Tennessee
Valley
Authority
Division of Environmental
Planning
Chattanooga TN 37401
TVA/EP-78/09
United States
Environmental Protection
Agency
Research and Development
Office of Energy, Minerals, and
Industry
Washington DC 20460
EPA-600/7-78-128
July 1978
Effects of Thermal
Discharges
on Aquatic Insects
in the Tennessee
Valley
Interagency
Energy/Environment
R&D Program
Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
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mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-78-128
TVA/EP-78/09
July 1978
EFFECTS OF THERMAL DISCHARGE ON AQUATIC INSECTS
IN THE TENNESSEE VALLEY
by
Kenneth J. Tennessen and Johnny L. Miller
, Division of Environmental Planning
Tennessee Valley Authority
Muscle Shoals, Alabama 35660
Interagency Agreement No. D8-E721-DR
Project No. E-AP 80-BDR
Program Element No. INE-625A
Project Officer
Clinton W. Hall
Office of Energy, Minerals, and Industry
U.S. Environmental Protection Agency
Washington, DC 20460
Prepared for
OFFICE OF ENERGY, MINERALS AND INDUSTRY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, DC 20460
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DISCLAIMER
This report was prepared by the Tennessee Valley Authority and has
been reviewed by the Office of Energy, Minerals, and Industry, U.S.
Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and
policies of the Tennessee Valley Authority or the U.S. Environmental
Protection Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
ii
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ABSTRACT
The primary objectives of this research project are (1) to determine
the thermal tolerances of selected aquatic insects and (2) to investigate
growth and emergence of selected aquatic insects in the vicinity of Ten-
nessee Valley Authority electric generating plants. The information may
help establish thermal effluent limits to protect the aquatic ecosystem.
The burrowing mayfly Hexagenia bilineata (Say) and the midge
Coelotanypus sp. were chosen for study because they are abundant and
they occur in areas affected by thermal discharges from Tennessee Valley
Authority electric generating plants.
The thermal{plume in the vicinity of Johnsonville Steam Plant
(TRM 98 to 101)
only during the
were subjected
'Humphreys County, Tennessee, reached the river bottom
fall and winter (1976-1977). Therefore, benthic insects
.o above-ambient temperatures during the coldest part of
the year. In early spring, H. bilineata nymphs collected from the
area influenced by the thermal plume were larger on the average than
those collected from the ambient station. However, growth at the ambient
station accelerated during late spring, and adult emergence occurred
almost simultaneously at both stations.
Tolerance of the immature stages of both study species to thermal
shock was great; abrupt changes in temperature of 20°C (at low accli-
mation temperature of 10 and 15°C) resulted in low percentages of
mortality although sample numbers were low.
Another stage in the life cycle that is subjected to ATs resulting
from thermal plumes is the egg. The optimum range of constant tempera-
tures for development of H. bilineata eggs is from 31 to 34°C; the
upper limit for egg development is near 37°C. Eggs subjected to a brief
(5 to 15 rain) shock of 10°C at the time of oviposition yielded a mean per-
centage of hatching comparable to that of the control treatment. However,
a shock of 15°C resulted in a greatly reduced mean percentage of hatching.
No difference in fecundity of adult females was found between the
ambient and thermal plume stations at Johnsonville Steam Plant. Adult
males emerging from the heated discharge channel were significantly
larger on the average than males from the ambient station.
A drift study conducted at TVA's John Sevier Steam Plant using damsel-
fly nymphs (Enallagma spp.) and mayfly nymphs (Stenonema spp.) in a thermal
plume resulted in little or no mortality at ATs that normally result from
the heated water.
This report was submitted by the Tennessee Valley Authority, Division
of Environmental Planning, in partial fulfillment of Energy Accomplishment
Plan 80-BDR under terms of Interagency Agreement D8-E721-DR with the
Environmental Protection Agency. Work was completed in October 1977.
iii
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CONTENTS
Page
Abstract iii
List of Figures vii
List of Tables x
List of Abbreviations and Symbols xi
Acknowledgments xii
1. Introduction 1
2. Conclusions 2
3. Recommendations 3
4. Experimental Procedures 4
Field studies 4
Laboratory studies • 9
5. Results and Discussion 12
Temperature profiles at Johnsonville Steam
Plant and implications for aquatic insects .... 12
Growth and emergence time of
H. bilineata 12
Size and fecundity comparisons of
H. bilineata 28
Thermal tolerance of immature aquatic insects .... 28
Effects of entrainment within thermal plume
on aquatic insects 33
Egg development and thermal tolerance 36
References 48
Glossary 49
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LIST OF FIGURES
Number
Outline map of Kentucky Lake in vicinity of
Johnsonville Steam Plant showing locations of
the five sampling stations
Emergence trap used to collect emerging
mayflies
Flotation device used to hold aquatic insects
for drift study
4 Plexiglas flow-through container for culturing
H. bilineata eggs 10
5 Vertical temperature profiles at five stations
in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from October 1976 to March 1977 .... 13
6 Vertical temperature profiles at five stations
in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from April to August 1977 14
7 Vertical temperature profiles at five stations
in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from August to October 1977 15
8 Substrate temperatures at two stations near
Johnsonville Steam Plant, Kentucky Lake,
from October 19, 1976, to September 21, 1977 16
9 Average head width and fore wing pad length
of H. bilineata nymphs collected at stations
1 and 3 near Johnsonville Steam Plant at
3-week intervals from March 31 to August 3, 1977 ... 18
10 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on March 31, 1977 19
11 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on April 19, 1977 20
vii
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Number Page
12 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on May 12, 1977 21
13 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on June 2, 1977 22
14 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on June 22, 1977 23
15 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on July 13, 1977 24
16 Comparison of frequency (%) of H. bilineata
nymphs in various size classes (based on head
width) at stations 1 and 3 near Johnsonville
Steam Plant on August 3, 1977 25
17 Comparison of frequency (%) of H. bilineata
nymphs in six size classes of head width
(interval =0.5 mm) from March to August 1977
at Stations 1 and 3 near Johnsonville Steam Plant . . 26
18 Percentage of H. bilineata nymphs having black
wing pads at stations 1 and 3 on three sampling
dates, 1977 27
19 Scatter diagram of relationship between
abdomen length and number of eggs in
H. bilineata females 30
20 Predicted and observed development times (in
days) for H. bilineata eggs cultured at seven
nearly constant (±1°C) temperatures 38
21 Average percentage of hatching of H. bilineata
eggs due to main effects of shock temperature (A),
shock duration (B), and day after oviposition (C) . . 44
viii
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Number Page
22 Surface response curves for shock temperature and
shock duration (interaction) effects on mean per-
centage of hatching of H. bilineata eggs over a
4-day hatching period 45
23 Effect of shock temperature on mean cumulative
percentage of hatching of H. bilineata eggs
exposed to thermal shock immediately after
oviposition 46
24 Interaction of shock duration and hatching day
on the mean percentage of hatching of H. bilineata
eggs exposed to thermal shock immediately after
oviposition 47
ix
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LIST OF TABLES
Number
1 Mean Values (x), Standard Deviations (s), and
Number of Observations (n) for Male and Female
H. bilineata Wing Length, Abdomen Length, and
Egg Count at Stations 1 and 3 near Johnsonville
