THERMAL EFFECTS ON ECOLOGICAL SYSTEMS
-------
THERMAL EFFECTS ON ECOLOGICAL SYSTEMS
A. F. Bartsch, Director
Pacific Northwest Water Laboratory, Federal
Water Pollution Control Administration, Dept.
of the Interior, Corvallis, Oregon.
and
D. I. Mount, Director
National Water Quality Laboratory, Federal
Water Pollution Control Administration, Dept.
of the Interior, Duluth, Minnesota.
"Temperature, a catalyst, a depressant, an activator, a restrictor,
a stimulator, a controller, a killer is one of the most Important and most
influential water quality characteristics to life in water. Temperature deter-
mines those species that may be present; it activates tho hatching of young,
regulates thair activitysand stimulates or suppresses their growth and
development; it attracts, and kills when the water becomes too hot or becorr.es
chilled too suddenly. Colder water generally suppresses development; war.T.er
water generally accelerates activity and may be a primary cause of aquatic
plant nuisances when other environmental factors are suitable."
What I have Just read is taken verbatim from the Introduction of a
Federal Water Pollution Control Administration report titled "Temperature
and Aquatic Life." ^ It points to many of the considerations that arise
when we think of thermal effects on ecological systems.
So that all of us are thinking in the same terms, let me define this
new popular word "ecology" as the study of the interrelationships between
organisms and their environment. We are concerned today with environments
that are modified through augmented heat input. There are three ecological
aspects I wish to explore: (1) the broad implications for this planet,
(2]l effects on ecological .systems in the water environment, and (3) potential
uses of heat.
Implications for This Planet
In the current issue of BioScience, (2) LaMont C^.Cole, currently-
Ptesldent of the American Institute of Biological Sciences, examines the
earth's heat budget and man's effect on it. Let me briefly paraphrase his
Analysis for you.
Of all the earth's sources of energy,-99.999% reaches us as radiation
from the sun. Through photosynthesis over the ages, some energy from this
Source has been stored in organic fuels which, at some future time, rr.ay
release heat into the environment. Heat also emerges from the center o£
the earth, perhaps from natural radioactivity. There are several other
minor heat sources.
117
-------
If the surface of the earth is to maintain its present mean tempera:
which lies in the neighborhood of 59°F, It must rid itself of a quantity 0«
heat equal to the input. This is.important because a mean temperature n
of only 5.4°F is believed likely to melt the icecaps of Greenland and
Antarctica, raise the sea level by some 328 feet, put Florida under waicr
and drown most of the world's major cities. For this to happen would
require only a 4.2% increase in the earth's heat budget.
So, let's look at what people do to the heat budget. The amount of
energy now being produced by man is exceedingly trivial—only about 25/
of i% of the total radiated by the earth. It is thus obvious that this ac:Y,
now has an absolutely insignificant direct effect on the average tempera:-.
of the earth's surface. But the question is—Will this still be true as we
go on increasing our demands for power? What will happen, for example,
If power production and non-electrical uses of fuel Increase at the .now
anticipated rate of 7% per year? The answer is that in 91 years there ecu
be a warming of 1.8°F, which could result in some shifts in plant cornniL;
distribution. But to reach that critical 5.4°F increase and face all the du
consequences I mentioned would take about •gStf years! Well, that's fine
and so let's relax, but let's also keep this prospect in the back of our mL
as we concentrate on the more urgent problemsj that are here today.
108
Responses to Heat in the Water Environment
So our planet seems secure; let's go on then to examine the responi
to heat in the smaller sphere of the water environment.
As temperature in water environments rises, the rates of various
chemical and biochemical reactions are accelerated. Production of hydro
sulfide in bottom sludges doubles with a rise of 18°F. The BOD reaction,
by,which organic matter is stabilized, is most rapid at 86°F, so that a
Stream may be cleansed of its waste load more quickly as temperature goe
up. But this accomplishment is not without cost. As dissolved oxygen is
used up more rapidly to satisfy the needs of the process, rising tempera-
ture impairs, reaeration. As a result, the stream's oxygen resources
diminish, and all the undesirable side effects of oxygen depletion can
come into being. Elevated temperature has been noted to substantially
reduce the assimilation capacity in some rivers. &) As a result, waste
treatment performance must beimproved or streamflow for dilution must be
increased.^)
These and many other responses help to create a new heat-modified
environment to which living organisms must respond. Through its ihfluenc
on molecular movement and speed of chemical reactions, temperature con'-
118
-------
the rate of metabolism and activity of all organisms. This applies to
aquatic plants. It Is true of animals that can maintain a relatively
constant temperature; It also affects those whose temperature approxi-
mates that of the environment the so-called cold-blooded animals. For
this reason, temperature may be the most important single environmental
factor affecting life and life processes.
