69°F;
Figure 6). Thus, in one year in three, the addition of heat to the
spawning areas at the start of the spawning season (May 15) would
cause the optimum temperature for spawning to be exceeded, and the
addition of heat towards the end of the spawning season would cause
the females to abort their eggs.
Lake Michigan alewives spawn from early June, when
temperatures in spawning areas rise above 60°F5 through mid-August,
if temperatures remain below 82°F (Edsall, 1970). Although most
Lake Michigan alewives spawn in flowing water in tributary streams,
spawning is common in the sheltered areas of Green Bay in northwestern
Lake Michigan, and occurs occasionally along the unprotected shoreline
of Lake Michigan proper when the lake water is warm enough. The
warming of lake waters by heated effluents will facilitate lake
spawning by alewives where spawning now occurs only infrequently.
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63
Any increase in the abundance of alewives that is likely to result
from an increase in the spawning areas, however, is contrary to
present management objectives (see section on fishery resources)
for Lake Michigan.
D. EFFECTS ON INCUBATION REQUIREMENTS
The available evidence suggests that a normal self-
sustaining fish population may continue to exist successfully only
in areas where temperatures are in the range that permit the pro-
duction of viable fry from at least 50 percent of the eggs that
are spawned (Alderdice and Forrester, 1968). Information on the
effects of temperature on survival and development of eggs and fry
of Great Lakes coregonid fishes is scanty; published work is limited
to only a few studies on the influence of temperature on early sur-
vival and development. Lawler (1965) found that year classes of
whitefish in Lake Erie were strong only when suitable temperatures
prevailed; fall temperatures must drop early to 43°F, the decrease
to the optimum temperatures for development must be steady, and
spring temperatures must increase slowly and late in the season to
provide prolonged incubation near the optimum developmental tempera-
tures. Christie (1963) found production of larger year classes of
whitefish in Lake Ontario to be associated with cold Novembers
followed by warm Aprils. Price (1940), who incubated whitefish eggs
at constant temperatures from 32 to 54°F, found that the optimum
hatching temperature was 33°F and at temperatures above 43.2°F the
hatch of viable fry fell below 50 percent. Colby and Brooke (1970),
who incubated lake herring eggs at constant temperatures ranging from
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64
32 to 54°F, demonstrated that the highest temperature at which 50
percent of the eggs produced viable fry was 44.6°F, and that the
optimum temperature was about 42°F. Most of the mortalities
occurred during the early stages of development (gastrulation and
organogenesis) when the eggs were most sensitive to adverse tem-
peratures. According to the data of Price (1940), Colby and Brooke
(1970), and Figure 6, lake temperatures are already at the maximum
tolerable for the successful incubation of whitefish and cisco eggs
and the addition of heat to the lake in the fall in areas where the
eggs of whitefish or ciscoes are incubating will reduce the viable
hatch below the 50 percent level.
It is obvious that a 10°F rise over natural maximum
tolerable temperatures during spawning (from 42 to 52°F for white-
fish and from 39 to 49°F for lake herring) would cause high mor-
tality among eggs during the critical period of early embryo
development. A 5°F rise over natural temperatures (to 47°F) would
kill whitefish eggs or increase the incidence of abnormalities,
and a 3.6°F rise shortens the incubation period of lake herring by
at least 29 days (Colby and Brooke, U. S. Bureau of Commercial
Fisheries, manuscript in preparation), causing the fish to hatch in
a potentially hostile environment in which light may not be of the
right intensity, or food may not be of the proper kind (species),
size, or density to ensure survival. Braum '(1967) reported that
Coregonus eggs incubated at 39°F hatched after 65 days. Eggs
spawned in December hatched at the end of February, when plankton
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is scarce. Modern German hatcheries incubate eggs- at 34°F to delay
hatching until April, after 120 days of incubation, to take advantage
of the larger plankton population than available. Einsele (1966)
stated that it is now firmly established that in the Austrian Alpine
lakes only 1 to 10 adults will result from 10,000 naturally spawned
coregonid eggs. In the laboratory, however, survival can be varied
from nearly 100 percent to nil by varying food density and light
intensity. Einsele suggested that the feeding conditions for fry
improve as the year proceeds from March to the end of April and
early May, when the light intensity may rise above 100 lux and the
number of copepodites per liter may increase to 20 or more. Fry
stocked at this time would most likely have the best chance of
survival. He also pointed out that in Alpine lakes the feeding
situation for coregonid fry does not improve continuously as the
year proceeds, but that there is a turning point towards the end
of May when diurnal plankton migration begins and crustacean plankton
moves down to 10-20 meters during the daytime. The light intensity
for fry may be critical at 5 meters and is certainly too low below
10 meters. Also, at this time the many zooplankters may not be in
the appropriate size range for food of fry. Einsele also stated
that stocking fry from hatcheries in January and February had little
or no effect on the fish population.