Steam Plant 29
2 Results of t-Tests Comparing Mean Size and
Fecundity of H. bilineata Subimagoes at Stations
1 and 3 near Johnsonville Steam Plant 31
3 Number of H. bilineata Nymphs Surviving
Four Experimental Thermal Shocks 32
4 Number of Coelotanypus sp. Larvae Surviving
Four Experimental Thermal Shocks 34
5 Number of Damselfly and Mayfly Nymphs Surviving
after 8 Hours of Exposure in the Thermal Plume
and at Ambient Station near John Sevier Steam
Plant, July 20, 1976 35
6 Mean Cumulative Percentage of Hatching
Through 4 Days of H. bilineata Eggs Cultured
at 8 Constant Temperatures 37
7 Summary of Hatching Results at Constant
Temperature and Tests for Significance of
Difference Between Means as Determined by
Duncan's Multiple Range Test 39
8 Percentages of Hatching of H. bilineata Eggs
Exposed to Thermal Shocks (ATs of 5, 10, and
15°C) for Three Durations (5, 10, and 15 min)
Immediately after Oviposition 40
9 Analysis of Variance of 3-Factor Thermal
Shock Experiment on H. bilineata Eggs 42
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LIST OF ABBREVIATIONS AND SYMBOLS
AT — change in temperature above ambient
°C — degrees Celsius
df — degrees of freedom
DO — dissolved oxygen
h — hour
HRM — Holston River mile
km — kilometer
m — meter
min — minute
ml — milliliter
mm — millimeter
n — number of individuals in a sample
P — probability
r — correlation coefficient
s — standard deviation
TRM — Tennessee River mile
TVA — Tennessee Valley Authority
x — mean value
xi
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ACKNOWLEDGMENTS
The cooperation of several people in TVA's Water Quality and
Ecology Branch, Division of Environmental Planning, is gratefully
acknowledged: Mr. Barry 0. Bell, who assisted in collecting the field
and laboratory data; Ms. Sylvia A. Murray, who helped in the experimental
design of temperature effects on mayfly eggs, helped with the analyses,
and critically reviewed the manuscript; and Mr. Thomas W. Toole, who
calculated statistical parameters for the fecundity data and generated
the regression equation for egg development. We especially thank
Dr. Richard D. Urban for his initial planning of the thermal effects
research on aquatic insects and for advice and criticism throughout
the study. Mr. James R. Marsh, Laboratory Branch, is also acknowledged
for his fine work in the design and fabrication of the emergence traps
and flow-through egg containers.
xii
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SECTION 1
INTRODUCTION
The continued increase in demand for electric power increases the
amount of heated water discharged from fossil-fueled electric generating
plants, which in turn further alters the temperature regimes of aquatic
environments. How much can temperatures be altered before changes occur
in the biology of aquatic plants and animals? What are the limits on
thermal discharge that will not jeopardize a balanced indigenous flora
and fauna?
The theory that diversity in an ecosystem ensures stability is
generally supported by results of ecological research. Insects are a
major component of diversity in aquatic ecosystems, and their importance
in the food we)b and energy flow is well documented. Yet relatively
little is known about the thermal tolerances of aquatic insects,
especially species in the southeastern United States.
In this study, the thermal tolerances of selected species of
aquatic insects in the Tennessee River Valley were investigated.
Emphasis was placed on those stages of the life cycle that are subject
to thermal discharge from Tennessee Valley Authority (TVA) electric-
generating plants. These stages include the eggs, the immatures
(stationary or drifting), and the stage of emergence to the adult
insect.
Several questions were asked about what actually happens in a field
situation:
1. What stages of the selected species' life cycle are influenced
by thermal discharge?
2. What magnitudes of change in temperature above ambient (AT)
do these stages experience?
3. What are the thermal tolerances of these stages?
4. Does entrainment within a thermal plume affect survival?
5. How do elevated temperatures affect growth rate, emergence
time, and fecundity?
The species chosen for study were the burrowing mayfly, Hexagenia
bilineata (Say) (Ephemeroptera: Ephemeridae) and the midge, Coelotanypus
sp. (Diptera: Chironomidae), both of which are important food items for
fish. Both species are sufficiently abundant to facilitate experimenta-
tion, and both occur in areas subject to thermal discharges. Also,
mortality of these species due to laboratory conditioning is low. Dam-
selflies of the genera Enallagma and Ischnura and mayflies of the genus
Stenonema were also studied.
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SECTION 2
CONCLUSIONS
Results from this study support other reports that insects inhabiting
large rivers and reservoirs are quite tolerant of thermal shock. Eggs of
the burrowing mayfly Hexagenia bilineata developed and hatched (mean
hatching percentage was 63%) after a 15-min exposure to 40°C (ambient =
30°C, AT = 10°C) immediately after oviposition. However, a 5- to 15-min
exposure to 45°C (AT = 15°C) resulted in a low mean percentage of hatch-
ing (13%). A constant temperature of 37°C limited egg development.
Nymphs of H. bilineata and larvae of the midge Coelotanypus sp. withstood
thermal shocks as high as 20°C in the laboratory at low acclimation
temperatures (5 to 15°C).
Although acute effects from moderate thermal shocks in the labora-
tory were minimal, effects on several aspects of the life cycle of H.
bilineata were found. Nymphal growth was greater in areas where the
thermal plume extends to the bottom during the winter and early spring
than in ambient areas. However, development in ambient areas accel-
erated in late spring so that adults emerged at about the same date as
those in thermal areas. Size and fecundity of female H. bilineata
emerging from thermal plume areas and from ambient areas did not differ
significantly, although males from thermal plume areas may be significantly
larger. These differences in the mayfly's biology found to date were not
expected to adversely affect the species in the study area. Damselfly
and mayfly nymphs (Enallagma and Stenonema.) were held in the thermal plume
at John Sevier Steam Plant, resulting in no significant mortality,
compared with controls.
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SECTION 3
RECOMMENDATIONS
The effect of various acclimation temperatures on the thermal toler-
ance of aquatic insects should be investigated further; results may he
useful for predicting seasonal effects. Tolerance to cold shock should
be determined. Organisms that survive experimental heat and cold shocks
should be observed afterward for latent mortality and chronic effects.
The experiment on the effect of thermal shock on H. bilineata eggs
should be repeated with better control. The study of the effects of
thermal discharges at Johnsonville Steam Plant on the time of emergence,
size, and fecundity of H. bilineata should be continued for another
year. j
Establishing temperature limits to protect aquatic insects will
require study of species from other orders because tolerances no doubt
differ. From the information gathered in this study, it appears that
thermal plumes extending to the river bottom that are below 37°C in
summer would fully protect the most sensitive stages of H. bilineata.
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SECTION 4
EXPERIMENTAL PROCEDURES
Workers use two approaches to study the effects of temperature
increase. In the field, qualitative and quantitative changes in the
fauna are monitored, and results are usually reported as changes in
population structure and diversity indexes. In the laboratory, various
stages in the life cycle are subjected to different temperature regimes
to determine thermal tolerances. Rarely have these approaches been
combined. This study used both approaches. The field studies were
aimed at discovering (1) which species and which stages of the life
cycles of those species are influenced by a thermal plume and (2)
whether the plume affects growth, time of emergence, and fecundity.
Laboratory experiments were devised to investigate implications from
field data under controlled conditions.
