WATER POLLUTION CONTROL RESEARCH SERIES
16010 EXE 12/71
THE EFFECTS
OF
ARTIFICIAL AERATION
LAKE ECOLOGY
U.S. ENVIRONMENTAL PROTECTION AGENCY
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and abatement of pollution
in our Nation's waters. They provide a central source of
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activities in the Environmental Protection Agency, through
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Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications Branch
(Water), Research Information Division, R&M, Environmental
Protection Agency, Washington, D.C. 20^60.
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THE EFFECTS OF ARTIFICIAL AERATION
ON LAKE ECOLOGY
Arlo Wade Fast
Michigan State University
East Lansing, Michigan
for the
ENVIRONMMTAL PROTECTION AGENCY
Project No. 16010 EXE
December 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price $4.25
Stock Number 6601-0232
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EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the 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 EFFECTS OF ARTIFICIAL AERATION
ON LAKE ECOLOGY
By
Arlo Wade Fast
Two northern Michigan lakes were artificially aerated
using compressed air. Hemlock Lake, a eutrophic lake, had
only its hypolimnion aerated while thermal stratification
was maintained. A special hypolimnion aeration device was
used. Section Four, an oligotrophic lake, was completely
destratified by releasing air from a perforated pipe at the
deepest point in the lake. Both lakes were studied during
1969 under normal conditions, and during 1970 under test
conditions.
Artificial hypolimnion aeration of Hemlock Lake caused
oxygen concentrations to increase from 0.0 mg/1 to over
10.0 mg/1 while thermal stratification was maintained.
Zooplankton, zoobenthos and fish distributed throughout the
lake after aeration, while limited to shallow depths before.
Midges emerged from the deepest point following aeration.
Aeration apparently reduced anaerobic nutrient regeneration,
but increased nutrient regeneration through aerobic decompo-
sition of the profundal sediments. These sediments were
ill
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highly organic and incompletely decomposed due to the
previous anaerobic conditions.
Artificial destratification of Section Four Lake
greatly increased the minimum temperatures and heat budget.
Although zoobenthos and surface phytoplankton standing crops
were reduced, destratification had little apparent effect on
the biota. Midges emerged from greater depths during
aeration but depth distributions of most organisms, other
than the crayfish, were not greatly altered. Crayfish
distributed evenly throughout the lake during aeration.
Changes in their distribution suggests that the thermal
gradient and aggressive behavior of the male are the most
important factors determining their normal depth distribu-
tions.
IV
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TABLE OF CONTENTS
Page
LIST OF TABLES vii
LIST OF FIGURES x
INTRODUCTION . . 1
METHODS 21
Physical-chemical ..... 21
Phytoplankton ....... 28
Primary Production 29
Periphyton 33
Zooplankton ........... 33
Zoobenthos 34
Crayfish . . 36
Emergent Insects. ...... . . 36
Rainbow Trout ....... . . 40
Statistics. 50
DESCRIPTION OF THE LAKES 51
HEMLOCK LAKE 72
Hypolimnion Aerator .............. 72
Description 79
Compressor ......... 90
Operation. ................ 90
Aeration efficiencies. ..... 92
RESULTS 97
Physical-chemical Parameters. .... 97
Thermal stability. ............ 115
pH, alkalinity and conductivity 120
Phosphorus 127
Ca, Na, K, Mg, DOM, POM 129
Primary Production 129
Phytoplankton 129
Periphyton 133
v
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TABLE OF CONTENTS—continued Page
Zooplankton .........«......=. 138
Zoobenthos. ............. 143
Crayfish. 193
Rainbow Trout 196
DISCUSSIONS AND CONCLUSIONS. ..... 211
Physical-chemical Parameters. . . 211
Primary Production. .............. 218
Zooplankton .................. 228
Zoobenthos. ............ 235
Crayfish. ................... 255
Rainbow Trout ........ 257
SECTION FOUR LAKE. ........ 270
Destratification System ...... 270
Compressor ................ 275
Compressor operation ........... 275
RESULTS. ........... o .... 276
Physical-chemical Parameters. ......... 276
Temperature and oxygen 276
pH, alkalinity and conductivity. ..... 290
Phosphorus ................ 297
Ca, Na, K, Mg, DOM, POM. ......... 297
Primary Production. .............. 301
Phytoplankton. .............. 301
Periphyton ................ 305
Zoobenthos. .................. 305
Crayfish. ........... . 363
Rainbow Trout ................. 366
DISCUSSION AND CONCLUSIONS ............. 372
Physical-chemical Parameters. . . 372
Primary Production. .............. 375
Zoobenthos. .................. 385
Crayfish. 389
Rainbow Trout ................. 396
AERATION TO PREVENT WINTERKILL ... 401
LITERATURE CITED ........... . 415
APPENDIX ...... ..... 426
ACKNOWLEDGEMENTS . . . . . . . . „ „ „ „ „ „ „ „
vi
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LIST OF TABLES
TABLE Page
1. Section Four Lake limnological data collected
August 1, 1932 by the Institute for Fisheries
Research, Michigan Department of Natural
Resourceso Secchi disc depth was 6.8 meters
on this date. ................. 63
2. Hemlock Lake limnological data collected July
28, 1932 by the Institute for Fisheries
Research, Michigan Department of Natural
Resources. Secchi disc depth was 4.2 meters
on this date. ................. 69
3. Hemlock Lake total phosphorus and total dis-
solved phosphorus collected July 22, 1969. Two
water samples were collected from each depth. . 128
4, Hemlock zooplankton collected June 11 and July
15, 1970. Three samples were collected from
each two meters depth interval. Totals repre-
sent the sum of the average number of zooplank-
ters per liter from each depth. Total samples
on each date = 27 ............... 142
5. Hemlock Lake zoobenthos collected during the
summers 1969 and 1970 with an Ekman dredge.
125 dredge samples were taken each summer. Wet
weights are shown ...... o ........ 144
6. Emergent midge adults collected from 600
samples during 1969, and 650 samples during
1970. All specimens are from Hemlock Lake and
were collected in emergent insect traps .... 147
7. Section Four total phosphorus and total dis-
solved phosphorus collected July 22, 1969. Two
water samples were collected from each depth
interval. ................... 300
8. Section Four Lake zoobenthos collected during
the summers 1969 and 1970 with an Ekman dredge.
125 dredge samples were taken each summer. Wet
weights are shown ...... .... 310
vn
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LIST OF TABLES—continued
TABLE Page
9. Emergent midge adults collected from 600 sam-
ples during 1969, and 650 samples during 1970.
All specimens are from Section Four Lake and
were collected in emergent insect traps. ... 319
A-l. Hemlock Lake 17 day periphyton weights during
1969 and 1970. Samples were incubated on
plastic slides during June, July and August
each year. Four slides were incubated at each
of five depths. Ash-free dry weight is shown
for each sample. ...............
A-2. Hemlock Lake accumulative periphyton weights
during 1969 and 1970. Samples were incubated
starting June 15 each year and a portion was
retrieved at different times during the summer.
Samples were incubated on plastic slides.
Three slides were incubated at each of five
depths. Ash-free dry weight is shown for each
sample ....................
A-3. Section Four Lake 17 day periphyton weights
during 1969 and 1970. Samples were incubated
on plastic slides during June, July and August
each year. Four slides were incubated at each
of five depths. Ash-free dry weight is shown
for each sample. ...............
A-4. Section Four Lake accumulative periphyton
weights during 1969 and 1970. Samples were in-
cubated starting June 15 each year and a por-
tion was retrieved at different times during
the summer. Samples were incubated on plastic
slides. Three slides were incubated at each of
five depths. Ash-free dry weight is shown for
each sample. ..........
A-5. Hemlock Lake zoobenthos collected with an
Ekman dredge during 1969 and 1970. Numbers
and wet weights for the seven most abundant
taxa are shown in this table for each sample.
125 samples were collected each summer. The
less abundant taxa are listed in Table A-6.
To verify the total organisms for a given sam-
ple, consult both tables. Depth is in meters
and weight is in grams ............
Vlll
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LIST OP TABLES—continued
TABLE Page
A-6. Hemlock Lake zoobenthos collected during 1969
and 1970. The less abundant organisms are
listed in this table. To obtain a total for
a given sample, add the values for each sample
(check each organism) to the values for that
sample given in Table A-5. Wet weights are
shown. ............ , .
A-7. Section Four Lake zoobenthos collected with an
Ekman dredge during 1969 and 1970. Numbers
and weights for the seven most abundant taxa
are shown in this table for each sample. 125
samples were collected each summer. The less
abundant taxa are listed in Table A-8. To
verify the total organisms for a given sample,
consult both tables. Depth is in meters and
weight is in grams
A-8. Section Four Lake zoobenthos collected during
1969 and 1970= The less abundant organisms
are listed in this table. To obtain a total
for a given sample, add the values for each
sample (check each organism) to the values for
that sample given in Table A-7. Wet weights
are shown. ...................
A-9. Area-capacity table for Hemlock Lake based on
January 1957 survey of the lake. .......
A-10. Area-capacity table for Section Four Lake
based on January 1957 survey of the lake . . .
A-ll. Hemlock Lake calcium, sodium, potassium, mag-
nesium, dissolved organic matter (DOM) and
particulate organic matter (POM) collected
during 1970. Samples were collected from six
depths seven times during the summer. The
mean concentration for the entire lake is
shown. These analyses were made by R. G.
Wetzel ...............
A-12. Section Four Lake calcium, sodium, potassium,
magnesium, dissolved organic matter (DOM) and
particulate organic matter (POM) collected dur-
ing 1970. Samples were collected from six
depths seven times during the summer. The mean
concentration for the entire lake is shown.
These analyses were made by R. G. Wetzel . . .
ix
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LIST OF FIGURES
FIGURE Page
1. Hypothetical phosphorus cycle within a lake
showing the three main compartments. The comr-
ponents of the littoral compartment are also
shown 7
2. Hypothetical destratification patterns caused
by diffuse aeration system. Figure A illus-
trates a stratified lake, and Figure B a lake
being destratified 13
3. Hypolimnion aerator of Bernhardt (1967). From
Fast (1968) , 17
4. X-sectional view along principle sample tran-
sect. Raft, emergent insect traps, gill nets
and transect float are shown 23
5. View of Section Four Lake taken from basin rim.
Emergent insect traps are stacked on the raft.
The periphyton float is on the left of the
transect barrel, and the gill net rollers are
to the right of the barrel. (Photo by Dr.
0. E. Kurt.) 25
6 (a). Phytoplankton incubation chamber. Four sub-
merged sample bottles are on the rotating
wheel. (Photo by author.) 31
(b). Periphyton ring- Five plastic periphyton
slides are visible clamped to the ring.
(Photo by author.) 31
7(a). New emergent insect trap. (Photo by Dr. 0. E.
Kurt.) .......... 38
(b). Styrofoam trap used in collection jar on the
emergent insect trap. (Photo by Dr. O. E.
Kurt.) 38
(c). Replacing collection jar on emergent insect
trap. Trap is suspended from bracket on the
raft and not taken out of the water during
transfer. (Photo by Dr. O. E. Kurt,) 38
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LIST OF FIGURES—continued
FIGURE Page
8(a). Vertical gill net and roller. Gill net is
suspended between raft pontoons as during
sample collection process. (Photo by author=) 43
(b) . Robert Hoffman removing fish from vertical
gill net. (Photo by author.) 43
9. Acclimation cage used to hold rainbow trout at
specific depths in Hemlock Lake. Rubber hoses
led to water pumps on a raft. Cage is covered
with polyethylene plastic and chicken wire.
(Photo by author.) 46
10„ Configuration of Hemlock Lake acclimation
cages. Fin clip of rainbow trout held in each
cage is shown. The oxygen and temperature
profiles during the acclimation period are
also shown 48
11. Contour map of Hemlock Lake showing sample
transects and aerator. Depth intervals are in
meters 53
12. Contour map of Section Four Lake showing
sample transect and air line. Air was re-
leased from the dashed section of the air
line. Depth intervals are in meters 55
13. Hemlock and Section Four relative irradiance
measurements on August 11, 1969. . 59
14. Section Four transect profile illustrating
percent organic carbon and percent CaCOa-car-
bon at different depths 61
15. Hemlock transect profile illustrating percent
organic carbon and percent CaCOs-carbon at dif-
ferent depths 66
16. Hemlock Lake carbon dioxide, alkalinity, pH and
conductivity profiles on August 13, 1969.
This is representative of pre-aeration condi-
tion. Chemocline of monimolimnion is evident
below 12 meters 68
17. Cross-sectional view of Hemlock Lake hypolim-
nion aerator. Dotted lines represent projected
edges. Tower is tilted toward the viewer, and
parts are drawn approximately to scale .... 74
xi
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LIST OF FIGURES—continued
FIGURE Page
18. Hemlock hypolimnion aerator in operating posi-
tion. Only the upper three meters are visible.
Air supply line enters the scene from the left.
Above water styrofoam flotation units are a
safety feature to prevent tower from sinking if
submerged units should fail. Ladder on side of
aerator permits access to top of tube. (Photo
by author.) ........... 76
19(a). Arrival of Hemlock hypolimnion aerator tubes
from the factory. Top three meters section of
aerator is separated and located next to the
truck cab. The tower was unloaded on the
wooden cradle and logs in the foreground and
fittings were attached before it was shoved in
the lake. (Photo by author.) 78
(b). Hemlock hypolimnion aerator floating horizon-
tally- Temporary floats kept the lower end up
while the current deflector was attached. The
lower end is closest to the viewer. Deflectors
could not be added until the aerator was float-
ing horizontally in the lake. (Photo by
author.) 78
(c). Hemlock hypolimnion aerator tilting into sampl-
ing position. The temporary floats have just
been removed by the author using SCUBA. (Photo
by Robert Hoffman.) r . . . 78
20. Cross-sectional view and parts of hypolimnion
aerator. A. Cross-section of aerator taken
near the top. Two styrofoam flotation units
and one barrel flotation unit are shown.
B. Styrofoam flotation unit. C. Barrel flota-
tion unit showing the tee structure used to
attach it to the aerator. D. Cross-section of
tee inside the slot structure. The slot is
welded to the outside of the aerator 81
21. Hemlock hypolimnion aerator current deflector
before they were attached to the aerator.
Anchors in foreground were used to anchor the
tower in its operating position. (Photo by Ed
Schultz.) 83
xn
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LIST OF FIGURES—continued
FIGURE Page
22(a). Styrofoam flotation unit used on the Hemlock
Lake hypolimnion aerator. The tee structure
used to attach the unit to the aerator is
shown on top. (Photo by author.) 86
(b). Slots for flotation unit tee's being welded on
the side of the aeration tower. The iron
plates used to position the inner tube are
shown projecting through the outer tube to the
left of the workmen. (Photo by author.) ... 86
(c). Sliding styrofoam flotation unit into slot on
side of aeration tower. Logs and "runway" are
shown leading into the lake. (Photo by Ed
Schultz.) 86
23. Air diffusor used on the hypolimnion aerator.
The hole site spacing along one arm are
shown. Three holes were drilled at each site
as shown in the cross-sectional view of one
arm 89
24. Water flow rates through the hypolimnion aera-
tion tower as a function of air input and
tower level. The (0) level is when the top of
the inner tube is level with the lake1s sur-
face. (+) level is with the inner tube's top
0.5 m above the lake's surface, and the (-)
level is with it 0.5 m below the lake's sur-
face. See text for discussion of true flow
rates 94
25. Hemlock Lake's isotherms during the summer
1969, before aeration began. Isotherms are
in °C. . . 99
26, Hemlock Lake's top, bottom and average oxygen
concentrations during the summers 1969 and
1970. Continuous aeration occurred between
June 14 and September 7, 1970. 101
27. Hemlock Lake's total chlorophyll A, phaophytin
A, oxygen and temperature profiles during
August 13, 1969. These are representative of
values before aeration began 103
Xlll
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LIST OF FIGURES—continued
FIGURE Page
28. Hemlock Lake selected oxygen profiles during
the summers 1969 and 1970. Continuous aera-
tion occurred between June 14 and September
7, 1970 105
29. Hemlock Lake's isotherms during the summer
1970. Continuous aeration occurred between
June 14th and September 7th., Isotherms are
in
108
30. Hemlock Lake selected temperature profiles
during the summers 1969 and 1970,, Continuous
aeration occurred beeween June 14 and
September 7, 1970. 110
31. Hemlock Lake hypolimnetic oxygen isopleths
(mg/1) along the air line transect one day be-
fore aeration began and after one day of
hypolimnion aeration ..... 112
32. Hemlock Lake hypolimnetic oxygen isopleths
(mg/1) along the air line transect one day be-
fore aeration began, and after nine days of
continuous hypolimnion aeration 114
33. Hemlock Lake's maximum, minimum and average
temperatures ( C) during the summers 1969 and
1970. Continuous aeration occurred between
June 14 and September 7, 1970. ........ 117
34. Hemlock Lake's stability values during the
summers 1969 and 1970. Continuous aeration
occurred between June 14 and September 7,
1970 ......... ....... 119
35. Hemlock Lake's bottom, top and average pH
values during the summers 1969 and 1970.
Continuous aeration occurred between June 14
and September 7, 1970. 122
36. Hemlock Lake's bottom, top and average alka-
linity values during the summers 1969 and 1970.
Continuous aeration occurred between June 14
and September 7, 1970. ..... 124
37. Hemlock Lake's bottom, top and average conduc-
tivity values during the summers 1969 and
1970- Continuous aeration occurred between
June 14 and September 7, 1970. „ 126
xiv
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LIST OF FIGURES—continued
FIGURE Page
38. Hemlock Lake secchi disc transparencies, sur-
face primary production potentials, surface
phytoplankton densities and surface production
efficiencies during the summers 1969 and 1970.
Continuous aeration occurred between June 14
and September 7, 1970. . 131
39. Foam spilling over the top of the hypolimnion
aerator during August 1970. (Photo by author.) 135
40. Hemlock Lake periphyton standing crops based
on 17-day incubation periods and continuous
incubation. The 95% confidence interval is
shown about each average value. Continuous
aeration occurred between June 14 and Septem-
ber 7, 1970. 137
41. Hemlock Lake zooplankton depth distributions
three days before aeration began, and after
one month of aeration. Oxygen and tempera-
ture profiles are shown for each date.
(x" = average depth.) 141
42. Hemlock Lake zoobenthos percent composition
during the summers 1969 and 1970. Percent of
wet weight and percent of number are shown for
each taxa. Total weights and total numbers
collected each summer are also shown. Samples
from dredge collections only ..,.„.... 146
43. Hemlock Lake Chironomid larvae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods. . 150
44. Hemlock Lake Chironomid larvae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods 152
45. Hemlock Lake Chironomid pupae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods. . 155
xv
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LIST OF FIGURES—continued
FIGURE Page
46. Hemlock Lake Chironomid pupae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods. 157
47. Total midge emergence from Hemlock Lake by
depths during the summers 1969 and 1970.
Aeration occurred continuously between June 14
and September 7, 1970. Total include Chaobor-
inae and Chironomid midges from emergence
traps only 159
48. Total estimated weekly midge emergence from
Hemlock Lake during the summers 1969 and 1970.
Totals include Chaoborinae and Chironomid
midges from emergence traps only. Aeration
occurred continuously between June 14 and
September 7, 1970. .............. 161
49. Total estimated Chironomid larvae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred con-
tinuously between June 14 and September 7,
1970. Totals from dredge samples only .... 164
50, Total estimated Chironomid pupae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about, each estimate. Aeration occurred con-
tinuously between June 14 and September 7,
1970. Totals from dredge samples only .... 166
51. Depth emergence of selected insects from Hem-
lock Lake during the summers 1969 and 1970.
White areas during the sampling periods repre-
sent no observed emergence. A= Frocladius
denticulatus, B= Tanypus, C= Dicrotendipes,
D= Mayflies (Ephemoreptera) . Aeration occur.-
red continuously between June 14 and September
7, 1970. Totals from dredge samples only. . . 169
52. Total estimated emergences from Hemlock Lake.
Samples from emergence traps only. Aeration
occurred continuously between June 14 and
September 7, 1970. .............. 171
xvi
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LIST OF FIGURES—continued
FIGURE Page
53. Total estimated Chaoborus larvae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred con-
tinuously between June 14 and September 7,
1970. Totals from dredge samples only .... 175
54. Total estimated Chaoborus Pupae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred con-
tinuously between June 14 and September 7,
1970. Totals from dredge samples only .... 177
55. Total estimated emergences of Hemlock Lake
Chaoborus flavicans and C_. punctipennis during
1969 and 1970. Total estimated larvae and
pupae are also shown. All samples are from
emergence traps. Aeration occurred continu-
ously between June 14 and September 7, 1970. . 179
56. Depth distribution of Chaoborus during the
summers 1969 and 1970. All samples were col-
lected by emergence insect traps. A=
Chaoborus f lavicans emergent adults, B= C_.
punctipennis emergent adults, C= Chaoborus
larvae, D= Chaoborus pupae. White areas dur-
ing emergence periods represent no observed
specimens. Aeration occurred continuously
between June 14 and September 7, 1970. .... 182
57. Hemlock Lake Chaoborus larvae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods. . 184
58. Hemlock Lake Chaoborus pupae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods. . 186
59, Total estimated Mayfly (Ephemeroptera) number
and wet weight in Hemlock Lake during the sum-
mers 1969 and 1970. One standard error is
shown about each estimate. Aeration occurred
continuously between June 14 and September 7,
1970. Totals from dredge samples only .... 189
xvii
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LIST OF FIGURES—continued
FIGURE Page
60. Hemlock Lake Mayfly (Ephemeroptera) depth dis-
tribution as percent of number during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods. .......... 192
61. Hemlock crayfish depth distributions during
the summers 1969 and 1970. Total numbers dur-
ing each sample period and their average
depths are shown. The shaded area represents
the 1969 distributions. Aeration occurred
continuously between June 14 and September 7,
1970. ................ 195
62. Hemlock Lake Rainbow trout depth distribution
during 1969. These fish were stocked during
June 1969 and marked with a right-abdominal
fin clip. Each square represents one fish . . 198
63. 1970 depth distribution of Hemlock Lake rain-
bow trout stocked during June 1969. Each
circle represents one fish- These fish were
marked with a right-pelvic fin clip. Aeration
occurred continuously between June 14th and
September 7th. ................ 201
64. 1970 Hemlock Lake depth distribution of right-
pectoral clipped rainbow trout stocked during
June 1970. These fish were held in the 3 m
covered cage which received 12 m water for one
week before their release. Each circle repre-
sents one fish. Aeration occurred continuous-
ly between June 14 and September 7, 1970 . . . 203
65. 1970 Hemlock Lake depth distribution of left-
pectoral clipped rainbow trout stocked during
June 1970. These fish were held in the 12 m
covered cage which received 3 m water for one
week before their release. Each circle repre-
sents one fish. Aeration occurred continuous-
ly between June 14 and September 7, 1970 . . . 205
66. 1970 Hemlock Lake depth distribution of left
pelvic clipped rainbow trout stocked during
June 1970. These fish were held in a screened
cage at 12 m for one week before their re-
lease. Each circle represents one fish.
Aeration occurred continuously between June 14
and September 7, 1970. ............ 207
xviii
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LIST OF FIGURES—-continued
FIGURE Page
67. 1970 Hemlock Lake depth distribution of anal-
clipped rainbow trout stocked during June
1970. These fish were held at 3 m in a
screened cage for another week before their
release. Each circle represents one fish.
Aeration occurred continuously between June
14 and September 7, 1970 209
68. Hypothetical changes in Hemlock Lake limiting
nutrient, phytoplankton, zooplankton and
Chaoborus densities during 1970. Aeration
began June 14th and continued through Septem-
ber 7th. Major food chain relationships are
also shown 230
69. Hemlock Lake oxygen and temperature condi-
tions for trout during August 1969 and August
1970. Adequate temperature is temperature
less than 24 C, and adequate oxygen is values
of 5 mg/1 or more 266
70. Cross-sectional view of Section Four diffuse
aeration system. The air was released from
the last 10 meters of pipe, situated near the
deepest point in the lake 272
71. View of Section Four Lake taken from the
basin rim. Rising air and water is seen near
the center of the lake (Photo by Author.) . . 274
72. Section Four isotherms during the summer,
1969, before aeration began. Isotherms are
in C ............. 278
73. Section Four selected oxygen profiles during
the summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970 .... 280
74. Section Four maximum, minimum and average
temperatures ( C) during the summers 1969 and
1970. Aeration occurred between June 16 and
September 7, 1970 283
75. Section Four top, bottom and average oxygen
concentrations during the summers 1969 and
1970. Aeration occurred between June 16 and
September 7, 1970 285
xix
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LIST OF FIGURES--continued
FIGURE Page
76. Section Four selected temperature profiles
during the summers 1969 and 1970. Aeration
occurred between June 16 and September 7,
1970 287
77. Section Four isotherms during the summer
1970. Aeration occurred between JuneQ16th
and September 7th. Isotherms are in C . . . 289
78. Section Four stability values during the
summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970 .... 292
79. Section Four's bottom, top and average pH
values during the summers 1969 and 1970.
Aeration occurred between June 16 and Septem-
ber 7, 1970 . 294
80. Section Four bottom, top and average alkalin-
ity values during the summers 1969 and 1970.
Aeration occurred between June 16 and Septem-
ber 7, 1970 296
81. Section Four bottom, top and average conduc-
tivity values during the summers 1969 and
1970. Aeration occurred between June 16 and
September 7, 1970 .............. 299
82. Section Four secchi disc transparencies, sur-
face primary production potentials, surface
phytoplankton densities and surface produc-
tion efficiencies during the summers 1969 and
1970. Aeration occurred between June 16 and
September 7, 1970 303
83. Section Four periphyton standing crops based
on 17-day incubation periods and continuous
incubation. The 95% confidence interval is
shown about each average value. Aeration
occurred between June 16 and September 7,
1970 307
84. Section Four zoobenthos percent composition
during the summers 1969 and 1970. Percent of
weight and percent of number are shown for
each taxa. Total weights and total numbers
collected each summer are also shown.
Samples from dredge collections only 309
xx
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LIST OF FIGURES—continued
FIGURE Page
85. Section Four oligochaete (microdriles) depth
distribution as percent of numbers during the
summers 1969 and 1970. Shaded histograms
represent aerated periods .... 313
86. Section Four oligochaete (microdriles) depth
distribution as percent of wet weight during
the summers 1969 and 1970. Shaded histograms
represent aerated periods . . . ....... 315
87. Section Four total estimated oligochaete
number and biomass during the summers 1969
and 1970. One standard error is shown about
each estimate. Aeration occurred between
June 16 and September 7, 1970 ........ 318
88. Section Four Chironomid larvae depth distri-
bution as percent of number during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods . ............ 322
89. Section Four Chironomid larvae depth distri-
bution as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods ......... .... 324
90. Total estimated Chironomid larvae number and
wet weight in Section Four during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred be-
tween June 16 and September 7, 1970. Totals
from dredge samples only. 326
91. Section Four Chironomid pupae depth distribu-
tion as percent of number during each sampl-
ing period during the summers 1969 and 1970.
Shaded histograms represent aerated periods . 329
92. Section Four Chironomid pupae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods . ...... 331
xxi
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LIST OF FIGURES—continued
FIGURE Page
93. Total estimated Chironomid pupae number and
wet weight in Section Four during the summers
1969 and 1970- One standard error is shown
about each estimate. Aeration occurred be-
tween June 16 and September 7, 1970. Totals
from dredge samples only, .......... 333
94. Total midge emergence from Section Four by
depths during the summers 1969 and 1970.
Aeration occurred between June 16 and Septem-
ber 7, 1970. Totals include Chironomid
midges from emergence traps only. ...... 336
95. Total estimated weekly midge emergence from
Section Four during the summers 1969 and 1970.
Totals include Chironomid midges from emer-
gence traps only- Aeration occurred continu-
ously between June 16 and September 7, 1970 338
96. Total estimated midge emergences from Section
Four. Samples from emergence traps only.
Aeration occurred between June 16 and Septem-
ber 1, 1970 ................. 340
97. Depth emergence of selected Section Four
midges during the summers 1969 and 1970.
White areas represent no observed emergence.
A= Procladius, B= Ablabesmyia mallochi, C=
Clinotanypus thoracicus. Aeration occurred
between June 16 and September 7, 1970 .... 342
98. Depth emergence of Section Four midges and
mayflies during the summers 1969 and 1970.
White areas represent no observed emergence.
A= Lauterborniella spp., B= Chironomini, C=
Mayflies (Ephemeroptera). Aeration occurred
between June 16 and September 7, 1970 .... 344
99. Section Four Mayfly (Ephemeroptera) depth
distribution as percent of number during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods 347
100. Total estimated Mayfly (Ephemeroptera) number
and wet weight in Section Four during the
summers 1969 and 1970. One standard error is
shown about each estimate. Aeration occurred
between June 16 and September 7, 1970.
Totals from dredge samples only ....... 349
xxii
-------
OF FIGURES—continued
FIGURE Page
101. Total estimated Amphipod number and wet weight
in Section Four during the summers 1969 and
1970. One standard error is shown about each
estimate. Aeration occurred between June 16
and September 7, 1970. Totals from dredge
samples only . . . 352
102. Section Four Amphipod depth distribution as
percent of number during each sampling period
during the summers 1969 and 1970. Shaded his-
tograms represent aerated periods. . 354
103. Section Four Trichoptera depth distribution as
percent of number during each sampling period.
during the summers 1969 and 1970. Shaded
histograms represent aerated periods ..... 356
104. Total estimated Trichoptera number and wet
weight in Section Four during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred be-
tween June 16 and September 7, 1970. Totals
from dredge samples only ........... 358
105. Section Four Heleidae (=Ceratopogonidae) depth
distribution as percent of number during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods. ............. 360
106. Total estimated Heleidae (=Ceratopogonidae)
number and wet weight in Section Four during
the summers 1969 and 1970 . One standard error
is shown about each estimate. Aeration occur-
red between June 16 and September 7, 1970.
Totals from dredge samples only. 362
107. Section Four crayfish depth distributions dur-
ing the summers 1969 and 1970. Total numbers
during each sample period and their average
depths are shown. The shaded area represents
the 1969 distributions. Aeration occurred be-
tween June 16 and September 7, 1970 365
108. Section Four rainbow trout depth distributions
during 1969. Open Squares represent fish
stocked during June 1969 and marked with a
right-pectoral fin clip. Solid squares are
fish stocked during 1964-65 and lack fin clips.
Each square represents one fish. 368
xxiii
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LIST OF FIGURES —continued
FIGURE Page
109. Section Four rainbow trout depth distribution
during 1970. Open circles represent fish
stocked during May 1970 and marked with a
left-pelvic fin clip. Solid circles represent
fish stocked during June 1969 and marked with
a right-pectoral fin clip. Solid squares
represent fish stocked during 1964-65 and lack
fin clips. Each symbol represents one fish. . 371
110. Hypothetical residence times for a passive,
neutral buoyancy object with the photic and
aphotic zones of a stratified and unstratified
lake ................ 378
111. Ratios of Section Four surface/bottom phyto-
plankton concentrations during 1969 and 1970.