Although factors governing egg and fry survival in Lake
Michigan have not been studied intensively at the Great Lakes
Fishery Laboratory, evidence from a local field study in progress
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suggests that shortening the incubation period could be potentially
deleterious to the fish stocks.
Preliminary investigations of lake herring feeding
habits by the Great Lakes Fishery Laboratory show that they have
some specific food requirements. Fry begin feeding about 6 days
after hatching, which is well before the yolk-sac is absorbed.
The diet is composed primarily of Crustaceans of the order
Eucopepoda - suborders Cyclopedia and Calanoida for the first
2 to 3 weeks (or until they reach a total length of 15 mm) at
which time species of the suborder Harpacticoida are found in
their gut. The range of mean total length of food eaten (to 0.6 mm)
by fry 12 to 18 mm long is less than the mean total lengths of the
preferred food available (0.6 to l.mm). Thus fry are selecting food
organisms that are small enough for them to ingest or that have
swimming speeds or behavior patterns that enable the fry to capture
them. In either case the food organisms ingested are not adults but
rather juveniles of a stock that has recently reproduced. Evidence
from a food selectivity study shows an increase in abundance of
cyclopoid juveniles coinciding with the hatching and appearance of
lake herring (cisco) fry. At this time the stock of calanoids is
increasing in density but decreasing in average size, indicating a
younger population. This population is increasingly fed upon by the
lake herring fry as the density of cyclopoids drop (P. J. Colby,
Bureau of Commerical Fisheries, manuscript in preparation).
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The timing of these natural events is no doubt essen-
tial for the perpetuation of these fish stocks and has evolved as
a result of natural selection, e.g., fish which spawned earlier or
later were selected against by the environment. Any heat discharge
which would interfere with this natural timing (e.g., cause the fry
to hatch when the natural preferred foods are lacking or scarce)
would jeopardize the survival of that stock.
Temperatures above 64°F will cause mortality in excess
of 50 percent of the eggs of yellow perch during the first 24 hours
after the eggs are spawned (FWQA, Duluth; unpublished data).
According to Figure 6 the average temperatures on May 15 (the start
of the spawning season), June 1, and June 15 (the end of the spawning
season), were 49, 53, and 58°F respectively; and in one year of three
they might be as high as 53, 58, and 64°F. Temperature elevations of
15°F on May 15, 11°F on June 1, and 6°F on June 15 would bring the
water temperature to 64°F, the lethal limit. In one year of three
temperature rises of 11 and 6°F could bring lake temperatures to 64°F
on May 15 and June 1; on June 15 the temperature may already equal
the lethal 1imit.
Although 50 percent of the eggs spawned may hatch at
temperatures below 64°F, the most viable fry are produced only from
eggs incubated at temperatures below 61°F (FWQA, Duluth, unpublished
data). Temperature rises of 12, 8, and 3°F on May 15, June 1, and
June 15, respectively, could bring the average water temperature to
61°F (Figure 6). In one year of three temperature rises of only 8°F
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on May 15 and 3°F on June 1 might bring the temperature to 61°F,
and after June 7 the temperature may already exceed that value.
E. EFFECTS ON FRY REQUIREMENTS
Fry of whitefish, lake herring (cisco), smelt, alewife,
and yellow perch occupy inshore waters during at least the early
stages of their development; limited evidence suggests that those
which move into deeper water later in the fry stage inhabit upper
levels.
Hart (1930) found that whitefish in the Bay of Quinte
(Lake Ontario) spawned mostly in water 8-15 feet deep, and that
the eggs began hatching in about mid-April. The newly hatched fry
remained near the surface, and about 2 weeks after hatching began
to school and concentrate in water less than 18 inches deep. About
4 weeks after hatching they moved into water 3 or 4 feet deep, but
always remained near the surface. Reckan (1970) found whitefish
A
fry in South Bay, Lake Huron, in shallow areas (less than 3 feet
deep) in late June and early July. Studies of the early life
history of whitefish now being conducted by the University of
Wisconsin-Milwaukee in Green Bay and northwestern portions of Lake
Michigan have shown that Lake Michigan whitefish also use the
inshore areas for egg incubation and nursery grounds; about 90 per-
cent of the larvae were at water depths of 10 feet or less (Walter
Hogman, University of Wisconsin, personal communication).
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Pritchard (1930) reported that cisco spawning in the Bay of
Quinte took place in water 8-10 feet deep, and that the eggs hatched
in late April and early May. The fry ranged in shallow water with
whitefish fry until they were about 1 month old, when they moved into
deeper water. Cisco fry have also been observed in shallow water in
Lake Huron (Faber, 1970). The cisco fry were often present in the
upper 8 inches of water very near shore (e.g., around docks); small
numbers, however, were regularly taken in surface collections over
deep water.