Aquatic algae are affected profoundly by temperature changes (Fig. 1).
From 68-75°F, diatoms dominate the algal population. As temperatures
rise to 86-95°F, green algae are most common. Above 95°F, blue-green
algae predominate. No one has a good word to say for blue-green algae.
They are unattractive as food for aquatic life, they cause blooms and
drifting windrows of stinking scum, they destroy recreation, and create
difficult and costly water supply problems. Sometimes, especially in the
Midwest, they even become toxic and cause catastrophic deaths of livestock,
game animals, birds, and fish.
We are concerned on a national scale with the exploding problem of
eutrophication, or lake aging. The most distasteful symptom is the
abundance of these same unwanted blue-green algae. The principal remedial
attack now used is to limit the input of stimulatory plant nutrients through
tertiary treatment of municipal sewage. Apparently now we must keep an
eye on the heat budgets of susceptible waters as'well.
It has been known since the turn of the century that the character-
istics of bottom-dwelling organism populations are clues to the quality
of the environment. When the habitat becomes more stringent, as it does
from the addition of pollutants, the variety of surviving organisms becomes
progressively less. This commonly known principle is the basis for
diagnostic schemes still used to detect and measure pollution. Studies
on a Pennsylvania stream (5) show this principle is valid for elevated tem-
perature, also (Fig. 2). The number of kinds of organisms decreased by
55% as temperature went up from 80 to 87°F. When temperature increased
further to 93°F, there was a 24% additional loss. Such population changes
under the influence of heat are an important reason for concern. Because
these organisms are the food of sport and commercial fishes, they need
to be preserved, for without them the fisheries also will disappear.
The physiologist considers a number of vital mechanisms when he is
concerned with the direct impact of heat on fishes. Oxygen consumption
goes up as temperature rises because the fish begins to live at a faster
pace. But unfortunately for the fish, both water in the stream and heir.o-
globin in the fish's blood can hold less oxygen at elevated temperature.
The result—less efficient gill function, breathing rate goes up, and
greater energy output is required just to stay even.
119
-------
Enzyme activity performs all the basic functions of the body. But
when temperature is high enough, heat-stimulated enzymes malfunction b
exhausting their substrates, or by producing toxic byproducts, or by heat
denaturation which, in effect, destroys the enzyme molecule. No one
knows w,hy trout die from heat at temperatures that allow carp to thrive.
We still ask — Why do fish die from heat? Is it from enzyme failure?
These are crucial questions now being examined by scientists in the
Pacific Northwest Water Laboratory at Corvallis, Oregon.
- Nutrition and growth are intimately related to temperature so that
a temperature rise within limits stimulates more activity, Increased food
consumption, and accelerated growth. Beyond these limits, the fish's
well-being deteriorates rapidly.
The physiologist looks also at reproduction, because this is vital
to production of a harvestable fish crop. This function is most sensitive
and vulnerable to temperature modification. Similarly, it has been found
that many diseases are induced by high temperatures. -It appears that
heat makes fish more susceptible and the pathogens more prolific and viru
lent. Faster breathing also brings pathogens moving over the gills at a
greater frequency,
Heat also influences toxicity. Elevated temperatures enhance the
'action of toxicants, so less is required to affect aquatic life. In rivers
that contain a variety of potential toxicants, their synergistic inter-
actions are usually intensified by increased temperature. Such a case
was reported recently on the Miramichi River in New Brunswick '°I where
Zinc and copper weakened the fish and elevated temperature promoted
a fish kill caused by disease.