FIELD STUDIES
Field studies were conducted at TVA's Johnsonville Steam Plant and
vicinity (TRM 98 to 101), on Kentucky Lake in Humphreys County,
Tennessee, and at TVA's John Sevier Steam Plant on the Holston River
(HRM 106.5 to 106) in Hawkins County, Tennessee.
Stages of Life Cycle Subjected to Thermal Plume
To determine whether the benthic, immature stages of H. bilineata
and Coelotanypus sp. are subjected to the thermal plume from Johnson-
ville Steam Plant, monthly vertical temperature profiles were determined
with a calibrated thermistor. Temperatures were measured at 1-m
intervals at five stations (Figure 1) between October 1976 and October
1977. Bottom temperatures indicate whether the thermal plume reached
the benthic habitat and reveal the magnitude of ATs experienced by the
benthos.
Mating swarms of H. bilineata were observed in the vicinity of
Johnsonville Steam Plant on June 5, 1977, around dusk. Mated females
were observed to determine whether oviposition takes place in the
discharge channel, which would expose eggs to above-ambient temperatures.
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-5-
TRM 99+
-N-
TRM
DISCHARGE CHANNEL
JOHNSONVILLE
STEAM PLANT
INTAKE CHANNEL
'.70
Figure 1. Outline map of Kentucky Lake in vicinity of Johnsonville
Steam Plant showing locations of the five sampling stations.
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-6-
Determination of Growth, Time of Emergence, and Fecundity
To compare growth rates of H. bilineata nymphs in ambient tempera-
tures with those in thermal plume temperatures, five samples were taken
with a Ponar dredge at stations 1 and 3 (TRM 100.6 and TRM 99.5 respec-
tively) at 3-week intervals from March 31, 1977, to August 24, 1977.
The sediments were field-washed on a 48-mesh sieve, and the mayfly
nymphs were preserved in an 80% ethanol solution.
Nymphal head capsule widths and wing pad lengths were measured
with an ocular micrometer on a binocular microscope. Because individual
instars cannot be exactly determined for H. bilineata,1 size categories
of 0.2 mm were established for head capsule width. Data were trans-
formed to percentages of each size category, and histograms were con-
structed. Mean head width and mean wing pad length were calculated for
each station and sampling date.
Time of emergence of H. bilineata at stations 1 and 3 was deter-
mined by trapping emerging subimagoes with 1-m2 floating traps (Figure
2). Three traps were anchored at each station from June 1 to June 6,
1977; trapped adults were collected and preserved in the mornings.
Fore wing and abdomen lengths were measured with a millimeter rule.
Egg count for each female was estimated by stirring the eggs in 10 ml of
distilled water and pipetting a 1-ml subsample for counting. A linear
correlation of size and fecundity was drawn for each station, and the
two stations were compared. Student's t-test was used to compare the
mean lengths of wing and abdomen and mean egg counts between the two
stations.
Entrainment
A drift study was conducted at John Sevier Steam Plant on July 20,
1976, to determine the effect of the thermal plume on survival. This
site was chosen because of the distance the thermal plume extends down
the Holston River (over 8 km) and the usually high ATs (6 to 10°C) that
occur. These two factors create conditions for a maximum-exposure field
test.
The experimental insects, damselfly nymphs of the genus Enallagma
and mayfly nymphs of the genus Stenonema, were collected from the
cooling-water intake channel. Ten insects were placed in each Plexi-
glas box attached to a flotation apparatus (Figure 3). One flotation
apparatus was anchored in the thermal plume, and another was anchored in
the ambient temperature area near the right bank. After 6 h of exposure,
the insects were removed, and the dead organisms were counted.
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-7-
Figure 2. Emergence trap used to collect emerging mayflies
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ALUMINUM
ANGLE BAR
EYE BOLT
AND SNAP
POLYURETHANE
FLOAT
ALUMINUM
PLATE
h-6-in.3 HOLDING CAGE
00
Figure 3. Flotation device used to hold aquatic insects for drift study.
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-Q-
LABORATORY STUDIES
Testing Immature Stages for Thermal Tolerance
Larvae of Coelotanypus sp. were collected from Shoal Creek (near
TRM 264.5) in Lauderdale County, Alabama, on November 18, 1976. The
larvae were acclimated to 15°C for three days in the laboratory.
After the acclimation period, larvae were shocked at three different
temperatures—25, 35, and 40°C--which exposed them to ATs of 10, 20,
and 25°C, respectively, above the control temperature of 15°C. Ten
larvae were used for each treatment. Mortality was checked at 15-
min intervals for 2.5 h. Death was assumed when larvae did not respond
when squeezed gently with a pair of forceps. At the end of the test the
larvae were held at 25°C for 8 h to check for latent mortality.
Nymphs jof H. bilineata were collected from impounded areas of
Second Creek (near TRM 275) near Highway 72 West, Lauderdale County,
Alabama, on November 22, 1976; substrate temperature was 10°C at time of
collection. The nymphs were acclimated in aerated aquariums in sub-
strate from their natural habitat at 10°C for 8 days. The nymphs were
then subjected to ATs of 10, 20, and 30°C; a control group was held at a
constant temperature of 10°C. The treatment consisted of ten nymphs per
replicate and three replicates per treatment. The number of dead were
counted at 15-min intervals for 3.5 h. Dissolved oxygen was determined
with an oxygen meter (YSI model 54).
Thermal Tolerance of H. bilineata Eggs
Two experiments were conducted: (1) Eggs were cultured at dif-
ferent constant temperatures to determine the upper limit and the optimum
range for development; and (2) eggs were exposed during oviposition to
several ATs for various durations to simulate deposition of eggs in a
thermal plume before they sink to an ambient temperature.
Experiment (1). Constant Temperature and Development—
About 300 mated females were collected under lights between 9 and
10 p.m. along Brush Creek (near TRM 264.5) in Lauderdale County, Alabama,
on July 8, 1977. The females were placed in 27°C water, where they
released their eggs. The eggs were transported to the laboratory,
where 1-ml aliquots (700 to 2000 eggs) were placed in Plexiglas flow-
through chambers (Figure 4). Twenty chambers were placed in each of
eight aquariums that were half-filled with 27°C water. Each aquarium
was placed in a refrigerator-size incubator set at one of eight tempera-
tures— 19, 22, 25, 28, 31, 34, 37, and 40°C. The aquariums were gently
aerated, and the temperatures were allowed to equilibrate overnight. By
the next day the eggs had adhered to the bottom of the chambers. The
aquariums were then filled, and the water was circulated with Dynaflow-II
motor filters.
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-10-
Figure 4. Plexiglas flow-through container for culturing H. bilineata
eggs.
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-11-
Wheu hatching began, five chambers were removed each day for four
days, and the number of eggs hatched and the number not hatched were
recorded. The data were transformed to percentage hatched and analyzed
by a 2-factor analysis of variance.
Experiment (2). Egg Tolerance to Brief Thermal Shock—
About 200 females were collected around 9 p.m. at Shoal Creek
(near TRM 264.5) in Lauderdale County, Alabama. About 50 individuals
were simultaneously placed in each of four large glass dishes containing
water of four different temperatures—30, 35, 40, and 45°C. These
temperatures subjected the females to ATs of 0 (control), 5, 10, and
15°C. After 3 min these females were removed; 5 min after oviposition
some of thejjeggs from each dish were transferred to separate, labelled
containers of 30°C water. The same was done after 10 and 15 min of
exposure, yielding 12 treatments of varying temperature and duration.