Smelt spawn in early spring in tributary streams and along
shore in Lake Michigan (as evidenced by the concentrations of sport
fishermen during smelt spawning time). How long the fry remain in
the shallow water is not known, but Wells (1968) demonstrated that
most remain in the warm upper strata until late summer. In eastern
Lake Erie young smelt frequent shallow epilimnial waters and at times
are heavily concentrated near shore (Ferguson, 1965).
Alewives spawn in late spring and early summer in tributary
streams (and along shore in some areas) in Lake Michigan (Edsall , 1970).
Soon after hatching, which is primarily in June and July, the young
are mostly in the upper few feet of water very near shore, but as they
grow older some rapidly disperse into the upper warm levels over
deeper areas, and may be found in midlake by late summer (BCF, unpublished
data; Wells, 1968).
Yellow perch spawning areas in Lake Michigan are not completely
known but most apparently spawn among weeds or on rocky shoals. These
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areas provide substrates to which the ribbon-like egg masses can
cling. Hatching occurs mostly in June, at least in southeastern
Lake Michigan. Largest catches of fry by BCF have been in water
about 16 feet deep, and few fry have been caught in water deeper
than 33 feet. Sampling has been extremely limited in water
shallower than 16 feet, but on the basis of perch fry distribution
in other lakes, it seems extremely likely that the fry in Lake
Michigan are most abundant in water shallower than that depth.
Although the distribution of the fry of a number of other
species is poorly known, some undoubtedly occupy inshore areas of
Lake Michigan. The larvae of burbot and deepwater sculpins (both
present in Lake Michigan), for example, have been observed in
association with whitefish fry in very shallow water in Lake Huron
(Faber, 1970). Two common Lake Michigan forage species, trout-perch
and spottail shiners, are mostly in water less than 30 feet deep
when they are in spawning condition in early summer (Bureau of
Commercial Fisheries, unpublished data; Wells, 1968).
Published information on the thermal tolerance of larval
fishes, including coregonids, is almost totally lacking. Recent
studies in which newly hatched cisco fry acclimated at 38°F were
subjected to temperature shock showed that 100 percent of the fry
were immobilized in about 700 minutes at 73°F, 55 minutes at 77°F,
and 5 minutes at 81°F (T. Edsall, unpublished data). Studies by
Coutant (1969) on the effect of acute sublethal temperature shock
on juvenile salmonids revealed that heat doses only 25 percent as
large as those required to cause loss of equilibrium caused a
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significant increase in the susceptibility of the shocked fish to
predation. No records were made of the heat doses required to
produce loss of equilibrium in cisco fry, but they were considerably
lower than those required to produce immobilization (T. Edsall,
unpublished data). Although studies of the susceptibility of
cisco fry to predation were not made, the available information
suggests that cisco fry that hatch in middle to lake April and are
subjected to temperatures of less than 10°F above the average for
that date (Figure 6) have an increased susceptibility to predation.
F. OTHER EFFECTS
1. Effects on Fish
Historically, there is little doubt that increased
temperatures and lower flows in tributary streams following
deforestation and settlement were important factors associated with
the reduction or elimination of stocks of whitefish, lake herring,
and lake trout that spawned in rivers and shallow areas of the
Great Lakes. Heavy exploitation, mill dams, and pollution were also
suspected of being contributing causes; however, even after these
factors were eliminated as influences, the stocks did not recover
while the temperature increases persisted (forests were not
replanted, and industries and cities that caused aquatic warming
grew larger).
Increased temperature is still considered today the
most likely cause for the reduction in numbers of whitefish, lake
herring, and lake trout from tributaries and shallow areas of all
of the Great Lakes, and the virtual elimination of all of these
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species from the St. Clair River, Lake St. Clair, the Detroit River,
and Lake Erie, where they were once abundant. Lakes St. Clair and
Erie recovered to some degree from this loss because they are shallow
and thus are favorable for members of the perch family (walleyes,
blue pike, saugers, and yellow perch), which can tolerate warmer
waters. These species cannot, however, live in the cold, deep water
of the other Great Lakes, nor can other species--as is illustrated
by Lake Ontario, where all large lake species (including those of the
perch family) are greatly reduced or absent. Fish are very scarce in
Lake Ontario throughout the offshore region, which includes some 70
or 80 percent of the area of the lake.
Grossman (1969) noted that, although the increase of 2°F
in average water temperature in Lake Erie since the period 1918-27
does not seem large, it is actually equivalent to moving the lake 50
miles to the south—and many of the prime species, such as lake trout,
whitefish, and ciscoes (lake herring) were already at the southern
limit of their temperature tolerance in Lake Erie before settlement.