.As yet, we do not know the full impact of fluctuating temperature on
aquatic life. This may be an important consideration where thermally
produced power forms the basic electrical supply with peak power needs
met by Intermittent use of hydroelectric facilities. It is known that
fish acclimate faster to rising than to declining temperatures, so that"
slugs of cold water from the base of a dam could cause serious harm in
a warm river.
With this as a brief background, I wish now to examine specific
examples of some of these heat Impacts on fishes.
To illustrate the effect of a range of constant temperatures on the
reproductive potential, one can use a minnow that is widely distributed
In the United States. The fathead minnow (Fig. 3) is an important food
120
-------
source for sport and commercial fishes. Observations show that a
constant temperature of 79°F, as compared to 72°F, resulted in a 25%
loss In"reproductive capacity. At 86°F, reproduction was almost nil.
A temperature of 92°F would cause no mortality but would nonetheless
eliminate the species because reproduction would be Inhibited. This
illustrates the great sensitivity of the reproductive stage.
Scientists at the Pacific Northwest Water Laboratory currently are
investigating the survival, fertility, and condition of adult salmon that
were forced to-make a simulated spawning migration at elevated temperatures,
Neither cohos nor sockeye survived 72°F for. two weeks, and relatively few
survived 68° for one month.' The resulting influences on fertility among
the survivors is unknown at this time. Finally, the condition of fish
held at 50°F was judged far superior to that of fish held at 62°F. For
example, both male and female sockeye in colder water lost about 8% of
their body weight, but at 62°F males lost about 10.5% and females lost
about 13.2%.
The National Water Quality Laboratory at Duluth has examined the
effect of temperature on the growth rate of the white sucker, a commer-
cially Important fish in the Midwest. As shown in Fig. 4, rising tem-
perature has a beneficial effect up to a point. Beyond that point,
adverse effects show up rapidly. From 50°F to 81°F, there is pronounced
increase in the growth of the suckers. When the temperature exceeds
81°F, growth Is reduced. At 86°F, it is only one-seventh of that occurring
at 81°F. Even worse, a temperature of 90°F will kill this fish in a 96-hour
period! It is important to note that the best temperature for growth is
very close to the lethal temperature. One, two, or three degrees may
determine the difference between high production and complete elimination
of a fish population.
All fishes are not alike; species vary In the temperature at which
they do best. Fig. 5 shows this characteristic for three species —
largemouth bass, northern pike, and brook trout. The temperature providing
best growth increases from 59°F for the brook trout, to 70°F for the
northern pike, to 81°F for the largemouth bass. This emphasizes the
principle that the best temperature and also the maximum permissible
temperature depend on the species that are being considered. If a brook
trout stream is warmed to 81°F, its temperature would be suitable as a
largemouth bass stream. The trout would be killed, pike would be in an
Undesirable temperature range, but largemouth bass would be at their
optimal temperature environment. This emphasizes the significance of
temperature in determining whether a given river supports cold water or
warm water species of fish.
121
-------
I call your attention next to. a theoretical consideration of the way
in which heat input can shorten the miles of stream suitable for habita-
tion by salmonids (Fig. 5). This chart was prepared by the National
Water Qua-lity Laboratory at Duluth. It shows a situation in which the
effect ofa'dded heat does not occur at the point of discharge but, instead
at some point many miles downstream. The stream represented here is cc'
considering the climate in which it exists, and usually it is fed by
springs or snow melt. Many trout and salmon streams are like this. The-/
naturally warm up progressively downstream without any artificial heat
addition. The lower curve of the graph shows the natural temperature
pattern that would exist from headwaters to mouth if no heat were added.
At 100 miles downstream, the temperature naturally exceeds the limit for
trout. If heat is added at a point 17 miles below the headwaters, suffi-
cient to raise the stream temperature 2°F, the stream is not harmed at
that point for the production of trout. But downstream the temperature
reaches the limit for trout sooner, at approximately 83 miles. As a
result, the lower 17 miles of the stream are unfit for trout production
even though the heat was added 60 miles upstream. If'the heat input
upstream raises the temperature 5°F rather than 2°F, destruction of trout
habkat extends farther upstream. The upper line in the graph shows that
there has now been a loss of 42 miles of trout waters as a result of
upstream heat addition.