The lake was destratified during 1970 381
112. Section Four oxygen profiles during January
1970 and 1971. The 1970 profile is after a
summer of normal stratification, while the
1971 profile is after a summer of artificial
aeration ................... 405
113. Hemlock Lake oxygen profiles during December
1969 and 1970, and January 1970 and 1971. The
December 1969-January 1970 profiles are after
a summer of normal stratification, while the
December 1970-January 1971 profiles are after
a summer of artificial aeration. ....... 408
114. Artificial aeration of Hemlock Lake du£ing
January 1971. The compressor was towed onto
the lake and run for two days. A rubber air
line leads to the aeration tower ....... 411
115. Effects of artificial aeration on the oxygen
regime during January 1971. The January 22nd
figure shows the oxygen profiles before winter
aeration began, but after a summer of artifi-
cial aeration. The January 23rd profile is
after 24 hours of air injection and the
January 24th profile is after 48 hours of air
injection. ........... 413
xxiv
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LIST OF FIGURES—continued
FIGURE Pag-e
A-l. Length histograms of hatchery reared rainbow
trout at time of stocking in Hemlock Lake dur-
ing June 6, 1969 and June 25, 1970. Only one
lot of fish were stocked during 1969, whereas
four lots were stocked during 1970. Each lot
received a separate fin clip. Total numbers
(n), average fish lengths (x) and fin clips
for each lot are shown 465
A-2. Length histograms of hatchery reared rainbow
trout at time of stocking in Section Four
Lake during June 6, 1969 and May 23, 1970.
One lot was stocked each year. Total numbers
(n), average fish-lengths (x) and fin clips
for each lot are shown. 467
xxv
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INTRODUCTION
Essentially all temperate lakes follow thermal strati-
fication cycles. Yearly cycles are the most important and
have the greatest influence on lake processes. Chemical
and biological stratification are related to thermal
stratification.
Typical temperate lakes are isothermal in the spring.
As the seasons progress, the upper lake water is heated
faster than the lower. Wind generated water currents
distribute this heat to the lower depths. Wind mixing
efficiency decreases greatly with increasing depth and the
lake is divided into three thermal zones by early summer:
(i) Epilimnion. The warm water zone. It is circulated by
the wind and oxygen concentrations are generally near satura-
tion. Temperature and chemical properties are nearly
homogeneous throughout. Daily and seasonal temperature
variation is much greater here than in the other zones.
Most of the biota is restricted to this zone in eutrophic
lakes. (ii) Metalimnion. A zone of rapid change in tempera-
ture, density and chemical properties. Characterized by a
1.0 C or greater change per meter change in depth.
(iii) Hypolimnion. The cold water zone of the lake. This
zone is sealed off from the surface. It characteristically
-------
stagnates by early summer in organically rich, eutrophic
lakes. Stagnation results in an oxygen deficit, buildup of
hydrogen sulfide, increased iron, phosphate and manganese
concentrations, anaerobic conditions and overall deteriora-
tion of water quality- Aerobic biota are often excluded
from the hypolimnion of eutrophic lakes. The rate of hypo-
limnetic oxygen depletion is a measure of the lake's organic
richness. Organically poor, oligotrophic lakes characteris-
tically do not develop oxygen depletions. Oligotrophic
lakes differ markedly in their chemical and biological prop-
erties although their temperature regimes are similar to
eutrophic lakes. Chemical concentrations are often uniform
throughout oligotrophic lakes and restrictions to biotic
distributions are minimal. Anaerobic biota are either
conspicuously absent, or restricted to subsurface mud.
Hypolimnetic biotic concentrations can be greater than
epilimnetic concentrations.
As the seasons progress, the epilimnion cools and
approaches the hypolimnion temperature during late summer
and fall. The lake becomes isothermal again during the fall.
Most temperate lakes develop ice cover and inverse thermal
stratification during the winter. The coldest water, at
0.0 C, is just under the ice, whereas warmer water at about
. o
4 C is near the bottom of the lake. Chemical and biological
values often stratify in response to this winter thermal
stratification. Oxygen may be completely depleted from
-------
eutrophic lakes during the winter with a resultant loss of
aerobic biota. Oligothrophic lakes generally have high
oxygen concentrations all winter at all depths.
Lake stratification often conflicts with man's exploi-
tation of the water body. Thermal stratification of
eutrophic lakes often results in deterioration of drinking
water quality, anaerobic and corrosive conditions, increased
evaporation rates, reduced heat budgets and other undesir-
able properties within the lake. Stratification of oligo-
trophic lakes is generally not undesirable.
In general, lakes are thought to undergo a succession
from oligotrophy through mesotrophy and eutrophy to dystrophy
(Lindeman, 1942). This natural process is called eutrophica-
tion. Accelerated and undesirable eutrophication due to
man1s activities is termed organic pollution. Although
lakes may enter this scheme at any point based on their
origin, morphometry, and other factors, they generally prog-
ress towards dystrophy and extinction. Productivity per unit
area increases at least through the eutrophic stage and may
decline at dystrophy due to volume reduction and unfavorable
conditions, such as low pH. Increased productivity is
associated with higher nutrient levels and oxygen depletion
of deep water during periods of stagnation. Indeed, this
loss of oxygen is seen as a pivot point between oligotrophy
and eutrophy. Aging is greatly accelerated once eutrophy
is attained. Oxygen depletion is often credited with greatly
-------
accelerating eutrophication since anaerobic-sis results in
accelerated generation of nutrients from profundal sediments.
These sediments are rich in essential nutrients, especially
phosphorus. Although many factors may limit production in a
given system at a given time, phosphorus is generally the
one most limiting factor in a cosmopolitan spatial and
temperal sense; especially of primary production. Considerable
effort has been expended trying to define its behavior in
lakes, but its movements and forms are still very poorly
understood. Although our understanding is imperfect, certain
characteristics are apparent. Much of the following phosphorus
discussion is based on a conversation with Dr. F. H. Rigler
of the University of Toronto. The fact that lakes act as
nutrient traps is of special importance when considering the
phosphorus cycle. Only 20 to 70% of the phosphorus entering
a lake will leave the lake (Figure 1; B = (0.2 to 0.7) x A) .
The remainder, 30 to 80%, remains in the lake and most of
this ultimately resides permanently in the sediments.
The behavior of phosphorus before its eventual sedimen-
tary incorporation determines the level of eutrophication.
In general, the greater the amount of phosphorus in circula-
tion, the more eutrophic the lake will be. Our conceptual-
ization of phosphorus cycling in a lake is facilitated by
envisioning compartments that roughly correspond to the major
lake zones. Phosphorus behavior within each compartment is
somewhat independent of its behavior within the other
-------
compartments, but the compartments are very much interrelated.
The three general compartments are limnetic, littoral and
profundal. Phosphorus is exchanged between these compart-
ments, as well as within components of each compartment.
Relationships within the limnetic and littoral compartments
are probably the most complex, and those within the former
are best understood. The components, or forms limnetic phos-
phorus assumes can be categorized as sestonic and soluble
(Figure 1)« Each category is again divisible into subcate-
gories. These categories appear discrete, but in fact there
is much overlap. In a static sense, about 70% of the total
phosphorus is found within the sestonic forms. In a dynamic
sense this picture may be reversed since the movements be-
tween components is very rapid. For example, although solu-
ble inorganic phosphorus probably represents less than 6% of
the total limnetic phosphorus at any given time, its turnover
rate is from 1 to 7 minutes. The small algae and bacteria
are most important in this movement. The main pathway
within the limnetic compartment is from soluble phosphorus
to the bacteria and in algae (Li). Phosphorus then moves
back to the soluble form (L2) and into the zooplankton (LS)
in about equal proportions (L2 2rLs)° Phosphorus is also
directly taken up by larger limnetic algae and zooplankton,
but at a lesser rate. Zooplankton excrete and secrete phos-
phorus, with secretion exceeding excretion (Johannes and
Satomi, 1967; Rigler, 1964). Most of the zooplankton-voided
-------
Figure 1. Hypothetical phosphorus cycle within a lake showing the'three
main compartments. The components of the littoral compartment
are also shown.
-------
Limnetic Phosphorus
I Seston
(a) >70ju. zooplankton
& large phytoplanton (25%)
(b).45ju.-70xL bacteria
& aigae (35%)
Soluble
(a) Inorganic orthophosphate (6%)
(b) .1—.45ju. non-living particles (9%)
(c) Other organic phosphorus (25%)
fl
-------
8
phosphorus is orthophosphate. The dynamics of these exchanges
and those between lake compartments is such that the concen-
tration of the soluble component does not fluctuate widely.
The rates of movement within compartments and between com-
partments is probably the key factor controlling eutrophica-
tion. The vast majority of studies have measured only static
phosphorus concentrations within certain compartments. These
measurements have contributed something to our understanding
of the role phosphorus plays, but all too often they have led
to confusion and conflicting conclusions. Rates of movement
in a total lake system have not been thoroughly analyzed.
We know that ultimately most of the phosphorus ends up
in the profundal compartment, and there is a net movement
out of the limnetic compartment. Hutchinson and Bowen (1947)
indicate the net movement is from the littoral to the lim-
netic to the profundal. Rigler (1956) and Coffin et al.
(1949) later found a net movement during the summer from the
limnetic to the littoral with less than 5% from the limnetic
to the profundal. Presumably there was a net movement from
the littoral to the profundal especially during the fall and
winter breakup of littoral vegetation. McCarter et al.
(1952) have shown that very little phosphorus moves from the
profundal to the other compartments during thermal strati-
fication, but no studies to date have evaluated movements
between compartments on a yearly basis. They are all incom-
plete and taken singularly often lead to misinterpretations.
-------
The movement of phosphorus between the profundal compart-
ment and the trophogenic zone is especially important in
understanding eutrophication in general, and the specific
applicability of artificial aeration as a corrective measure
for eutrophication. As discussed, the onset of profundal
oxygen depletion is considered a most important event in the
eutrophication process. Anaerobiosis may result in a sig-
nificant increase in nutrient movement from the profundal
compartment back into the limnetic and littoral. This move-
ment occurs mostly during spring and fall overturns. Before
anaerobiosis, phosphorus was tightly held by the aerated
sediments and little was returned during overturns. After
anaerobiosis, a large, but undetermined quantity is returned
to the trophogenic zone. What fraction this represents of
the total input to the profundal compartment is unknown.
If this fraction is relatively small, then the onset of
anaerobiosis may represent only a signpost on the road to
dystrophy and our efforts to retard eutrophication by aera-
tion will be ineffective. In this case, the total input of
phosphorus to the lake is seen as the dominant factor.
Studies on artificial fertilization infer this may be the
case. Artificially fertilized lakes typically return to
their former level of production soon after nutrient input
ceases, even though prodigious quantities of nutrients were
added and a high degree of anaerobiosis was attained.
On the other hand, if anaerobiosis results in the return
of a significant fraction of nutrients to the trophogenic
-------
10
zone, then artificial aeration may be a useful method of
reversing eutrophication. This would be achieved by keeping
the profundal sediments well oxidized and thus preventing
the release of nutrients once they were incorporated in
these sediments. This also assumes that the nutrient input
into the lake is not accelerated. If it is, this may more
than compensate for reduced regeneration from the profundal
compartment and many of the characteristics of eutrophication
would not diminish. In any case, the anaerobiosis would be
diminished or eliminated by artificial aeration. This is
not always the most important characteristic, however. This
in essence forms the basis of my artificial hypolimnion
aeration of Hemlock Lake. Rather than attempt to measure
changes in phosphorus transfer rates from the profundal zone
associated with artificial aeration, I chose to measure cer-
tain biotic parameters and thereby infer changes in the phos-
phorus transfer rates. This approach has two important
advantages: (1) it is probably impossible to accurately
measure phosphorus transfer rates with our present technology,
while biota parameters are estimable in many cases, and
(2) the effects of aeration on the biota are ultimately the
most important factors. Although we may not materially
affect phosphorus regeneration from the profundal sediments,
some other event related to the aeration may result in re-
duced biotic productivity. Thus the net effect might be
desirable, although the effect on regeneration might be in-
consequential. This is in fact how many important scientific
-------
11
advances occur. We first find out what will work, and later
possibly how it does work. The major disadvantage of moni-
toring only the biota is that results not conforming to the
theory are very difficult to explain. To be sure, direct
measurement of phosphorus movements is desirable, but impos-
sible from a practical standpoint.
Until recently, little was done to economically reduce
stratification. Artificial destratification was attempted
with mechanical pumps (Hooper et al., 1952; Irwin et al.,
1969), but this method is generally slow and relatively inef-
ficient. Several artificial destratification techniques
using compressed air have been developed. Fast (1968) re-
viewed several of these techniques in greater detail. Their
common principle is that compressed air is released near the
bottom of the thermally stratified lake. The rising air
generates vertical water currents that diverge horizontally
upon reaching the lake's surface (Figure 2). This upwelled
water is much colder and denser than the surface water.
Upon converging with the warm surface water and sinking, the
cold water mixes with the epilimnion and metalimnion water
along its periphery to form water of intermediate tempera-
ture and density.
This mixed water now spreads out horizontally at levels
of equal density. The depth of outflow depends on the degree
of mixing and initially may be confined mostly to the
metalimnion. As the mixing process progresses, the shape of
-------
Figure 2. Hypothetical destratification patterns caused by diffuse
aeration system. Figure A illustrates a stratified lake, and £
Figure B a lake being destratified.
-------
D, < D2 < D3 < D4 < D5
D= den sity
^-s*+**^*~*~*-s*~***
-m
D, D7
-}! t
D4 •" I 1 ,
Ail H
^a/
3/
B.
D7
-------
14
the iso-density strata changes. Concomitant with this change
is a change in the rate of mixing. The rate of destratifica-
tion is greatest when air injection begins and approaches
zero apparently as an exponential function as the lake ap-
proaches isothermy (Koberg and Ford, 1965). The lake will
approach either an isothermal or a steady-state condition as
the mixing continues. The time it takes to reach this condi-
tion depends on the time of year, size of lake, and method
of injection. The best method of injection and equipment
specifications for a given lake situation is not well defined.
Artificial destratification of a lake by compressed air
is commonly called "lake aeration." The reasons for this
are two-fold: (1) Eutrophic lakes experience an oxygen
deficit below the metalimnion during the summer. By artifi-
cially circulating the lake, the oxygen deficit is reduced
or eliminated, and (2) compressed air is used to circulate
the water. While the compressed air adds oxygen directly
to the upwelled water, oxygen is also gained from contact of
the water with the atmosphere and by photosynthesis of aquatic
plants. The term "aeration" applied to oligotrophic lakes
is somewhat of a misnomer since these lakes typically have
adequate oxygen levels. Destratification and aeration are
generally used synonymously.
The purpose of artificial destratification is to reduce
the density barrier to complete circulation. After artifi-
cially induced circulation of a reservoir, the water
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15
temperature is about equal from top to bottom and many of
the chemical properties are likewise homogeneous. The whole
water mass and bottom area is theoretically habitable by
the aerobic biota which otherwise could only inhabit the
epilimnion and metalimnion of a eutrophic lake.
Artificial destratification also increases the lake's
heat budget. After destratification, the entire lake is
about as warm as the epilimnion before aeration began. This
warming occurs with continuous air injection (Fast, 1968),
as well as intermittent air injection (Fast and St. Amant,
manuscript in preparation). Although an increased heat
budget generally benefits eutrophic lakes, it may have seri-
ous repercussions in oligotrophic lakes by eliminating those
cold water organisms inhabiting the hypolimnion.
A new method of aerating the hypolimnion of eutrophic
lakes was more recently developed (Bernhardt, 1967). Using
Bernhardt's aerator (Figure 3) the hypolimnion is aerated
but not greatly heated. Hypolimnion aeration is only applic-
able to eutrophic lakes, since oligotrophic lakes already
have high oxygen concentrations. Bernhardt's aerator con-
sists of a large diameter pipe extending from the lake bottom
to above the lake surface. Inlet ports are located near the
bottom of the pipe and outlet ports are located below the
metalimnion. The top of the pipe is open to the atmosphere.
Air is released and passes through a diffusor near the bottom
of the pipe. As air rises in the pipe, water is drawn in
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16
Figure 3. Hypolimnion aerator of Bernhardt (1967)
From Fast (1968).
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-------
18
through the bottom ports and rises. Oxygen diffuses into
the water as it rises. Water and air are carried to the top
of the pipe where the air escapes to the atmosphere. The
water, however, cannot escape at the surface and sinks to
the outlet port level where it flows back into the hypolimnion.
Once a hydraulic head is established in the pipe, water may
flow directly from the inlet to outlet ports without rising
to the top of the pipe. Consequently, hypolimnion water is
aerated, but not significantly heated or mixed with epilim-
nion or metalimnion water. Thermal stratification is not
affected by this technique if the outlets are below the
metalimnion.
Bernhardt used his hypolimnion aerator in Wahnbach
reservoir near Siegberg, Federal Republic of Germany. This
domestic water supply reservoir is about 37xl66 cubic meters
volume with 43.4 meters maximum depth. His main objective
was to supply cold, well-oxygenated water for domestic and
industrial uses. Previously, he used a diffused air injec-
tion system to aerate the water, but this technique increased
the water temperatures to undesirable levels.
Bernhardt estimates 0.167x106 cubic meters per day are
aerated by the hypolimnion aerator using about 117 cfm of
compressed air. Contact time within the aerator is about 54
seconds and increases the oxygen concentrations from about
5 mg/1 to about 10-11 mg/1 at steady state.
Oxygen transfer occurs primarily within the bottom 7.5
to 20.0 meters of pipe and decreases rapidly thereafter.
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19
This is primarily a function of: hydrostatic pressure,
oxygen saturation of the water, oxygen content of the air
bubbles, and bubble size. As water and air rise higher in
the pipe, conditions for oxygen transfer become progressively
less favorable. It may be possible to increase the oxygen
concentration of the hypolimnion to greater levels than
found in the epilimnion or metalimnion. This is possible
because of the greater hydrostatic pressures and lower
temperatures of the hypolimnion water.
My present investigation actually consisted of two
separate, but related aeration studies. One oligotrophic
lake, Section Four Lake, was thermally destratified. This
study was conducted principally to determine the effects of -
an increased heat budget on the coldwater biota and the other
characteristics of the lake. This is one of the first studies
to evaluate the influence of continuous summertime destratifi-
cation on a oligotrophic lake. Most destratification studies
were conducted on eutrophic lakes where the benefits from
and needs for artificial destratification are greatest.
Hemlock, a eutrophic lake, was aerated with a new hypolim-
nion aerator of my own design. This study was conducted
principally to determine the value of this aeration system
for eutrophication control and to evaluate its effect on the
vertical distribution of rainbow trout (Salmo gairdneri).
While Bernhardt (1967) was mainly interested in improving
water quality by artificial hypolimnion aeration, I am more
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20
interested in the specific effects of this aeration system
on the biota.
The experimental design is essentially the same for both
lakes. The lakes were studied under natural conditions
during 1969 and artificially aerated during 1970. Special
emphasis was placed on the oxygen, temperature, zoobenthos
and rainbow trout depth distributions.
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METHODS
The transect method was used to collect most samples.
A rope extended from a post on shore to a steel barrel
anchored near the center of the lake (Figures 4 and 5).
A pontoon raft was hand-pulled along the rope and samples
collected as desired. Unless otherwise indicated, samples
were collected at the barrel. The summer sample periods
extended from June 15, 1969 through September 5, 1969 and
from June 7, 1970 through September 7, 1970. In addition,
one set each of oxygen, temperature, pH, alkalinity and
conductivity measurements were made during December 1969,
January 1970, December 1970 and January 1971.
Physical-Chemical
Water samples for chemical determination were collected
each two meter depth interval from each lake with a PVC
plastic water sampler. Samples for pH, alkalinity and con-
ductivity were placed in plastic bottles at the lake and
taken to the laboratory for analysis. Total alkalinity and
pH were measured with a glass electrode pH meter, A 4.4 pH
endpoint was used for total alkalinity. Specific conductance
was measured on a Type RC, Industrial Instruments conductivity
21
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Figure 4. X-sectional view along principle sample transect. Raft, emergent
insect traps, gill nets and transect float are shown.
to
to
-------
Transect Post
Transect Float
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24
Figure 5. View of Section Four Lake taken from basin rim.
Emergent insect traps are stacked on the raft.
The periphyton float is to the left of the
transect barrel, and the gill net rollers are
to the right of the barrel. (Photo by Dr.
0. E. Kurt.)
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,,
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26
bridge during 1969, and on a different Type RQ bridge during
1970. A correction value was determined for each instrument.
Temperature-depth measurements were made with a re-
sistance thermometer at weekly intervals or less. Thermal
stability was calculated from temperature data as described
by Fast (1968) using Schmidt's (1915) and McEwen1s (1941)
formulations.
Most oxygen determinations were made from water samples
collected with the PVC water sampler. A few sets of deter-
minations during June 1970 were taken with a Precision
galvanic cell D.O. analyser. Oxygen values were determined
by the Alsterberg modification of the Winkler method, except
that Phenylarsene oxide (PAO) was substituted for thiosulfate
and thyodene was substituted for starch solution. Samples
were taken weekly during the summer 1969, most of the summer
1970, and each winter from one location, but were taken more
often from both lakes during June 1970. In addition to the
standard sampling location in Hemlock Lake, depth samples
were taken at several locations along a transect from the
aeration tower to a point near the compressor. Most of the
Hemlock Summer 1970 and January 1971 oxygen and temperature
measurements were made along this transect.
Transparency was generally measured daily with a standard
black and white 20-cm secchi disc. Only one set of light
transmittance measurements were made in each lake with a
subsurface photometer.
-------
27
Carbon dioxide concentrations were estimated using a
monograph from pH and total alkalinity values (Moore, 1939).
Total dissolved organic matter, total particulate
organic matter, Ca, K, Na, and Mg were analyzed by R. G.
Wetzel. He used slight modifications of Stickland and
Parsons' (1965) methods for DOM and POM; and simple atomic
absorption for the cations (Jarrell-Ash Model 82-700).
Relative irradiance measurements were made with a sub-
marine photometer. Both deck and submerged cells were used
without filters.
Chlorophyll analyses were made only once. Water was
filtered through Whatman GFIC glass filters. A small quantity
of magnesium carbonate was placed on the filter to prevent
acidification and the filters were stored at about -23 C.
Samples were macerated with a tissue grinder and chlorophyll
extracted for 24 hours in 90% acetone. Optical densities
were measured over a 1.0 cm pathlength. Chlorophyll values
were computed using formula of Parsons and Strickland (1963)
and Lorenzen (1967).
Area-capacity values are based on topographic maps
constructed by the Institute for Fisheries Research, Michigan
Department of Natural Resources. They constructed these
maps from surveys made of each lake during January 1957.
I constructed area-capacity tables (Tables A-9 and A-10) from
these maps as described by Welch (1948).
-------
28
Phosphorus measurements were made in both lakes during
1969. Samples were collected in glass bottles and a portion
of each was filtered through HA millipore filters. The
samples were then acid-digested and analyzed using the
stannous chloride method for orthophosphate (American Public
Health Association, 1965). Total phosphorus and total solu-
ble phosphorus were calculated from these measurements.
Sediment total carbon content was measured using a new
method developed by Dr. Frank D1Itri of Michigan State
University. Briefly, a finely ground sample of dry sediment
(dried at 105°C) is oxidized by heating with potassium di-
cromate and concentrated sulfuric acid. Carbon dioxide is
produced in proportion to the amount of carbon present.
The carbon dioxide is absorbed by sodium hydroxide and de-
termined gravimetrically. Sediment carbonate content was
measured using an acid neutralization method (Allison and
Moodie, 1965). Organic carbon is estimated by the difference
between total carbon and carbonate carbon.
Phytoplankton
Brian Moss identified and counted the phytoplankton.
Three 500-ml samples were collected twice a week from each
lake during 1969. These samples were collected from 0, 5 and
15 meters depths. One ml of Lugol's solution was added and
the samples were shipped to East Lansing for examination.
During 1970, 11 samples were collected each time from Hemlock
-------
29
and 9 from Section Four. One thousand ml were collected for
each sample, and collections were taken once or twice a week.
These samples were placed in plastic graduated cylinders,
four ml of Logol's was added and they were allowed to settle
for two days. After two days, the supernate was drawn off
through a small glass tube inserted in the side of the
cylinder. About 30 ml of concentrate remained after decant-
ing. This was drawn off through a larger glass tube inserted
at the bottom of the cylinder. The cylinder was rinsed with
distilled water and added to the concentrate. About 60 ml
of concentrate was thus obtained. This was shipped to East
Lansing for examination.
A subsample of each sample was filtered through a HA
millipore filter. After filtering, a drop of oil was added
and the sample examined at 150x to 600x magnifications.
From 10 to 50 fields were examined, depending on the algal
concentrations, to give an estimated ± 5% error.
Primary Production
Primary production estimates were made using the carbon-
14 technique in a constant light intensity chamber (Figure 6
(a). Water samples were collected with a PVC water sampler
and transferred to 125 ml Pyrex bottles. One light bottle
and one dark bottle were collected from 0.3m. These samples
were immediately placed in a light tight box and taken to
the incubation chamber. About 25 minutes passed between
-------
30
Figure 6. (a) Phytoplankton incubation chamber. Four
submerged sample bottles on the rotating
wheel. (Photo by author.)
(b) Periphyton ring. Five plastic periphyton
slides are visible clamped to the ring.
(Photo by author.)
-------
Fig. 6a
Fig. 6b
-------
32
collection and incubation. Each Hemlock Lake sample was
inoculated with 1.0 uc 14C in 1.0 ml distilled water both
years. Each Section Four sample was inoculated with 1.0 uc
in 1.0 ml distilled water during 1969, but 2.0 uc in 20 ml
distilled water during 1970. The samples were incubated
in the light chamber for four hours. They were placed on
their side on a revolving horizontal wheel. The wheel was
45 cm in diameter and turned at 5 revolutions/min. The water
was usually kept within 5°C at the lakes' surface tempera-
tures. The bottles revolved 33 cm from 6 Sylvania Gro-Lux,
20-watt fluorescent bulbs and 20 cm (minimum distance) from
two G.E., 150-watt spotlight bulbs. After incubation, 50 ml
of Hemlock sample was filtered through a 25 cm diameter HA
millipore filter (0.45 u). Fifty ml of each Section Four
sample was filtered during 1969, but 100 ml was filtered
during 1970. Each filter was rinsed with three percent
formalin after the sample water had passed through. After
drying in the dark, the filters were exposed for 15 minutes
to HC1 fumes (Wetzel, 1965). Sample activity was measured
using a Tracerlab Omniguard Low Background, internal gas
flow Counting System; the efficiency of which was determined
from samples of known activity. Efficiency averaged about
12%. Total inorganic carbon available for photosynthesis-
and the rate of carbon fixation was estimated using Saunders
et al. (1962) method.
-------
33
Periphyton
Periphyton standing crop was measured as ash-free dry
weight. The periphyton grew and collected on 6mm x 50mm x
127mm plexiglass slides that were suspended horizontally in
the lake at six depths. The slides were fastened with metal
clips to a plastic ring (Figure 6 (b)). The ring was sus-
pended by rope from a horizontal bar held above the lakes'
surface by floats. One series consisted of four slides at
each depth. These were usually incubated 17 days before
collection. The second series consisted of three slides at
each depth. These samples were incubated 34, 51 or 68 days
and represented total, undisturbed accumulations during the
sample period. Periphyton samples were scraped from the
slides and stored in 90% ETOH at -15°C until dried. They
were dried at 105°C four days and held in a dessicator until
incinerated. They were incinerated at 550 C for 10 minutes.
They were cooled in the dessicator before weighing. Weights
to the nearest 0.1 mg were measured. All periphyton weights
collected are presented in the Appendix (Tables A-l through
A-4) .
Zooplankton
Two series of zooplankton samples were collected during
1970. Three samples from each depth were collected by fil-
tering 22 liters of water through a Wisconsin plankton net.
The net was suspended on the pontoon raft and water was
-------
34
pumped via a garden hose into the net. About 8 liters of
water per minute were pumped. The concentrated zooplankton
were preserved in 3% Rose Bengal solution made from 90%
ETOH. The stained specimens were later filtered through a
HA millipore filter with a printed grid. The filter was
then placed over a drop of glycerin in a plastic millipore
petri dish. This gave a permanent, mount and the grid
facilitated counting.
Zoobenthos
Zoobenthos samples were collected along one transect
in each lake with a screened Ekman 15-cm square dredge
(Welch, 1948). The screen was No. 30 brass sieve. Five
samples were collected from each depth interval each sample
period. Five collections were made in each lake each year,
and the depth intervals in meters were: 0.0-3.7, 3.7-7.3,
7.3-11.0, 11.0-14.6, and 14.6-maximum depth. Maximum depth
was 18.6 meters in Hemlock and 19.1 in Section Four.
Collections were made at three-week intervals beginning in
mid-June each year. A total of 125 samples were collected
from each lake each year. Samples were sifted through a
No. 30 brass sieve (0.59 mm opening) at the lake and later
preserved with 20% formalin. Reisch (1959) found that
about 93% by biomass of his marine zoobenthos were retained
by a No. 20 sieve. The No. 30 sieve used in this study
probably retained comparable biomass, but Jonasson (1955)
-------
35
has shown that zoobenthos population estimates can be biased
by sieve size. These samples were later stained with a 3%
Khodamin B solution in 90% ETOH and sorted into 90% ETOH
using Anderson's (1959) sugar flotation technique. An il-
luminated magnifier (2x) lamp was used in the sorting. Fast
(1970) found the efficiency of sugar .flotation is high for
such groups as midge larvae and pupae, but much lower for
oligochaetes. I feel these efficiencies were somewhat
greater in my present study because the present samples were
stained and a better magnifier was used to sort. Sixteen
zoobenthos categories were identified, and organisms were
sorted into these categories. These include: oligochaetes
(microdriles) , oligochaetes (megadriles), Chironomid larvae,
chironomid pupae, amphipods, dragonflies (Anisoptera),
damselflies (Zygoptera), mayflies (Ephemeroptera), Chaoborus
spp. larvae, Chaoborus spp. pupae, clams, Heleidae (=Cera-
topogonidae)larvae, Trichoptera larvae, Tabanid larvae,
Megaloptera and leeches. No attempt was made to determine
relative species compositions of each category, but represen-
tative specimens of certain categories were sent to taxon-
omists for the respective group. The number of organisms
in each category were counted for each sample, and their wet
weight measured to the nearest 0.001 mg. Before weighing,
excess moisture was removed using King and Ball's (1964)
technique, but were centrifuged for 4 minutes instead of 30
seconds. All numeric and weight data are presented as wet
weights in the Appendix (Tables A-5 through A-8).
-------
36
Crayfish
Crayfish (Orconectes virilis) were collected with modi-
fied wire minnow traps (Momot and Gowing, 1970) suspended
from the transect line at ten depths. After collection they
were either removed from the lake, or released near the
center of the lake. Four collections were made from each
lake between August 12 and August 30, 1969, but 22 collec-
tions were made from each lake between June 7, 1970 and
September 4, 1970. Times between collections varied from
one day to one week. Crayfish were sexed upon collection.
Emergent Insects
Emergent insects were captured using a new half-square
meter submerged trap (Figure 7a) . The trap has a steel frame
on which clear polyethylene plastic is attached. On hard
substrate, it is held off the bottom by legs, thus permitting
water to circulate between the trap and the lake. A glass
jar is attached to the top of the trap and collects the in-
sects as they rise to the surface. A removable funnel and
perch apparatus is situated in the jar mouth (Figure 7b).
The funnel is made from two styrofoam drinking cups. The
bottom cup has a small hole in its top to permit entry of the
insects and fine mesh netting on one side. The other styro-
foam cup has most of its sides cut away and is glued to the
first cup to form a perch for emerged insects. Water is added
-------
Figure 7. (a) New emergent insect trap. (Photo by Dr. 0. E. Kurt.)