The eggs that had been transferred were then transported to the labora-
tory and placed in flow-through containers as described in experiment (1),
except that all incubators were set to maintain a temperature of 30°C.
When hatching began, three containers (replicates) per treatment
were removed each day for four days (total 144 samples). Data were
collected, transformed to percentage hatched, and analyzed by a 3-factor
analysis of variance.
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-12-
SECTION 5
RESULTS AND DISCUSSION
TEMPERATURE PROFILES AT JOHNSONVILLE STEAM PLANT AND IMPLICATIONS FOR
AQUATIC INSECTS
Surface temperature data from October 1976 to October 1977 indicate
that the thermal plume extended from 1 to 2 km downstream from the plant.
Surface temperatures at station 5 ranged from 0 to 3.0°C above ambient
throughout the year. These results agree with a mathematical model of
the plume.2
The vertical temperature profiles revealed that the depth to which
the thermal plume extended was variable (Figures 5 through 7), depending
on time of year. Throughout late fall and winter at station 3 and
throughout winter at station 4, the thermal plume extended to the river
bottom (Figure 5). During this 5-month period, the substrate, which is
inhabited by benthic insects, was about 4 to 6°C above ambient (Figure
8). The greatest AT measured was 6.5°C, which occurred in February
1977. Beginning in April 1977, the depth of the thermal plume diminished,
and bottom temperatures in the discharge channel were at or very near
ambient throughout the spring, summer, and early fall (Figures 6 and 7).
These temperature data indicate that the organisms inhabiting the
substrate of the discharge channel were living at temperatures 4 to
6.5°C above ambient throughout the coldest part of the seasons. The
average bottom temperature at station 3 from November 17 to March 31 was
15.2°C, compared with 10.6°C at station 1 (average based on five samples).
Growth of H. bilineata nymphs becomes negligible at 10°C, according to a
field study,3 and at 14°C, according to a laboratory study.4 Tempera-
ture of the substrate at station 3 was never below 10°C on any of the
sampling dates, whereas at station 1 it was well below 10°C on December
22, 1976, and February 16, 1977.
GROWTH AND EMERGENCE TIME OF H. BILINEATA
If growth of H. bilineata nymphs becomes negligible as temperatures
approach a low of 10°C, nymphs inhabiting heated areas, where tempera-
tures stay above 10°C (Figure 8), should be larger than those in ambient
areas by the end of winter. Therefore, nymphs in heated discharge areas
should mature faster, and it is plausible that they would emerge sooner
as adults.
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Figure 5. Vertical temperature profiles at five stations in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from October 1976 to March 1977.
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20
30
1,2 5 A3
30
5/12/77
10
20
TEMPERATURE (°c)
7/13/77
0 10 20
TEMPERATURE (°c)
30
30
6/2/77
10
8/3/77
10
20
20
30
Figure 6. Vertical temperature profiles at five stations in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from April to August 1977.
-------
0 T
1
2
3 -
5 .
6
7 J
8
8/31/77
20
9/21/77
10
20
215
30
TEMPERATURE (°L )
10/19/77
213,4,5
20
30
Figure 7. Vertical temperature profiles at five stations in vicinity of Johnsonville Steam Plant,
Kentucky Lake, from August to October 1977.
-------
___ STATION 3
OCT
9
NOV
17
DEC
22
FEE
16
MAR
16
MAR
31
APR
19
MAY
12
JUNE
2
JUNE
22
JULY
13
AUG
3
AUG
31
SAMPLING DATE (1976-77)
Figure 8. Substrate temperatures at two stations near Johnsonville Steam Plant,
Kentucky Lake, from October 19, 1976, to September 21, 1977. No data
were obtained in January 1977.
SEPT
21
OCT
19
-------
-17-
Measurements of head capsules and wing pads of H. bilineata nymphs
near Johnsonville Steam Plant show that mean size was greater at station
3 (in the heated discharge channel) than at station 1 from March 31 to
June 2 (Figure 9), with the exception of mean head width on June 2.
Frequency histograms of nymphs in size classes of 0.2-mm head width
showed higher percentages of large nymphs at station 3 from March 31 to
June 2 (Figures 10 through 13). After June 2, mean head width was slightly
greater at station 1 (Figure 9). The percentage of nymphs with head widths
greater than 2.8 mm on June 22 was higher at station 1 (Figure 14); on
July 13 and August 3, these percentages were again higher at station 3
(Figures 15 and 16). Mean wing pad length was greater at station 3 on
all sampling dates except June 22 (Figure 9). The total number of
nymphs collected (n) on successive sampling dates decreased, probably
because of drift and increased predation by fish.
The differences in percentages of nymphs in different size classes
(based on OJ5-mm intervals of head width) and the changes in these
percentages through time are shown in Figure 17. A greater percentage
of nymphs were in the larger size classes (2.0 to 3.5 mm) at station 3
from March 31 to at least June 2. Nymphs at station 1 first reached
the 3.0- to 3.5-mm size class sometime between May 12 and June 2. How-
ever, on June 2, nearly equal percentages of nymphs were in the 3.0- to
3.5-mm class at the two stations.
These data on nymphal head size through time indicate that, although
the nymphs in the heated discharge channel were larger on the average
than those at the unheated station throughout most of the spring, nymphal
growth at station 1 accelerated, yielding a mean size comparable to
that at station 3 by June 2.
Emergence to the subimago (adult) stage occurs shortly after the
wing pads become thickened and black. No emergence occurred in the
vicinity of Johnsonville Steam Plant before the first week of June 1977.
On June 2, 1977, 14 of 57 nymphs (19.7%) collected at station 3, as
compared with 1 of 27 (3.7%) at station 1, had thick, black wing pads
(Figure 18). A chi-square test showed the difference to be significant
(P < 0.05) although the number of observations was low. The differences
in the percentages for June 22 and July 13 are not significant.
Emergence to the adult occurred about two or three days earlier at
station 3. On June 2, one adult was seen at station 3 in the discharge
channel; no adults were seen at station 1. On the night of June 4, a
large number of emerging mayflies were collected in emergence traps at
station 3. No mayflies were trapped at station 1, although subimagoes
were present along the nearby bank on the morning of June 5. Subimagoes
were also present 2 to 6 km downstream from the steam plant. Another
large emergence at station 3 occurred on the night of June 5; an emer-
gence also occurred at station 1, but again no adults were found in the
emergence traps. Therefore, subimagoes were later netted at station 1
for size and fecundity comparisons with those trapped at station 3.
-------
5.0
4'0 -
2.0
0.0
STATION 1
...... STATION 3
4.0
3.0
g
x 1.0
0.0
1
1
1
_L
MAR
31
APR
19
MAY
12
JUNE
2
JUNE
22
JULY
13
JL
AUG
3
Figure 9.
Average head width and fore wing pad length of H. bilineata nymphs collected at
stations 1 and 3 near Johnsonville Steam Plant at 3-week intervals from March 31
to August 3, 1977.
oo
i
-------
50
40
STATION 1 (n = 144)
STATION 3 (n = 144)
30
uj 20
a
m
10
Figure 10.