He also stated that, for whitefishes, temperatures only slightly above
a critical level during incubation seriously reduce the number of eggs
that hatch and the number of young fish that will be added to the
population.
Several studies and observations support the hypothesis
that temperature is presently limiting the natural distribution of
coregonid fishes in the Great Lakes area (Frey, 1955; Lawler, 1965;
Colby and Brooke, 1969; Grossman, 1969; Edsall and Colby, 1970).
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Some of the potential insidious effects of heated
effluents on the spawning grounds in Lake Michigan include the
changing of the ecology of this critical habitat. Milner (1874)
reported that lake trout in Lake Superior spawn in 7 to 90 feet
of water, and James Reckahn (Ontario Department of Lands and Forests,
personal comnunication) has noted that whitefish spawn over water
from a few inches to 20 feet deep.
Hart (1930) found whitefish eggs in crevices and under
stones. They were observed most commonly at a depth of about 8 feet
and none were observed below a depth of about 15 feet. Whitefish
and lake trout both spawn over suitable bottom areas where wave
action and currents keep the bottom swept clean. The observations
of Merriman (1935), Royce (1936), and Royce (1951) show that lake
trout spawning areas are restricted to bottoms of clean gravel or
rubble, free of sand and mud. Royce (1951) stated: "As the fish
make no effort to bury the eggs, the bottom must have crevices into
which the eggs can fall, if eggs and larvae are to be protected."
Because crevices and interstices are required for protection of eggs
of whitefish, lake herring, and lake trout in shallow water, any heat
addition that will accelerate production and deposition of organic
matter, prolong decomposition reactions and contribute decomposition
products to these confined microhabitats will have deleterious effects
on egg survival. These subtle changes may already be taking place in
the Great Lakes; research on the problem is much needed. It is im-
portant that water quality in the bottom-water interface does not
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approach conditions described over fiber deposits by Colby and Smith
(1967) if fish survival is to be ensured. Anoxic conditions, with
associated production of bacteria similar to those over fiber beds,
could occur in areas of increased heat in the presence of adequate
nutrient sources. Such a situation could result where a sewage
treatment plant and a power plant discharge effluents in the same
vicinity.
2. Mortality of Water Birds
Multiplication of bacteria is encouraged by increasing
summer lake temperatures. One particular organism of concern is
Clostridium botulinum type E, the bacterium which has caused dieoffs
of fish-eating birds on Lake Michigan and has caused human mortalities.
Although this organism readily grows at low temperatures, it has an
optimum range of about 68-86°F. Since it becomes most common in
areas of high localized temperatures, any increase in temperature
within this range will stimulate both multiplication of the organism
and production of its toxin.
3. Intake Damage
Although the major share of attention so far has been
focused on the thermal effects of cooling water discharges on the
metabolism of Lake Michigan fish, several other consequences of using
the lake waters for cooling also merit serious consideration.
Thermal shocking of aquatic organisms pulled into a
power plant is an important consideration when judging intake damage.
Just as important are the physical jarring and smashing to which
organisms (adult fish, fish fry, and plankton) are subjected when
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they are brought up against the fish screens and internal piping of
the intake structures. Assuming a use rate of 91,000 cfs (by the
year 2000), about 1.1 percent of the total volume of the water
inside the 30-foot depth contour (where the eggs, larvae and juveniles
of many important Lake Michigan fishes are most abundant) will be
passed through the cooling systems of power generating plants daily;
and in one year a water volume equal to several times the entire
water mass inside the 30-foot contour would pass through these
cooling systems. Available information on the effect of thermal
shock on larval fishes (see the section of fry requirements for
information on the thermal tolerance of larval lake herring) indi-
cates that the expected temperature rise alone experienced by these
fishes while passing through the cooling system would be very
injurious or immediately lethal. Similar undesirable effects are
anticipated for other important aquatic organisms, including phyto-
plankton (Morgan and Stress, 1969) that serve as food for Lake
Michigan fishes.
4. Discharge Damage
The addition of chemicals to clean cooling systems may
also cause damage to Lake Michigan fishes and food organisms. Chlorine
is generally used to limit the growth of algae on condenser surfaces.
The amount of chlorine used depends on the installation but chlori-
nation to 0.1 mg/liter for about one-half hour, three times daily,
is typical. Although the amount of chlorine introduced to the lake
will not significantly increase the chloride content of the lake, the
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the chlorine will have a bactericidal and algicidal effect on
organisms in the treated water. Preliminary data obtained to
determine the potential of chlorine for use as a fish toxicant
indicate that even short exposures to concentrations of less than
0.1 mg/liter are lethal to young coho salmon in natural Michigan
surface waters (L. Allison, Michigan Department of Natural Resources,
personal communication). Other toxicants such as chromates and
copper sulfate (used to combat algal problems in cooling facilities)
may also be present in the discharge water and have a serious effect
on the aquatic environment.