(b) Styrofoam trap used in collection jar on the emergent
insect trap. (Photo by Dr. O E. Kurt.)
(c) Replacing collection jar on emergent insect trap.
Trap is suspended from bracket on the raft and not
taken out of the water during transfer. (Photo by
Dr. O. E. Kurt.)
-------
Fig. 7a
Fig. 7b
Fig. 7c
-------
39
to the jar as needed to assure that the water level will be
between the top of the first cup and bottom of the perch
when the trap is in sampling position. The amount of water
added will depend on sampling depth. At 20 meters, for
example, no water is added beforehand since hydrostatic
pressure will reduce the air space to 1/3 its surface volume.
On the other hand, the shallow water bottles must have 2/3
their volume filled to assure an adequate level. As the deep
water traps are lowered, water will flow into the bottle
through the hole on the top, and the netting. As they are
raised, the water will flow out these same apertures. If
the netting were not present, the water would be forced to
flow between the jar lip and the cup. The netting prevents
this while retaining organisms and exuvia that are still in
the water.
Five pair of insect traps were used in each lake; two
at each of the same depth intervals indicated for the zoo-
benthos. The traps were used to collect insects five days
each week. They were attended and moved daily, and allowed
to dry out during the other two days each week to prevent
insect attachment. The first day of each week the traps
were placed in the water and suspended from the raft by a
hook. The sample jar was added and the trap lowered to the
bottom by a rope. The next day the trap was raised to the
surface and again suspended from the hook while the sample
jar was removed and another jar added (Figure 7 (c)).
-------
40
The trap was then lowered to the same depth interval, but at
a slightly different location. The body of the trap was not
taken out of the water during the sampling period. It was
not taken out for two reasons: (1) to prevent entrapment of
insects on the surface of the lake in the trap. This was
sometimes a problem during the first sampling period of each
week. Aquatic and terrestial insects will accumulate on the
lake1s surface and be entrapped as the trap is lowered into
the lake; and (2) it is more efficient and easier not to re-
move the trap. The collection jars were taken back to the
laboratory where the insects were removed. At the laboratory,
a small amount of tap water was added to the jar if needed
and the jar was vigorously shaken to disorient the adult
insects. The top and funnel were then removed and the water
passed through a small fine mesh net into a white enamel tray.
The funnel and jar were rinsed into the net. Insects and their
exuvia were preserved in 90% ETOH vials for later identifica-
tion and counting. Water was added to the jars as needed and
the cap secured to be used for the next day's set of samples.
Emergent insect samples were collected from June 15, 1969
through September 5, 1969 and from June 7, 1970 through
September 4, 1970. Six hundred and 650 samples were collected
from each lake during 1969 and 1970 respectively-
Rainbow Trout
One thousand right-pectoral fin clipped rainbow trout
(RBT) were stocked in Section Four on June 6", 1969, and
-------
41
1,002 right-pelvic fin clipped RBT were stocked in Hemlock
on June 6, 1969. These fish were mostly one-year-olds raised
at the Michigan Department of Natural Resources (DNR) trout
rearing ponds at Wolverine, Michigan. Both lots averaged
7.3 inches (188 mm) fork length (Figures A-l and A-2).
The fish were released at one point on the shore of each
lake. We measured each fish at the rearing ponds after they
were anesthetized with MS-222. We observed only a few dead
fish in each lake after their release.
One thousand seventy-one left-pelvic fin clipped RBT
were released in Section Four on May 23, 1970. These fish
were one-year-olds raised at the DNR's Wolverine rearing
ponds. The fish averaged 7.9 inches (200 mm) fork length
(Figure A-2). They were measured and handled the same as
during 1969, except that they were sorted at Wolverine with
wooden sorting trays. This was necessary to assure larger-
sized fish than were stocked during 1969. Only a very few
fish of less than 8.0 inches (215 mm) were captured by our
gill nets. Two vertical gill nets similar to those described
by Horak and Tanner (1964) were used in each lake (Figure 8
(a)). The stretched mesh sizes were 3.4 inch (19.0 mm) and
1.0 inch (25.4 mm). The nets were tied to the transect line
at its deepest point (Figure 4). The nets were pulled once
a day and the depth of capture and fin clip of each fish was
determined (Figure 8 (b)).
The RBT stocked in Hemlock during 1970 were handled
much differently than during 1969. About 2,000 one-year-olds
-------
42
Figure 8. (a) Vertical gill net and roller. Gill net is
suspended between raft pontoons as during
sample collection process. (Photo by author.)
(b) Robert Hoffman removing fish from vertical
gill net. (Photo by author=)
-------
Fig. 8a
Fig. 8b
-------
44
were transferred from the DNR's Wolverine rearing ponds to
their hatchery at Grayling about June 1, 1970. These fish
were sorted through wooden sorting trays at Wolverine. On
June 25, 1970 these fish were divided into four lots of over
500 fish each. Each lot was measured as before and clipped
with a different fin clip. These fish averaged 8.0 (203 mm)
and 8.1 inches (206 mm) fork length (Figure A-l) . The four
lots were transported to Hemlock June 26, 1970 and each lot
was put in a separate cage. The tops and bottoms of the
cages were hexagons with each segment being 2.2 meters
(Figure 9) . One meter separated the top and bottom of each
cage and they each contained 11.6 cubic meters of water.
Two of the four cages were completely covered by wire and
plastic, while the other two cages had only the top and
bottom covered with plastic and wire and the sides were
covered with aluminum window screen. One covered cage with
the right-pectoral clipped fish was held at 3m depth
(Figure 10). About 4,000 gallons/hour (15 m3/hour) were
pumped from 1 meter for the first day, and from 12 meters
for the remainder of the acclimation period. The temperature
within this cage was measured with a resistance thermometer
and found to be the same temperatures as water at 12 meters.
One screened cage with the anal-fin clipped fish was held
at 3 meters depth. The other screened cage with the left
pelvic clipped fish was lowered to 5 meter depth for one day
and then to 12 meters. The other covered cage with the left
-------
45
Figure 9. Acclimation cage used to hold rainbow trout at
specific depths in Hemlock Lake. Rubber hoses
led to water pumps on a raft. Cage is covered
with polyethylene plastic and chicken wire.
(Photo by author.)
-------
-------
Figure 10. Configuration of Hemlock Lake acclimation cages. Fin clip of
rainbow trout held in each cage is shown. The oxygen and
temperature profiles during the acclimation period are also
shown.
-------
0
Oxygen
4 8 ]2
0-
2-
4-
? 6-
a
a>
a
14
^' "
-I
^r>
Covered Cage
Rt. Pec. Clip
1
.
T
i—> '•
«MH
\
Screened Cage
Left Pel. Clip
-^
L
^^^^-^
1
Screened Cage
Anal Clip
1
Covered Cage
Left Pec. Clip
Temperature
10 15 20
184
-------
49
pelvic clipped fish was lowered to 7 meters for one day and
then to 12 meters. About 15 m3/min. of water from one meter
depth was pumped into this cage during the entire acclima-
tion period. Water left the two cages through 5-inch diam-
eter (127 mm) irrigation pipe. The pipes were screened to
prevent fish passage. The pipe extended from 12 meters to
6 meters in the case of the 12 meter covered cage, and from
3 meters to 9 meters in the case of the 3 meter covered cage.
On July 1, 1970, the covered 3-meter cage and 12-meter
cages were opened and left at their respective depths.
Water was pumped into each covered cage as usual for another
8 hours. The 12-meter screened cage was opened at 12 meters
and then floated to the surface. Over 200 RBT remained in
the cage as it surfaced. The screened sides were then en-
tirely removed, but the fish were reluctant to leave. Rather
than open the screened surface cage at the surface as orig-
inally planned, I lowered this cage with the anal-fin clipped
fish to 12 meters on July 1, 1970. They remained there until
July 7, 1970 at which time I opened the cage at the 12-meter
depth and left it there.
A few left-pectoral and left-pelvic fish were caught in
the gill nets between June 25th and July 1st. These fish
may have escaped from the cages, or escaped when the fish were
being placed in the cages from the planter truck. The cages
were later inspected but no obvious openings were present.
The length, weight and scale samples were recorded for each
-------
50
fish collected in the gill nets, and gross estimates of their
stomach contents were made.
Only a few dead fish were observed in Hemlock following
stocking during 1970 but 15 dead fish were observed in
Section Four after they were released in May.
Statistics
All confidence estimates placed on means, or totals
were computed using the appropriate t and standard error
values. Non-homogeneous and non-rectifiable variances negated
the use of analysis of variance tests and other parametric
statistics. For these reasons these tests were not applied.
The graphical method (Dice and Leraas, 1936) is used to
compare appropriate means in many cases. Most of the calcu-
lations were performed on Michigan State University's CDC
3600 computer. Most figures were drawn using this computer
and their CalComp plotter.
-------
DESCRIPTION OF THE LAKES
Hemlock and Section Four lakes are located in the
Pigeon River State Forest, about 85 km south of the Straits
of Mackinac. The Pigeon River Trout Research Area includes
these lakes, four other lakes and 8.7 mg of the Pigeon River,
and has special use restrictions. All the lakes were closed
to public angling and certain other activities during our
study. Hemlock Lake is in Cheboygan County and Section Four
is in Otsego County. These two lakes are only 3 km apart,
but possess much different properties.
Earlier observers (Eschmeyer, 1938) thought these lakes
were glacial pit lakes (Scott, 1921), but later evidence
indicates they are actually lime sinks (Tanner, 1952, 1960).
This latter hypothesis was partly substantiated when the
west shore of Section Four collapsed during May 1950. The
lakes are apparently enlarging in this manner, and scallop-
ing of their margins is evident from aerial observation
(R. C. Ball, personal communication).
The lakes are nearly circular in outline with concentric
depth contours (Figures 11 and 12). Although not shown on
Hemlock's contour map, a marshy area is situated just north
of and confluent to the lake. This area is in direct contact
51
-------
52
Figure 11. Contour map of Hemlock Lake showing sample
transects and aerator. Depth intervals
are in meters.
-------
S 33320
Hemlock Lake
Scale: 25.6mm = 30.0meters
0 10 20 30
scale
-------
54
Figure 12. Contour map of Section Four Lake showing
sample transect and air line. Air was
released from the dashed section of the
air line. Depth intervals are in meters.
-------
Sample Transect
Section Four Lake
Scale: 31.6mm = 30.0 meters
-------
56
with the lake, but contains only a few inches of water.
Very dense vegetation undoubtedly restricts communication
between the lake and the marsh.
Tanner (1952) indicates that during his September 1950
surveys of the lakes Hemlock had a maximum depth of 19.5
meters and surface area of 2.4 hectares, whereas Section
Four was 22.8 meters and 1.0 hectares. Based on the 1957
surveys and my depth soundings during January 1970, Hemlock
was 18.6 meters maximum depth and 1.8 hectares, while Section
Four was 19.1 meters and 1.2 hectares. My Hemlock surface
area value does not include the marsh area to the north of
the lake. The 1957 surveys measured 18.1 meters maximum
depth in both lakes. These data indicate that Hemlock water
level has been relatively stable, but Section Four's has
changed as much as 4.6 meters between 1950 and 1957. This
change may have been due in part to the basin collapse
during May 1950 (Tanner, 1952). The collapse could have
caused greater siltation of the basin, or increased seepage
from the basin. Tanner's September 1950 lake survey did not
indicate an immediate depth change due to the collapse.
Section Four's water level was stable during the summer
1969, fluctuating only a few centimeters. Its early summer
1970 level was within a few centimeters of the 1969 level,
but decreased about 0.3 meters by the end of the summer.
The greatest rate of decrease occurred during August 1970.
Hemlock's water level was very stable both summers and fluc-
tuated only a few centimeters during the study period.
-------
57
Although both lakes are designated marl lakes, they
differ greatly. Section Four is a typical marl lake. It is
oligotrophic with plentiful oxygen at all depths all year.
During 1969-70 Chara spp. was found at all depths. It was
sparse in the shallow depths, but formed large beds in
deeper water. Other rooted plants were sparse except at the
shoreline. Phytoplankton was very sparse, with the result
that secchi disc transparencies often exceeded 12 meters.
On August 11, 1969, more than 15% of the surface irradiance
was still present at 12 meters (Figure 13). Secchi disc was
10.25 meters on this date. The water had the greenish-blue
coloration typical of marl lakes.
Section Four's sediments are mostly calcarious. They
range between 1.2% and 12.2% as CaCOa-C on a dry weight
basis (Figure 14). Organic carbon ranges between 0.0% and
6.4%. The profundal sediment measured 3.4% organic carbon
and agrees well with Barrett's (1952) post-collapse data.
Before the collapse of the west shore during May 1950, Sec-
tion Four's profundal sediments average 41.2% as organic
matter. After the collapse they averaged 6.2%. This indi-
cates that the profundal sediments were blanketed with a
layer of sand and silt which in effect sealed in the rich
organic matter. This occurrence is also evidenced by changes
in the phosphorus content of Section Four's profundal sedi-
ments. These sediments averaged 37.2 mg PO4/kg air-dry soil
before the collapse, but only 1.7 mg/kg after. The removal
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58
Figure 13. Hemlock and Section Four relative irradiance
measurements on August 11, 1969.
-------
Percent of Surface Irradiance
20 40
i I i i i I
0 80
I i i i I i i
100
6-
9-
12-
/' Hem.
15-
-------
Figure 14. Section Four transect profile illustrating percent organic
carbon and percent CaCO3-carbon at different depths.
-------
2-
4-
6-
Q.KH
0)
Q
12-J
14 -
16-
18-
Distance From Shore (m)
1 I I I I I f I I
TO
i 1 i
20
I I I I I I
30
j I i
,5f
HU CaCO3-C%
I 1 Organic-C%
20
10
- 0
C
0)
0)
-------
62
of this nutrient-rich material from the lake ecosystem should
decrease productivity. This was not immediately evident
following the collapse because of artificial fertilization
during 1949 and 1950 (Tanner, 1952). Long-term comparisons
indicate productivity has decreased. Survey data from August
1932 (Table 1) indicates a sharp oxygen reduction below the
metalimnion, approaching zero at the bottom. Carbon dioxide
and total alkalinity increased markedly below this depth.
Secchi disc was only 6.8 meters. During August 1969, oxygen
values were more than 4.5 mg/1 at all depths. Carbon dioxide
was less than 8 mg/1 and alkalinity was not stratified.
Secchi depths were generally greater than 10 meters. These
comparisons indicate that primary productivity decreased as
a result of the basin collapse and organic profundal sedi-
ments entrapment.
Hemlock Lake is not a typical marl lake. Although it
is highly alkaline, and has marl deposits in shallow water,
these sediments are covered with a thick layer of peaty
organic material, The organic material originated mostly
from the surrounding forest and the marsh bordering the lake.
It is very loosely compacted in shallow water, but gelatin-
ous in deep water. These profundal sediments float to the
lake's surface when broken loose from the bottom by sampling
gear. The surrounding forest contains mostly deciduous
species which shed much of their leaves into Hemlock Lake.
Tree leaf remains are evident in the profundal sediment.
-------
Table 1 . Section Four Lake limnological data collected
August 1, 1932 by the Institute for Fisheries
Research, Michigan Department of Natural
Resources. Secchi disc depth was 6.8 meters
on this date.
Depth
(m)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Temp.
C°c)
24.4
22.8
22.5
22.2
21.7
20.6
16.1
13.3
12.2
11.1
9.4
8.3
7.8
7.2
6.7
6.1
6.0
5.6
5.6
5.6
5.2
5.0
5.0
Oxygen
9.1
- _
—
11.1
—
—
1.8
- -
_ _
Trace
- _
Free
co2
0.0
_ -
_ _
- -
- -
- -
4.0
—
—
- -
—
_ -
13.9
- -
- -
_ -
22.0
_ _
pH
7.9
- _
—
—
- -
7.6
- -
7.3
- -
- -
- -
7.2
_ _
Total
Alkalinity
154
_ _
_ _
- -
174
- -
187
- -
_ _
198
_ _
-------
64
Section Four Lake, on the other hand, is surrounded mostly
by evergreens. Hemlock's sediments range from 0.0% to
43.1% as organic carbon, and from 0.0% to 26.1% as CaC03
carbon (Figure 15). During 1949-50 Hemlock's profundal
sediments averaged 53% as organic matter, compared to 43%
for 1968-69 (Barrett, 1952). This difference is probably
due to analytical and sampling differences rather than
changes in the sediment.
Unlike Section Four, Hemlock Lake is eutrophic and
meromictic. Prior to aeration, the bottom few meters were
amictic and formed a monimolimnion that did not circulate
following spring and fall turnovers. This zone was anoxic
and contained high concentrations of carbon dioxide and
other gases. Water samples drawn from this depth effervesced
due to the release of dissolved gases. These gases were held
in solution by hydrqstatic pressure. Carbon dioxide,
alkalinity, and conductivity values increased sharply in this
zone (Figure 16). Oxygen values were always 0.0 mg/1 and pH
was about 6.6. A small unidentified bacterium (Brian Moss,
personal communication) , was very abundant in this zone and
was apparently responsible for the greenish tint of the moni-
molimnion water. Fine green needles appeared suspended in
the water. Abundant filamentous algae or bacteria have often
been found in the monimolimnion of other meromictic lakes.
Hemlock's meromixis developed after 1932, since survey data
collected during July 1932 indicate no monimolimnion (Table 2)
-------
Figure 15. Hemlock transect profile illustrating percent organic
carbon and percent CaC03-carbon at different depths.
cn
-------
Distance From Shore (m)
i i i I i ........ I i i I i t I
.
Q— ,-t M ' I I » I I I I I I I I I I I I I i i I I I I I I I I i i I i i , i i i 1
mm Caco3-c%
Organic-C%
-------
67
Figure 16. Hemlock Lake carbon dioxide alkalinity, pH
and conductivity profiles on August 13, 1969.
This is representative of pre-aeration con-
dition. Chemocline of monimolimnion is
evident below 12 meters.
-------
-6
Conductivity (10 mhos)
9 300 600 900
x-^
E
\^
1L
0)
Q
<
6
1
f\
0—
2
4
6-
8-
10 -
12-
14-
16-
18-
— i I i i — i — i i i i i — I—I — l — i — 1 — i — I — I — r—
Carbon Dioxide (mg/l)
3 100 200
i i 1 1 1 1 1 1
1 1 1 1 i 1 i 1
0 70 Ph 8.0 9
Total Alkalinity (mg/l)
200 400 6V
J
\
Alk. > ,,
|PH
\" , Cond. \
. x
• \?
i /
i /
i /
\ 1 ^
^ ! ^^
\ i ^-^'
\ i /'
' \ • /
. V, \\ /
Co\v Vy'
/'^^^^£H£^
-------
Table 2 . Hemlock Lake limnological data collected July
28, 1932 by the Institute for Fisheries Research,
Michigan Department of Natural Resources. Secchi
disc depth was 4.2 meters on this date.
Depth
(m)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Temp.
(°C)
21.1
20.6
20.6
20.0
19.4
14.4
13.3
10.0
6.7
6.7
6.1
6.1
6.1
6.1
6.1
5.6
5.6
5.6
5.6
5.6
Oxygen
8.7
- -
_ -
6.0
_ _
_ _
2.3
Free
co2
10
. _
_ _
- .
_ _
_ _
_ _
_ _
_ w
_ _
12
_ _
_ w
_ _
_ _
_ _
_ _
_ .
w _
39
pH
8.1
- -
_ _
- -
_ _
_ _
_ _
_ _
_ _
8.0
w •
. .
_ _
. .
. .
. -
* *
— —
7.4
Total
Alkalinity
160
_ _
.. .
«. _
_ _
M M
_ _
_ _
— _
_ .
156
• •
. -
w .
• •
w .
• ••
• -
— —
198
-------
70
Oxygen was 2.3 mg/1 at the bottom compared to zero during
1969. Carbon dioxide and alkalinity increased below 10
meters, but not dramatically. pH was 7.4 at the bottom
compared to 6.6 during 1969. The 4.2 meter secchi disc read-
ing is comparable to 1969 values.
Due to its organic richness, Hemlock secchi disc trans-
parency seldom read more than five meters prior to aeration.
On August 11, 1969 less than 1% of surface irradiance was
still present at 9 meters (Figure 13) . Secchi disc was 6.25
meters on this date. The water supported abundant phytoplank-
ton and zooplankton standing crops. Submergent aquatic plants
were very sparse, while emergents were abundant only along
the shore and in the marsh.
During 1969-70, Hemlock Lake contained bluntnose minnows
(Pimephales notatus) and redside dace (Gila elongata). Both
species were abundant and reproduce in the lake. They are
primarily littoral in habit, but are sometimes found in open
water near floating objects. Neither apparently inhabit depths
greater than a few meters, even when the lake is isothermal.
One brook trout (Salvelinus fontinalis) was caught on the
first net set in 1969, but none were found thereafter.
Section Four Lake contained a residual population of
rainbow trout at the time my study began, but no other fish
species. These fish were stocked during 1964 and 1965.
Three thousand trout, at 2,200/kg, were stocked each year
(Carl Latta, personal communication)• These fish averaged
about 33 cm FL during 1969-70, but were very emaciated.
-------
71
They typically had disproportionately large heads and "slab""
sides. The lack of abundant, large zooplankters or other
desirable forage undoubtedly accounts for their condition.
They fed almost exclusively on adult insects that fell on
the lake1s surface. Detritus and benthic filamentous algae
were often present in their stomachs. They very seldom fed
on crayfish or zoobenthos, although both were relatively
abundant. Trout mature sexually, but do not reproduce in
either Hemlock or Section Four lakes.
Tanner (1952, 1960), Barrett (1952) and Siler (1968)
describe in greater detail the history and artificial ferti-
lization of these lakes. Both lakes were fertilized during
1949 and 1950. Their productivities were greatly increased
and they became more eutrophic. They apparently returned to
their prefertilization conditions by 1967, however-
-------
HEMLOCK LAKE
Hvpolimnion Aerator
The aerator used in Hemlock Lake is a new design. It
differs significantly from one used by Bernhardt (1967) and
one designed by R. E. Speece (Fast, 1968). It is only the
second hypolimnion aerator to ever have been used success-
fully.
The aerator free-floats in the center of the lake
(Figures 17 and 18) . Styrofoam and steel barred floats sus-
pend it off the bottom, and air is delivered through a 38 mm
I.D. plastic pipe from a shore compressor. The aerator is
held in place by four anchors and ropes. The aerator was
partly fabricated by Armco Steel Corporation at their Indiana
plant. It was trucked to Hemlock Lake where it was unloaded
onto a wooden cradle (Figure 19 (a)) . The 3.1m section that:
extends above the lake's surface was then banded to the lower
section. The wooden cradle provided support for the aerator
while the floats and hardware were attached, and made it
easier to slide the aerator into the lake. The cradle
rested on 27 round wooden posts. The post, in turn, rested
on two wooden "rails" that ran into the lake. After the
floats and hardware were attached, the aerator rolled down
72
-------
73
Figure 17. Cross-sectional view of Hemlock Lake
hypolimnion aerator. Dotted lines repre-
sent projected edges. Tower is tilted
toward the viewer, and parts are drawn
approximately to scale.
-------
, Air Line
Styrofoam Safety
Flotation Unit
Barrel
Flotation Unit
Styrofoam
Flotation Unit
Current
Deflector
Air Diffusor —
Epilimnion
Hypolimnion
-------
Figure 18. Hemlock hypolimnion aerator in operating position. Only the
upper three meters are visible. Air supply line enters the
scene from the left. Above water styrofoam flotation units
are a safety feature to prevent tower from sinking if sub-
merged units should fail. Ladder on side of aerator permits
access to top of tube. (Photo by author.)
-------
—"-—="—— - - —£
-------
77
Figure 19. (a) Arrival of Hemlock hypolimnion aerator tubes
from the factory. Top three meters section
of aerator is separated and located next to
the truck cab. The tower was unloaded on
the wooden cradle and logs in the foreground
and fittings were attached before it was
shoved in the lake. (Photo by author.)
(b) Hemlock hypolimnion aerator floating hori-
zontally. Temporary floats kept the lower
end up while the current deflector was
attached. The lower end is closest to the
viewer. Deflectors could not be added until
the aerator was floating horizontally in the
lake. (Photo by author.)
(c) Hemlock hypolimnion aerator tilting into
sampling position. The temporary floats
have just been removed by the author using
SCUBA. (Photo by Robert Hoffman.)
-------
Fig. 19a
Fig- 19b
Fig. I9c
-------
79
the rails on the posts and into the lake. Temporary styro-
foam floats were attached to the bottom of the tower so the
tower floated horizontal in the water (Figure 19 (b)). This
was necessary since the current deflector had to be attached
after the tower was in the lake. After the current deflector
was attached, the temporary floats were cut loose and the
tower swung into its vertical operating position (Figure 19
(c)).
Description. The aerator consists of two corrugated, 14-
guage, galvanized iron tubes (Figure 17). One 1.85 meters
diameter tube extends 3.1 meters above the lake surface, to
9.2 meters below the surface. The other 1.38 meters diameter
tube is partly located inside the larger tube and extends
from the lake's surface to the 15.5 meters depth. The smaller
tube is attached to, and positioned within the larger tube
by eight 13 mm x 0.31 m x 0.49 m iron plates. These plates
are welded to the outside of the smaller tube, extend through
slots cut in the larger tube and are also welded to the larger
tube around the slot (Figure 20). Four plates are thus
located near the top of the small tube and four near the bot-
tom of the large tube. The plates are spaced 90° apart
around the circumference of the tubes at each site and are
positioned with their long axis vertical.
A current deflector is attached to the small tube by
clamps and is located one meter below the bottom of the large
tube (Figures 17, 19 (b) and 21). It is 6.3 meters in
-------
80
Figure 20. Cross-sectional view and parts of hypolimnion
aerator.
A. Cross-section of aerator taken near the
top. Two styrofoam flotation units and
one barrel flotation unit are shown.
B. Styrofoam flotation unit.
C. Barrel flotation unit showing the tee
structure used to attach it to the aerator.
D. Cross-section of tee inside the slot
structure. The slot is welded to the out-
side of the aerator.
-------
-------
Figure 21. Hemlock hypolimnion aerator current deflector before they
were attached to the aerator. Anchors in foreground were
used to anchor the tower in its operating position.
(Photo by Ed Schultz.)
-------
-------
84
diameter. The deflector was constructed in halves. Each
half has a central axis of 14 guage corrugated iron. The
iron is curved with the same radius as the small tube and
is 0.31 m wide. Seven 13 mm I.D. pipes are welded perpen-
dicular to the axis. These pipes are 2.5 meters long.
A 6 mm x 51 mm piece of flat iron is welded to the ends of
the pipes to form a large semi-circular rim of radius 3.15
m. Two additional 2.5 m length of flat iron extend from
the axis to the outer flat iron rim. Galvanized fencing
(2 cm x 2 cm holes) is wired to the pipes and flat iron.
A nylon parachute covers the top of the fencing and is drawn
tight about the axis. Chicken wire (6 cm diameter holes)
covers the parachute and holds it firmly against the fencing".
The aerator is free-floating. It is buoyed up by six
styrofoam flotation units and four 220 liter steel drums
(Figures 19 (b) and 20) . Each drum has a 12 mm aperture on
its bottom that is open to the water. A 3 mm copper tube
and globe valve extends from the top of the drum to above
the water level. Air may thus be let out of the drum by
opening the valve. The buoying of the aerator is thus
adjusted with these drums. Each styrofoam flotation unit
consists of four 0.15 m x 0.46 m x 2.5 m pieces of styroform
(Figure 22 (a)). These are sandwiched between two pieces of
19 mm marine plywood and banded by 6 mm x 51 mm flat iron
strips. Both barrel and styrofoam units are attached to the
aerator via a 6 mm thick, 51 mm x 38 mm iron tee (Figures 20
and 22 (a)). The tee is 1.8 m long and slides into an iron
-------
85
Figure 22. (a) Styrofoam flotation unit used on the Hemlock
Lake hypolimnion aerator. The tee structure
used to attach the unit to the aerator is
shown on top. (Photo by author.)
(b) Slots for flotation unit tee1s being welded
on the side of the aeration tower. The iron
plates used to position the inner tube are
shown projecting through the outer tube to
the left of the workmen. (Photo by author.)
(c) Sliding styrofoam flotation unit into slot
on side of aeration tower. Logs and "runway1
are shown leading into the lake. (Photo by
Ed Schultz.)
-------
o
CM
CM
O)
Fig. 22 b
Fig. 22 c
-------
87
slot welded to the side of the large tube (Figures 22 (b)
and 22 (c)) .
Not shown in Figure 17 are two small styrofoam units
that were attached on opposite sides of the tower to the lower
steel plates that connect the inner and outer tubes. These
floats are attached with block and tackle to the portion of
the plate that extends through the outer tube. These styro-
foam units were used to adjust the vertical position of the
tower in the water. Also not shown in Figure 17 is a 220-
liter steel drum filled with cement and attached near the
bottom of the tower. This was added after the tower was in
its operating position and I discovered there was too much
buoyancy. Parts of the submerged styrofoam units were cut
away using SCUBA to further reduce buoyancy.
Air was released from an air diffusor located one meter
from the bottom of the aerator (Figure 23). A PVC plastic,
38 mm-diameter air line passed over the top rim of the
aerator and down to the diffusor. The air line was fastened
to the walls of the aerator with clamps and sheet metal
screws. The diffusor consisted of four 61 cm long, 38 mm
diameter steel pipes joined by a side-armed cross fixture.
Four 6.8mmx58.8mmx30 cm pieces of flat iron were welded
over the outer ends of the pipes. A hole was drilled in each
piece of flat iron and a bolt used to fasten them to the
walls of the aerator. Each of the four diffusor arms con-
tained 24 3.18 mm diameter holes. Eight sets of holes were
-------
88
Figure 23. Air diffusor used on the hypolimnion aerator.
The hole site spacings along one arm are
shown. Three holes were drilled at each
site as shown in the cross-sectional view of
one arm.
-------
CO
•no— •ooo-—
n if >o i
distances (cm) to holes
-------
90
unevenly spaced along each arm. At each site, one hole was
drilled on the top of the pipe, while the other two were
drilled on opposite sides, 45° from the top. The holes
were spaced in this manner to assure an even distribution
of air and to impart an upward thrust to the water.
Compressor. A Jenbach air-cooled JW 156 diesel compressor
supplied air to the tower during the summer 1970. The com-
pressor had three set speeds: (a) 1500 rpm delivering 147
Cfm at 100 psi; (b) 1200 rpm delivering 125 cfm at 100 psi;
and (c) 1000 rpm delivering 100 cfm at 100 psi. The pres-
sure in the system was only about 28 psi. An 8,000 liter
fuel tank was connected to the compressor. The compressor
used less than 4 liters of diesel fuel per hour at 1500
rpm.
During January 1971, I used a Jaeger air compressor.
This has a maximum air output of 75 cfm at 100 psi. It ran
at about two-thirds maximum capacity. This is a very rough
estimate since we did not measure air output.
Operation. I began aerating June 13, 1970, but only ran
the compressor for 10 minutes. A great deal of water and
air leaked through the tower, especially where the two sec-
tions were banded. The tower was then raised so that the
inner tube was 0.5 m above the water level and we plugged
some of the holes with an epoxy material. The epoxy hardened
overnight. June 14th we resumed air injection. The tower
was kept at its elevated position and the compressor run at
-------
91
1000 rpm. Water rose in the inner tube and cascaded over
one side of the tube. The tower tilted at an 80 angle to
the lake surface. We tried to correct the tilt with floats/
but without success . Air rising in the tower displaces
water and decreases the specific density of the tower-water
system. Water is also elevated 0.5 m above the lake level
within the tower. The center of gravity is thus raised and
the tower tilts. This condition could be corrected with
proper anchoring, and/or addition of ballast.