SIZE CATEGORIES OF HEAD WIDTH (mm)
Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on March 31, 1977
-------
50
40
30
20
S
8E
10
I
STATION 1 (n = 102)
STATION 3 (n = 144)
O
I
SIZE CATEGORIES OF HEAD WIDTH (mm)
Figure 11. Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on April 19, 1977.
-------
50
40
30
STATION 1 (n = 69)
STATION 3 (n = 110)
20
10
0
i
to
Figure 12.
SIZE CATEGORIES OF HEAD WIDTH (mm)
Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on May 12, 1977.
-------
50
40
30
>-
S 20
10
STATION 1. (n = 28)
STATION 3 (n = 71)
to
N>
I
SIZE CATEGORIES OF HEAD WIDTH (mm)
Figure 13. Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on June 2, 1977.
-------
50
40
30
5
H
20
10
I
STATION 1 (n * 51)
STATION 3 (n = 48)
CO
•
o
I
IO
•
o
C3O
I
oo
•
o
I
cvj
NJ
co
i
0
CVJ
1
CO
,J
CVJ
CVJ
1
0
cvj
•*
CVJ
1
CVJ
cvj*
«3
CVJ
1
*!•
CVJ
CO
CVJ
1
10
cvj
O
CO
1
00
cvj
CVJ
CO
1
o
ro
Figure 14.
SIZE CATEGORIES OF HEAD WIDTH (mm)
Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on June 22, 1977.
-------
50
40
30
20
10
I STATION 1 (n = 24)
STATION 3 (n = 37)
SIZE CATEGORIES OF HEAD WIDTH (mm)
to
.p"
Figure 15. Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on July 13, 1977.
-------
60
40
30
a
20
10
I
STATION 1 (n = 16)
STATION 3- (n = 40)
j
CM
I
•si-
•
CM
1
00
•
CM
I
UD
•
CM
N5
Ul
O
•
CO
I
co
•
CM
Figure 16.
SIZE CATEGORIES OF HEAD WIDTH (mm)
Comparison of frequency (%) of H. bilineata nymphs in various size classes (based
on head width) at stations 1 and 3 near Johnsonville Steam Plant on August 3, 1977
-------
-26-
to
3
o
CO
o;
ff
b
o
STATION 3
WR APR MAY JUNE JUNE JULY AUG
31 19 12 2 22 13 3
Figure 17. Comparison of frequency (%) of H. bilineata nymphs in six
size classes of head width (interval = 0.5 mm) from March
to August 1977 at stations 1 and 3 near Johnsonville
Steam Plant.
-------
STATION 1
STATION 3
JUNE 22 JULY 13
Figure 18. Percentage of H. bilineata nymphs having black wing pads at stations 1 and 3 on
three sampling dates, 1977.
-------
-28-
That elevated water temperatures can induce early emergence of
aquatic insects, by as much as six months, has been established.5'6
In contrast to these reports, a dragonfly has been shown to develop in
the laboratory at a rate similar to that in the field, despite higher
temperatures during the winter.7 A field study showed that Ephemerop-
tera, Trichoptera, and Megaloptera below a power station in England do
not emerge earlier than those in ambient areas.8 Adult H. bilineata
live only two or three days, in which time they must mate and lay eggs.
Therefore, synchronization of emergence to the adult stage is critical
for propagation of the next generation. H. bilineata near Johnsonville
Steam Plant completed development sooner in the spring of 1977 in areas
receiving thermal effluent, but evidently did not emerge appreciably
earlier in these areas than in ambient areas. Some combination of
extrinsic factors, rather than just temperature, must control the timing
and hence synchronization of emergence. Although daylength may be an
important cue, the exact mechanism is unknown.9
SIZE AND FECUNDITY COMPARISONS OF H. BILINEATA
The mean values for H. bilineata wing length, abdomen length, and
egg count are given in Table 1. The number of eggs per female was posi-
tively correlated with abdomen length. The correlation coefficient r for
females at station 1 was 0.58, slightly higher than that found at station
3 (0.52); both values are significant (P = 0.01). However, the variation
in egg count for a particular abdomen length was very large (Figure 19).
Results of t-tests on mean size and fecundity between stations 1
and 3 are given in Table 2. Males at station 1 were significantly
smaller on the average than those at station 3. Females differed in
average abdomen length, but not in average wing length or number of
eggs. Unfortunately, the specimens from station 1 were collected on a
later date (June 25, 1977) than those from station 3 (June 4 and 5,
1977). Possibly, a seasonal decrease in size, a phenomenon known to
occur in Hexagenia spp.,9 is responsible for the differences in male
size. This study will be repeated to ensure collection of individuals
from the two stations on the same date.
THERMAL TOLERANCE OF IMMATURE AQUATIC INSECTS
H. bilineata Nymphs
Results of the thermal shock experiment are given in Table 3. All
nymphs survived the control and the 10°C AT, and 29 of 30 survived the
20°C AT after 4 h of exposure. Mortality was high at the 30°C AT; 23
nymphs died within the first 15 min of exposure. Dissolved oxygen (DO)
was probably not a factor in mortality, because nymphs can survive at
DO levels less than 6.5 ppm at lower temperatures.
-------
-29-
TABLE 1. MEAN VALUES (x), STANDARD DEVIATIONS (s), AND NUMBER OF OBSERVA-
TIONS (n) FOR MALE AND FEMALE H. BILINEATA WING LENGTH, ABDOMEN LENGTH,
AND EGG COUNT AT STATIONS 1 AND 3 NEAR JOHNSONVILLE STEAM PLANT
Wing length (mm) Abdomen length (mm)
Male Female Male Female Egg count
Station 1 (6/25/77)
x 14.07 17.63 9.93 12.71 3779.79
s 1.143 0.992 1.201 1.369 1058.24
'•n 29 24 29 24 24
Station 3 (6/4/77-6/5/77)
x 14.95 17.73 11.41 13.82 3548.61
s 1.36 1.73 1.28 1.76 1623.17
n 44 108 44 108 108
-------
10
o
o
o
UJ
fe
-30-
DISCHARGE, STATION 3
JUNE 4 and 5 (s = 1618,6)
CONTROL, STATION 1
JUNE 25 fe = 1058.2)
L
• *
t
10 11 12 13 14 15 16 17 18 19
FEMALE ABDOMEN LENGTH (mm)
Figure 19. Scatter diagram of relationship between abdomen length and
number of eggs in H. bilineata females.
-------
-31-
TABLE 2. RESULTS OF t-TESTS COMPARING MEAN SIZE AND FECUNDITY OF H.
BILINEATA SUBIMAGOES AT STATIONS 1 AND 3 NEAR JOHNSONVILLE STEAM PLANT
Character
Male wing length
Male abdomen length
Female wing ^length
Female abdomen length
Egg count
df
71
71
130
130
130
Value of t
2.88**
4.95**
1.62
2.89**
0.07
P
<0.01
<0.01
0.11
<0.01
>0.95
-------
TABLE 3. NUMBER OF H. BILINEATA NYMPHS SURVIVING FOUR EXPERIMENTAL THERMAL SHOCKS
Thermal shock Dissolved Replicate
temperature3 (°C) oxygen (ppm) number
10 (AT =0) 9.2 1
2
3
20 (AT = 10) 8.6 1
2
3
30 (AT = 20) 7.4 1
2
3
40 (AT = 30) 6.5 1
2
3
Number of survivors
15 rain
10
10
10
10
10
10
10
9
10
1
2
4
30 min
10
10
10
10
10
10
10
9
10
0
0
3b
45 min
10
10
10
10
10
10
10
9
10
1
60 min
10
10
10
10
10
10
10
9
10
1
of exposure duration of
90 min
10
10
10
10
10
10
10
9
10
120 min
10
10
10
10
10
10
10
9
10
180 min
10
10
10
10
10
10
10
9
10
240 min
10
10
10
10
10
10
10 ,
OJ
to
9 '
10
a
Acclimation temperature was 10°C.