Heated effluents from power plant cooling systems will
be saturated or supersaturated with dissolved gases and will cause
the formation of emboli in fishes that will damage gills, eyes,
epidermis and other tissues and may be lethal. Newly hatched white-
fish and lake herring larvae are highly susceptible to damage from
supersaturation (T. Edsall, Bureau of Commercial Fisheries, personal
communication; J. Reckahn, personal communication). Larvae of other
Lake Michigan fishes are probably also susceptible.
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V. EUTROPHICATION
The general effects of increased water temperature on the
phytopiankton and other algae are known, but are not well de-
lineated—particularly with respect to lakes. Patrick (1969)
stated: "Blue-green algae will increase due to Increased organic
load and/or to rise in temperature .... In general, the blue-
green algae have more species that prefer temperatures from 35°C
[95°F] upward, whereas the green algae have a relatively large
number of species that grew best in temperatures ranging up to
35°C [95°F] although some can grow at higher temperatures. Most
of the diatom species prefer lower temperatures--that is, tem-
peratures below 30°C [86°F]. The natural succession of species
which we find is largely due to the fact that species can out-
compete each other under varying temperature conditions. Of course,
other ecological conditions also control the kinds of species which
we find present at various; seasons of the year. These conditions
are light, nutrients, and so forth." The synergistic effect of
increased temperature and increased nutrient concentration sug-
gested by Dr. Patrick may be of particular concern with respect
to present and projected conditions in Lake Michigan.
In Lake Erie, the most eutrophic of the Great Lakes, a suc-
cession of algal pulses occurs each year. Diatoms appear first in
late winter or early spring when temperatures begin to rise above
freezing, following the winter period of relatively little algal
activity. Diatoms reach their maximum at temperatures of 35°F to
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50°F. When the temperature rises above 50°F, green algae become
dominant and remain dominant until the temperature nears its
maximum of about 75°F. Above 75°F blue-green algae appear, and
as the lake begins to cool, very large blooms frequently occur.
The algal succession as described above for Lake Erie has
not been generally observed in Lake Michigan, even though tem-
perature ranges are similar. The reason for the difference is that
Lake Erie is richer and more variable in nutrient content; algal
succession is not due to temperature alone, but is the result of
temperature and adequate nutrient supply. The response in Lake
Erie to artificial heat rise could be expected to be a change in
the time of the algal succession during the warming season.
Pulses of diatoms, green algae, and blue-green algae would prob-
ably occur earlier than would be expected naturally. In addition,
artificial warming would lengthen the period of dominance of
blue-green algae by simply sustaining temperatures above 70°F for
a longer period.
In Lake Michigan, however, indications are that nutrients in
the inshore waters are approaching levels commonly found in the
central basin of Lake Erie. Lake Michigan inshore waters receive
a substantial and increasing load of nutrients in the form of
nitrogen, phosphorus, and other fertilizing agents from domestic
effluents and agricultural runoff. Therefore, it can be expected
that the inshore waters of Lake Michigan, if nutrients are not
sufficiently controlled, will attain conditions of algal production
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similar to those in Lake Erie. When these conditions are reached,
temperature becomes a very important factor. Dominance of green
and blue-green algae will become more frequent and persistent.
Blue-green algae, which are especially responsive to higher tem-
peratures, will become more prolific in direct proportion to
temperature increase. Stoermer and Yand (1969) reported that,
although the dominant phytoplankters in Lake Michigan are still
diatoms, the numbers of taxa that are associated with degradation
of water quality have increased, and that a number of species which
were able to thrive only in the naturally enriched areas near shore
and in estuaries are now found in some areas of the open lake. They
stated: "Consideration of distribution and relative abundance of
the major components of the plankton flora leads one to the conclusion
that Lake Michigan is probably at the present time about at the 'break
point1 between rather moderate and transient algal nuisances, largely
confined to the inshore waters, and drastic and most likely irreversible
changes in the entire ecosystem." Temperature increases, whatever the
amount, will tend to promote these undesirable changes, especially in
inshore waters.