Water and air continued to leak through the tower,
although less than before. This was due in part to the tilt
of the tower, but in larger part to improper construction of
the culvert tubes. The tubes are constructed of galvanized
iron plates. The plates were bent and riveted together.
Caulking should have been applied between the plates before
they were fastened, but was not.
June 17, 1970 the tower was lowered 0.5 meters and the
compressor run at 1500 rpm. The compressor was always run
continuously, except when shut down for maintenance or
repair. The aerator was run in this manner until July 15th.
At this time it was lowered another 0.5 meters and run at
1000 rpm. This schedule was maintained until September 7th,
at which time operation was discontinued.
I injected air through the aeration tower for 48 con-
tinuous hours beginning January 22, 1971. The tower was in
its lowermost position, such that the inner tube was 0.5m
-------
92
below the lake's surface level. Holes were chopped in the
ice inside the aerator to vent the air. All the ice in the
tower melted quickly after aeration began.
Aeration Efficiencies. We wished to determine the most
efficient means of aerating, in terms of air input, as well
as the maximum aeration rate with our aerator. To do this,
we had to determine the relationships between the operating
variables. These variables include water flow rates through
the tower, air input to the tower, elevation of the tower
and oxygen absorption. Water oxygen concentrations at the
top of the tower were always at or near saturation. This
indicates the most efficient level of air input was below
our range of input, and therefore I will not include oxygen
absorption in the following analysis.
We may consider water flow rate our dependent variable,
with air input and tower elevation our independent variables.
Tower elevation is the more important independent variable
over the range of air input values tested, since its influ-
ence on water flow rate is much greater (Figure 24). At low
air input almost twice as much water flows through the tower
when the inner tube is 0.5 m below the lake's surface level,
compared to when it is 0.5 m above. This difference dimin-
ishes at the higher air input levels, but the lower tower
elevation is still the most effective level. On the average,
water flow rates are 1.3 times as great as high air input,
compared to low air input. A more thorough analysis of the
-------
93
Figure 24. Water flow rates through the hypolimnion aera-
tion tower as a function of air input and tower
level. The (0) level is when the top of the
inner tube is level with the lake's surface.
(+) level is with the inner tube's top 0.5 m
above the lake's surface, and the (-) level is
with its top 0.5 m below the lake's surface.
See text for discussion of true flow rates.
-------
60-1
Air Volume (m3/min.PZO kg/cm2)
3.0 3.4 3.8 4.2
504-
x
D
0)
£
0)
404-
30 4-
I I T
4-69
4-63
" 1
"
+45
4-39
4-33
(U
E
0)
I
100
120
140
Air Volume (c.f. m. @ 100 p. s. i.)
-------
95
flow characteristics should include a wider range of air
input. We were limited in this analysis to only three levels
because we could not accurately determine air input other than
at the standard compressor speeds.
The efficiency of air input can be measured by water
volume/day divided by air volume/min. Comparing air input
efficiencies, we see that the efficiency decreases for the
(0) and (-) tower levels as the air input is increased. The
efficiency is relatively unchanged for (+) tower level,
however. This indicates that more water is moved per unit
of air input at the lower air input levels. Tne most effi-
cient level of air input is undoubtedly below our range of
values. However, as air input is decreased, the water oxygen
concentration may decrease below saturation. If this occurs,
then the measure of efficiency must also account for oxygen
concentration as well as water flow rate.
Our measured -water flow rates may be excessive. The
current meter does not measure the direction of flow, only
the rate. It measured horizontal as well as vertical flow.
The horizontal component may be very important, since the
flow pattern was eccentric. Because the tower tilted, air
tended to rise along the higher side of the tube. In con-
trast, the return water flow was much greater on the lower
side than the upper at all three tower elevations. As much
as a seven-fold difference in return flow rates was observed
between the upper and lower side. This disparity is un-
doubtedly due to water flow around the tower as well as
-------
96
through it. The horizontal flow was measured as vertical
flow and resulted in excessive flow-through estimates.
The measured flow rates are probably relative to each other,
however, and therefore can be used to compare tower eleva-
tion and air input rate efficiencies.
-------
RESULTS
Physical-Chemical Parameters
Temperature and Oxygen. Hemlock Lake stratified normally
during 1969. By early June the metalimnion extended from
3 to 8 meters (Figure 25), and the monimolimnion began at
14 meters. Temperatures during early June 1969 ranged from
o o
18 C at the surface to 4.5 C at the bottom. During this
same period, oxygen values averaged 8.0 mg/1 at the surface
and 0.0 mg/1 at the bottom (Figure 26). Metalimnion oxygen
maxima of as much as 15.0 mg/1 were often observed through-
out the summer. These oxygen maxima were caused by high
photosynthetic efficiencies and reduced mixing and diffusion
rates. Chlorophyll concentrations were not very great in
either the epilimnion or metalimnion (Figure 27), indicating
the oxygen maxima were not caused by algal concentrations.
As the season progressed, the metalimnion depth increased
slightly. By late August it extended from 4 to 10 meters.
The 7 C through 15 C isotherms have a nearly parallel decline
throughout the summer. Maxima surface temperatures of over
25 C were observed during mid-July 1969 and again during
mid-August. Minimum temperatures were nearly constant at
4.5 C. The oxygen depletion depth was nearly constant at 10.5
meters during the entire summer 1969 (Figure 28).
97
-------
Figure 25. Hemlock Lake's isotherms during the summer 1969, before
aeration_began. Isotherms are in C.
-------
July
10 20
August
10 20 1
-------
Figure 26. Hemlock Lake's top, bottom and average oxygen concentrations ,_,
during the summers 1969 and 1970. Continuous aeration occurred o
between June 14 and September 7, 1970. °
-------
12-
9-
O)
£
6-
C
0)
O)
0-
1969
BOTTOM
1970
r
-—\
1 10 20 1 10 20
June July
1 10 20
August
11 10 20
June
I ' I ^ T ' I
1 10 20
July
1 10 20 1
August
-------
102
Figure 27. Hemlock Lake's total chlorophyll A, phaophytin
A, oxygen and temperature profiles during
August 13, 1969. These are representative of
values before aeration began.
-------
Chlorophyll (mg/m3)
20
I
40
i
60
80
TemperaturefC)
6 12 18
24
Oxygen (mg/l)
0 2 46 8 10 12 14
i i . i , I i i i i i i i i
2-
4-n*ot.Chl. A
It
-------
104
Figure 28. Hemlock Lake selected oxygen profiles during
the summers 1969 and 1970. Continuous aera-
tion occurred between June 14 and September
1, 1970.
-------
Oxygen (mg/|)
o-
. i . .
8
I
12
. I . .
VI-18/
*"*. \VI-13
5—
10-
1970
1969
15-
/•^
£ 0-
a
0)
a _
VIM
5-
VI I- 30,
IX-2
10-,'
VII-29
IX-2
15-
-------
106
Before aeration began during June 1970, the thermal
regime was similar to that of June 1969 (Figure 29).
Temperatures ranged from 21°C at the surface to 4.5 C at
the bottom (Figure 30). Although the surface temperature
was warmer during June 1970, the thermal profile was other-
wise similar, Oxygeri values before aeration began during
1970 were likewise very similar to the 1969 values. Oxygen
depletion began at 12 meters, and a maxima occurred within
the metalimnion.
Continuous artificial hypolimnion aeration began June
14, 1970 and caused significant alterations of the physical-
chemical regime. A tongue of 1.0 to 4.0 mg/1 oxygen extended
from the aeration into the hypolimnion after one day of con-
tinuous aeration (Figure 31). After nine days of aeration,
much of the hypolimnion had over 8 mg/1 oxygen (Figure 32) .
Shortly thereafter the entire hypolimnion had more than 10
mg/1 oxygen.
Bottom oxygen concentrations at maximum depth increased
from 0.0 mg/1 to 9 mg/1 during the first week of aeration,
and remained above 10 mg/1 most of the summer (Figures 26 and
28). Oxygen maxima still occurred within the metalimnion,
but they were not as distinct as during pre-aeration periods.
Average oxygen concentrations were always greater during
aeration, and surface values were generally greater. Average
oxygen concentrations during mid-July 1970 were 12 mg/1 com-
pared to 8.5 mg/1 during mid-July 1969 (Figure 26).
-------
Figure 29. Hemlock Lake's isotherms during the summer 1970. Continuous
aeration occurred between June 14th and September 7th.
Isotherms are in °C.
-------
August
a
Q>
a
-------
109
Figure 30. Hemlock Lake selected temperature profiles
during the summers 1969 and 1970. Continu-
ous aeration occurred between June 14 and
September 7, 1970.
-------
Temperature (°c)
Q.
0)
Q
16-
0-
4-
8-
12-
16-
7-30-69
'7-29-70
9-2-69
9-2-70
-------
Figure 31. Hemlock Lake hypolimnetic oxygen isopleths (mg/1) along the
air line transect one day before aeration began and after one
day of hypolimnion aeration.
-------
70
60 50 40 30 20 10
10 20 30 40 50 60 70
Distance From Aerator (m)
-------
Figure 32. Hemlock Lake hypolimnetic oxygen isopleths (mg/1) along the i-
air line transect one day before aeration began, and after nine
days of continuous hypolimnion aeration.
-------
70
60 50 40 30 20 10
10 20 30 40 50 60 70
Distance From Aerator (m)
-------
115
Another conspicuous alteration of Hemlock's physical-
chemical regime is the gradual warming of the hypolimnetic
waters. Their temperature increased more than 2 C/week
(Figures 29 and 33). This increase is marked by the gradual
and continued extinction of 18 C or less isotherms, "into
the bottom of the lake." The minimum temperature increased
greatly to over 17°C during September 1970, compared to 4.5°C
the previous September. The average temperature increased
to a maximum of 19.5°C during August 1970, compared to 17.5°C
summer maximum during August 1969. Surface temperatures were
slightly cooler during July 1970, and several degrees cooler
during late August 1970 compared with 1969. The hypolimnetic
warming is attributed to heat conductions throughout the
tower, whereas the surface cooling is attributed to mixing
of hypolimnetic waters with surface waters. This led to a
gradual destratification of Hemlock Lake in disaccordance
with my experimental design. Although the lake did destratify
almost completely by September 1970, I did maintain a distinct
thermal gradient during most of the summer.
Thermal Stability. Thermal stability increased from 7x108
kg-m during June 1969 to 18x108 kg-m during July and August.
These two peaks correspond to surface temperature maxima
(Figure 34). The increased stability reflects the general
surface warming trend, increased epilimnetic volume and
thermal gradient maintenance during 1969. Thermal stability
followed a much different pattern during 1970. It increased
-------
Figure 33. Hemlock Lake maximum, minimum and average temperatures ( C)
during the summers 1969 and 1970. Continuous aeration
occurred between June 14 and September 7, 1970.
-------
Hemlock
4-
1 10 20 1 10 20 1 10 20 1] 10 20 1 10 20 1 10 20 1
June July August June July August
-------
118
Figure 34. Hemlock Lake stability values during the
summers 1969 and 1970. Continuous aera-
tion occurred between June 14 and September
7, 1970.
-------
20-
0>
•s
i
2
.•= 10-.
= 5-
ja
(T3
11 ii 11 ii ii |in i nil i [i i iii71 riTfTTTii i ii 11 ii [rmrjnrrnil riT|M 1111 up IITI UN p u MI n ni| n 111
1 10 20 1 10 20 1 10 20 1
June
July
August
-------
120
from 8x108 kg-rn during early June 1970 to a 14.5x108 kg-m
maximum during mid-June. Thereafter it decreased gradually
to almost zero by September 1970. This gradual decrease in
stability reflects the gradual destratification of the lake.
pH, Alkalinity, and Conductivity. During 1969, pH values
were consistently low within the monimolimnion, but about
8.0 near the surface (Figure 35) . The low monimolimnetic
values are attributed to high carbon dioxide concentrations
associated with decomposition of seston and sediments.
After aeration began during 1970, the bottom pH values in-
creased and eventually equaled the surface values. Surface
values were greater during early 1970 than during 1969, but
gradually declined. The high surface pH values are attributed
to photosynthesis, whereas the increases in bottom pH values
are attributed to carbon dioxide elimination. Carbon dioxide
was removed from the bottom water as it passed through the
aerator tower.
Surface and bottom total alkalinity values differed
greatly during 1969. Surface values were relatively constant
at 120 mg/1, but bottom values were about 500 mg/1 (Figure
36). Aeration caused a marked decrease in bottom alkalinity,
but a gradual increase in surface alkalinity. The average
alkalinity was relatively constant and about the same as
during 1969.
Conductivity followed the same general pattern as total
alkalinity (Figure 37). Bottom conductivity during 1969
-------
Figure 35. Hemlock Lake's bottom, top and average pH values during the
summers 1969 and 1970. Continuous aeration occurred between
June 14 and September 7, 1970.
-------
8.5-
8.0-
7.0-
6.5-
6.0-
1969
TOP
**»,.
"x
MEAN
BOTTOM .
1970
June
1 10 20 1 10 20 1 10 20 1
10 20 1 10 20 1 10 20 1
July
August
June
July
August
-------
Figure 36. Hemlock Lake's bottom, top and average alkalinity values
during the summers 1969 and 1970. Continuous aeration
occurred between June 14 and September 7, 1970.
-------
500-
400-
300-
O 200-
I-
100-
1969
BOTTOM
MEAN
TOP
1970
~~l—'—\—
10 20
June
~i—'—r
1 10 20
June
10 20 1 10 20
July August
i i
1 10 20
July
~i—'—r
1 10
20
August
-------
Figure 37. Hemlock Lake's bottom, top and average conductivity values
during the summers 1969 and 1970. Continuous aeration
occurred between June 14 and September 7, 1970.
-------
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June July August
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10 20 1 10 20 1 10 2b i
June July August
-------
127
averaged 950 micromhos compared to 250 at the surface.
Following aeration during 1970, the bottom conductivity
decreased rapidly to 400 micromhos and then gradually con-
verged with surface conductivity. When the lake destrati-
fied, the surface and bottom conductivity were essentially
equal.
Phosphorus. Total phosphorus concentrations during July
1969 were ten times as great in the monimolimnion as in the
holomixion (Table 3). They ranged from 0.020 mg/1 at the
surface to 0.280 mg/1 at the bottom. Total dissolved phos-
phorus did not follow this same pattern. It was more vari-
able, but about twice as great below the metalimnion.
Surface to 3.7 meter samples averaged .011 mg/1 whereas
those below 10 meters averaged .021 mg/1. Phosphorus deter-
minations were not made during 1970, but changes in their
concentrations can be inferred. Oxygen depletion leads to
low redox potentials in the mud and a net movement of phos-
phorus from the mud to the water (Mortimer, 1941, 1942).
This situation was evident before aeration began. After
aeration began the redox potential increased rapidly as the
oxygen increased. This caused a re-absorption of phosphorus
by the aerated mud (Fitzgerald, 1970) and precipitation of
phosphorus. The net concentration of phosphorus should thus
decrease. Subsequent accelerated biodegradation of the
sediments may have caused a regeneration of phosphorus. The
net result of the processes is speculative.
-------
Table 3. Hemlock Lake total phosphorus and total dissolved
phosphorus collected July 22, 1969. Two water
samples were collected from each depth.
Total Phosphorus
(mR/1)
Depth
0.0
1.9
3;7
5.6
7.4
9.2
11.0
12.8
14.6
Xl
0.020
0*015
0.025
0.008
0.008
0.040
0.025
0.020
0.300
X2
0.020
0.020
0.015
0.010
0.020
0.040
0.030
0.030
0.250
Mean
0.020
0.018
0.020
0.009
0.014
0.040
0.028
0.025
0.280
Total Dissolved
Phosphorus (rng/1)
xl
0.010
0.008
0.020
0.002
0.005
0.008
0.025
0.020
0.020
X2
0.015
0.008
0.008
0.005
0.020
0.040
0.015
0.025
0.020
Mean
0.012
0.008
0.014
0.004
0.012
0.024
0.020
0.023
0.020
-------
129
Ca, Nat K, Mq, DOM and POM. These constituents were measured
only during the summer 1970. The average concentrations of
sodium and magnesium were relatively constant during the
summer (Table A-ll). Particulate organic matter was especial-
ly variable. Calcium, potassium and dissolved organic matter
had intermediate variability.
Primary Production
Phytoplankton. Relative to 1970, Hemlock's phytoplankton
parameters were relatively stable during 1969*. Secchi disc
measurements during 1969 ranged between 2.5 and 6.5 m (Figure
38) . Surface phytoplankton densities were always less than
4,000 cells/ml, and surface 14C production estimates were
always less than 50 mg C/m3/4 hrs.
A small, unidentified bacterium was very abundant within
the monimolimnion during the summer 1969. Brian Moss found
that its density often exceeded 300,000 cells/ml. Water from
this region had a distinct green tinge, although the bacter-
ium was pink when preserved. Gallionella was occasionally
collected from 15 m while not found at 0 m or 5 m. Other
phytoplankters were infrequently collected at 15 m, but were
presumably produced at shallower depths.
After aeration began during June 1970, dramatic changes
occurred. Secchi disc measurements decreased to 1.7 m after
a week of aeration. Concurrently, phytoplankton densities
increased to over 30,000 cells/ml. Primary production also
-------
130
Figure 38. Hemlock Lake secchi disc transparencies, surface
primary production potentials, surface phyto-
plankton densities and surface production
efficiencies during the summers 1969 and 1970.
Continuous aeration occurred between June 14 and
September 7, 1970.
-------
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E 200-
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0-
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gs
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1970
1970
1969
1969 --
1970
10 20
June
i
10
July
20 1 10 20
August
-------
132
increased, but did not reach its maximum of almost 400 mgC/
m3/4 hrs. until mid-July, at which time phytoplankton densi-
ties had declined. Following the tremendous increase in
phytoplankton production, standing crops declined to an all
time low by the first week of August. This is exemplified by
the Secchi disc measurement of over 9 meters. This is the
deepest Secchi measurement ever recorded for Hemlock Lake.
Surface phytoplankton standing crop and 14C production
approached zero during the first week of August.
Following this phytoplankton decline, there was a gradual
increase that continued throughout August. Secchi disc
measurements declined to about 2 meters and 14C estimates
increased to over 300 mgC/m3/4 hrs. by September. Phytoplank-
ton densities also increased to about 10,000 cells/ml, which
is about one-third their June maxima.
The bacterium that was so abundant in the monimolimnion
during 1969, disappeared soon after aeration began during
June 1970. Several phytoplankton species were found in the
hypolimnion during the summer 1970, but these were typically
more abundant at shallower depths and were probably produced
at shallower depths. Densities near the bottom, at 16.5 m
followed the same seasonal pattern as found at the surface.
Densities were greater than 3,000/ml on June 26th, July 2nd
and July 9th, but declined to only I/ml on July 31st.
Densities gradually increased thereafter to 1,700/ml by
September.
-------
133
Associated with changes in the plankton, an unusual
event occurred. Beginning about August 1, 1970, voluminous
quantities of foam were generated in the aerator. This
foam was tan-colored and had a musty odor. Algal cells and
Daphnia ephypia were mixed with it. It was sticky, but
easily dissolved in water. When dried, it was a dark green
or black color, presumably due to entrapped chlorophyll.
Large quantities were generated during the night and spilled
over the top of the aerator (Figure 39). Large amounts of
foam floated about the lakes' surface early in the morning,
but were gone by mid-day. The foam was apparently "melted"
by the sunlight and/or increased temperatures. From midday
on, it completely filled the tower, above the water level, but
did not cascade over the rim. It again resumed overflow
starting sometime during the night.
The foaming ceased from about August 15th through August
18th. This coincides with a dip in the surface Secchi and
14C measurements. Foaming started again August 19th and
continued until we terminated operations. This second time
foaming began coincides with an upturn in 14C production at
the surface and secehi decreases.
Periphvton. Average periphyton standing crop during 1969,
based on 17-day incubations, ranged between 0.004 and 0.020
gm/day (Figure 40). Minimum values occurred during June and
maximum during late July and August. Periphyton accumula-
tions in Hemlock were most abundant between the surface and
-------
Figure 39. Foam spilling over the top of the hypolimnion aerator during
August 1970. (Photo by author.)
-------
-------
136
Figure 40. Hemlock Lake periphyton standing crops based
on 17-day incubation periods and continuous
incubation. The 95% confidence interval is
shown about each average value. Continuous
aeration occurred between June 14 and September
7, 1970.
-------
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• 1970
01969
1
T
10
20
June
I ' I- ' T
1 10 20
July
August
-------
138
2 meters both years. Five meter slides often contained many
Hydra, especially during June and early July 1970.
Periphyton standing crop during early June 1970 was
significantly less than during the same period 1969. After
aeration began during 1970, periphyton standing crops in-
creased to over 0.030 gm/day during July. It then declined
to 0.016 gm/day during early August, and increased a second
time to 0.025 gm/day by late August. These changes closely
approximate changes in the phytoplankton, both in changes
of relative abundance, as well as times of maxima and minima.
Total accumulative periphyton standing crop increased
throughout the summer both years. These increases were al-
most linear between June and September (Figure 40). An
average maximum value of over 0.7 gm was attained by August
21, 1969. Although accumulated periphyton was less during
June 1970 compared to June 1969, it was significantly greater
during the remainder of the summer 1970. Total accumulated
periphyton reached a 1»2 gm maxima by August 21, 1970. This
was almost twice the 1969 maximum value.
Zooplankton
Only two sets of zooplankton samples were collected.
One set was collected just before aeration began, June 11,
1970. The other set was collected after one month of aera-
tion. Both sets were collected during daylight hours.
-------
139
Before aeration began, zooplankters were mostly limited
to depths above the oxygen depletion (Figure 41). Diaptomas
adults, Bosmina, and Diaphanosoma were most abundant within
or below the metalimnion. Over 85% of Diaptomas nauplii
were found within one meter of the surface, and Daphnia pulex
were scattered throughout the water column. After one month
of aeration, the depth distributions of Diaptomas adults,
Diaphanosoma and D. pulex were much changed. Diaptomas adults
extended their maximum depth from 9 m to 18.6 m and their
average depth from 4.5 m to 6.0 m. Diaphanosoma were most
abundant after aeration near the surface and just off the
bottom. Their depth distribution was much altered by aera-
tion, but their average depths were about the same. D. pulex"
increased their average depth from 4.6 m before to 13.8 m
after aeration. Over 80% of the Diaptomas nauplii were still
found in the upper meter after aeration, and Bosmina had
essentially the same depth distribution as before aeration.
More astonishing than the changes in depth distribution
were the changes in population numbers. All zooplankters
increased significantly (0.05 level) except Diaptomas
nauplii (Table 4). Diaptomas nauplii decreased from a total
of 71 to 13. Increases in E>. pulex, Diaphanosoma and Bosmina
were 88x, 21x and 3.Ix respectively- No further information
is available concerning the seasonal patterns of these zoo-
plankters, other than for D. pulex. D. pulex became an
important rainbow trout food item during the first week of
July 1970 and remained so throughout the summer. It was also
-------
Figure 41. Hemlock Lake zooplankton depth distributions three days before
aeration began, and after one month of aeration._ Oxygen and
temperature profiles are shown for each date. (x = average
depth.)
-------
Temp. (°C) Oxygen
Percent of Numbers
Diaptomas spp. Adults Diaptomas spp. nauplii
5 10 15 20 0
10 15
1111 11111
4 8 12 45 30 15 0 15 30 45 75 50 25 0 25 50 75
I I I I I I I I ll I I I I I I l I I I I I I I I I I I I 1 I II I I I I I I II I I I I M I I I I I I I I I I i I i i i I I I
a.
a>
a
7-15-70
x-0.8
6-11-70
x=4.5
6-11-70
x=0.6
6-11-70
x-8.0
7-15-70
x=78
6-11-70
x=4.6
7-15-70
1 x=13.8
45 30 15
15 30 45 45 30 15
15 30 45 45 30 15 0 1
Bosmina spp. Diaphanosoma spp. Daphnia pulex
Percent of Numbers
-------
Table
Hemlock zooplankton collected June 11 and July 15, 1970. Three
samples were collected from each two meters depth interval.
Totals represent the sum of the average number of zooplankters
per liter from each depth. Total samples on each date = 27.
June 11, 1970
Organism
Diaptomas spp.
acTults
Diaptomas spp.
nauplii
Bosmina spp.
Diaphanosoma spp.
Daphnia pulex
Total
162.
71.
1,366.
7.
2.
951 C.I.
156.
61.
1,254.
6.
1.6
on Total
168.
81.
1,478.
8.
2.4
Total
193.
13.
4,228.
157.
176.
July 15, 1970
95% C.I.
188.
11.
4,100.
143.
160.
on Total
198.
15.
4,456.
171.
192.
-------
143
commonly collected in the emergent insect traps after the
first of July- These observations are not quantitative, but
give some idea of D. pulex relative abundance during the
summer. It seemed to be most abundant about mid-July- On
July 28th/ over 75% of the individuals carried ephypia.
This indicates adverse conditions, such as those associated
with the large decline in the phytoplankton population at
that time. Ephypia were not common thereafter, and D. pulex
seemed moderately abundant the remainder of the summer.
Zoobenthos
The three most important zoobenthos taxa in Hemlock,
not including craybish, are the Chironomidae, Anisoptera and
the Chaoborinae (Table 5 and Figure 42). Together they com-
prise more than 75% of the biomass and more than 95% by
numbers of the benthic macro-organisms. Seven other taxa
comprise the remainder. Chironomids are numerically the
most abundant/ but Anisoptera have the largest biomass.
These estimates of relative abundance are based on static
measures, namely standing crop. If production rates were
known, the relative composition of these groups may be much
different.
At least 12 species of Chironomid midges were identi-
fied by D. R. Oliver (Canada Dept. of Agriculture), from
emergent adult specimens (Table 6) . Only four species were
relatively abundant in the emergent samples: Procladinus
denticulatus. Tanypus, Tanytarsus, and Dicrotendipes.
-------
Table 5.
Hemlock Lake zoohenthos collected during the summers 196? and 1970 with an Fkman dredge.
taken each summer. Wet weichts arc shown.
125 drectce samples were
Total
1969
Oligochaetes
(microdriles)
Chironomid L.
Chironomid P.
Amphipods
Dragonf lies
Damself lies
Mayflies
Chaoborus spp.
L.
Chaoborus spp.
P.
Heleidae
Trichoptera
Tabaniid
Leeches
Total
Grams
0.00347
0.32719
0.03928
0.00044
0.83401
0.01013
0.04548
0.040378
0.13232
0.05514
0.01608
0.00000
0.54629
2.41360
Percent
0.1
13.6
1.6
0.0
34.6
0.4
1.9
16.7
5.5
2.3
0.7
0.0
22.6
100.0
Weight
1970
Grams
0.13473
0.49652
0.02301
0.00069
0.97448
0.00380
0.02483
0.31419
0.04911
0.02370
0.00008
0.00024
0.02961
2.07497
Percent
6.5
23.9
1.1
0.0
44.7
0.2
1.2
15.1
2.4
1.1
0.0
0.0
1.4
100.0
Total
1969
Number
4
1,459
32
3
17
IS
115
535
91
96
28
0
1
2,396.
Percent
0.2
60.9
1.3
0.1
0.7
0.6
4.8
22.3
3.8
4.0
1.2
0.0
0.0
100.0
Numbers
1970
Number
267
2,401
80
3
14
3
110
1,336
77
96
1
1
1
4,390.
Percent
6.1
54.7
1.8
n.i
0.3
0.1
2.5
30.4
1.8
2.2
0.0
0.0
0.0
100.0
Number of
Samples Found In
1969
4
72
19
3
12
3
18
78
41
25
1
0
1
1970
33
98
32
3
8
3
26
88
39
32
1
1
1
Mean Number of
Individuals /gram
1969
1,153
4,459
815
6,818
20
1,481
2,529
1,325
688
1,741
1,741
--
2
1970
1,982
4,836
3,477
4,348
14
789
4,430
4,252
1,568
4,051
12,500
4,167
34
-------
145
Figure 42. Hemlock Lake zoobenthos percent composition
during the summers 1969 and 1970. Percent
of wet weight and percent of number are
shown for each taxa. Total weights and total
numbers collected each summer are also shown.
Samples from dredge collections only-
-------
70-
60-
fl)
JJ 50-
E
3
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x
CO
c 30-
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u
0. 20-
10-
60
50-
O)
x
CO
c 30-
4)
u
0)
o. 20-
10-
0-
o.
o
>o
K
Total Number: 1969=2,396
1970 = 4,390
I 11969
o
co
CO
CN
CN
Total Weight: 1969=2.41360
1970=2.07497
I11969
r*^^^n 107^
o
co
•o
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•O
CN
CN
o — .
•- 10
CX CN
>o
0* >
-------
Table 6 . Emergent midge adults collected from 600 samples during 1P69, and 650 samples during 1970.
* are from Hemlock Lake and were collected in emergent insect traps.
All specimens
1969
Family - Chironomidae (Tendipedidae)
Subfamily - Pelopiinae (Tanypodinae)
Procladius (Psilotanypus) bellus
P., (s.s.) denticulatus
Tanypus spp. I/
Subfamily - Chironominae (Tendip«dinae)
Endochironomus spp. I/
Zavrelia spp.
Chironomus spp. 2/
C. (s.s.) staegeri
Polypedilum (Pentapedilum) sordens
Cladotanytarsus viridiventris
Tanytarsus spp.
Dicrotendipes spp.
Paratendipes albimanus
Family - Culicidae
Subfamily - Chaoborinae
Chaoborus flavicans
C. punctipennis
Totals
Total
Number
27
76
43
0
2
1
0
4
2
117
105
6
47
0
4.30
Percent
of Total
Number
6
18
10
0
1
1
0
1
1
27
24
1
11
0
100
No. of
Samples
20
34
26
0
2
1
0
4
2
53
42
6
35
0
225
No. of
Dates
16
26
19
0
2
1
0
4
2
37
31
6
21
0
Total
Number
30
261
86
2
4
7
1
44
0
86
231
2
84
212
1,050
1970
Percent
of Total
Number
3
25
8
1
1
1
1
4
0
8
22
1
8
20
100
No. of
Samples
21
80
S7
2
3
6
1
14
0
32
37
2
51
57
363
No. of
Dates
19
48
35
2
3
5
1
11
0
27
24
2
29
22
I/ Probably a new species
2/ C. tentans identified from larvae
only
-------
148
Procladius and Tanypus are generally thought to be pre-
daceous while the other two genera are generally thought to
be omnivorous, feeding mostly on plant material and
detritus. One species each of Tanypus and Endochironomus
may be new species. Positive identification of many of the
species was impossible because of the small sample sizes
with few males. Only 430 adult midges were collected during
1969, and 1,050 during 1970- These values are very low con-
sidering 1,250 emergent trap sets were made. Only 225 of
600 samples contained any emergent midges during 1969, and
363 of 650 samples contained emergent midges during 1970.
The relative abundance of the emergent midge species
may not reflect their actual relative abundance in the lake.
Many species have peak emergence in May (Miller, 1941), but
we did not begin our collections until mid-June. Chironomus
tentans was collected as larvae, but not as adults. This
species appeared relatively abundant in the hypolimnion after
aeration.