Removed and slowly brought to 25°C.
-------
-33-
The nymphs exposed to 20 and 30°C ATs immediately ceased moving; 3
min later the nymphs exposed to 20°C AT showed gill and leg movements,
but no movement was seen in the nymphs exposed to 30°C AT. At all three
higher ATs, air bubbles appeared on the gills of many nymphs. At the
15-min check, most of the nymphs exposed to 30°C AT were floating; those
alive showed very little gill movement. The three nymphs still living
after 30 min were slowly brought to 25°C; two died within 15 min, but
one survived.
Although the number of nymphs available for the tests was low,
results indicate that H. bilineata can tolerate relatively high thermal
shocks (at least 20°C) for short periods when acclimated to a low tempera-
ture. Determination of the effects of various acclimation temperatures
on thermal tolerance would be helpful for establishing seasonal tolerances.
Coelotanypus! sp. Larvae
\
Results of the thermal shock experiment on Coelotanypus sp. larvae
are given in Table 4. Survival after 2.5 h was high (90 to 100%) at all
four temperatures. After the larvae were slowly brought to 25°C, some
mortality was observed in larvae exposed to shock; the highest mortality
(40%) occurred in the 25°C AT treatment. The effects of acclimation
temperature on survival of these larvae should also be determined.
EFFECTS OF ENTRAINMENT WITHIN THERMAL PLUME ON AQUATIC INSECTS
Results of the field study at John Sevier Steam Plant on July 20,
1976, are presented in Table 5. The difference in temperature between
the thermal plume station and the ambient station was 6 to 7°C through-
out the 8-h test. Of the two damselfly nymphs that died, one had been
partially eaten and was therefore probably killed by another damselfly.
The other had drowned as it tried to emerge to the adult stage without a
suitable support. The single dead mayfly may have been killed by a
damselfly nymph present in the test basket.
The thermal plume from John Sevier Steam Plant sometimes extends
several kilometers down the Holston River.10 An insect drifting the
length of the plume could be exposed to the heated water for many
hours. Although the test was limited, the data indicate that damsel-
fly nymphs of the genus Enallagma and mayfly nymphs of the genus
Stenonema, common inhabitants of the Holston River, would probably
experience little or no mortality due to the heated water. A simulated
laboratory study11 showed that mayflies of the genus Isonychia and
caddisflies of the genus Hydropsyche were not adversely affected until
shock temperatures neared the upper lethal limits.
-------
TABLE 4. NUMBER OF COELOTANYPUS SP. LARVAE SURVIVING FOUR EXPERIMENTAL THERMAL SHOCKS
Thermal shock
temperature3 (°C)
15 (AT
25 (AT
35 (AT
40 (AT
= 0)
= 10)
= 20)
= 25)
15 min
10
10
10
10
30 min
10
10
10
10
Number of survivors of exposure duration of
45 min
10
10
10
9
60 min
10
10
10
9
75 min
10
9
10
9
90 min
10
9
10
9
120 min
10
9
10
9
150 minb
10
9
10
9
210 min
10
9
10
8
10 h
10
9
9
7
48 h
10
8
8
6
Acclimation temperature was 15°C.
Temperature in each treatment was brought slowly to 25°C.
•o
I
-------
-35-
TABLE 5. NUMBER OF DAMSELFLY AND MAYFLY NYMPHS SURVIVING AFTER
8 HOURS OF EXPOSURE IN THE THERMAL PLUME AND AT AMBIENT STATION
NEAR JOHN SEVIER STEAM PLANT, JULY 20, 1976
»*
Number of survivors per replicate
Thermal plume Ambient
Insect station station
1234 1 2
Damselflies 8 10 10 10 10 10
Mayflies 10 10 9
o
10 nymphs per replicate.
-------
-36-
EGG DEVELOPMENT AND THERMAL TOLERANCE
The results of egg hatching at seven constant temperatures are
summarized in Table 6. No eggs hatched at 40°C, and although eggs
hatched at 37°C, the percentage was low (21%) and the development
time was comparatively long (minimum of 12 days). The shortest develop-
ment time was 8 days, both at 31 and 34°C. These data agree with
Fremling's report4 of 8 days for development at 32°C and indicate a
range of optimal temperatures for development. The relationship between
temperature and incubation time is shown in Figure 20. The regression
equation is Y = 139.44 - 8.437t + 0.1349t2, where Y is development time
in days and t is temperature. The observed values lie close to and twice
coincide (at 25 and 37°C) with the predicted values.
The average cumulative percentages of hatching (at the end of the
4-day sampling period) at 31 and 34°C are significantly different at the
1% level, as determined by Duncan's multiple range test (Table 7). The
abrupt drop in average cumulative percentage of hatching from 34 to 37°C
indicates that 34°C is the peak temperature for speed of development. (See
Davidson12 for discussion on speed of development.)
Embryos never developed in eggs cultured at 40°C. After 5 days at
this constant temperature, the cytoplasm was concentrated near the
center of the oval eggs and the ends were translucent. After 2 weeks
at 40°C, most of the eggs were almost entirely transparent, containing
only small scattered pieces of opaque material. At 37°C, most of the
eggs that did not hatch after 2 weeks were opaque, but very few embryos
could be seen. Some eggs had the cytoplasm centered, with the ends
translucent. Dissolved oxygen was maintained at the saturation level
for each temperature and therefore was not a limiting factor.
Because 34°C is close to the upper temperature limit for develop-
ment of H. bilineata eggs, 30°C was chosen as the culture temperature to
follow the thermal shocks. Results of the thermal shocks simulating
females laying eggs in a thermal plume are given in Table 8. Dissolved
oxygen values were above 8.0 ppm. The hatching percentages were highly
variable, partly because of the variable number of eggs placed in the
containers. Some containers had fewer than 100 eggs, whereas others
contained over 2000. These discrepancies resulted from the total number
of eggs the females laid in each treatment. Especially notable was the
comparatively low number of eggs laid in the 45°C water.
The average percentages of hatching in the control treatments (AT =
0°C) were low compared with the percentages reported for the constant
temperatures 28 and 31°C. Reasons for this discrepancy are not clear;
it is doubtful that the physical transfer of the eggs caused the lower
percentage of hatching. Possibly the later date of collection (August 10
compare^ with July 8) was an important factor.
The 3-factor analysis of variance is summarized in Table 9. The
three main effects—shock temperature, shock duration, and hatching day
(day after oviposition)—were partitioned by one-degree-of-freedom tests
for significant responses. All interactions were found to be significant.