C. L. Schelske and Stoermer, in the abstract of a paper entitled
"Depletion of Silicon and Accelerated Eutrophication in Lake Michigan,"
presented at the meetings of the American Society of Limnology and
Oceanography in August 1970, have commented further on this. They
stated: "During the past 30 years, the relative abundance of diatom
species commonly associated with degradation of water quality has
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increased. In the summer of 1969, the plankton diatoms comprised
less than 10 percent of the phytoplankton in samples from the southern
part of the lake, which was a significant deviation from previous
years when the diatoms comprised at least 65 percent of the phyto-
plankton The evidence compared with data from Lake Erie
and Lake Superior suggests that accelerated eutrophication in Lake
Michigan is rapidly approaching the point of a severe environmental
change in which the diatom flora will be reduced or replaced by green
and blue-green algae." The overall effect of heated discharges will
be to reinforce an increase in warmwater algal species at the expense
of more desirable coldwater species.
Hawkes (1969) cited the work of Poltoracka-Sosnowska (1967) in
which the phytoplankton was compared among three Polish lakes having
different temperature ranges:
"Lichen Lake received thermal discharges from the electricity-
generating stations at Konin and had a temperature range of 7.4°C
[45.3°F] to 27.5°C [81.5°F]. Slesin Lake was not influenced by
thermal discharges and had a temperature range of 0.8°C [33.4°F] to
20.7°C [69.3°F]. The third lake was only slightly influenced by
thermal water. It was found that Lichen Lake, the warmest lake,
supported the richest phytoplankton flora: 285 forms; and Slesin
Lake, the least number: 198. In contrast with the other lakes, the
phytoplankton flora of Lake Lichen was comparatively constant. It
was observed that, as the temperature of Lichen Lake rose, the numbers
of phytoplankton species increased. The characteristic dominant forms
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in Lichen Lake were the diatom Melosira granulata and the blue-
green alga, Microcystis aeroginosa. These two algae are charac-
teristic of eutrophic situations. In the cold water of Lake Slesin,
the diatom Stephanodiscus astraea (an oligotrophic form) was dominant.
"Patalas (1967) compared the productivity of Lichen Lake with
that of a natural cold-water lake in the same lake system. It was
found that the primary productivity of the heated lake (7.3 g/m^/d)
was almost twice that of the cold lake, 3.75 g/m2/d. Secondary
productivity in the form of phytophagous Crustacea and rotifers was
4.5 g/rrr/d in the heated lake, compared with 1.06 g/nr/d in the
unheated lake."
The rate of eutrophication is controlled primarily by nutrient
supply and water temperature. Either can be a limiting factor to
productivity. Nutrient control measures are being undertaken at
municipal and industrial effluent outfalls on a lake-wide basis;
however, many diffuse sources of nutrients are not now amenable to
control (e.g., agricultural and urban runoff and sediment erosion).
Waste heat inputs, on the other hand, are entirely "point" sources
and, on an overall basis, can be controlled much more efficiently
that can nutrients. Thus, the control of waste heat provides greater
assurance that the expensive productivity-limiting objectives of
nutrient control will be attained.
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VI. ECOLOGICAL RAMIFICATIONS OF THE ADDITION
OF WASTE HEAT TO LAKE MICHIGAN
A. INTRODUCTION
Details of the resource, the mechanism and projected magnitude
of waste heat input, and pertinent interactions of aquatic life and
temperature have been reviewed in earlier sections. It is the pur-
pose of the present section to examine the ecological ramifications
of waste heat addition to Lake Michigan. The effects of individual
plumes on aquatic life at specific sites are discussed, as well as
the broader lake-wide aggregate effects of the projected waste heat
rejection that would result from once-through cooling in coming
decades.
B. GENERALIZED PLUME IMPACT
Unless a discharge is located sufficiently far from shore and
in deep water, waste heat will under normal lake current conditions
frequently be carried to the beach water zone, where the ecological
impact will be essentially the same as that of a shoreline dis-
charge. For this reason, attention is focused primarily on shore-
line point and jet discharges.
A single plume, depending principally on effluent volume and
temperature, will exert a thermal influence over a significant lake
area. For example, the "dilution only" model study for the Davis -
Besse Nuclear Plant indicated that the plume for an 18°F temperature
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rise would at equilibrium cover 28 square miles to the 2QF isotherm
and 373 square miles to the 1°F isotherm (Table 14). Thus, organisms
in substantial areas of the inshore waters would be exposed to the
biological influence of the unnaturally warmed water.
A more extensive variation of a single plume ecological effect
is the situation where two or more waste heat discharges are close
enough to interact. An additive effect will cause the thermal
ecological impacts from the interaction to be more intense than if
only one heat source existed.
The once-through cooling process will thermally shock and
physically jar adult fish, fry, and plankton. Physical damage occurs
against fish screens, internal piping, and intake structures. Industrial
and power operations also frequently add algicides to cooling water with
resultant adverse effects on organisms. It is desirable to relate this
once-through cooling damage to the large volume of water required for
a single plant. A 600 cfs effluent would require 142 billion gallons
of lake water per year and a 3500 cfs effluent, 826 billion gallons.