During 1969, most of the Chironomid larvae were re-
stricted to 9 meters or less by hypolimnion stagnation
(Figures 43 and 44). Less than five percent were found be-
tween 9 and 15 meters, and none were ever collected between
15 meters and maximum depth. Larvae living in deep water
were generally larger than the shallow water larvae. For
example, on September 6, 1969 five percent of the larvae by
number were found between 9 and 15 meters, but 15 percent by
weight were in this interval.
-------
149
Figure 43. Hemlock Lake Chironomid larvae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
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151
Figure 44. Hemlock Lake Chironomid larvae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and 1970
Shaded histograms represent aerated periods.
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Depth (m)
-------
153
Although substantial numbers and biomass of Chironomid
larvae were present below 7 meters during 1969, very few
emerged from these depths. Pupae were collected below 7
meters only during August 5, 1969, and then only between
7.5 and 11 meters (Figures 45 and 46). Emergent adults were
most abundant above 4 meters depth and were collected below
8 meters only during late July (Figure 47). Emergence in
the 0 to 4 meter interval ranged between 70% and 95%.
Relatively more midges emerged from 0 to 4 meters during
June than during August. Miller {1941) reports this same
situation in Costello Lake, Ontario, Canada.
Total emergence during 1969 was generally less than
3. x 10s individuals/week (Figure 48). Emergence does not
have any obvious pattern, due in part to its composite nature.
The species composition changes from week to week, but
Tanytarsus and Dicrotendipes were generally most abundant.
These two midges comprised 51% of the total emergence during"
1969.
Ghironomid larvae gradually extended their depth dis-
tribution after aeration began June 14, 1970 (Figures 43 and
44) . Less than 1% by number or 2% by weight were found below
11 meters on July 3rd. By September 4th more than 15% by
number and 40% by weight were found below 11 meters.
Chironomid larvae were first taken from dredge samples near
maximum depth on August 4th. Larvae were observed in the
emergent trap samples before this date, however. By September
4th 5% by number and 15% by weight were present between
-------
154
Figure 45. Hemlock Lake Chironomid pupae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
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156
Figure 46. Hemlock Lake Chironomid pupae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods.
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158
Figure 47. Total midge emergence from Hemlock Lake by
depths during the summers 1969 and 1970.
Aeration occurred continuously between
June 14 and September 7, 1970. Totals include
Chaoborinae and Chironomid midges from emerg-
ence traps only.
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Depth (m)
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160
Figure 48. Total estimated weekly midge emergence from
Hemlock Lake during the summers 1969 and
1970. Totals include Chaoborinae and Chirono-
mid midges from emergence traps only.
Aeration occurred continuously between June 14
and September 7, 1970.
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June
July
August
-------
162
14.5 m and maximum depth. Total numbers of Chironomid larvae
increased greatly during aeration. An estimated 2.5x107
maximum number were present during 1970, compared to a
l.SxlO7 maximum for 1969 (Figure 49). Biomass also increased
during aeration to a 44 gm maxima during July I960, compared
to a 38 gm maxima during 1969. There was a 65% increase in
total number collected during 1970 compared to 1969, and a
52% increase in weight (Table 5).
Chironomid emergence during 1970 also gradually extended
into deeper water at about the same rate as the larvae.
Pupal concentrations by numbers were always greatest above
7 meters, but much larger pupae were collected below 11
meters on August 4th and September 4th than in shallower water
(Figures 45 and 46) . Total numbers of chironomid pupae were
much greater during 1970. An estimated maxima of 12xl05 were
present during July 1970 compared to a 3x105 maxima for 1969
(Figure 50) . Interestingly enough, total biomass was essen-
tially the same both summers, indicating the 1970 pupae were
smaller. Total number of pupae collected during 1970 in-
creased 250% compared to 1969, but total weight decreased 41%
(Table 5). Total emergent adults were always most abundant
between 0 and 4 meters (Figure 47). More than 5% of the
total emergence between June 29th and July 10th occurred in
the 12 m to 16 m interval. Emergence from maximum depth
occurred during July, but was not abundant until mid-August.
Adults almost never emerged below 8 meters during 1969.
-------
163
Figure 49. Total estimated Chironomid larvae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred con-
tinuously between June 14 and September 7,
1970. Totals from dredge samples only-
-------
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1969
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10 20
June
10
~20~
July
10 20
August
-------
165
Figure 50. Total estimated Chironomid pupae number and wet
weight in Hemlock Lake during the summers 1969
and 1970. One standard error is shown about
each estimate. Aeration occurred continuously
between June 14 and September 7, 1970. Totals
from dredge samples only.
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10 ' 20
June
July
August
-------
167
Procladius denticulatus nev:er emerged below 12 meters
during 1969 (Figure 51). After aeration it emerged below
16 m in early July and was more numerous below 8 m during
late July and early August. During 1969 its peak emergence
occurred during August, with no individuals observed before
July 10th (Figure 52). During 1970 its peak emergence
occurred about July 15th and individuals were observed all
summer. Total individuals observed in the traps was 261 for
1970 compared to 76 for 1969.
Tanypus never emerged below 4 m during 1969, but
emerged below 16 m during August 1970 (Figure 51). Its emer-
gence pattern was rather uniform during 1969, but during
1970 it reached peak values during late July and late August.
About twice as many Tanypus emerged during 1970 compared to
1969 (Figure 51) .
Dicrotendipes modestus emerged from slightly deeper
depths after aeration began (Figure 51). During 1969 its
emergence was limited to less than 8 m, but during August
1970 it emerged below 8 m. Almost twice as many emerged
during 1970, compared to 1969 (Figure 52).
Tanytarsus were almost entirely restricted between 0
and 4 m both years. Only one emergent adult was collected
between 4 and 8 m during 1969, and none were collected below
8 m. During 1970 one emergent adult was collected between
4 and 8 m and one between 8 and 12 m. No adults were col-
lected below 12 m during 1970.
-------
168
Figure 51. Depth emergence of selected insects from
Hemlock Lake during the summers 1969 and 1970.
White areas during the sampling periods repre-
sent no observed emergence. A= Procladius
denticulatus, B= Tanypus, C= Pierotendjpes.
D= Mayflies (Ephemeroptera). Aeration occurred
continuously between June 14 and September 7,
1970. Totals from dredge samples only.
-------
90-
1 10 20 1 10 20 1 10 20 11 10 20 1 10 20 1 10 20 1
June July August June July August
1969 1970
4-8
8-12 :yv:^' 12-16
16-18.6
-------
170
Figure 52. Total estimated emergences from Hemlock Lake.
Samples from emergence traps only. Aeration
occurred continuously between June 14 and
September 7, 1970.
-------
a
a>
(A
I
E
3
Z
Procladius denticulatus (]Q4
Tanypus spp. (10)
Dicrotendipes modestus (10)
Mayflies Adults (104)
August
June
July
-------
172
Total weekly emergence was much greater during 1970
compared to 1969. A maximum of over 12x105 individuals
emerged about August 1, 1970 compared to a 3x105 maximum
for the summer 1969. One thousand fifty adults were col-
lected from the traps during 1970 compared to 430 for 1969.
The greatest percentage increase occurred with the Chaoborus.
Chaoborus comprised 11% of the total emergence during 1969,
but 28% during 1970 (Table 6).
Two species of Chaoborinae were identified by B. V.
Peterson and D. M. Wood (Canada Dept. of Agriculture).
Chaoborus flavicans was present both years, comprising 11%
of the emergence during 1969 and 8% during 1970. C_. puncti-
pennis was not observed during 1969, but comprised 20% of the
emergence during 1970. This large increase in emergent adults
during 1970 and species shift is reflected by an increase in
numbers of larvae and decreased average size. Chaoborus
larvae collected by the dredge totaled 535 during 1969 and
1,336 during 1970 (Table 5). Average size of those larvae
decreased from 1,325/gm during 1969 to 4,252/gm during 1970.
This decrease is probably due to two factors: increased
proportions of C_. punctipennis and increased population size.
C- punctipennis is smaller than C. flavicans. More than
twice as many C_. punctipennis adults were collected during
1970 compared to C_. f lavicans. No C. punctipennis adults
were observed during 1969.
Increased population size will result initially in larger
numbers of the smaller instars. Instars three and four are
-------
173
essentially the only ones collected by the dredge. Instars
three and four were usually the only ones collected in the
emergence traps, but instars one and two were also occasion-
ally captured. Chaoborus larvae collected by the dredge
reached a maximum estimated population size of 20x106 indi-
viduals during July 1970 (Figure 53). Their 1969 maximum
was 6x106. Maximum total biomass was only slightly greater
during 1970, however. Total numbers increased 250% during
1970 compared to 1969, but total weight decreased 22%.
Chaoborus larvae comprised 22.3% of the macro-zoobenthos by
number during 1969 and 30.4% during 1970 (Figure 42).
However, the percent of Chaoborus larvae in the zoobenthos
biomass decreased from 16.7% during 1969 to 15.1% during
1970.
Much lower Chaoborus larvae and pupae population sizes
were estimated from the emergent insect trap samples (Figures
53, 54 and 55). A maximum larval population size of 48xl05
was estimated from the traps during July 1970, compared to
20x106 from the dredge samples. By their very nature, the
emergent trap samples are not expected to quantitatively
sample the larval population. Larvae that live in the mud
part of the day, but do not migrate during the sampling
period will not enter the traps. Work by Roth (1968) indi-
cates that some larvae do not migrate everyday- The propor-
tion migrating may also be related to temperature (Stahl,
1966) . Furthermore, in lakes with pronounced oxygen deficits
-------
174
Figure 53. Total estimated Chaoborus larvae number and
wet weight in Hemlock Lake during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred con-
tinuously between June 14 and September 7, 1970,
Totals from dredge samples only.
-------
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O
0>
>
1_
o
o
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June
July
10 20
August
-------
176
Figure 54. Total estimated Chaoborus pupae number and wet
weight in Hemlock Lake during the summers 1969
and 1970. One standard error is shown about
each estimate. Aeration occurred continuously
between June 14 and September 7, 1970. Totals
from dredge samples only.
-------
20-
o
a
O
-Q
O
O
15-
10-
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1970
1969
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1 10 20
June
T
1 10 20
July
lo
20
August
-------
178
Figure 55. Total estimated emergences of Hemlock Lake
Chaoborus flavicans and C. punctipennis dur-
ing 1969 and 1970. Total estimated larvae
and pupae are also shown. All samples are
from emergence traps. Aeration occurred con-
tinuously between June 14 and September 17,
1970.
-------
18-
12-
18-
12-
6-
U
a>
c o
^haoborus fqvicans (104)
1969
1970
Chaoborus punctipennis (105)
O 40-
aJ 30
.Q
3 20
10-
Chaoborus Larvae (105)
Chaoborus Pupae (105)
6-
4-
2-
0-
I '—I—I—r~
1 10 20
1—' 1 ' r-
1 10 20
June
July
1 10 20
August
-------
180
in the deep water, all four instars may remain in the water
and not nestle in the mud during the day (Northcote, 1964;
Teraguchi and Northcote, 1966). In other lakes, first and
second instar are limnetic throughout the day, while the
third and fourth instars typically nestle in the profundal
sediments during the daylight hours.
Even though estimates of larval abundance in the emer-
gence traps are much lower than dredge estimates, the esti-
mates of relative changes in population sizes are very
similar from the two methods (Figures 53 and 55). Estimates
of Chaoborus pupal population size are not only much lower
from the emergence traps, but relative changes in pupal
population size are also dissimilar (Figures 54 and 55).
These data indicate that emergence traps and dredge samples
provide comparable estimates of relative changes in the
larval population, but not the pupal population. The reason
for this difference is not obvious.
During 1969, Chaoborus larvae were never collected
above 4 m in either the emergence traps or by the dredge
(Figures 56, 57 and 58) . They were most abundant in the 8
to 12 m depth interval and about 20% were generally present
in the 16 to 18.6 m interval. Pupae were present in all
depths during 1969, but were generally most abundant between
4 and 12 m (Figures 56 and 58) . C. flavicans only emerged
from the 0-4 m interval during 1969 (Figure 56).
Chaoborus depth distributions changed greatly following
aeration. Larvae concentrations in the 4 to 8 m interval
-------
181
Figure 56. Depth distribution of Chaoborus during the
summers 1969 and 1970. All samples were col-
lected by emergence insect traps. A= Chaoborus
flavicans emergent adults, B= C_. punctipennis
emergent adults, C= Chaoborus larvae, D=
Chaoborus pupae. White areas during emergence
periods represent no observed specimens.
Aeration occurred continuously between June 14
and September 7, 1970.
-------
9(H
0
1 10 20 1 10 20 1 10 20 11 10 20 1 10 20 1 10 20 1
June July August
1969
|$ 0-4 :^9 4-8 H
June July August
1970
8-12 §:^ 12-16 16- 18.6
-------
183
Figure 57. Hemlock Lake Chaoborus larvae depth distribution
as percent of number during each sampling period
during the summers 1969 and 1970. Shaded histo-
grams represent aerated periods.
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Depth (m)
-------
185
Figure 58. Hemlock Lake Chaoborus pupae depth distribution
as percent of number during each sampling period
during the summers 1969 and 1970. Shaded histo-
grams represent aerated periods.
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Depth (m)
-------
187
increased steadily until about July 20, 1970 at which time
about 60% were collected from this interval. About this
same time, larval numbers reached a peak. Thereafter larval
numbers declined and pupal numbers increased and C.. puncti-
pennis emerged in large numbers. There was also a sharp
reduction in number of larvae in the 4 to 8 m interval and
a large increase in larvae in the 16 to 18.6 interval. Pupal
depth distributions in the emergence traps were similar to
larval distributions, but dredge sample distributions are
spurious.
Ephemeroptera (mayflies) constituted less than two per-
cent of the macro benthos total weight each year, and less
than five percent of the numbers (Table 5; Figure 42).
T. Wilson Britt (Ohio State University) identified at least
three species of mayflies from Hemlock Lake based on nymphs
and emergent adults: Caenis simulans McDunnough (most abun-
dant) , Stenonema tripunctatum (Banks) and Callibaetis (least
abundant) . Mayfly standing crops were about the same each
year. Estimates of total numbers in the lake ranged between
zero and 2x106 individuals, and estimates of total biomass
ranged between zero and 900 grams (Figure 59) . One hundred
fifteen individuals were collected by the dredge during
1969, and 110 individuals during 1970 (Table 5). Even though
standing crops were essentially the same each year, more
mayflies emerged during 1970 than during 1969. Peak emer-
gence was over 8xl05/week during August 1970, compared to
5xl05/week during June 1969. This greater emergence rate
-------
188
Figure 59. Total estimated Mayfly (Ephemeroptera) number
and wet weight in Hemlock Lake during the
summers 1969 and 1970. One standard error is
shown about each estimate. Aeration occurred
continuously between June 14 and September 7,
1970. Totals from dredge samples only.
-------
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June July
ib 2'o I
August
-------
190
may reflect increased rates of production not obvious from
estimates of standing crop. An interesting feature of
mayfly emergence is the similarity of peak emergences each
year. Both years peak emergences occurred about July 1st and
August 20th. Maximum emergences differed by about 15 days
between the two years. These emergence patterns may be
caused by different species emerging at different times, but
this was not evaluated.
Mayflies were always most abundant between 0 and 4 m
depth. Over 85% were always found in this interval (Figure
60). A few individuals were occasionally collected below 8
meters, but never below 11 meters. This distribution per-
sisted both years. Emergence during 1969 was mostly between
4 and 8 m (Figure 51). About 20% of the total emergence 1969
occurred between 0 and 4 m. During 1970, all mayflies
emerged from less than 4 m.
One Heleidae was identified by J. A. Downes (Canada
Dept. of Agriculture). It belonged to the tribe Stenoxenin;
and was probably Jenkenshe1pa maqnipennis (Johannsen).
Heleids were not common in the emergents, but comprised about
2% of the biomass standing crop and about 3% of the numeric
standing crop.
T. Wayne Porter (Michigan State University) identified
only one species of Amphida as Hyalella azteca. Only three
amphipods were collected each year.
Jarl K. Hiltonen (United States Bureau of Commercial
Fisheries) identified three species of Oligochaeta from
-------
191
Figure 60. Hemlock Lake Mayfly (Ephemeroptera) depth
distribution as percent of number during each
each sampling period during the summers 1969
and 1970. Shaded histograms represent aerated
periods.
-------
75-_
25-
0~
75-
Number
KJ Ol
:> 0» O
1 1 ! 1 1 1 1 1 1 1 1 1
**- "
0 75^
c :
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tn 0-~
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50 -:
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0 "
(
6-13-69
7-4-69
•sr-2.1
7-25-69
x-1.8
8-5-69
x.1.8
9-6-69
x- 2.0
-
,->-
6-12-70
X- 2.4
| ,
7-3-70
If. 1.8
7-24-70
x-1.8
8-4-70
x=2.4
t- :z~.-.: \
9-4-70
x=>2.4
1 ' i i i i iii i i i | i i i i i i i i ' i i i i i i i i i |
) 4 8 12 16 0 4 8 12 16
Depth (m)
-------
193
Hemlock: Tubifex tubifex, Limnodrilus hoffmeisteri and
Ilyodrilus templetoni. L. hoffmeisteri was most abundant
and T_. tubifex least abundant. Only 4 oligochaetes were
collected during 1969, but 267 were collected during 1970.
Oligochaetes were found at all depths. They were more abun-
dant at intermediate depths, but no persistent pattern was
obvious.
One species of Damselfly (Zygoptera) Enallagma, and
two species of Dragonflies (Anisoptera), Gomphus spicatus
Hagan and Ladona julia (Uhler) were identified by Leonora
K. Gloyd (University of Michigan). Anisoptera comprised
over 35% of the biomass standing crop each year, but less
than 2% of the total numbers. Odonata were always most
abundant between 0 and 4 m. Naiads were frequently collected
in the emergence traps, but adults never emerged in the
traps. A very large emergence of G. spicatus occurred June
1, 1970, No estimate of its magnitude was made, nor were
emergences observed at any other time.
Trichoptera, Tabaniids and leeches were not identified
to lesser taxonomic categories because of their small con-
tribution and difficulties in identification.
Crayfish
Crayfish were collected from Hemlock Lake during 1969
only from August 12th through August 30th. furing this
period, they were found between 0 m and 8 m (Figure 61) .
-------
Figure 61. Hemlock crayfish depth distributions during the summers 1969
and 1970. Total numbers during each sample period and their
average depths are shown. The shaded area represents the
1969 distributions. Aeration occurred continuously between
June 14 and September 7, 1970.
-------
Percent
a
0)
Q
0.
-
5-
10-
-
-
5-
10 —
15-
60 40 20
• i i i i j
n = 8
7=1.9
6-7-70
6-16-70
n=32
x=3.9
p
7-31-70
8-21-70
C
20 40 60
i l i l i l i
J
cf
n=89
x=4-l
d*
60 40 20 C
L
7=1.9
6-16-70
7-3 -70
n=25
7=6.2
9
r
8-21-70
9-4-70
) 2,0 40 60
J
c*
-,- n=Hl
P 7=6.7
Cf*
6,0 4,0 20 C
• i i i i i i
n=10
7=3.2
7-3-70
7-31-70
*> «',
: s
^
n-27
7=4.0
9
T
-12-69
8-30-69
) . 2P . 4P , 6I° ,
C/1
•f^'
« f > ":
- '
n-53
7=4.3
cf
-------
196
Oxygen and temperature at 8 m were greater than 5 mg/1,
and about 8°C. Oxygen was not limiting, but temperature is
colder than normal for sustained activity of crayfish (Momot,
1967). Females average depth was 4.0m, and males had a
4.3 m average. Their sex ratio was 1:2 in favor of the
males.
Before aeration began during 1970, the crayfish were
confined to 6 m depth or less. The females had an average
depth of 1.9 m and the males 1.5 m. Oxygen and temperature
at 6 m were 6 mg/1 and 7°C respectively. Continuous aera-
tion began June 14, 1970 and continued throughout the summer.
After one week of aeration, there was always more than 5
mg/1 oxygen in all parts of the lake. The hypolimnetic
temperature increased more than 2 C/week.. Concurrent with
the continuous aeration, the average crayfish depth increased
gradually. By the end of the summer, crayfish were found at
all depths. The depth distribution for males and females
are similar all summer. During August 12th to September 4th
females had an average depth of 6,2 m and males 6.7 m. The
female to male sex ratio during 1970 was 1:3.6.
Rainbow Trout
Rainbow trout ranged between the surface and 10 meters
during June and early July, 1969 (Figure 62). Their lower
depth range was undoubtedly defined by the anoxic condition
of the deep water. Those fish captured below 7 meters were
-------
Figure 62. Hemlock Lake rainbow trout depth distribution during 1969. i-
These fish were stocked during June 1969 and marked with a -j
right-abdominal fin clip. Each square represents one fish.
-------
June
August
10
0-
IIII111 I ll 111 11 111111111 11
nn-n cmp
aaa ati
•*- 10 --
-------
199
always dead and moribund. During late July and August 1969,
the trout generally ranged between the 7°C and 21°C iso-
therms. Their lower range was related to the anoxia, but
their upper extent appeared limited by warm water.
Before June 14, 1970, the 1969 stocked rainbow trout
were again limited to shallow depths. They ranged from the
surface to 6 meters (Figure 63). Their lower depth range is
again related to anoxia. Continuous artificial hypolimnion
aeration began June 14 and continued through September 7,
1970. The trout gradually extended their depth distribution
after June 14 and eventually distributed throughout the lake
by July 4, 1970. The remainder of the summer 1970, they
were found at all depths, with an apparent preference for
the bottom during late July and early August.
The rainbow trout held in cages during 1970 distributed
throughout the lake when released (Figures 64, 65, 66 and 67)
They were most abundant in the 2 to 6 meter zone soon after
release (between 10°C and 17°C isotherms), but their range
extended from the surface to the bottom. A slight concen-
tration also initially existed at 12 to 15 meters. This
general pattern existed for all four lots and indicates that
acclimatization did not greatly affect their distribution.
Their concentration at 2 to 6 meters persisted for several
weeks; thereafter their distribution was more uniform.
Throughout the summer they avoided water 21°C or warmer-
This same avoidance was also apparent both years with the
1969 stocked trout.
-------
Figure 63. 1970 depth distribution of Hemlock Lake rainbow trout stocked N>
during June 1969, Each circle represents one fish. These §
fish were marked with a right-pelvic fin chip. Aeration
occurred continuously between June 14th and September 7th.
-------
June
10 20
July
10 20
August
1 10 20
-------
Figure 64. 1970 Hemlock Lake depth distribution of right-pectoral clipped NO
rainbow trout stocked during June 1970. These fish were held S
in the 3 m covered cage which received 12 m water for one week
before their release. Each circle represents one fish.
Aeration occurred continuously between June 14 and September 7,
1970.
-------
August
10 20 1
-------
Figure 65. 1970 Hemlock Lake depth distribution of left-pectoral clipped
rainbow trout stocked during June 1970. These fish were held
in the 12 m covered cage which received 3 m water for one week
before their release. Each circle represents one fish.
Aeration occurred continuously between June 14 and September 7,
1970.
-------
August
10 20 ]
-------
Figure 66. 1970 Hemlock Lake depth distribution of left pelvic clipped
rainbow trout stocked during June 1970. These fish were held
in a screened cage at 12 m for one week before their release.
Each circle represents one fish. Aeration occurred continuously
between June 14 and September 7, 1970.
-------
August
1 10 20
-------
Figure 67. 1970 Hemlock Lake depth distribution of anal-clipped rainbow o
trout stocked during June 1970. These fish were held at 3 m °o
in a screened cage for one week, and then at 12 m in a
screened cage for another week before their release. Each
circle represents one fish. Aeration occurred continuously
between June 14 and September 7, 1970.
-------
August
10 20 1
-------
210
Rainbow trout grew rapidly in Hemlock Lake both years.
Fish less than 200 mm were seldom caught in the gill nets.
Although the 1969 stocked fish averaged only 188 mm and the
1970 about 200 mm, many of the smaller fish grew sufficiently
during the summers to become vulnerable to the nets. RBT
growth rates will not be presented in this thesis.
-------
DISCUSSION AND CONCLUSION
Physical-Chemical Parameters
A lake1s oxygen and temperature regimes are very useful
indicative parameters. Yearly extremes, and the distribu-
tion of oxygen and temperature at any given time reveal much
about a lake. Indexed, the kind of life and its spatial and
temporal distribution is usually determined in part by the
oxygen and temperature regimes. Normally, aerobic biota
were excluded from Hemlock's profundal zone by anoxia.
Continuous anoxia existed in the monimolimnion,, Oxygen was
typically depleted in the hypolimnion below 12 meters.
This combination of anoxia and cold water undoubtedly con-
tributed to the accumulation of organic debris within the
lake, and its enriched condition.
Artificial hypolimnetic aeration greatly altered Hemlock
Lake's limnology in general, and its oxygen and temperature
regimes in particular. Although the lake gradually destrati-
fied during 1970, a well-defined meltalimnion existed most
of the summer. As a result of aeration, the monimolimnion
was eliminated by mixing with the hypolimnion, and oxygen
concentrations were greatly increased throughout the hypolim-
nion. Hypolimnetic oxygen values often exceeded surface
211
-------
212
values. This hypolimnetic super saturation relative to the
surface was possible due to hypolimnetic low water tempera-
tures and greater hydrostatic pressures.
Based on hypolimnetic oxygen concentration, Hemlock
lake was eutrophic prior to aeration, but "oligotrophic"
after aeration began. Oxygen values increased from zero
before to over 11 mg/1 after aeration. This alteration
greatly affects the chemical and life processes within the
lake. Before aeration, the hypolimnetic waters and profundal
sediments were characterized by anaerobic decomposers.
These forms are metabolically less efficient than aerobic
forms. As evidenced by the highly organic nature of the
profundal sediments, these decomposers could not break down
the input of organic detritus. The profundal sediments were
gelatinous and adhesive before aeration. After aeration
began, these sediments readily fell apart when handled.
I would attribute this change in character to decomposer
changes from anaerobic types to aerobic, and invasion of the
profundal zone by macrozoobenthos. The latter include midge
larvae and oligochaetes. These zoobenthos accelerate the
aeration of the sediments by burrowing and circulating
aerated water through their burrows.
Increased hypolimnetic temperatures during aeration
must have also affected chemical reaction rates and the
growth of microorganisms and zoobenthos. By September
1970, aeration increased hypolimnetic temperature more than
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213
12°C above its usual level. Chemical reactions and metabolic
processes generally double with every 10°C temperature in-
crease.
Increased hypolimnetic temperature was partly caused
by heat conductance through the aeration tower. As the water
flowed through the tower and back into the hypolimnion, it
absorbed heat through the metal walls of the outer tube
(Figure 21) . This heating occurred over that region of the
outer pipe where the outside water temperatures were greater
than the inside temperature. This heating also occurred
through the pipe above the lake1s surface where the inside
water was elevated due to the rising air. During most of
the summer this heating through the pipe occurred between 8
meters depth and 0.5 meters above the lake's surface. This
heating can and should be virtually eliminated in future
designs by insulating the outer pipe. Polyeurothane foam
sprayed on the sides of the outer pipe would provide such
insulation and also contribute to the tower's buoyancy.
This heating should be eliminated if cold aerated water is
desirable. If warm aerated water is desired, then an arti-
ficial destratification system employing the free release
of air is more desirable, since such a system is much more
efficient than the one used.
The compressed air temperature is not important as a
factor affecting the water temperature. This is true because
of low mass and specific heat of the air relative to that of
the water, even though the air temperature may exceed 100°C.
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214
Based on my conservative calculations, the compressed air
did not raise the hypolimnetic temperature more than 0.5°C
during the entire summer of continuous aeration.
The slightly lower epilimnetic water temperatures, and
the altered metalimnion profile, were caused mainly by hypo-
limnetic water mixed with epilimnetic and metalimnetic
waters. This mixing was caused by two factors: (1) Leakage
of hypolimnetic water through the upper walls of the aerator,
and (2) Leakage of air through lower walls of the aerator.
The escaped hypolimnetic water mixed with epilimnetic and
metalimnetic waters to form water of intermediate tempera-
ture and density. This water flowed into the metalimnion
causing it to increase in volume. Air escaping from the
lower section of the tower caused hypolimnetic water to upwell
around the tower and mix with surface and metalimnion water.
This mixed water also flowed into the metalimnion and in-
creased its volume. The metalimnion volume increase should
lead to lower epilimnetic water temperatures as normal wind-
driven currents erode the metalimnion from above. Higher
hypolimnetic temperatures and aerator-driven hypolimnetic
currents also erode the metalimnion from below. Heat loss
from the surface waters into the tower also contributed to
this process, but is probably of less importance. Water
and air losses from the tower were caused by faulty design.
The riveted plates forming the pipe walls should have been
caulked, but were not. Water and air passed through the
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215
pipes at the joints. This fault can easily be overcome in
future designs by either caulking between the plates, or by
using welded pipe which lacks overlapping plates and is
watertight.
Schmidt (1915) defines thermal stability in terms of
energy required to change a thermally stratified lake to
one of equal temperature throughout. A thermally stratified
lake has a shallower center of gravity than an isothermal
lake. This fact arises from water1s specific density proper-
ties as a function of temperature. Pure water is at maximum
density at 3.94 C and less dense above or below this tempera-
ture. The less dense water is near the surface. Thermal
stability is zero when a lake is isothermal and reaches
maximum value when the lake is well stratified. Stability is
therefore a measure of destratification. It is not an ab-
solute measure, since Fast (1968) found it partly a function
of water volume. Hemlock's thermal stability was greater
during June 1970 than during June 1969 because of warmer
surface waters during June 1970. It gradually decreased to
near zero during the summer 1970 as the lake gradually de-
stratified. It thereby reflects the gradual converging of
maximum-minimum water temperatures during 1970. An opposite
trend occurred during 1969 when the stability was near maxi-
mum by the end of the summer.
I had expected an increase in average pH and a decrease
in average alkalinity following aeration. As carbon dioxide
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216
was removed from the hypolimnetic water by the injected air,
I expected the following net reaction:
Ca++ + HC03 v CaC03Y + H2C03 * C02 I + H20
This should result in a net decrease in calcium ions in solu-
tion, an increased pH and decreased total alkalinity- Average
alkalinity was slightly higher after aeration (Figure 36) ,
while average pH was slightly lower (Figure 35). Calcium
showed the most variability (Table A-ll). It decreased from
an average 47.7 mg/1 on June 13, 1970 to a 40.8 mg/1 average
minimum during July 17th. The greatest decreases occurred in
the deep water. This suggests that during this period CaC03
was precipitated within the hypolimnion as the carbon dioxide
was driven off. From July 17th to August 15th the average cal-
cium concentration increased greatly to 55.4 mg/1 maximum.
The greatest increases occurred in shallow water. The lake's
gradual destratification in late August may have caused this
increase. The free carbon dioxide concentration of shallow
waters may have been increased and caused a re-solution of
shallow water CaC03 deposits. Surface C02 concentrations
were 1.4 mg/1 on June 13th, but 5.4 mg-1 on September 2nd,
although the average COa concentrations for the lake on these
dates were 22.0 mg/1 and 5.4 mg/1 respectively. The shallow
water sediments were much richer in CaCO3 than the profundal
sediments (Figure 15).
I had expected greater changes in the dissolved organic
matter. The average concentrations varied between 7.04 and
-------
217
10.46 mg/1. For any given date surface concentrations were
similar to bottom concentrations. I anticipated precipita-
tion of DOM as it passed through the aeration tower. H. B.