-------
-37-
TABLE 6. MEAN CUMULATIVE PERCENTAGE OF HATCHING THROUGH 4 DAYS
OF H. BILINEATA EGGS CULTURED AT 8 CONSTANT TEMPERATURES3
Day after
oviposition
1-7
8 |
9 ;
10
11
12
13
14
15
16
17
18
19
20
21-28
29
30
31
32
Mean cumulative hatch (%) at constant temperature of
40°C 37°C 34°C 31°C 28°C 25°C 22°C 19°C
74.8 62.5
93.1 85.9
94.7 87.8 26.1
95.4 89.1 76.1
9.5 87.6
14.4 88.1 34.8
19.8 81.6
21.0 85.1
88.0
12.7
40.7
66.7
81.6
2.5
12.0
24*. 1
35.8
3Each value is the mean of five replications.
-------
32
30
28
26
24
22
20
18
16
p 14
12
-38-
UJ g
6
2 _
0
19
PREDICTED VALUES
OBSERVED VALUES
Y = 139.44 - 8.437t + 0.1349t
22 25
28 31
34 37
CULTURE TEMPERATURE (<>c)
Figure 20.
Predicted and observed development times (in days) for
H. bilineata eggs cultured at seven nearly constant
(±1°C) temperatures.
-------
-39-
TABLE 7. SUMMARY OF HATCHING RESULTS AT CONSTANT TEMPERATURE
AND TESTS FOR SIGNIFICANCE OF DIFFERENCE BETWEEN MEANS AS
DETERMINED BY DUNCAN'S MULTIPLE RANGE TEST
Constant
temperature (°C) Mean cumulative hatch (%)
19 35.8 a
22 81.6 b
25 88.0 c
28 88.1 c
31 89.1 c
34 95.4 d
37 21.0 e
3Means followed by different letters are significantly different
at the 1% level.
-------
-40-
TABLE 8. PERCENTAGES OF HATCHING OF H. BILINEATA EGGS EXPOSED TO THERMAL SHOCKS
(ATs OF 5, 10, AND 15°C) FOR THREE DURATIONS (5, 10, AND 15 MIN) IMMEDIATELY
AFTER OVIPOSITION
Pulse Pulse Date
temperature duration hatched
(°C) (min) (1977)
30
(AT =0) 5 8/18
8/19
8/20
8/21
10 8/18
8/19
8/20
8/21
15 8/18
8/19
8/20
8/21
35
(AT =5) 5 8/18
8/19
8/20
8/21
10 8/18
8/19
8/20
8/21
15 8/18
8/19
8/20
8/21
40
(AT = 10) 5 8/18
8/19
8/20
8/21
10 8/18
8/19
8/20
8/21
Hatching percentage (%)
by replicate number
1
35.79
60.44
37.09
43.75
44.32
13.04
58.00
45.05
14.20
45.29
34.29
47.22
16.98
53.62
71.43
83.23
29.69
62.37
51.49
88.17
15.38
78.32
89.91
82.79
7.81
43.52
29.23
62.92
10.96
52.26
69.92
59.84
2
27.91
90.91
44.95
49.49
85.71
22.62
51.43
21.26
8.13
27.03
75.14
34.62
28.07
56.18
90.11
79.79
7.84
62.50
30.69
79.02
5.71
79.31
87.57
90.25
11.70
41.09
35. C8
63.32
8.46
52.36
36.87
71.54
3
13.16
42.80
39.47
44.09
27.50
53.42
43.33
64.00
16.44
18.93
75.82
41.77
20.83
59.26
91.49
92.04
28.27
78.72
38.89
87.93
2.80
79.80
89.87
88.65
13.59
42.63
46.13
58.73
6.88
35.39
64.35
54.13
Total
(%)
76.86
194.15
121.51
137.33
157.53
89.07
152.76
130.32
38.77
91.25
185.25
123.61
65.88
169.06
253.03
255.06
65.80
203.59
121.07
255.12
23.89
237.43
267.35
261.69
33.10
127.24
111.04
184.97
26.30
140.01
170.53
185.51
Average
(%)
25.62
64.72
40.50
45.78
52.51
29.69
50.92
43.44
12.92
30.42
61.75
41.20
21.96
56.35
84.34
85.02
21.93
67.86
40.36
85.04
7.96
79.14
89.19
87.23
11.03
42.41
37.01
61.66
8.77
46.67
56.84
61.84
-------
-41-
TABLE 8 (continued)
Pulse Pulse Date
temperature duration hatched
(°C) (min) (1977)
15 8/18
8/19
8/20
8/21
45
(AT = 15) 5 8/18
1 8/19
8/20
| 8/21
10 8/18
8/19
8/20
8/21
15 8/18
8/19
8/20
8/21
Hatching percentage (%)
by replicate number
1
12.32
42.03
60.53
73.52
0.00
22.84
0.00
63.48
2.91
0.00
1.01
3.25
3.54
3.39
12.39
5.35
2
9.76
35.96
64.01
69.72
0.00
11.54
6.90
14.05
1.36
0.00
7.69
9.35
3.13
2.53
9.18
3.67
3
11.53
43.00
67.05
54.72
0.86
12.16
27.27
11.54
0.41
0.00
1.79
2.97
33.33
3.43
14.39
3.40
Total
(%)
33.61
120.99
191.59
197.96
0.86
46.54
34.17
89.07
4.68
0.00
10.49
15.57
40.00
9.35
35.96
12.42
Average
(%)
11.20
40.33
63.86
65.99
0.29
15.51
11.39
29.69
1.56
0.00
3.50
5.19
13.33
3.12
11.99
4.14
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-42-
TABLE 9. ANALYSIS OF VARIANCE OF 3-FACTOR THERMAL SHOCK EXPERIMENT ON
H. BILINEATA EGGS
Source of variation
Replications
Shock temp., T (t = 4)
Linear response
Quadratic response
Cubic response
Shock duration, D (d = 3)
Linear response
Quadratic response
Hatching day, H (h = 4)
Linear response
Quadratic response
Cubic response
TD (t-l)(d-l)
TH (t-l)(h-l)
DH (d-l)(h-l)
TDK (t-l)(d-l)(h-l)
Error
df
2
(3)
1
1
1
(2)
1
1
(3)
1
1
1
6
9
6
18
96
Mean square
11.51
(17,046.26)
25,134.29
25,183.05
821.46
(175.79)
8.61
342.97
(8,869.24)
23,008.16
3,094.33
505.25
363.32
1,538.56
549.84
479.18
75.373
F
333.47**
334.11**
10.90**
0.114
4.55**
305.26**
41.05**
6.70**
4.82**
20.41**
7.30**
6.36**
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-43-
The mean percentages of hatching due to the three main effects are
shown in Figure 21. The average percentage of hatching after a shock of
15°C was much lower than that after lesser shocks (Figure 21A). Shock
duration appeared to have no effect on hatching response when averaged
over all treatments (Figure 21B). Cumulative percentage of hatching
increased through time as expected (Figure 21C).
Partitioning the main effect of shock temperature showed that there
was a highly significant linear response of hatching to shock temperature,
but also that the response was curvilinear (Table 9). These results indi-
cate that the increase in hatching at the 5°C AT, as shown in Figure 21A,
is significant. The main effect of shock duration showed a significant
quadratic response when partitioned. The reason for the lower hatching
response to the 10-min treatments is unknown. The main effect of hatch-
ing day showed significant linear, quadratic, and cubic responses. Hatch-
ing increased sharply from day 1 to day 2, but then tended to reach a
plateau (Figure 21C).