In the course of an operational year, a proportionately large amount
of plankton would be destroyed or placed under unnatural stress.
There will frequently be a sector which will exhibit temperatures
sufficiently higher than ambient lake temperatures to be lethal or
immobilizing to nearly all species in Lake Michigan. The size of the
sector so affected depends, among other things, upon the discharge
temperature and velocity, lake current velocity, and tolerances of
specific organisms. Intolerant organisms of all life stages must
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avoid this sector or suffer stress or mortality; thus they are
prevented from normal habitation or utilization of this zone.
There will also be a heated sector adjacent to the one
nearest the outfall that is not lethal, but from time to time
actually attracts certain species of fish. Angling success is
reputedly sometimes improved in such sectors. The vicinity of
the plant outfall will from time to time be "flushed" by storms
and upwellings; the frequency of such occurrences is discussed
in section II. The physical dynamics are not clearly understood
but the mixing will predictably occur—sometimes with great
rapidity and accompanied by sharp drops in temperature in the
area of the thermal discharge. At such times, fish attracted by
the warm water and acclimated to it are exposed to stress. Such
stress can be sufficient to cause fish mortalities, as happened
at the Campbell Plant near Port Sheldon, Michigan, in August 1968.
It is suspected that a similar stress condition might occur when
the heat source is shut off, as when a power plant goes off line.
An unnatural, three-dimensional continuum of temperature
decrease extends from the warmest water at the discharge out to
where the lake mass exhibits ambient temperatures. Within this
continuum of thermal influence of the plume, the waste heat will
directly and indirectly influence life processes of fishes, in-
cluding feeding rate, maturation, growth, spawning, incubation,
vulnerability to predation, hatching, and larval development.
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Adverse physiological effects will result when optimum thermal limits
for a particular life process are exceeded in the plume; these in-
fluences will generally increase in subtlety with distance from the
discharge. Evidence discussed in section II indicates that only
slightly elevated temperatures, properly timed and sufficiently long,
can be critical in the various life history stages of Lake Michigan
species. The evidence also indicates that adverse thermal limits
are already approached by existing water temperature regimes; and
that in warmer years, the lake temperatures may for several species
already exceed these limits. For example, Lake Michigan temperature
regimes may now be at borderline limits for optimum growth, repro-
duction, and/or survival of yellow perch, whitefish, lake trout, lake
herring, alewives, and coho salmon. Thus, it appears that artificial
heating would aggravate and intensify existing critical adverse effects
and perhaps create new ones. Particularly in warmer years, temperature
increases induced by waste heat would detrimentally affect these species
or reduce their habitat in the area influenced by the plume.
An extensive zone of thermal influence would affect the species
composition of algae and bacteria, in favor of species preferring
higher temperature; for example, green and blue-green algae would be
favored over diatoms. Such a localized eutrophication effect is
particularly important in lake zones where nutrient concentrations are
h i gh.
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In addition to "flushing" in the actual vicinity of the discharge,
the entire area influenced by waste heat will also be purged from time
to time with colder lake water. Since the addition of waste heat
serves to "inflate" local natural temperatures in the shallow water
environment, one resultant net effect is to exaggerate the natural
temperature extremes caused by the flushing out process and thereby
complicate ecological adjustments to the extremes.
C. POTENTIAL IMPACT OF CUMULATIVE WASTE HEAT
Assuming the once-through cooling technique, the projected year
2000 situation in which 431 billion Btu/hr of waste heat would be
discharged to Lake Michigan requires a rrore general approach to
ecological evaluation. The number of discharges under such a situation
is unknown, although estimates as high as 100 have been advanced.
Several definite impacts are recognizable, if not quantifiable.
It has been demonstrated that waste heat addition in coming decades
could significantly raise the temperature in extensive areas of the
inshore waters, particularly the beach water zone. Waste heat from
individual shore discharges are capable of thermally influencing many
miles of lake shore. As the frequency of discharges along the shore
increases, many plumes would eventually be so close together that their
effects would merge. With the magnitude of projected waste heat, it is
not difficult to envision a very sizable proportion of the beach water zone
and certain adjacent waters physically affected by artificial temperature
increases.
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The aggregate influence of waste heat from increasing numbers of
plants around the perimeter of the lake would proportionately magnify
the unnatural effects on fish and other aquatic organisms caused by a
single plume. Where several plants would exist in proximity, ecological
problems would be intensified with interaction of their thermal zones
of influence.
Under such warmed conditions and in those areas where nutrients
are approaching critical levels, changes toward increased eutrophication
would be expected. The increased eutrophication would be evidenced by
dramatic increases in blue-green algae.