Hynes (personal communication, University of Waterloo),
observed such precipitation when DOM from leaf extract was
mechanically agitated in a flask. This process should have
caused a reduction in DOM within the lake. Concurrently I
expected an increase in DOM as the profundal microbiota
changed from anaerobic to aerobic forms and accelerated the
decomposition of the highly organic profundal sediments.
Possibly these two processes did occur to a significant but
nearly equal extent and balanced each other's effects.
R. G. Wetzel (personal communication, Michigan State Univer-
sity) feels that a more likely explanation is that the DOM
fraction is composed mostly of biologically highly refrac-
tory organic compounds that are not subject to much change
and there was little net input from the sediments. The
particulate organic matter varied greatly during the summer.
This variation is related to changes in organic production
rates. R. G. Wetzel plans to evaluate the effects of aera-
tion on DOM, POM, Ca, K, Na and Mg in much greater detail in
a later publication.
We originally planned a more intense evaluation of
phosphorus. However, due to the inherent variability and
limited resources, this plan was aborted. Barrett (1952)
studied the effects of artificial fertilization on the
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218
phosphorus contents of these lakes in greater detail than
we intended. His results were often incongruous with ex-
pected results. To be sure, phosphorus is an important
nutrient and often the limiting factor, or is associated
with the limiting factor of primary production. However,
other nutrients such as Mo, Co, Zn, or Mn can also be limit-
ing (Goldman, 1962). Many other conditions or substances
can also affect production. As Rigler (1964) quite skill-
fully points out, we do not know very much about the cycling
of phosphorus with a lake ecosystem. The forms phosphorus
takes, its concentrations with ecosystem "compartments" and
especially the rate functions between compartments are
unknown and not easily measured. The best we could hope for
in our study was to determine the changes in the vertical
concentrations of total and dissolved phosphorus; but this
could readily be inferred from changes in oxygen concentra-
tion. With these facts in mind, I decided to discontinue
phosphorus determinations after 1969 and concentrate my
efforts on evaluating the effects of aeration on production
and standing crops of the biota.
Primary Production
Primary production changes are sensitive indications of
changes in nutrient availability, as well as many other
basic conditions in a lake. Unicellular primary producers
respond very rapidly to these changes. They integrate
-------
219
changes in a large number of variables to produce a given
response, a feat not fully understood. Responses include
changes in species composition as well as production rates.
Happenings at the primary producer level are ultimately
passed along to higher trophic levels. Although the trans-
mission route is not fully understood, high primary pro-
duction generally leads to high production at higher trophic
levels. High primary production also leads to eutrophy and
hypolimnion stagnation, conditions I intended to eliminate
by artificial hypolimnion aeration.
Although aeration did eliminate hypolimnion stagnation,
it did not reduce primary production during the entire
summer. My hypothesis is that if nutrient regeneration due
to hypolimnetic anoxia constitutes a significant input to
the nutrient cycle, then hypolimnion aeration should reduce
this input and lead to reduced nutrient and primary produc-
tion levels. Unless a net nutrient flow exists from the
anoxic hypolimnion to the trophogenic zone, then primary
production reductions should not occur until the fall turn-
over following aeration, and during subsequent periods if
high profundal oxygen concentrations are maintained.
Almost immediately following the beginning of artificial
aeration during June 1970 an intense plankton bloom devel-
oped. I attribute this bloom to leaks in the aeration
tower. When aeration began, hypolimnetic water was especial-
ly rich in nutrients. Significant quantities of this water
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220
leaked through the tower into the epilimnion. These nutrients
undoubtedly led to the intense plankton bloom. The bloom
subsided to a very low level by the end of July 1970. At
that time, the lake was clearer than at any known time, while
planktonic primary production and standing crops were less
than during 1969. I attribute this decline primarily to
nutrient deprivation. Although hypolimnetic water leaked
through the tower all summer, I believe many of the nutrients
became oxidized and effectively removed from the hypolimnetic
water soon after aeration began. The profundal mud surface
was oxidized by the artificial aeration. Such a surface has
a large capacity to remove phosphorus from the water by
sorption (Fitzgerald, 1970) . Nutrients such as iron, phos-
phorus and manganese were probably precipitated directly by
the advent of aerobic conditions, higher redox potentials
and higher pH.
Another indication that nutrient limitation contributed
to the plankton decline during July 1970 is reduced primary
production efficiencies. Efficiency is measured as the rate
of primary production in mgC/ms/4 hours per phytoplankton
cell. A more appropriate measure of phytoplankton biomass
could be used, such as cell volumes or chlorophyll concen-
trations, but these measures were not available. The
Observed production rate is actually a measure of the
"production potential" and not the true in situ production
rate. As will be demonstrated later for Section Four Lake,
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221
these two properties can be quite different. The production
rate was measured in a constant light-intensity chamber and
many of the variable lake influences are thereby eliminated
or diminished. In any event, this production rate is a
valuable measure of production potential, and the efficiency
ratio provides a measure of the ability of each cell to grow
and reproduce. High efficiencies imply an adequate environ-
ment and vigorous population. Low efficiencies imply nutri-
ent limitation or some other deleterious condition.
We observed a nearly uniform efficiency value of less
than 5 mgC/m3/4 hrs/ln cell during most of 1969. This ef-
ficiency increased markedly after aeration began, to more
than 45 and subsequently declined to less than 5 by late
July. The efficiency increase implies more desirable con-
ditions for phytoplankton growth, such as provided by in-
creased nutrient concentrations. Decreased efficiencies could
be attributed to the removal of the same factor. It should
be noted that maximum efficiencies do not coincide with
maximum phytoplankton standing crops during June and July
1970. A number of factors could contribute to this situa-
tion, such as: (1) changes in phytoplankton species composi-
tion, with different species having different growth poten-
tials and nutrient requirements, (2) change in size of the
phytoplankters. Since we have essentially equated all cells
in our efficiency parameters, cell size alone could influ-
ence the parameter, and (3) zooplankton grazing. Standing
crop reduction without a corresponding production efficiency
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222
reduction may be due to intensive zooplankton grazing„
Nutrient limitation should not produce these effects, but on
the contrary cause a corresponding reduction in efficiency,
Harvey et al. (1935) have demonstrated that zooplankton can
exert a substantial influence on the phytoplankton popula-
tion. Intense grazing could possibly reduce the plankton
population without reducing the production efficiency.
Large zooplankton population sizes probably occurred in Hem-
lock during early and mid-July, coinciding with maximum
primary production efficiencies. Brooks and Dodson (1965)
suggest that the kind and quantity of zooplankton can effect
the kind and quantity of phytoplankton. Large standing crops
of large zooplankton should lead to reduced phytoplankton
standing crops, whereas large standing crops of small zoo-
plankters should favor large phytoplankton standing crops.
HrbacJ-ek et al. (1961) found that dominant small zooplankters
favor the abundance of nannoplankton, as well as larger
phytoplankters- Small zooplankters presumably cannot harvest
small phytoplankton as efficiently as large zooplankters,
nor can they handle large phytoplankters. The large zoo-
plankter Daphnia pulex became very abundant in Hemlock during
July, and a large increase in the smaller zooplankter Bosmina
was also observed. The kind of zooplankton that is present
is largely controlled by fish predation. Changes in phyto-
plankton species composition caused by zooplankton grazing
could account in part for the lag in production efficiency
relative to standing crop in Hemlock Lake, but probably not
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223
the large decrease in efficiency during late July.
The very low phytoplankton production and standing crop
values during late July and early August suggest that there
could ordinarily be a net movement of nutrient from the
hypolimnion during hypolimnetic stagnation. This suggestion
is supported by the lower plankton populations during this
period of 1970 when the hypolimnion was aerated, than during
the same period of 1969 when the hypolimnion was anoxic.
There was probably a net movement of nutrients from the
limnetic compartments into the littoral and profundal com-
partments during June and July 1970 (Figure 1)„ Aerobic
hypolimnetic conditions prevented nutrient regeneration from
the hypolimnion. Aerobic littoral muds and plant growth
prevented regeneration from the littoral zone. These net
losses would result in lower phytoplankton production.
Following the 1970 phytoplankton minima, there was a
gradual increase in standing crop, production potential and
production efficiency during the remainder of the summer.
I believe this recovery can also be attributed to changes
in nutrient levels, but by a different mechanism than
associated with the earlier plankton bloom. I believe there
were two main sources for the nutrients that sustained the
August bloom: nutrients released from the littoral compart-
ment, and nutrients released from the profundal muds.
Hutchinson (1941) found large increases in phosphorus con-
centrations associated with temperature increases. He con-
cludes, "... that this phosphorus can only have come from
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224
the marginal sediments. Such a sudden excess of the element
is undoubtedly due to an increased rate of organic decomposi-
tion in the shallowest mud and in the organic debris in the
weed beds of the lake." (Hutchinson, 1957.) If this is
true, then this same mechanism could have resulted in aerobic
nutrient regeneration from the profundal sediments. These
nutrients would have become available to the limnetic algae
from leaks in the tower, but more importantly by the in-
creased thermal destratification that occurred during August
1970. This destratification rate was accelerated as tempera-
ture differences diminished between shallow and deep water.
Increased oxygen and temperature content of the profundal
sediments should have greatly accelerated their decomposition.
These sediments are very high in incompletely decomposed
organic matter. Before aeration, decomposition was hindered
by anaerobiosis and low temperatures. Aeration increased
oxygen concentrations from zero to over 10 mg/1, and tempera-
tures from less than 5°C to 19 C. Aerobic bacteria are more
efficient decomposers and undoubtedly accelerated decomposi-
tion rates. Macrozoobenthos such as Chironomids and oli-
gochaetes undoubtedly accelerated this process by burrowing
through the sediments. Increased decomposition rates and
water circulation through the sediments may have caused
aerobic nutrient regeneration. This process was probably
greatest during late summer and probably accounts in large
part for the August plankton bloom.
-------
225
It may seem incongruous to credit nutrient depletion
for cessation of the bloom during July, and nutrient regen-
eration for the August bloom. I am guessing that the
nutrient depletion was caused by precipitation and sorption
of nutrients by the sediments. A net influx of nutrients
to the profundal sediments could have occurred during early
summer, before they were greatly heated and before microbial
and macrozoobenthic populations were established. A net
output from the profundal sediments could have occurred
later in the summer due to increased decomposition. The
latter hypothesis may be partly supported by the foam produc-
tion. Foam first became noticeable about August 1, 1970.
This coincides with the commencement of the second phyto-
plankton bloom. Although the composition and source of the
foam is unknown, it is probably a dissolved organic substance.
It could have been generated by the accelerated decomposition
of the profundal sediments. H. B. Hynes (personal communi-
cations) observed the precipitation of DOM from leaf litter.
This precipitation was promoted by shaking. Particles of
larger size were formed by longer periods of agitation.
Increased profundal decomposition could have released DOM
as well as other nutrients. Our estimates of DOM concentra-
tion are too incomplete to shed much light on this hypothesis.
Furthermore, complete concentration estimates might not pro-
vide the answer since the rates of generation and utilization
and the nature of the material is of greater importance.
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R. G. Wetzel (personal communications) feels that most of
the DOM generated may be utilized very rapidly by the
microbes, such that essentially only the refractory fraction
remains. Static measures, such as concentration, would
therefore not give an accurate picture of its role.
A minimum DOM value of 4,68 mg/1 at 15.6 m was observed
August 15, 1970. This occurred during a 4 or 5 day cessation
in foam production. Foaming began again on August 19th and
continued until we stopped aeration. A maximum DOM concen-
tration of 10.89 mg/1 was observed September 5th. If foam
is formed from DOM produced by decomposition of the profundal
sediments, then it also indicates that other nutrients are
also being generated by this decomposition. This supports
my hypothesis that the second plankton bloom was promoted by
nutrient regeneration from the profundal sediments.
If primary production is to be reduced, then it appears
essential that nutrient regeneration from the profundal
sediments be greatly reduced. Whether this regeneration is
by anaerobic decomposition, or by aerobic decomposition, the
results could be the same; but it is too early to tell.
Continued hypolimnion aeration could lead to a well-oxidized
and mineralized "crust" on the profundal sediments. This
could occur due to microbial decomposition and continuous
oxidation of the sediment surface. Once this crust is formed,
aerobic nutrient regeneration might be minimal, or at least
less than the former anaerobic nutrient regeneration. Even
on a short-term basis, a leakproof aeration tower will
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greatly reduce the impact of nutrient regeneration. These
nutrients may mostly remain in the hypolimnion during the
warm summer months and be essentially unavailable for plank-
ton growth until turnover, sometime in the fall,,
Periphyton standing crop may be taken as a measure of
attached algal net production. This is not strictly true
since many kinds of biota are included in this measurement,.
In most cases, it probably affords a simple measure of
attached algal relative production.
Long-term periphyton accumulations were significantly
greater following aeration compared to comparable non-
aerated periods. Likewise, short-term accumulations were
significantly greater except during late July and early
August 1970. During this later period, accumulation rates
were similar both years. Even long-term accumulations had
a slight slump during late July 1970= These changes in
periphyton accumulation rates indicate that both populations
were affected by the same variables, the most likely being
nutrients. It seems unlikely that herbivore grazing on
both kinds of primary producers could cause such similar
response patterns. Under some circumstances, increases in
phytoplankton production could lead to reductions in peri-
phyton production due to shading or nutrient deprivation.
Conversely, periphyton growth could limit phytoplankton by
nutrient deprivation, but not by shading. Neither event was
apparent in Hemlock Lake. This was probably due in part to
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the vertical distribution of the periphyton. It was mostly
concentrated in the upper few meters and thus not greatly
affected by shading due to dense phytoplankton populations.
Likewise, both populations seemed to "share" the nutrients
and thus responded in a similar manner.
Periphyton never appeared overly abundant on logs or
other suitable substrate. Submerged aquatic plants and algal
mats were likewise sparse. Tanner (1952) observed similar
responses at moderate fertilization rates. He also observed
a primary response by the phytoplankton. Ball (1949) and
Ball and Tanner (1951) on the other hand observed no more
than a moderate increase in plankton production at heavy
fertilization levels. Their primary response was by attached
forms and floating algal mats. Heavy fertilization led to
winterkill conditions, whereas winterkill conditions were
approached with moderate fertilization.
Zooplankton
After phytoplankton, the zooplankton appeared to give
the greatest response to artificial aeration. Daphnia pulex,
Diaphanosoma and Bosmina had especially large increases in
total numbers. Unfortunately, we do not have estimates of
their seasonal abundance patterns. Figure 68 illustrates
the hypothetical changes in limnetic zooplankton, phytoplank-
ton, Chaoborus and limiting nutrients during the summer 1970.
It also shows the major food chain relationships. D. pulex1 s
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Figure 68. Hypothetical changes in Hemlock Lake limiting
nutrient, phytoplankton, zooplankton and
Chaoborus densities during 1970. Aeration
began June 14th and continued through September
7th. Major food chain relationships are also
shown.
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C/5
C
o
o
c
o
o
Phyfroplankton
Chaoborus
Zooplankton
Limiting
Nutrients
I
June I July
Aeration begins
August
Phytoplankton
Zooplankton
Chaoborus
Phytoplankton
Zooplankton
Phytoplankton
Zooplankton
Chaoborus RBT Chaoborus—> RBT
RBT
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abundance seems related to predation by trout, phytoplankton
abundance and hypolimnion oxygen depletion. D. pulex was
scarce before aeration began. I attribute this scarcity to
predation by rainbow trout. Before aeration, D. pulex were
mostly limited to depths above 9 meters by hypolimnetic
oxygen depletion. In this zone they were especially vulner-
able. After aeration began, they inhabited the dimly lit
depths of the lake. This sanctury, in addition to increased
primary production, allowed their population to increase very
rapidly. By the second week of July they were very abundant.
About the end of July they formed ephypia and their popula-
tion appeared to decline. This reduction is associated with
the reduction in phytoplankton abundance. After early July,
D. pulex constituted the major food item of the rainbow
trout. Before then and all during 1969, the trout fed almost
exclusively on Chaoborus spp. larvae and pupae. From early
July through mid-August, Chaoborus were a secondary trout
food item. By the end of August, trout ingested D. pulex
and Ghaoborus in about equal proportions. This is especially
interesting since Chaoborus also became more abundant after
aeration began, and Chaoborus are larger than D. pulex;.
The small cladocera, Bosmina spp., and medium-sized
cladocera, Diaphenosoma spp. and the copepod Diaptomas spp.
were virtually untouched by rainbow trout at any time
although they were very abundant. These observations agree
well with those of Galbraith (1967) . He found that rainbow
trout in two Michigan lakes feed almost exclusively on
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Daphnia greater than 1.3 mm. This predation led to the near
extinction of Daphnis pulex in one lake and apparently
favored the survival of smaller species of zooplankton.
Hall (1964) demonstrated that fish predation accounted for
as much as a 25% per day loss from the Daphnia galeata
mendotae population in a southern Michigan lake. Predation
on sub-adult individuals is critical to their survival and
is probably the major factor leading to the extinction of
D. pulex and other zooplankters that mature at a larger size.
My observations conflict somewhat with Brooks and
Dodson's (1965) size efficiency hypothesis: namely, that
planktiverous fish generally decimate the larger zooplankton
species and thus favor the survival of smaller species. In
Hemlock, this hypothesis may effectively apply to the
D_. pulex, Bosmina, Diaphanosoma and Diaptomas group, but not
to p. pulex and Chaoborus. Chaoborus is much larger than
D. pulex, but D. pulex appears to be the much preferred food
item, even though Chaoborus were much more abundant after
aeration than before. Chaoborus larvae and pupae consti-
tuted over 90% by volume of the trouts' diet before aeration
began, but about only 5% to 50% after aeration. D. pulex
constituted 50% to 95% after aeration.
Chaoborus were much larger on the average before than
after aeration began. This change in average size could be
due to species shift (Table 6) and/or to increased produc-
tion rates. Increased production following aeration would
skew the size distribution, with the smaller instars
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becoming mote abundant. Even though the Chaoborus average
size decreased following aeration, they were still much
larger than D. pulex.
These findings suggest that factors other than absolute
size are directing food selection by the trout. Chaoborus
are more transparent than D. pulex and may therefore have a
smaller "effective" size. Likewise/ their particular diel
migration pattern and habit of nestling in the mud may reduce
their vulnerability. Rainbow trout very seldom feed on the
benthos. Galbraith concluded that rainbow trout feed
selectively, rather than merely straining plankton from the
water. My findings tend to substantiate his conclusion.
Cladocera and other zooplankters commonly exhibit diel
vertical migrations (Gushing, 1951; Hardy, 1956; Wynne-
Edwards, 1962). I did not try to measure their migration in
Hemlock Lake. The typical pattern is for the zooplankter to
inhabit the dimly lit depths during the day, and the surface
waters at night. Some zooplankton have just the opposite
behavior, or do not migrate according to any fixed pattern.
In our case, ID. pulex and Bosmina appear to conform to the
typical pattern. Since both collections were made during
the day, we would expect the zooplankton that migrate in the
usual pattern to be concentrated near the bottom of the lake,
or at some gradient barrier (Harder, 1968). D. pulex was
most abundant near the bottom of the lake after aeration,
whereas Bosmina was most abundant within the metalimnion,
during both collections. ]D. pulex' s distribution was not
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related to the temperature gradient, but Bosmina's distribu-
tion apparently was. The distribution of the other zoo-
plankters after aeration did not appear to be related to the
temperature gradient.
One common hypothesis to explain vertical migration is
that the zooplankton migrate to escape predation by sight
feeders. Those inhabiting the depths during the day are
less conspicuous than those in shallow water and predation
is thus reduced on the deep-living individuals. They migrate
to the surface under the protection of darkness to feed.
Their upward, movement generally coincides with sunset, while
their downward movement is initiated or timed by sunrise.
In our case, rainbow trout and Chaoborus are probably the
two most important planktivores. Of these two, the trout
are probably the most important and feed largely on the
D. pulex. Furthermore, trout feed on Chaoborus and thereby
reduce the latter's predatory impact. Since the other zoo-
plankter species were not preyed upon by the trout, there
was probably no incentive for them to migrate. They could,
therefore, inhabit the surface waters during the day and
thereby prolong their grazing time. If anything, it might
have been advantageous to disperse throughout the lake or
migrate to the depths after dark to avoid possible predation
by Chaoborus.
In El Capitan Reservoir, California, copepods responded
to artificial destratification by concentrating along the
bottom during the day (Fast, 1971) . They were formerly
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restricted within or above the metalimnion by oxygen deple-
tion. The threadfin shad (Dorosoma petenensa) was very
abundant in this lake and large zooplankters were scarce.
Small copepods constituted about 90% of the net zooplankton.
The Hemlock copepod adults did not concentrate at the bottom
after aeration. The reason for this is not clear. It could
be related to the temperature gradient, or some other factor
such as lack of significant predation on their population.
Predation pressure could be an important factor affecting
zooplankton migration behavior. It could partly explain why
a given species may migrate in one situation, but not in
another.
Any future investigation of this aeration system should
include a more thorough evaluation of the zooplankton re-
sponses. A detailed investigation was not included in this
case because I felt responses in the zoobenthos and other
components of the biota would be more important, and require
less effort to measure. Although significant changes did
occur in these other components, they were not all as rapid
or spectacular as those changes in the zooplankton.
Zoobenthos
Benthic organisms are sensitive indicators of changes
in their environment. These organisms may respond in one
or more ways depending on the nature and intensity of the
environmental change. These responses are interrelated and
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236
include changes in: standing crops, growth or metabolic
rates, species composition, species dominance, depth or
spatial distribution, survivorship, reproductive rates and
behavior. Changes in standing crop, species composition and
distributions are most easily measured. Most studies have
concentrated on these parameters and at best tried to infer
changes in the other parameters. Changes in the other para-
meters are presently difficult or impossible to measure
accurately.
Zoobenthos analyses are notoriously laborious. On the
average, each sample required over two hours of laboratory
and field work. This includes: collecting, sieving, sort-
ing from the sediments, sorting each taxa into separate
vials, counting each taxa, weighing each taxa and statistical
analysis.
Probably the single most important zoobenthic parameter
is its yearly production rate. From this you may infer how
much energy passes through this ecosystem component. This
information relates directly to how much energy was fixed
by the plants, and how much energy was made available to
higher trophic levels such as fishes. Ball (1948) found that
invertebrate production is related to fish production.
Good estimates of total zoobenthos production are im-
possible with our present knowledge and technology. Most
studies estimate zoobenthos standing crop, and possibly some
parameter of production such as adult emergence. From this
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237
they infer rates of production. A few studies attempt to
measure the productivity of a given species of zoobenthos
(Cooper, 1965; Hilsenhoff, 1967) but overlook changes in
the total benthic fauna assemblage. From the standpoint of
total energy flow, total zoobenthos production is much more
important and the production of particular species may be
relatively inconsequential. At present we cannot accurately
measure production rates of some organisms such as oligo-
chaetes or nematodes. We have methods for measuring pro-
duction of some organisms such as the midges, but the
techniques are greatly complicated by multivoltine species
populations, different generation times for each species or
even with a given species, rarity of some species and inef-
fectual sampling methods. Crayfish production is relatively
easy to measure, but requires different sampling techniques
than are generally used to measure zoobenthos standing crops.
Crayfish are omnivorous, feeding mostly on plant material
and detritus. Their trophic position is similar to other
zoobenthic organisms, but their production rates or standing
crops are seldom measured because of sampling problems.
Momot (1967) found that their production may be more than
eight times as great as the total production of other zoo-
benthos. Even for species where techniques of estimating
production are available, the techniques differ greatly.
Therefore, separate sampling programs, etc. may be necessary
to measure production of more than one taxa. This leads to
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238
exceptionally large expenditures of time and money and has
not yet been attempted.
Because of the foregoing considerations, I chose to
measure zoobenthos standing crops, and emergence rates of
certain taxa. From these data I hoped to infer in a larger
sense what changes occurred due to artificial aeration.
In fact, most of our time was devoted to the analyses of
the zoobenthos.
Between-sample variances are generally very large and
non-homogeneous. With the possible exception of the
Chaoborus larvae, there were not significant differences
between numbers or biomasses of specific taxa on any given
date. Even though trends are evident, their statistical
verification is not possible because of sample variance.
Variances were not only large in most cases, but non-
homogeneous and not a function of sample size. This problem
invalidated the use of certain powerful statistical tests.
However, I still feel we can draw some conclusions from
trends in the data, keeping in mind that their conclusions
are not statistically valid in all cases at the usual sig-
nificance levels.
Increased primary production generally increases zoo-
benthos production and standing crop. Tanner (1952) found
a large increase in Hemlock Lake1s phytoplankton and zoo-
benthos standing crops during artificial fertilization. He
added 71.5 kg of inorganic fertilizer to Hemlock during 1949,
and 56. kg during 1950. Zoobenthos total numbers (standing
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239
crop) increased 980% in 1949 compared to 1948, and 400% in
1950 compared to 1948. Chironomidae accounted in large part
for this increase. They increased 1078% the first year.
All other zoobenthos taxa also increased, but not at the
same rate. This led to changes in zoobenthos species compo-
sition. Before fertilization, Anisoptera were dominant in
terms of biomass. After aeration, Trichoptera, Ephemeroptera
and Chironomidae were more abundant. Tanner attributed
these changes to increased primary production. Secchi disc
transparency decreased from between 3.1m and 4.6 m before
fertilization to less than 1.5 m after. In this lake, secchi
measurements are representative of phytoplankton density.
Zoobenthos standing crop and production rates apparently
increased during artificial aeration of Hemlock Lake. Total
numbers of zoobenthic organisms almost doubled. Total bio-
mass decreased slightly, but not for the more important
species. Relatively unimportant, but large leeches comprised
25% of the biomass during 1969 but less than 1% during 1970.
Only one leech was captured each year. Total midge emer-
gence more than doubled during aeration, indicating increased
production rates. I attribute these increases to increased
sediment decomposition and primary production, and increased
"lebensraum." These increases are directly attributed to
artificial hypolimnion aeration.
Hemlock Lake's zoobenthos populations were mostly re-
stricted to the epilimnion, in depths less than 4.6 m during
1948-50 (Tanner, 1952). Artificial fertilization did not
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greatly affect their summer depth distribution although
metalimnion and hypolimnion oxygen concentrations were
greatly reduced and the metalimnion depth became shallower.
Depth of oxygenated water decreased to about 75% of its
former value following fertilization, and the average
metalimnion depth decreased from 6.8 m before 4.5 m after
fertilization. This increase in anoxic conditions and
shoaled metalimnion should lead to decreased living space
and increased rates of organic sedimentation. Organic matter
settling within the anaerobic zone does not readily decom-
pose and is essentially unavailable to higher trophic levels.
Artificial fertilization also increases the availability of
organic production within the epilimnion and more than com-
pensated for the potential losses from the system due to
anaerobiosis.
Artificial hypolimnion aeration not only increased
primary production, but it increased the availability of
former organic production. Increased primary production
occurred inadvertently due to technical oversights. This
response may be avoided by use of different aerator designs
and construction. Increased availability of previously
produced organic matter, on the other hand, was a primary
goal. Before aeration much of the lake was uninhabited and
underexploited by the zoobenthos due to anaerobiosis. This
accounts in part for the highly organic profundal sediments.
The peat bottom developed in part because the browsers and
decomposers could not utilize all the allochthonous and
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autochthonous inputs of organic matter. McConnel (1968)
found that alloehthonous organic litter contributes a
significant food input to Pena Blanca Lake, Arizona. Based
on an estimated ecological efficiency of 0.56%, he estimates
that this input may account for as much as 16.7% of the
yearly largemouth bass (Micropterus salmoides) harvest.
The lake1 s bottom, ana other eutrophic lake bottoms like
it, have become depositaries for organic materials and
nutrients. Anaerobiosis accelerates the rate of accumulation
and filling of the lake. After aeration, the entire lake
bottom was again accessible to aerobic decomposers and
macro-zoobenthos. Midges rapidly invaded the profundal zone
and capitalized on the rich supply of organic materials.
Certain other benthic organisms such as the mayflies and
Odonata did not invade the hypolimnion after aeration. This
may be due to low water temperatures, positive phototaxis,
preferred food concentrations, shelter, sediment composition
or some other factor.
Artificial hypolimnion aeration should lead to acceler-
ated decomposition of the profundal sediments. Increased
oxygen will favor aerobic decomposers which are more effi-
cient than anaerobic, and increased temperatures will
accelerate decomposition. Increased bacterial production and
concentration, plus their increased availability may lead to
increased production of macro-zoobenthic organisms such as
chironomidae and oligochaetes that feed on micro-organisms.
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Only four oligochaetes were collected during 1969 compared to
267 during 1970, and many of these latter worms were in the
profundal zone. Chironomids were also more abundant in the
profundal zone after aeration. Wirth et al. (1970) and
Ogborn (1966) reported increased biodegradation of organic
sediments following artificial destratification of eutrophic
reservoirs. Their observations are qualitative rather than
quantitative, however, since biodegradation of sediments is
very difficult to measure. Increased biodegradation and the
subsequent incorporation of this energy into the higher
trophic levels is a form of energy "recycling". Energy that
was formerly stored via organic compounds and lost to the
system is brought back into the system by artificial aeration.
This process may increase the overall lake productivity to a
level that cannot be sustained on a long-term basis.
Productivity may therefore decrease as the organic materials
are oxidized.
Artificial aeration may cause a net energy loss from
the profundal sediments on a short-term basis, but not on a
long-term basis. Nutrient exchanges with the sediments may
follow a similar pattern. Under anaerobic conditions, phos-
phorus and other nutrients are solubilized and a net movement
occurs from the sediment to the water (Mortimer, 1941). At
the spring and fall turnovers, these nutrients are distributed
throughout the lake. These turnovers also distribute oxygen
throughout the lake, oxidize the mud surface layers and at
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least temporarily cause a net influx of nutrients into the
mud. Fitzgerald (1970) found that aerobic muds have a con-
siderable capacity to remove phosphorous from the water by
sorption. Four tenths g (dry wt) of mud sorbed 0.05 mg
P04-P in less than 30 min. Artificial hypolimnion aeration
should not only oxidize the mud surface and increase its
sorption capacity, but it will pass water over the mud and
thereby increase contact between mud and water. Macro-
zoobenthos also increase the oxidation rate by burrowing
into the mud and pumping water through their burrows. This
will greatly increase oxidation over that expected from
diffusion and also increase biodegradation. Chironomid
larvae may burrow 50 cm or more into the sediments (Hilsen-
hoff, 1966). Chironomus riparius increased the oxygen supply
to the sediments and increased the redox potential by circu-
lating water through its burrow (Edwards, 1958). This circu-
lation is maintained to provide oxygen for respiration and
food. Oligochaetes are also active burrowers and probably
exceed that of the midges in both extent and duration.
The effect, of artificial aeration on the profundal
nutrients is open to question. Hasler (1963) found that cir-
culating water in an aquarium over mud, increased the phos-
phorus content of the water. Furthermore, the artificial
destratification of El Capitan Reservoir, California did not
appear to reduce phytoplankton primary production (Fast,
unpublished data), indicating that nutrient availability was
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not decreased. Other factors such as water volume increase
complicated this evaluation, however. The mechanism by
which phosphorus, or certain other nutrients, would be trans-
ferred from the profundal muds is unknown. It may well be
that significant quantities of nutrients may be regenerated
under both anaerobic and aerobic conditions. In the first
case regeneration is a function of redox potential. In the
latter case regeneration may be related to the amount and
kind of organic matter and its rate of decomposition. The
former process could account for the June 1970 plankton
bloom, and the latter process for the August 1970 bloom.