The interaction between shock temperature and shock duration is
illustrated in Figure 22. Hatching success responded in different pat-
terns at each shock duration, which showed the complex relationship
between these two variables. Increased shock duration for the 15°C AT
treatment decreased the hatching success, although the response is
curvilinear. The interaction between shock temperature and hatching day
revealed a lower hatching success at 15°C AT for each hatching day
(Figure 23). At the 0, 5, and 10°C ATs, the percentage of hatching
increased appreciably through the 4-day observation period, but at the
15°C AT the percentage increase was much less. The response of hatching
to the interaction between shock duration and hatching day was highly
variable (Figure 24). Shock duration apparently affects the percentage
of hatching differently on each day that eggs hatch.
The significant 3-way interaction (Table 9) indicates that the rela-
tionship between shock temperature, shock duration, and day after oviposi-
tion, as they affect egg development, is complex. The percentages obtained
in the experiment were quite variable, and trends are difficult to define.
Shock durations of 5 to 15 min did not appear to affect hatching success
significantly unless the temperature change was at least 15°C (ambient was
30°C); in this case, longer shock duration lowered the hatching responses,
although there was a slight cumulative increase in the response through
the 4-day observation period.
-------
100
90
80
70
60
• Ll- on
< o 30
20
10
A
B
0
10 15
PULSE T (°C)
10
15
PULSE
DURATION (min)
HATCHING DAY
Figure 21.
Average percentage of hatching of H. bilineata eggs due to main effects of shock
temperature (A), shock duration (B), and day after oviposition (C).
-------
-45-
15
SHOCK DURATION (min)
Figure 22. Surface response curves for shock temperature and shock
duration (interaction) effects on mean percentage of
hatching of H. bilineata eggs over a 4-day hatching period.
-------
100
90
80
70
o 60
z
1—4
§ 50
u_
o
LU 40
I
B 30
a
| 20
10
0
-— 8lH DAY AFTER OVIPOSITION
— 9TH DAY AFTER OVIPOSITION
— 10TH DAY AFTER OVIPOSITION
'— llTH DAY AFTER OVIPOSITION
0V
0
Figure 23.
5 10
THERMAL SHOCK (°c)
15
Effect of shock temperature on mean cumulative percentage
of hatching of H. bilineata eggs exposed to thermal shock
immediately after oviposition.
-------
-47-
100
90
80
I70
u. 60
o
LU
"
30
20
SHOCK DURATION
5 min
10 min
15 min
10
11
DAY AFTER OVIPOSITION
Figure 24. Interaction of shock duration and hatching day on the mean
percentage of hatching of H. bilineata eggs exposed to
thermal shock immediately after oviposition.
-------
-48-
REFERENCES
1. Horst, T. J. 1976. Population dynamics of the burrowing mayfly
Hexagenia limbata. Ecology 57:199-204.
2. Orlob, G. T., I. P. King, and W. R. Norton. 1975. Mathematical
simulation of thermal discharges from Johnsonville Steam Plant.
An unnumbered report prepared for TVA by Resources Management
Association, 3706 Diablo Blvd., Lafayette, Calif.
3. Hunt, B. P. 1953. The life history and economic importance of a
burrowing mayfly, Hexagenia limbata, in southern Michigan lakes.
Mich. Conserv. Dept., Bull. Inst. Fish. Res. 4:1-151.
4. Fremling, C. R. 1967. Methods for mass-rearing Hexagenia mayflies
(Ephemeroptera: Ephemeridae). Trans. Amer. Fish. Soc. 96:407-410.
5. Nebeker, A. B. 1971. Effect of high winter water temperatures
on adult emergence of aquatic insects. Water Res. 5:777-783.
6. Coutant, C. C. 1967. Effect of temperature on the development
rate of bottom organisms. In Biological effects of thermal discharges,
pp. 11-12. Ann. Rep., Pacific N.W. Lab., U.S. AEC, Div. Biol.
Medicine.
7. Miyakaua, K. 1969. A study of the life history of Pseudothemis
zonata (Burm.) (Odon., Libellulidae). II. Immature Stage.
Kontyu 37:409-422.
8. Langford, T. E. 1975. The emergence of insects from a British
river, warmed by power station cooling-water. Part II. The
emergence patterns of some species of Ephemeroptera, Trichoptera
and Megaloptera in relation to water temperature and river flow,
upstream and downstream of the cooling-water outfalls. Hydrobiologia
47:91-133.
9. Fremling, C. R. 1973. Environmental synchronization of mass
Hexagenia bilineata (Ephemeroptera) emergence from the Mississippi
River. Verh. Internat. Verein. Limmol. 18:1521-1526.
10. Ungate, C. D. 1977. John Sevier Steam Plant hydrothermal investi-
gations. Part I; Thermal discharge effects near the plant. TVA
Report No. 32-14-1, April 1977.
11. Sherberger, F. F., E. F. Benfield, K. L. Dickson, and J. Cairns, Jr.
1977. Effects of thermal shocks on drifting aquatic insects: A
laboratory simulation. J. Fish. Res. Bd. Can. 34:529-536.
12. Davidson, J. 1942. On the speed of development of insect eggs
at constant temperatures. Aust. J. Exp. Biol. Med. Sci. 20:233-239.
-------
-49-
GLOSSARY
ambient: Surrounding environmental condition.
entrainment: Transport by the flow of a liquid.
fecundity: Ability to produce offspring; reproductive potential.
instar: A stage in the life cycle of an insect between molts.
subimago: Immature adult stage of mayflies, duller and darker than
adult to which it molts.
thermal plume: Warm water discharged from once-through cooling by
electric generating plants; boundary is 2°C above
ambient isotherm.
-------
-50-
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-128
3. RECIPIENT'S ACCESSION>NO.
4. TITLE ANDSUBTITLE
EFFECTS OF THERMAL DISCHARGE ON AQUATIC INSECTS IN THE
TENNESSEE VALLEY
5. REPORT DATE
July 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
K. J. Tennessen and J. L. Miller
8. PERFORMING ORGANIZATION REPORT NO
TVA/EP-78/09
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Division of Environmental Planning
Tennessee Valley Authority
Chattanooga, TN 37401
10. PROGRAM ELEMENT NO.
INE-625A
11. CONTRACT/GRANT NO.
80 BDR
12. SPONSORIN
U.S.
AGENCY NAME AND ADDRESS
nvironmental Protection Agency
Office of Research & Development
Office of Energy, Minerals & Industry
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
This project is part of the EPA-planned and coordinated Federal Interagency
Energy/Environment R&D Program.
16. ABSTRACT
The.Tennessee Valley Authority (TVA) conducted studies to (1) determine the
thermal tolerances of selected aquatic insects and (2) investigate growth and
emergence of those insects in the vicinity of TVA electric generating plants.
Results of the study will be used to help establish thermal effluent limits to
protect the aquatic ecosystem.
Tolerance of the immature stages of Hexagenia bilineata (Say) and Coelotanypus
sp. to thermal shocks (ATs) of up to 20°C was found to be great. However, eggs
subjected to a shock of 15°C resulted in a greatly reduced mean percentage of
hatching. No difference in fecundity of adult females was found between ambient
and thermal plume stations. Adult males from the heated discharge channel were
significantly larger on the average than adult males from the ambient station.
A drift study of Enallagma spp. and Stenonema spp. in a thermal plume showed
little or no mortality at ATs that normally result from the heated water.
17.
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