Extensive areas of waste heat influence would also favor species
of bacteria tolerant of relatively high temperatures. Under certain
conditions, the warming influence would assist in proliferating both
the abundance and toxin production of Clostridium botulinum type E
during summer and fall, and increase the probability and magnitude of
mass dieoffs of shore and water birds.
Finally, projected once-through cooling water requirements of
91,000 cfs for year 2000 would require a volume of lake water equal to
roughly 1 percent of the beach water zone daily, or 2.15 trillion
gallons per year. On the basis of shear volume of water used, thermal
and physical damage to aquatic organisms by once-through cooling could
be expected to reach considerable ecological significance.
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VII. CONCLUSIONS
(1) The inshore zone is in many respects the most important portion
of Lake Michigan. It is the most used by man and is the most
biologically productive.
(2) At times very large percentages (up to virtually 100 percent)
of the waste heat discharged to the lake are diffused into the
beach water zone; and studies of model plumes indicate that the
influence of the heated water from a single discharge can cover
many areal miles of the lake.
(3) Assuming that once-through cooling water requirements in the year
2000 will result in the discharge on the magnitude of 431 billion
Btu/hr of waste heat into Lake Michigan, a significant artificial
thermal load would be added to the beach water zone. Since this
waste heat load would equal a significant percentage of the
natural rate of heat input, it is not difficult to envision
resultant physical warming of a large proportion of the beach
water zone and certain adjacent waters.
(4) Heated plumes alter the natural habits of fish, exclude them from
discrete areas of heated water near shore, and produce the hazard
of stress and mortality in the event of rapid cooling. The plumes
also create a broad area of thermal influence in inshore waters,
which in an unnatural manner influences critical life history
stages of fish and other aquatic organisms in the vicinity of the
discharge. Evidence indicates that for several fish species,
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critical life history stages are adversely affected. Further-
more, during warmer seasons, the waste heat accelerates the
eutrophication process over and probably outside the discharge
vicinity, which is an undesirable effect in oligotrophic Lake
Michigan. The added heat also alters the normal species com-
position of algae during cooler seasons, and improves conditions
for the development of Clostridium botulinum type E bacteria
during warmer seasons.
(5) On the basis of available evidence, the practice of once-through
cooling, regardless of any temperature standard (except virtually
no heat addition), will impart the bulk of waste heat to the lake
mass for an ecologically significant period of time. In other
words, a 1,000-cfs discharge 5°F above the ambient temperature
will transmit essentially the same amount of heat into the lake
as a 250-cfs discharge with a 20°F rise, and for essentially the
same length of time. It follows that, regardless of any number
standard, the magnitude of ecological impact of the heat would
be on the same order (disregarding more direct effects, such as
fish mortalities near the discharge, which may perhaps be avoided
by more thoroughly diluting the effluent).
(6) If the projected amount of waste heat is an amount sufficient to
impart ecological damage to the lake, the only available alter-
native is to restrict the addition of waste heat to that level
which will minimize or avoid damage.
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(7) The timing of natural events is essential for the perpetuation
of Lake Michigan coldwater aquatic life that has evolved as a
result of natural selection. Any waste heat influence which
would interfere with this natural timing places the survival of
this aquatic life in jeopardy. Evidence presented in this
report indicates that only slightly elevated temperatures, if
properly timed and sufficiently long, can be critical in the
life history stages of Lake Michigan species.
(8) Assuming the projected year 2000 cooling water requirement of
91,000 cfs and once-through cooling, an amazing water volume
equal to 1.1 percent of the beach water zone volume would be
passed through the cooling systems of power generating plants
daily (4.4 percent per day for the Chicago-Gary sector). An
unquantified, but significant, amount of physical and thermal
damage would occur to plankton, eggs, larvae and juvenile fish.
Prevention of this damage can be achieved by simply avoiding the
technique of once-through cooling. Such an objective can be
readily achieved by the use of closed cooling systems.
(9) Rate of eutrophication is controlled primarily by nutrient supply
and water temperature, either of which may limit productivity.
Since nutrient levels in certain areas of Lake Michigan are now
approaching critical levels, a lake-wide shallow water warming
influence would contribute to accelerating eutrophication.
Therefore, the careful control of waste heat provides greater
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assurance that the productivity-limiting objectives of the
immensely expensive lake-wide pollution control program will
be attained.
(10) Environmental influences in Lake Michigan which are detrimental
to the species characteristics of large northern lakes pose a
serious threat to the United States-Canadian sea lamprey control
program, the State-Federal lake trout restoration program, the
coho and chinook salmon sport fisheries, alewife control, and
other fishery programs. Potential lake-wide effects of waste
heat discussed in this report are considered to constitute such
a detrimental environmental influence.
(11) On the basis of the above points, it is concluded for ecological
reasons that no significant discharge of waste heat into Lake
Michigan should be permitted.
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