It is my opinion that long-term artificial aeration will
result in the net transfer of nutrients into the mud as their
energy source is depleted, and a commensurate decrease in
the primary productivity of the lake. Mechanisms affecting
nutrient transfers and rates of transfers within lakes are
presently very poorly understood. Until we understand and
evaluate rates of transfer, we will be greatly hindered in
our understanding of lake ecology.
The primary method by which the Chironomidae invaded
the hypolimnion is unknown. They probably arrived by two
methods: Dispersion of eggs and just-hatched larvae, and
active migration of the late instar larvae. Eggs are gen-
erally broadcast over the entire lake1s surface (Hilsenhoff,
1966). They may settle and concentrate in certain depth
zones (Bardach, 1955; Gleason, 1961), but their development
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at the settling site depends on environmental factors. Even
the eggs of low oxygen tolerant species such as Chironemus
decorus (Gleason, 1961) or C. plumosus (Augenfeld, 1967;
Dugdale, 1955) will not hatch in the absence of oxygen.
Newly hatched larvae of C_. plumosus are free-swimming and
strongly phototropic in the absence of a suitable substrate
(Hilsenhoff, 1966). In the presence of suitable substrate
their phototropism diminishes and they remain in the mud.
Furthermore, the growth and density of the Chironomids
depends on the quantity and quality of the food supply.
Gleason found the greatest concentrations of C. decorus in
the zone receiving the greatest concentration of fresh sedi-
ments including a high percentage of phytoplankton.
Jonasson and Kristiansen (1967) found that availability of
fresh phytoplankton and oxygen concentration were the two
most important factors affecting the growth of profundal
.C. anthracins in Lake Esrom, Denmark. Their growth was
mostly limited to times of spring and fall turnover when
phytoplankton production was maximum and oxygen plentiful.
Growth during the summer was inhibited by low oxygen levels
and poor quality of the food. Food reaching the bottom was
partly decomposed, and under low oxygen levels the larvae
either spent much time in respiratory activity, or became
lethargic. Dugdale (1955) also found that Chironomus plumosus
growth and emergence is mostly restricted to spring and fall
when profundal oxygen and temperatures are greatest and
presumably food is optimal.
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Later instar Chironomid larvae may actively migrate
to the profundal zone. Dugdale (1955) found mature larvae
swimming between the surface and bottom shortly after sunset.
Mundie (1959) found Chironomid larvae swimming at the surface
of Lac La Ronge, Saskatchewan, Canada. Early and late in-
stars were found mostly over 5 m of water or more and con-
sisted of 60% Chironomini, 25% Tanypodinae and 15% Ortho-
cladinae. Active migration of Chironomid larvae could lead
to a rapid invasion of a new habitat. There is some evidence
that late instar larvae invaded Hemlock's profundal zone soon
after aeration began. Procladius denticulatus emerged from
between 16 and 18.6 m during the first week of July 1970,
after two weeks of aeration (Figure 50)„ Their emergence
during 1969 was restricted to 12 m or less. Tanypus spp.
emerged from between 8 and 12 m by mid-July 1970 and from
between 16 and 18.6 m during August. During 1969 Tanvpus
emergence was restricted to less than 4 m. Both these spec-
ies are predaceous, and migratory by nature (Miller, 1941).
Miller found that Procladius emerged from all depths of
Costello Lake, Ontario at about the same time during June
and July. He suggests this syncronous emergence is due to
larvae moving back and forth through the metalimnion in
search of prey. Larval development is partly related to
temperature. Larvae moving back and forth would thereby be
exposed to about the same average temperatures, develop at
about the same rate and emerge at about the same time. Other
non-predaceous midges emerged from the profundal zone, but
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not as soon as Procladius. Third and fourth instar larvae
of Ghironomus tentans were observed below 18 m during July
even though their adult form was never collected, even in
shallow water.
Hemlock1s zoobenthos standing crop is impoverished con-
sidering the level of primary production in this lake.
motal numbers and biomass collected during 1969 were 2,396
and 2.41360 gms, respectively (Table 5). Although Section
Four Lake appears much less productive, total numbers and
biomass collected during 1969 were 17,609 and 11.09227 gms.
Before fertilization, Tanner (1951) found averages of 83.5
organism/m2 in Section Four. During this same period in
Hemlock, he found only 48.5 organisms/m2. The reasons for
this impoverishment are not obvious, but are probably due in
part to fish predation and the nature of the substrate. Fish
predation can greatly limit the zoobenthos standing crop
(Ball and Hayne, 1952; Wilkins, 1952). Tanner (1951) observed
a sharp decrease in the zoobenthos standing crop during the
second year of fertilization of Hemlock and three other
neighboring lakes. He attributes these decreases to enhanced
survival of minnows during the first year of fertilization.
The bluntnose minnow and redside dace were very abundant in
Hemlock during 1969 and 1970. They were restricted to
shallow depths, generally less than 4 meters, and mostly near
shore. I concur with Tanner's conclusion that minnow preda-
tion on the zoobenthos greatly reduces zoobenthos standing
crop in shallow water but not in deep water after aeration.
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Some other factor is more important in the profundal zone.
The small profundal standing crop after aeration is partly
due to migration rates. These apparently are slow. We
witnessed a gradual increase during the summer, but profundal
standing crop probably did not reach its maximum value by
September 1970. Even with complete destratification of
El Capitan Reservoir, California profundal standing crop
did not appear to maximize until the second summer of
destratification (Fast, unpublished data). If we had started
aeration much sooner during 1970, it might have increased
more rapidly. Many species reproduce and become established
during May and early June. The hypolimnion was anoxic dur-
ing this period, and the organisms were probably well-
established in shallower depths before we began aeration
June 14th.
The nature of the sediments may be another reason for
the general impoverishment of Hemlock's zoobenthos standing
crop, and the slow profundal invasion rate. Bog lakes, or
lakes with abundant peat deposits, typically have impover-
ished zoobenthos populations. Hilsenhoff and Narf (1968)
correlated 14 physical-chemical parameters with standing
crops of 13 species of midges, Ostracoda and Copepoda in the
profundal zone of 14 Wisconsin lakes. They found significant
negative correlations between organic matter in the mud and
standing crops of copepoda, ostracoda, Palpomyia and
Chironomus plumosus. The reasons for this are unclear.
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249
In theory, this mass of organic matter should provide an
abundant food supply. In practice, it seems to inhibit
zoobenthic organisms. Three likely explanations are:
(].) The rich organic matter has a high carbon dioxide con-
tent which inhibits oxygen utilization by the midges. High
carbon dioxide concentration sharply inhibits oxygen utiliza-
tion by fishes (Black et al., 1954). This may also apply
to certain zoobenthic species. Midges collected from an-
oxic hypolimnions are typically relaxed and extended, which
is a sign of respiratory distress; (2) The accumulated plant
material possesses some inhibitory or antibiotic substance
that either directly affects the macro-zoobenthos or bacteria
used as food by the macro-zoobenthos. The plant detritus
accumulation is evidence that bacterial decomposition is not
optimum. This may be due to low nutritional value of the
detritus, or due to inhibitory substances. Hilsenhoff and
Narf also found a highly significant negative correlation
between organic matter in the mud and pH of the mud. Highly
organic muds had low pH, some being below 6.0. A highly
significant correlation existed between organic matter in
the mud and water content of the mud, and a highly significant
positive correlation between pH of the mud and pH of the
water. Low pH may be due to carbonic acid, humic acid or
some other acid associated with the organic matter. Low pH
in itself could deleteriously affect zoobenthos; and/or
(3) highly organic bottoms are often flocculant. Midge are
positively thigmotactic, requiring contact with a substrate.
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250
The high water content may not provide adequate contact for
the midges or facilitate tube building.
Differences in average Chironomid larval size at dif-
ferent depths was most pronounced. Shallow water larvae
were much smaller than deep-water larvae. On September 4,
1970, only 5% of numbers of Chironomid larvae were found
below 14.5 m, but these comprised over 15% of the biomass
(Figures 43 and 44). This condition is undoubtedly a result
of different species complexes at different depths. This
gradation in size from small species in shallow water to
large species in deep water is often found in moderately and
highly productive lakes (Brundin, 1951 and 1953). Large
larvae can better cope with oxygen microstratification at
the mud-water interface because of their greater capacity
for circulating water. This circulation disrupts the micro-
stratification and provides oxygen to the larvae. Further-
more, large larvae of the Chironomus type contain hemoglobin
and can withstand anaerobiosis for extended periods should
the oxygen microstratification lead to more general hypo-
limnion stagnation.
Although oxygen microstratification was not investigated,
it seems unlikely that this developed to any appreciable
extent after aeration began. Water currents, especially near
the aerator should have kept it to a minimum. If this is
true, then the carbon dioxide and BOD of the sediments could
have been the main factor. In either case, large larvae
would be favored because of their greater respiratory activities
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251
The extent of oxygen depletion greatly affects the kinds
of midges found in a lake. Indeed, lakes may be classified
according to their midge populations (Lenz, 1925, 1927;
Lundbeck, 1926, 1936; Brundin, 1953). Unproductive lakes are
characterized by Tanytarsus midges. These midges are small
and lack hemoglobin. They are very intolerant to low oxygen
concentrations, and are apparently better adapted for survival
in oxygen-rich lakes than are Chironomus midges. Chironomus
midges are typical of rich lakes that often develop oxygen
deficits within the hypolimnion. Bryce (1965) found differ-
ent species complexes in 17 shallow English acid peat pools.
Nine pools were dominated by Tanytarsus, while seven other
pools were dominated by Chironomus. One pool was intermediate
with about equal proportions of both species. All but one
pool was less than one meter deep. pH ranged between 4.0
and 6.0. Bryce did not indicate what factors seem to be
responsible for the species complexes.
Interestingly enough, oxygen concentration of the water
does not appear related to organic content of the sediments.
Hilsenhoff and Narf (1968) found no correlation. Hargrove
(1969) also found no significant relationship between these
variables. He found that sediment oxygen consumption is
by the microbiota and that the consumption rate is tempera-
ture-dependent. The rate was also accelerated by stirring
when oxygen concentrations fell below 6,0 mg/1.
Hemlock Lake's position on the Tanytarsus-Chironomus
scale is unclear. Tanytarsus accounted for 27% of the
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252
emergence during 1969, but only 8% during 1970. Most of
the other species, and certainly Chaoborus, are indicative
of rich Chironomus type lake. Indeed, different analyses
of the water indicate oxygen-limited conditions in the
profundal zone and high BOD of the sediments at all depths.
The true picture may be obscured by incomplete data. We
probably missed much of the total emergence because of our
sampling schedule.
Chaoborus are often categorized as benthic organisms,
but at other times as planktonic. In fact, they are both.
The first instar larvae are strictly planktonic and typically
inhabit the lower epilimnion and metalimnion. They are non-
migratory- Second and third instars are also planktonic
and exhibit weak diel migration. Some third instar larvae
inhabit the profundal muds. Fourth instar larvae have a
definite diel migration pattern (Teraguchi and Northcote,
1966; Roth, 1968). Typically they nestle in the profundal
muds during the day and migrate to near the surface after
dusk to feed. About dawn they descend into the mud again.
This migration is apparently temperature dependent. They
do not migrate during the winter. During early spring a
small percentage migrate, but during mid-summer migration is
maximal. However, even at that time a certain percentage
of the population may remain in the mud at night. Laboratory
tests indicate this diurnal rhythm is endogenous, but partly
controlled by light and temperature (LaRow, 1968).
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253
The diurnal activity pattern persisted as long as 10 days
under total darkness in the laboratory-
Although Chaoborus larvae are relatively insensitive to
low oxygen concentrations, they will avoid highly anoxic
conditions such as those found in the monimolimnion of
Hemlock during 1969. They are often found below the level
of oxygen depletion, during summer and winter, and are ap-
parently unaffected by winterkill conditions (Northcote,
1964). During the summer, fourth instar larvae may remain
in the deep water during the day rather than nestle in the
deep profundal muds (Teraguchi and Northcote, 1966) , presum-
ably because of highly anoxic conditions. In other lakes no
fourth instar larvae are found in the water during the day
(Roth, 1968) .
Their total distribution in Hemlock Lake is not known
since we did not adequately sample their planktonic distri-
bution. It is likely that a larger percentage of the fourth
instar larvae remained in the water during the summer 1969,
compared to 1970. Dredge and emergence trap samples indicate
relatively few larvae below 14.5 m during 1969. Some of
those supposedly captured below 14 m may actually have been
entrapped by the samplers as they were lowered. In any
event, Chaoborus emergence was restricted to 4 m or less
during 1969, but extended to all depths during 1970-
If fourth instar larvae were more planktonic during 1969
than during 1970, we may have underestimated their relative
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254
abundance during 1969. Benthic samples indicate a much
larger population during 1970. Emergence data also indicates
a much larger population during 1970. Chaoborus constituted
11% of the total midge emergence during 1969, but 28% during
1970. Their total numbers increased from 47 during 1969
to 296 during 1970. These data indicate a significant in-
crease in Chaoborus standing crop and production rate during
aeration.
Increased Chaoborus production may be related to in-
creased food, less severe environmental conditions, and re-
duced predation by fish. Chaoborus' preferred prey are
copepods, but they also feed on cladocera, chironomid larvae,
mosquitoes and other Chaoborus larvae (Stahl, 1966).
Increased densities occurred in all these categories (except
mosquitoes) during artificial aeration. Although they can
tolerate anoxic conditions, they probably are less restricted
under aerobic conditions. Under aerobic conditions a larger
percentage may have nestled in the mud and thus reduced
their vulnerability to predation. There was a large increase
in the number of larvae found below 14 m after aeration.
Over 90% of the larvae were found below 14 m during late
August and September 1970, compared to less than 20% during
1959 (Figures 56 and 57). As noted, Chaoborus avoid highly
anoxic conditions. Highly anoxic conditions were eliminated
by aeration during 1970. Chaoborus were by far the most
important trout food item before aeration began. After
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255
aeration, trput fed more on Daphnia pulex. This reduced
predation rate undoubtedly contributed to their population
increase.
The shift in Chaoborus species composition from C_.
flavicans to C. punctipennis is dramatic. C. flavicans is
much larger than £. punctipennis and was the only Chaoborus
adult found during 1969. Almost twice as many C_. flavicans
emerged during 1970 compared to 1969, but almost three times
as many £. punctipennis emerged during 1970 compared to
C_. flavicans. Some environmental change could have favored
this shift. C_. punctipennis, being smaller, may have fed
more efficiently on the small zooplankters such as Bosmina
that increased significantly during aeration.
Crayfish
Qrconectes virilis depth distributions during August
1969 differ markedly from those described by Momot (1969)
and Momot and Gowing (19¥0) for nearby lakes, and from the
August 1969 Section Four crayfish distributions. In these
other lakes, the females were found in deeper water than the
males. In Hemlock Lake, the females were more abundant in
shallow water. Momot (1967) proposed that the females'
migration to deeper water is associated with their sexual
maturation. Low temperatures and light intensity are associ-
ated with sexual maturation. It is difficult to draw definite
conclusions from my data because of small sample sizes and
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256
lack of information on age distribution. Yearlings appar-
ently respond differently than mature animals. However,
these data indicate that there is an avoidance of the males
by the females. The males have moved into deeper water,
possibly causing the females to move into shallow water.
The females apparently avoided moving into still deeper
water than the males because of the low temperatures. Less
than 10% of the crayfish were found below 6 m at temperatures
less than 13°C. Momot (1967) found that 0. virilis also
avoided temperatures of less than 13 C. In Section Four
Lake, 10 C was the lowermost temperature limit.
Depth distribution changes during 1970 are most diffi-
cult to explain. Before aeration began, their distributions
were as expected. Over 95% were in 0 to 4 m depth at
temperatures above 10 C. This distribution is similar to
those found in the other lakes at this time of the year.
After aeration began, oxygen concentration did not limit
their maximum depth distribution nor did temperature seem
to limit them to shallow depths. Hypolimnetic temperatures
warmed to over 16°C by August 20, 1970, but crayfish were
not found below 10 m. Some factor other than oxygen or
temperature seemed to limit their depth distribution. After
the lake destratified in late August, they distributed to
the bottom. This indicates that the inhibitory factor was
either distributed evenly throughout the lake, or eliminated
by destratification. There are also no obvious differences
in distribution between males and females during 1970.
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257
Rainbow Trout
Rainbow trout were restricted to levels above 8 meters
during 1969 by hypolimnion stagnation. Their upper limit was
related to the 21°C isotherm. Over 90% of the fish were
captured between these two restraints. Before aeration began
during 1970, these fish were again restricted to shallow
water by anoxia, but quickly extended their depth distribution
as the anoxia was eliminated. An oxygen deficit as well as
other chemical gradients are associated with anoxia. Hydro-
gen sulfide, carbon dioxide, ammonia and other detrimental
substances are present in high concentrations below the oxygen
depletion depth. The trout undoubtedly reacted to these
factors and others in avoiding the anoxic water. Black et al.
(1954) have shown that carbon dioxide above certain levels
sharply inhibits oxygen utilization by fishes. The carbon
dioxide concentration at which this inhibition becomes most
apparent is species specific. Fish adapted to low oxygen
levels, such as the brown bullhead (Ictalurus nebulosus) are
not as readily affected by carbon dioxide.
The depth preferences of the 1969 stocked trout are not
well defined after mid-July 1970. They seem to prefer the
bottom during late July and early August 1970, and then dis-
tribute throughout the lake after late August. However, this
pattern may be an artifact of small sample size.
The results of the acclimatization tests during 1970
are puzzling. The rainbow trout distributed throughout the
lake very soon after release and did not show preferences
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258
based on their acclimatization history. While these fish
were held in the cages they should have been acclimating to
several factors. These factors include temperature, light,
pressure, oxygen, carbon dioxide, and possibly scent.
Intuitively I expected temperature, light, pressure and
scent to be the most important factors. Many people have
demonstrated species specific temperature preferences in
both laboratory and field tests. Although a given species
will occupy a wide range of temperatures, it generally will
prefer and seek a given temperature. Bardach and Bjorklund
(1957) found that fish could detect temperature changes as
low as 0.05°C/min. Changes of 0.2°C/hr. were apparently not
detected. They trained fish to respond to temperature
changes and thereby demonstrated that fish can detect smaller
changes than they generally respond to. Various researchers
have found that light (Sullivan and Fisher, 1953; Brett,
1952; Pearson, 1952), feeding activity (Brett, 1952; Pearson,
1952) and social behavior (Pearson, 1952) can interfere with
temperature selection. Hasler (1966) clearly demonstrates
fishes ability to detect and respond to scents. Pressure
acclimation can also severely limit short-term vertical
movement of fish responding to temperature differences.
Phyoclists, fish with closed swimbladders, are especially
restricted against rapid upward movement above their equi-
librium depth. Jones (1952) estimates it would take Perch
(Perca flavescens) 50 hours to adjust to a 90% hydrostatic
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259
pressure reduction. Downward movement would be less re-
stricted. Physostomes, fish with an open duct connecting
the swimbladder with the alimentary canal, are much less
restricted in their vertical movements. The expanding air
associated with rapid ascent can be readily vented through
the mouth. The re-secretion of air following descent is a
slow process however (Ledebur, 1937). Hodgson and Richardson
(1949) report the ascent of prichards from 15 to 7 meters in
3 minutes. Prichards are marine Physostomes. Northcote
et al. (1964) observed marked diel migrations of sockeye
salmon (Oncorhvnchus nerka) and peamouth chub (Mylocheilus
caurinus) in a British Columbia lake. The fish migrated
over 10 meters and through a 4°C to 6°C temperature differ-
ence in less than 6 hours. Their estimates of fish depth
distribution from gill nets agreed well with their echo
sounding observations. Although they could not document
explanations for these migrations, food selection appears to
be an important factor.
Rainbow trout are physostomes and presumably capable
of rapid vertical movements. This ability should allow them
to rapidly respond to vertical temperature differences or
other factors affecting their depth distribution. This
ability allowed them to rapidly disperse throughout Hemlock
lake soon after release. Unfortunately we have no estimate
of their diel depth distribution. I would expect their diel
distribution to agree closely with the diel distributions of
their prey.
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260
Garside and Tait (1958) and Ferguson (1958) demon-
strated by laboratory tests that temperature alone can
determine the depth distribution of fishes. Their tempera-
ture preference is related to their recent thermal history
as well as genetically defined factors. Fry (1947) defines
their preferred temperature, or short-term preference, as
the "region, in an infinite range of temperature, at which
a given population will congregate with more or less pre-
cision." This short-term preference is related to their
recent thermal history. He also defines the final prefer-
endum temperature as "a temperature around which individuals
will ultimately congregate, regardless of their thermal ex-
perience before being placed in the gradient." The final
preferendum temperature, or long-term preferred temperature,
is largely species specific, although the final preferendum
temperature varies greatly with size and age for a given
species. Younger fish usually have a higher final prefer-
endum temperature. The final preferendum temperature is
usually measured as the point at which the preferred tempera-
ture equals the acclimation temperature. Fish acclimated
above the final preferendum will generally prefer cooler
temperatures, whereas those acclimated below the final prefer-
endum will generally prefer warmer temperatures. Ferguson
(1958) observes that the laboratory determined final prefer-
endum temperature is usually greater than the temperature
selected by most fish species in nature. He attributes
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261
these discrepancies to use of younger fish in the laboratory
studies than were observed in nature. Fry (1937) found in
nature that the young cisco (Leucichthys artedi), tended
to remain in the warm shallow water, while the older fish
moved into deep cooler water. The selected temperature in
nature can also be altered by physical or chemical limita-
tions such as oxygen depletion (Bendy, 1946, 1948; Botges,
1950) .
The degree of thermal gradient may also be an important
factor affecting response to temperature differences.
Although this has not been well documented for fish, Beeton
(1960) found that vertically migrating Lake Michigan Mysis
relica would not penetrate a thermal gradient of 1.67 C to
2.0°C/m, but some would penetrate a 0.66°C to 0.94°C/m
gradient. The latter individuals soon returned below the
gradient, however. During isothermal periods they would
migrate uninterrupted from the bottom to the surface.
Whether this response is due to preferred temperature,
temperature gradient or density discontinuity, is unclear.
Harder (1968) found-many marine zooplankters reacted to dis-
continuities in stratified laboratory cylinders. These
discontinuities included density gradients due to temperature,
salinity and density without temperature or salinity grad-
ients. Some organisms react more to these discontinuities
than others. Littorina spp. veliger larvae were distributed
almost entirely at the discontinuity, while young mysids did
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262
not significantly change their distribution after a discon-
tinuity was imposed. The mysids1 negative phototaxis prob-
ably outweighed their possible positive response to the
discontinuity-
Garside and Tait (1958) , using 10 to 15 cm fish in
laboratory tanks, observed a 13 C final preferendum for rain-
bow trout. This does not agree with the rainbow trout
temperature selections found by Horak and Tanner (1964) in
Horsetooth Reservoir, Colorado. There the trout were most
numerous in 18.9 to 21.1 C water. Although they ranged
throughout the reservoir, in temperatures from 7.7 to over
22 C, over 93 percent were found in or above the metalimnion
in temperatures above 10 C. Hypolimnetic oxygen, pH, carbon
dioxide or bicarbonate alkalinity did not appear limiting.
These trout were larger than those used by Garside and Tait,
ranging in length from 15.7 to 62.5 cm. Larger fish usually
prefer cooler temperatures. Although many factors undoubtedly
affected their depth distribution, Horak and Tanner felt that
food selection was a major factor affecting the trout depth
distribution. Although copepods were more numerically
abundant than cladocera (54.5% to 45.5%), the trout fed
selectively on cladocera. The cladocera were mostly distri-
buted above the thermoclirie.
Hemlock Lake rainbow trout fed almost exclusively on
Chaoborus larvae and pupae and D. pulex. Both organisms are
known to exhibit diel vertical migrations. They inhabit the
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263
deep, dimly lit regions of the lake during the day, and the
surface waters at night. They are presumably most vulnerable
to trout predation during dawn and dusk, the periods of their
vertical migrations.
The vertical migration of the trout as response to the
vertical migration of their prey could largely explain the
widespread distribution of the trout after aeration began.
Burbige (1969) found that the American smelt (Osmerus mordax)
underwent a vertical migration within the hypolimnion in
response to their major prey species, Chaoborus. Although
Chaoborus migrated from the bottom of the lake to the surface,
the smelt did not penetrate the thermocline. Galligan (1962)
found that lake trout (Salvelinus namaycush) greatly altered
their depth distribution in response to their prey's depth
distribution. Normally the trout preferred 24 to 31 meter
depths, but invaded 6 to 24 meter depths in response to spawn-
ing alewife (Alosa pseudoharengus) on which they preyed
heavily. It is my conclusion that as long as certain physical,
chemical, or behavior factors do not absolutely limit the
distribution of fishes, then the fishes will distribute in
response to their prey's distribution.
We can define adequate oxygen and temperature conditions
for trout as oxygen concentrations above 5.0 mg/1 and
temperatures less than 24°C. Trout can withstand tempera-
tures as great as 26.7 C for a few days, but prolonged
temperatures above 24°C lead to high mortality (Eipper, 1960).
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264
Likewise, they may also withstand oxygen concentrations of
less than 5.0 mg/1 at low temperatures, but 5.0 mg/1 is
generally considered a safe lower limit. Within these con-
straints we can clearly see that artificial hypolimnion
aeration greatly increased the "lebensraum" available to
the rainbow trout (Figure 69). During early August 1969,
24% of the lake had adequate oxygen, but the temperature was
too great. Forty-one percent had adequate temperature, but
the oxygen was too low. Thirty-five percent had both ade-
quate oxygen and temperature. During the same period 1970,
over 97% of the lake had both adequate oxygen and temperature
due to artificial hypolimnion aeration. If the aeration tower
had operated as intended, the surface water would still be
too warm, but in our case, the surface waters were apparently
cooled slightly because of the faulty design and construc-
tion. In many lakes, especially in the American southwest,
the portion of the lake with adequate oxygen and temperature
approaches zero due to very high surface temperatures and
hypolimnetic oxygen depletion within and below the metalim-
nion (Fast, 1968; Fast and St. Amant, in preparation) . Many
of these lakes are eutrophic and owe their richness in large
part to the high nutrient content of their basins, water-
sheds and water sources. This high nutrient content causes
plankton blooms, hypolimnetic oxygen depletion and many
other conditions deleterious to water management. Because of
water shortages, these lakes are managed intensively for
-------
Figure 69. Hemlock Lake oxygen and temperature conditions for trout during
August 1969 and August 1970. Adequate temperature is tempera-
ture less than 24 C, and adequate oxygen is values of 5 mg/1 or
more.
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^•^:-}i\\-:'< Adequate
^:M£.f£ Temperature
Adequate Oxygen
And Temperature
Adequate
Oxygen
70 60 50 40 30 20 10
10 20 30 40 50 60 70
Distance From Aerator (m)
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267
multiple uses. Many water managers have attempted to allevi-
ate the deleterious eutrophic conditions by artificially
destratifying their lakes with compressed air. Artificial
destratification of eutrophic lakes is a useful fisheries
management technique (Fast, 1968; 1971). It increases the
habitat and food available to many fishes. It reduces the
probability of oxygen depletion by algal decay and respira-
tion. It is most widely used to improve domestic water
quality. With continued complete mixing, it also increases
the heat budget and eliminates the deep, cold hypolimnetic
water. This water is generally anoxic. While artificial
destratification eliminates this anoxia, it also greatly
increases the bottom temperature. After continued destratifi-
cation, the entire lake is about the same temperature as the
surface before destratification began. These reservoirs,
whether destratified or not, presently support year-round
warmwater fisheries, but coldwater fisheries only when sur-
face temperatures are less than 24 C. Development of such
reservoirs for year-round coldwater fisheries will greatly
increase their fisheries potential. High angler demand for
trout coupled with the usual location of such reservoirs
near populous areas would result in manyfold increases in
angler patronage.
Presently, the only known method of creating suitable
coldwater habitat in an eutrophic lake is by artificial
hypolimnion aeration. This system of aeration can result in
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268
adequate oxygen values throughout the lake without intoler-
able increases in hypolimnion temperatures. Oxygen can be
added to the hypolimnion without mixing it with, or heating
epilimnetic or metalimnetic water. This may be accomplished
through modifications of my basic hypolimnion aerator
design, or use of other designs.
Artificial destratification of oligotrophic lakes may
result in the elimination of the coldwater species. The
oxygen concentration may be little affected, but the bottom
temperature will be greatly increased. Although destratifi-
cation will not greatly affect water quality, it may be con-
ducted to reduce evaporation rates. Annual evaporation may
be reduced from 4 to 10% (Koberg, 1964; Koberg and Ford,
1965; and personal communication). From the fisheries stand-
point, artificial destratification of oligotrophic lakes
can be deleterious. An exception is when stratified surface
temperatures normally are not limiting to the cold water
biota. In this case destratification may increase fish food
and trout production.
After artificial hypolimnion aeration is initiated, a
system for stocking coldwater fish into the cold, aerated
hypolimnion must be developed. Stocking the trout at the
lake's surface, in the usual manner, will cause mortality
due to thermal shock. Sharpe (1961) transported rainbow
trout in plastic bags to the hypolimnion of a Tennessee
reservoir. Some of these fish made short excursions towards
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269
the surface, but soon returned to the hypolimnion. Trout
stocked at the surface were greatly distressed and dis-
oriented; many died. A more appropriate method of stocking
could be devised. A simple method would use a length of
irrigation pipe extending from the shore, along the bottom
into the hypolimnion. Water could be pumped from the hypo-
limnion through a separate hose and used to flush the fish
into the hypolimnion. Fish could then be stocked directly
into the pipe from a hatchery truck.
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SECTION FOUR LAKE
Destratification System
The Section Four Lake artificial destratification system
was very similar to the diffuse aerator described by Fast
(1968). A 38 mm I.D. plastic pipe conducted air from the
rim of the lake's basin to the deepest point in the lake
(Figures 70 and 71) . The distal 19 meters were perforated
with 48 holes. The holes were 3.2 mm in diameter and located
at 12 sites. Four holes were located at each site, posi-
tioned at 90 intervals around the pipe. The hole sites were
unevenly distributed along the 19 meter section. From the
distal end, they were positioned in meters as follows: 0.0,
0.6, 1.2, 2.5, 3.7, 4.9, 7.4, 9.8, 12.9, 16.0, and 19.0.
The air line portion leading from the compressor to the shore
was covered with soil to prevent damage by porcupines.
Porcupines chewed the tires on the compressors and the plywood
decks on the barges at both lakes, but were not a problem
after we began aerating. The sound of the compressors appar-
ently kept them away. The air line portion in the lake was
anchored with several cement blocks. These were tied
directly to the air line.
270
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Figure 70. Cross-sectional view of Section Four diffuse aeration
system. The air was released from the last 10 meters of
pipe, situated near the deepest point in the lake..
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Compressor
Cement block Anchors
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Figure 71. View of Section Four Lake taken from the basin rim. tj
Rising air and water is seen near the center of the lake. ^
(Photo by author.)
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275
Compressor. We used a Jenbach JW78 diesel compressor. It
was always run at maximum speed and delivered 78 cfm at 100
psi. It was fueled with five gallons of diesel each day and
ran about five hours. On a few occasions it was fueled two
or three times on a given day.
Compressor Operation. Aeration began June 16, 1970.
Destratification was rapid but the bottom 3-4 meters were
not being circulated. Two factors contributed to this situa-
tion: (1) The end of the air line was not adequately
anchored; the air line bowed up and was four to six meters
off the bottom. Most of the air escaped at the top of the
bow due to reduced hydrostatic pressure, and (2) The air
was not released over the deepest point in the lake due to
the air line bow. Knoppert et al. (1970) produced a similar
result by purposely positioning their air line at an inter-
mediate depth. Their lake was totally mixed at depth
shallower than their air release, but not deeper.