Not cited specifically in th'is example is one of the most insidious
problems of thermal pollution. It is the fact that small increases in
temperature, while they may not kill the desirable cold water fishes, can •
foster the welfare and successful competition of warm water fish. In
most trout streams, warm water fishes do not reproduce because the numbs
of degree days is not sufficient for maturation of the gonads. Relatively
small changes can meet such needs and allow their reproductive prolifera-
tion. There then follows a population shift from desirable cold water
fishes to less desirable warm water ones. The latter can also serve as
a reservoir of diseases that can have devastating effects on trout and
salmon.
PotentialUses of Heat
After calling attention to these many ecological Implications of
thermal pollution, it is only fitting that I terminate these remarks in
some more optimistic tone. To do so, I wish to simply enumerate some
of the possibilities now considered for beneficial uses of waste heat.
In the United States — in fact, right here In Oregon — studies
supported by the Eugene Water and Electric Board are to demonstrate that
122
-------
warm water can stimulate and enhance plant growth and protect fruit trees
from killing frost. The Pacific Power and Light Company also is supporting
work at. Oregon State University to determine if growing seasons can be
lengthened and crop yields increased by warming the soil.
In Wisconsin, the Department of Natural Resources and the Wisconsin
Electric Power Company have joined in a program of intensive fish pro-
.ductlon in heated fish-rearing ponds. This program, to be located at
Two Creeks, should be in operation by 1971.
According to scientists at Massachusetts Institute of Technology, a
cooling 'trend in waters along the Maine coast has caused a decline in
growth rate of lobsters. Researchers have a plan to use power plant cool-
Ing water to warm the water in shoreline coves so lobsters will thrive
again. New York State is considering a similar proposal for a site on
Long Island near Montauk Point.
The Institute of Marine Science, at the University of Miami, has
joined the Florida Power and Light Company in a waste heat use project.
The-objective is to learn if a heated effluent can be used to raise pink
shrimp and pompaho.
,At Northport, New York, a 10,000 square foot oyster hatchery is being
built so that heated water from the Long Island Lighting Company power
plant can be used to maintain optimal temperature for oyster spawning and
production. Oysters in the heated water are expected to spawn ten months
out of the year rather than the normal three or four. As the young
oysters grow they will be placed on rafts and moved into Long Island
Sound.
In England, Scotland, and Russia there are several additional programs
to use waste heat in experimental or commercial production of fish and
shellfish.
Finally, at Tapiola, Finland, not far from Helsinki, cooling water
from the community power plant is routed through a piping system to
business and residential buildings. It provides heating, as needed, 270
days per year.
Conclusion
In conclusion, these are examples of the thermal effects on ecological
systems. The planet as a whole is not much affected by man's heat-
generating activities. But in the aquatic environment, there is a great
potential for destruction through thermal pollution. This can be avoided
if we give proper attention to the ecological knowledge now at hand.
123
-------
LITERATURE CITED
1. "Temperature and Aquatic Life. Laboratory Investigations - Number
Tech. Advy. & Investig. Br., Tech. Serv. Prog., FWPCA. U. S. Dep».
Int., Cincinnati, Ohio. Dec. 1967.
2. Cole, L.C. "Thermal pollution," BioScience 19, 989-992. Nov. 1969.
3. Krenkel, P.A., E. L. Thackston, and F. L. Parker. "Impoundment and
temperature effect on waste assimilation," J. San. Engrg. Div.,
Proc., Am. Soc. of Civil Engrs., Feb. 1969.
4. "FWPCA Presentations - ORSANCO Engineering Committee, " 17th
Meeting, Ohio Basin Region, FWPCA, U. S. Dept. Int., Cincinnati,
Ohio, Sept. 10, 1969.
5. Trembley, F. J. "Research Project on Effects of Condenser Discharge
Water on Aquatic Life," Prog. Report, 1969. The Inst. of Res.,
LehighUniv., 1961.
6. Pippyi J.H.C. and G. M. Hare. "Relationship of river pollution to
bacterial infection in salmon (Salmo salar) and suckers (Catastomns
commersoni)," Trans. Am. Fish. Soc. 98, 685-690. 1969.
124
------- |