On June 20, 1970, I added additional anchors to the air
line using SCUBA. Thereafter the air release was more uni-
form along the perforated section, and extended to the
deepest point in the lake. The entire lake was then circu-
lated.
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RESULTS
Physical-Chemical Parameters
Temperature and Oxygen. Section Four Lake stratified nor-
mally during 1969. By early June, a thermal gradient
extended from 3.5 to 12 meters (Figure 72). Strictly speak-
ing (i.e., a thermal gradient of l°C/m) the metalimnion
extended from 3.5 to 7.5 meters. This definition seems
somewhat arbitrary in this case since the gradient decreased
uniformly with depth. Although the gradient between 7.5 and
12 meters was less than 1°C, it appears to represent stable
stratification. Temperatures ranged from 7°C at the bottom
to 16 C at the surface. During this same period oxygen
concentrations were 8.7 mg/1 at the surface and 9.5 mg/1 at
the bottom (Figure 73). Metalimnion oxygen maxima occurred
during the summer 1969, but were not as pronounced as in
Hemlock Lake (Figure 36) . As the summer progressed, the
thermal gradient region increased in depth. By late August
it extended from 5.0 to 14.5 meters. The isotherms are
nearly parallel during the entire summer. Maximum surface
temperatures of over 23°C were observed during mid-July and
again during mid-August. These surface temperature maxima
coincide with maxima for Hemlock Lake. Minimum bottom
276
-------
to
Figure 72. Section Four isotherms during the summer, 1969, before
-------
July
10 20
10
August
20
-------
279
Figure 73. Section Four selected oxygen profiles during
the summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970.
-------
Oxygen (mg/|)
a
a>
O
03690369
n i i 1 i i 1 i i ii i i 1 i i 1 t i 1 i i
-
-
-
-
5-
-
10-
_
-
15-
-
5-
10-
15-
/
j
1970 f
___1969
VI-7
J
/I
\
\
,
/
1
i
, VI-18
1
-1
\
1
I
VII-30!
v
X^
i
|
1
I
'
1
1
f /
VII-30
\ "X^^
\ \
V |
\
\
\
I
\
1
1
VIM,
1
/
/ VII-30
\ /
y
j.
1
/
fjX-2
\ V.
IX-2\ ;'
1
/ 1
( 1
\ I
I /
L'
s 1
/ 1
-------
281
temperatures were stable, but increased about 1 C during
the summer 1969 (Figure 74). Average and surface oxygen
concentrations varied considerably during the summer 1969,
but were always above 6.0 mg/1 (Figure 75). Bottom oxygen
concentrations decreased during the summer 1969 but were
always above 4.0 mg/1.
Before aeration began during June 1970, the thermal
regime was similar to that of June 1969 (Figure 75).
Temperatures ranged from 21 C at the surface to 5.5 C at
the bottom. The thermal profiles were similar although the
surface was warmer, and the bottom slightly cooler during
1970. Oxygen values were likewise very similar to 1969
values. Oxygen concentrations ranged from 8.0 mg/1 at the
bottom to 9.2 mg/1 at the surface (Figures 73 and 74).
Artificial air injection began June 16, 1970 and caused
immediate and significant changes in the temperature regime
(Figures 76 and 77) . After four days of aeration the surface
temperature decreased from 21°C to 14 C and much of the lake
was isothermal. By July 1st, the lake was nearly isothermal
at 16 C except for the upper meter which approached 25 C.
By July 10th the entire lake was isothermal at 18.5°C. The
average temperature increased gradually and reached a 23.3 C
maximum, compared to a 19.7°C maximum average during 1969.
Surface temperatures were not greatly altered by artificial
elestratification, but bottom temperatures reached a 23.3 C
maximum during 1970, compared to 8°C during 1969. With
-------
Figure 74. Section Four maximum, minimum and average temperatures ( C)
during the summers 1969 and 1970. Aeration occurred between
June 16 and September 7, 1970.
-------
27-
244
Section Four
1969
u
20--
5 16-+
0)
a
£
1970
1 10 20 1 10 20 1 10 20 11 10 20 1 10 20 1 10 20 1
June July August June July August
-------
Figure 75. Section Four top, bottom and average oxygen concentrations oo
during the summers 1969 and 1970. Aeration occurred between *"
June 16 and September 7, 1970.
-------
10.0-
O)
£8.0-
c
0)
O)
X
O
6.0-
4.0-
1969
MEAN
BOTTOM
10 20 1 10 20 1 10 20
June
T~
1
1970
10 20 1 10 20 1 10 20 1
July August June
July
August
-------
286
Figure 76. Section Four selected temperature profiles
during the summers 1969 and 1970. Aeration
occurred between June 16 and September 7,
1970.
-------
Temperature (°C)
0-
12H
0)
Q
8 12 16 20 24 4 8 12 16 20
_j I I i i I I i i i
7-29-70
9-2-69
/
/
/
/
9-2-70
-------
Figure 77. Section Four isotherms during the summer 1970. Aeration r>o
occurred between June 16th and September 7th. Isotherms °°
are in C.
-------
June
10 20
July
10 20
August
1 10 20
0-
i Mijm=MJjiLU4-f-niiifim 11 inuiii 11 in
-------
290
continuous aeration, the entire lake became about as warm
as the surface waters were during stratified periods (Figure
74).
Thermal stability was 7x108 kg-m on June 10, 1970,
compared to 5x108 kg-m the previous year on this date
(Figure 78). After 4 days of artificial aeration stability
neared zero. It was always near zero after July 29, 1970,
whereas it reached a maximum value of over 12x10® kg-m on
August 20, 1969. These changes reflect the degree of strati-
fication and indicate the lake was nearly isothermal during
most of 1970.
Oxygen values were more uniform after aeration began.
Surface values were about the same, but bottom values were
always above 7.0 mg/1 compared to 4,5 mg/1 during 1969.
Oxygen maxima at intermediate depths were not present during
1970, and the oxygen profiles were nearly vertical.
pH, Alkalinity and Conductivity. During 1969, pH values
were variable, but always above 7.5 (Figure 79). Bottom
values were always lower than surface values, but on July
14, 1969 the average pH was higher than the surface pH. The
average pH increased from 7.7 on July 14, 1969 to 8.0 by
September 1969. After aeration began the pH was very uni-
form throughout the lake and nearly constant at 7.9 through-
out the summer 1970.
Alkalinity was quite consistent during 1969. Bottom
values averaged about 190 mg/1 and surface values about 170
mg/1 (Figure 80). After aeration began alkalinity was nearly
-------
291
Figure 78. Section Four stability values during the
summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970.
-------
£
Q>
10
June
August
-------
Figure 79. Section Four's bottom, top and average pH" values during
the summers 1969 and 1970. Aeration occurred between
June 16 and September 7, 1970.
-------
8.2-
X
Q,
7.4-
7.0-
1969
TOP
/ MEAN
BOTTOM
1—i—I
1970
—i—'—|—i—i—i—i—i—|—i 1-
10 20 1 10 20 1
June July
10 20 1 10 20 1 10 20
June July August
August
-------
Figure 80. Section Four bottom, top and average alkalinity values
during the summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970.
-------
225-
*T 200-
C
<
15
H
1969
BOTTOM.
MEAN
—i—i—i—i—i—i—i—'—i—'—i—'—i—'—i—
10 20 1 10 20 1 10 20
June July August
1970
10 20 i l6 ' 20 1 l6 ' 2b f
June July August
-------
297
constant at all depths. Average alkalinity reached a maximum
of over 200 mg/1 during 1970 compared to a 185 mg/1 maximum
during 1969.
Conductivity followed the same general pattern as
alkalinity during 1969 (Figure 81). Surface values averaged
about 350 micromhos and bottom values about 410 micromhos.
After aeration began, conductivity was somewhat erratic
until mid-July. It was nearly uniform on any given date
after aeration, but average values ranged between 365 and
415 micromhos during 1970, compared to 370 to 385 micromhos
during 1969.
Phosphorus. Phosphorus concentrations were measured only
during 1969. On July 22, 1969 total phosphorus ranged from
0,002 to 0.062 mg/1 (Table 7). Its distribution is erratic.
Total dissolved phosphorus was more uniform, but near the
limit of resolution for the analytical method used. It
ranged from 0.002 to 0.010 mg/1.
Ca, Na, K, Mg, DOM and POM. These constituents were measured
only during the summer 1970. Average calcium decreased from
56.0 mg/1 during mid-June to 52.6 mg/1 by August (Table A-12).
Calcium, like the other constituents, does not exhibit much
vertical variability, even before aeration began. Average
sodium and potassium concentrations were nearly constant all
summer. Average magnesium concentrations varied from 16.0
mg/1 to 9.8 mg/1. Dissolved organic matter and particulate
-------
Figure 81. Section Four bottom, top and average conductivity values
during the summers 1969 and 1970. Aeration occurred between [^
June 16 and September 7, 1970. oo
-------
420-
E
2 390-|
£
>
+-
'>
"o 360-
3
•o
C
O
O
330-
1969
BOTTOM
MEAN
TOP
N
\
1970
TO ' 20 i
June
10 ' 20 \ ' 10 20
July August
10 20
June
T ' ~| i 1 1 1 1 1 1 1—
10 20 I 10 20 1
July August
-------
Table 7. Section Four Lake total phosphorus and total
dissolved phosphorus collected July 22, 1969,
Two water samples were collected from each
depth interval.
Total Phosphorus
(ng/1)
Depth
0.0
2.8
5.6
8.3
11.0
13.7
16.5
17.8
Xl
0.002
0.003
0.003
0.025
0.025
0.003
0.100
0.025
X2
0.017
0.003
0.003
0.002
0.025
0.002
0.025
0.000
Mean
0.010
0.003
0.003
0.014
0.025
0.002
0.062
0.012
Total Dissolved
Phosphorus (mg/1)
xl
0.002
0.003
0.002
0.002
0.002
0.003
0.003
0.002
X2
0.017
0.003
0.002
0.002
0.001
0.002
0.002
0.002
Mean
0.010
0.003
0.002
0.002
0.002
0.002
0.002
0.002
-------
301
organic matter were most variable. Average DOM ranged be-
tween 2.74 mg/1 to 6.18 mg/1, whereas DOM ranged between
117.1 mg/1 to 436.2 mg/1.
Primary Production
Section Four appears very unproductive. Phytoplankton
and attached algal densities are sparse. Secchi disc read-
ings typically exceed 10 meters. Chara may be the main
source of primary production since dense beds extend over
as much as 10% of the lake's bottom. These plants were most
abundant below 5 meters and extended to maximum depth both
years. No estimates of the abundance or production rates
were made because of the obvious technical problems in-
volved. Instead, I concentrated on the phytoplankton and
periphyton in hopes that relative changes in these two
components would represent relative changes in the lake's
primary production as a whole.
Phytoplankton. Phytoplankton standing crop and production
rates were relatively low both years. Standing crop was
about one-tenth that found in Hemlock Lake, and production
ranged between one-fifth and one-thirtieth of Hemlock's.
Primary production potential during July and August 1969 was
fairly constant at 6 mg/m3/4 hrs. (Figure 82). Surface
standing crop averaged about 200 cells/ml during June and
early July, but increased to about 600 cells/ml during August
1970. Secchi measurements reflect this change by decreasing
from about 12 m to 10 m.
-------
302
Figure 82. Section Four secchi disc transparencies,
surface primary production potentials,
surface phytoplankton densities and sur-
face production efficiencies during the
summers 1969 and 1970. Aeration occurred
between June 16 and September 7, 1970.
-------
-C
«J
u
CO
o-
2-
4-
8-
10-
12
30-
20-
10-
CM
o
0)
u
0-
8-
6-
4-
2-
0-
3-
2-
1 -
o-
1970
1970
1969
1969
1970
1969
1 - i
i i
1 10 20 1 10 20 1 10 20 1
June July August
-------
304
Artificial destratification during 1970 resulted in
increased primary production potentials. Potentials during
August 1970 were about three times as great as during
August 1969.
Phytoplankton standing crops did not reflect the in-
creases in production potential. On the contrary, average
1970 standing crops were less than 1969. Phytoplankton
standing crops follow a similar pattern during June and July
both years. Concentrations increased from 200 cells/ml
during June 1970 to a maximum of over 600 cells/ml during
the first week of August. A sharp reduction back to 200
cells/ml followed. Secchi disc measurements responded some-
what differently during 1970. Secchi measurements were about
the same during June both years, but decreased to 6 meters
by August 1970, compared to 10 meters during August 1969.
This greater decrease occurred during 1970 even though sur-
face phytoplankton densities were somewhat less than during
1969. Furthermore, Secchi measurements showed only a slight
increase following the phytoplankton population decline dur-
ing August 1970. The lower transparency during 1970 is
probably due to suspension of detritus, sediments and other
materials by the compressed-air-generated water currents.
Brian Moss, who examined the samples, indicated that larger
quantities of such materials were present in the 1970
plankton samples than in the 1969 samples.
-------
305
Periphvton. Seventeen-day periphyton accumulation rates
during June 1970 were less than during June 1969 (Figure 83).
Thereafter, the 1970 values were always larger, with the
possible exceptions of July 15th and August 30th. Average
17-day accumulation rates were about 0.004 gm/day during
1969 and about 0.007 gm/day during 1970.
Differences in 17-day periphyton accumulation rates
were not reflected in total accumulation rates. Total accu-
mulation rates were lower during June 1970, greater during
early July 1970, but not different during late July and
August. As with Hemlock, these total accumulations were
almost linear during both summers. Accumulations increased
from near 0.0 gm to about 0.5 gm both years.
Zoobenthos
Oligochaetes and Chironomids dominated the Section Four
benthic fauna assemblage, exclusive of the crayfish.
Together, they comprise about 93% of the numbers and 90%
of the biomass during 1969 (Table 8 and Figure 84). During
1970, these percentages were 94 and 84 respectively. Ten
other taxa comprised the remaining macrobenthic fauna.
Chironomids were numerically more abundant than Oligochaetes
during 1969, but this situation was reversed during 1970.
Oligochaetes had more biomass than any other taxa both
years.
Zoobenthos biomass collected during 1969 totaled 11.9
gm and 7.93 mg during 1970 (Table 8). This is a 28% decrease
-------
306
Figure 83. Section Pour periphyton standing crops based
on 17-day incubation periods and continuous
incubation. The 95% confidence interval is
shown about each average value. Aeration
occurred between June 16 and September 7,
1970.
-------
.015-
«
u_
I
.
JT 0.2—
3
E
3
-------
308
Figure 84. Section Four zoobenthos percent composition
during the summers 1969 and 1970. Percent
of weight and percent of number are shown
for each taxa. Total weights and total
numbers collected each summer are also shown.
Samples from dredge collections only.
-------
70-,
Total Number: 1969-17,609
1970-11,979
I11969
FT""] 1970
_ _ CN CTi -«r "O o O «N {K •— CO O -^
d d d d d ° d o --' d d d d d
Total Weight: 1969=11.09227
1970= 7.93214
I11969
FZ31970
d CH odd do d odd odd
-------
Table 8. Section Four Lake zoobenthos collected durinp the SUPPCTS 1P6P and 1970 with an Ekman dredge.
taken each sunnier. I'.'et weights are shown.
125 dredee samples were
Total
1969
Oligochaetes
(microdriles)
Oligochaetes
(megadriles)
Chironomid L.
Chironomid F.
Amphipods
Dragonf lies
Damself lies
Mayflies
Chaoborus spp.
L.
Clams
lleleidae
Trichoptera
Tabaniid
Megaloptera
Grams
6.75189
1.54189
2.16182
0.05490
0.26445
0.09587
0.03211
0.05025
0.00000
0.03355
0.05561
0.02433
0.02278
0.00280
Percent
60.9
13.9
19.5
0.5
2.4
0.9
0.3
0.5
0.0
0.3
0.5
0.2
0.2
0.0
Weight
1970
Crams
3.86228
2.19364
0.59028
0.63301
0.25269
0.16457
0.05024
0.02288
0.00075
0.05209
0.02733
0.02772
0.05348
0.00118
Percent
48.7
27.7
7.4
8,0
3.2
2.1
0.6
0.3
0.0
0.7
0.3
0.3
0.7
0.0
Total
1969
Number
7,506
27
8,817
336
583
11
31
62
0
1
203
26
5
1
Percent
42.6
0.2
50.1
1.9
3.3
0.1
0.2
0.4
0.0
0.0
1.2
0.1
0.0
0.0
Numbers
1970
Number
6,684
12
4,041
163
771
13
32
61
1
8
102
38
45
5
Percent
55.8
0.1
33.7
1.4
6.4
0.1
0.3
0.5
0.0
0.1
0.9
0.3
0.4
0.0
Number of
Samples Found In
1969
89
10
121
74
60
7
18
35
0
1
54
20
4
1
1970
110
6
123
71
72
10
23
34
1
7
45
27
18
5
Mean Number of
Individuals/gram
1969
1,112
18
4,078
6,120
2,205
115
965
1,234
--
30
3,650
1,068
219
357
1970
1,730
5
6,846
257
3,051
79
636
2,666
1,333
154
3,752
1,371
341
4,237
Total
11.09227 100.0
7.93214
100.0
17,609. 100.0 11,976
100.0
-------
311
in total biomass during the summer of destratification.
Total numbers collected decreased 32% during this period
from 17,609 during 1969 to 11,976 during 1970. Decreases
in oligochaetes (microdriles) and chironomid larvae account
for most of this change. Interestingly, associated with
the decreases in biomass and numbers during 1970, the
average size of oligochaetes, Chironomid larvae, amphipods,
mayflies, Trichoptera, tabaniids and megaloptera also de-
creased substantially. Many of the minor species became
relatively more abundant following destratification
(Table 8) .
Jarl Hiltunen could identify only two oligochaete
microdrile species from Section Four: Limnodrilus hoffmis-
teri and Ilyodrilus ternpletoni. L. hoffmeisteri was much
more abundant in the samples from which the specific identi-
fications were made. Several large oligochaete megadrile
specimens were collected, but not identified. These speci-
mens closely resembled the common earthworm, and were only
found in a gravel outcropping at 10 to 15 meters depth.
Hiltunen tentatively identified these as Lumbricidae.
Oligochaetes were very abundant both years at depths
below 14 meters (Figures 85 and 86). Their average depth
for both numbers and biomass always averaged between 15 and
16 meters. There appears to be a slightly greater concen-
tration of worms, especially small individuals, in shallow
water after early July 1970 compared to 1969. Thermal
Stratification during 1969 may have led to their migration
-------
312
Figure 85. Section Four oligochaete (microdriles) depth
distribution as percent of numbers during
the summers 1969 and 1970. Shaded histograms
represent aerated periods.
-------
°— 1
-
75—
50^
25~
0-
—
-
75~
-------
314
Figure 86. Section Four oligochaete (microdriles) depth
distribution as percent of wet weight during
the summers 1969 and 1970. Shaded histo-
grams represent aerated periods.
-------
75—
5°-=
25-=
0 ~
75-=
50^
25—
r~-
£ o =
O) -
« 75-^
M- 50—
o -
*•* T* -
c 25—
0)
0 ~
»- 0 —
-------
316
into deeper water as the epilimnion warmed. The June 15,
1969 and July 15, 1969 samples contain some worms at all
depths, but on July 25th and thereafter none were collected
above 7 meters. When the lake was completely mixed after
mid-June 1970, their depth distribution during the entire
summer resembles the June distribution.
Total oligochaete (microdriles) biomass during 1970
decreased 43% from the 1969 total, and total numbers de-
creased 11% during this period (Table 8). The indication is
that this decrease occurred after aeration began during 1970
(Figure 87). Total estimated oligochaete numbers and biomass
were greater during mid-June 1970 than during mid-June 1969,
but the 1970 totals decreased after aeration began such that
by mid-July 1970 and thereafter both numbers and biomass
were less than the 1969 totals. Large variances obscure the
significance of these trends, but intuitively I believe they
represent the true population responses.
Oligochaete (microdrile) average size decreased during
1970 compared to 1969 (Table 8). They averaged 1,112 indi-
viduals per gram during 1969, but 1,730/gm during 1970.
D. R. Oliver identified more than 11 chironomid midges
based on adult emergence (Table 9). Four species, Lauter-
borniella. Prpcladius. Ablabesmyia mallochi and Clinotanvpus
thoracicus accounted for 67% of the total emergence during
1969 and 77% during 1970. Unidentified adult Ghironomidae
accounted for 10% of the total emergence during 1969 and 13%
-------
317
Figure 87. Section Four total estimated oligochaete
number and biomass during the summers 1969
and 1970. One standard error is shown
about each estimate. Aeration occurred
between June 16 and September 7, 1970.
-------
-------
Table 9 . Emergent midge adults collected from 600 samples during 1969, and 650 samples during 1970.
are from Section Four Lake and were collected in emergent insect traps.
All specimens
1969
Family - Chironomidae (Tendipidae)
Subfamily - Chironominae (Tendipedinae)
Lauterborniella spp.
Tany tarsus spp.
Polypedilum spp.
Chironomus spp.
Paratanytarsus spp.
Pagastiella spp.
Unidentified Chironomini (Tribe)
Subfamily - Pelopiinae (Tanypodinae)
Procladius spp.
Ablabesmyia mallochi
Clinotanypus thoracicus
Subfamily - Hydrobaeninae
Cricotopus spp.
Unidentified Adult Chironomidae
Total
Number
128
15
38
13
2
3
116
217
140
59
2
79
Percent
of Total
Number
16
2
S
2
1
1
14
27
17
7
1
10
No. of
Samples
51
13
18
11
2
2
57
70
73
35
2
47
No. of
Dates
32
12
17
8
2
1
38
38
41
24
2
34
Total
Number
96
5
3
22
5
0
34
57
307
101
0
98
1970
Percent
of Total
Number
13
1
1
3
1
0
5
8
42
14
0
13
No. of
Sampl es
42
5
3
14
5
0
28
47
130
69
0
65
No. of
Dates
32
5
2
11
5
0
26
31
53
34
0
40
Totals
300
381
728
100
408
-------
320
during 1970. These adults included Pseudochironomus netta,
Endochironomus, Tanypus, Dicrotendipes fumidus, Cryptochirono-
mus fulvus, Ablabesmyia monlis, Procladius bellus and possibly
other species. We had some problems of identification, and
added our counts to the "unidentified" category when there
was doubt as to the true identity.
Chironomid larvae were abundant at all depths both years
(Figures 88 and 89) . Both years they were numerically most
abundant in shallow water during June, but more abundant in
deep water by September. Biomass distribution follows a
similar trend, but the shallow water shift during June is not
as pronounced. This indicates that the deep water larvae
are much larger individuals, either because they are in later
instars and/or different species.
Total chironomid larvae collected decreased from 8,817
during 1969 to 4,041 during 1970, and biomass decreased from
2.16182 gm during 1969 to 0.59028 gm during 1970. These are
54% and 73% decreases respectively. Average size also
decreased from 4,078/gm during 1969 to 6,846/gm during 1970.
Contrary to changes in oligochaete population trends, Chiron-
omid larvae were less abundant during the entire summer 1970,
compared to 1969 (Figure 90). The mid-June samples were taken
before aeration began. These first samples indicate that
the larvae were numerically less than 50% as abundant during
1970, but almost as abundant in regards to biomass.
Chironomid pupae show the same numerical shift from
shallow to deep water during the summer 1970 as do the
-------
321
Figure 88. Section Four Chironomid larvae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
-------
45
i l l I l I l1 i ill i |" I i
15
Depth (m)
-------
323
Figure 89. Section Four Chironomid larvae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods.
-------
60
40-
20-
0
60-1
6-15-69
6-12-69
X=9.4
7-5-69
x=n.5
C
0>
o
7-25-69
X=12.6
a, 40-
s20-
•o o-
'E
*" 60
O
J4°-
020-
7-3-69
X=9.5
7-24-69
X=11.7
8-15-69
X=14.6
8-14-69
X=12.5
60-
40-
20-
9-6-69
X=13.3
9-4-69
1 I ' i '
12 16 o
8
12 16
Depth (m)
-------
325
Figure 90. Total estimated Chironomid larvae number and
wet weight in Section Four during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred be-
tween June 16 and September 7, 1970. Totals
from dredge samples only.
-------
o
-^ 60-
o>
o
-o 45-
'i
o
c
o
;! 30-
U
15-
E
=>
Z
1970
1969
o
•^ 25-
O
E
o 20
CO
(1)
o
t 15
o
o
c
o
10-
5-
T
\
10 20 j ib ' 20 110 '' 20 'T
June
July
August
-------
327
larvae (Figure 91). Over 55% by numbers were collected from
the shallowest interval during June 1970 and 5% from the
deepest. By September, only 20% were collected from the
shallow interval and over 30% from the deepest. The June
1970 pupal biomass distribution is more uniform than their
numeric distribution, but by September 1970 over 80% were
collected from the deepest intervals (Figure 92). Pupal
distributions during 1969 are not as definite as during 1970,
but indicate greatest concentrations between 4 and 11 meters
during most of the summer. Few pupae were collected below
15 meters at any time and none were collected below 15
meters during July and August 1969.
Total pupal biomass collected increased to 0.63301 gm
during 1970 from 0.05490 gm during 1969. However, total
numbers decreased from 336 during 1969 to 163 during 1970
(Table 8) . This represents a considerable increase in average
size of the pupae during 1970. They increased from 6,120/gm
during 1969 to 257/gm during 1970. Total estimated pupal
population trends are less spectacular (Figure 93). Both
numerically and biomass-wise pupae tended to be more abundant
during early summer 1969 than during 1970, and then tended
towards equal or slightly higher values by late summer 1970.
Total adult emergence reflects the decreases in larval
and pupal standing crops. Only 72 adults emerged during
1970 compared to 812 for 1969 (Table 9). Although total
emergence was less during 1970, they occurred in more samples
-------
328
Figure 91. Section Four Chironomid pupae depth distribu-
tion as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
-------
I I I I I I I I I I I I I I I
o
Depth (m)
-------
330
Figure 92, Section Four Chironomid pupae depth distribu-
tion as percent of wet weight during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods.
-------
12 16
Depth (m)
-------
332
Figure 93. Total estimated Chironomid pupae number and
wet weight in Section Four during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred between
June 16 and September 7, 1970. Totals from
dredge samples only.
-------
0)
D
Q.
E
o
I 2-
_c
U
0)
J2
E
3
Z
1970
1969
9-
IO
I 6'
O
CD
0)
I 3
Q.
Tl
'i
g o
O
—1—' 1
10 2i
June
1—'—T-
1 10
20
July
10 20
August
-------
334
during 1970 than during 1969, 408 compared to 381. This
change is reflected in a more uniform depth emergence follow-
ing destratification (Figure 94). During 1969, almost all
emergence was limited to less than 4 meters. No midges
emerged below 12 meters after mid-July 1969. During mid-
June 1970, emergence was again largely limited to less than
4 meters, but as aeration continued emergence increased at
the greater depths. Between 20% and 40% of the total emer-
gence occurred below 12 meters during August and September
1970, whereas none occurred in this interval during the
same period of 1969.
Total seasonal emergence was generally greater during
1969 (Figure 95). Two large peaks occurred during 1969,
one during mid-July and another during mid-August. These
coincide closely with periods of intense heating (Figure 73).
Emergence during 1970 has several peaks, but these coin-
cidences with periods of heating are obscure after mid-July-
Of the more abundant Chironomid adults, only Ablabesmyia
mallochi and Clinotanypus thoracicus showed much increase in
emergence during 1970 (Table 9; Figure 96) . The other
species either remained about the same or declined. These
two species belong to the predaceous sub-family Pelopiinae.
Of the more abundant adults, only C. thoracicus showed much
change in its emergence depth (Figures 97 and 98). Over 50%
of this species emerged below 16 meters during 1970 during
its peak emergence period. Its emergence during 1969 was
-------
335
Figure 94. Total midge emergence from Section Four by
depths during the summers 1969 and 1970.
Aeration occurred between June 16 and
September 7, 1970. Totals include Chironornid
midges from emergence traps only.
-------
60
40-
9fi -
—
60-
40-
mergence
o J^ o K:
3000o
L I I ii
LU
_ 0-
(9
"S 60-
40-
»*-
0 20-
*-*
c 0-
Q, 0
u
0) 60-
0.
40-
20-
0_
60-
40 -
20 -
0
o-io-ov
6-27-69
x=4.0
1 1 1
6-30-69
7-11-69
x=4.4
, 1 1
., ._ T 1 t if\
r >•*
-------
337
Figure 95. Total estimated weekly midge emergence from
Section Four during the summers 1969 and
1970. Totals include Chironomid midges from
emergence traps only. Aeration occurred
continuously between June 16 and September 7,
1970.
-------
30-
O
I 25
0)
JJJ
8, 2°-
| 15H
I
1 ion
UJ
— 5-
|2
0-
1970
1969/
I ' ! r
1 10 20
-7—I 1 1 1 r
1 10 20
_r_T__1 , r , r_r
1 10 20 1
June
July
August
-------
339
Figure 96. Total estimated midge emergences from Section
Four. Samples from emergence traps only.
Aeration occurred between June 16 and
September 7, 1970.
-------
45-
30-
15-
0-
12-
9-
Chironomini (10 )
Proclodius spp. (10 )
Ablobesmyia mallochi (104)
Clinotanypus thoracicus (10 )
1 10 20 1 10 20 1 10 20
June
July August
-------
341
Figure 97. Depth emergence of selected Section Four midges
during the summers 1969 and 1970. White areas
represent no observed emergence. A= Procladius,
B= Ablabesmyia mallochi, C= Clinotanvpus
thoracicus. Aeration occurred between June 16
and September 7, 1970.
-------
90-
1 10 20 1 10 20 11" ' 10' 20 i 10 20 1 10 20 1 10 20
June
July
August
June
July
August
1969
1970
: 0-4
4-8
8-12
v^>: 12-16
16-19.1
-------
343
Figure 98. Depth emergence of Section Four midges and
mayflies during the summers 1969 and 1970.
White areas represent no observed emergence.
A= Lauterborniella spp., B= Chironomjni,
C= Mayflies (Ephemeroptera). Aeration occurred
between June 16 and September 7, 1970,
-------
90
10 20 1 io ^
110201
June
Jul
1969
Au9ust
JulX August
1970
4-8
8-12
#££12-16
16-19.1
-------
345
limited to less than 12 meters during the entire summer.
A. mallochi also increased its emergence depth substantially
during August 1970, but not as much as C. thoracicus. Changes
in the other species were erratic.
N. Wilson Britt identified four species of mayflies
from Section Four: Caenis spp., Callibaetis spp. (probably
C. brevisostatus), Neocloeon alamance and Stenonema spp.
Caenis was the most abundant. Mayfly nymph biomass collected
by the dredges decreased by 55% during 1970 compared to 1969,
but total number collected were almost identical both years
(Table 8) . Total estimated nymph biomass was always less
during 1970 (Figure 100). Total numbers were less during
early summer 1970 but exceeded the 1969 values during August
1970. Nymph depth distribution was very similar both years
(Figure 99) . Nymphs were seldom collected below 11 meters
depth. They were never collected below 14.5 meters, and were
only abundant between 11 and 14.5 meters during September
1970. The emergence depth distribution largely reflects the
nymph distribution (Figure 98). Adults never emerged below
8 meters during 1969. Their peak emergence occurred during
early July 1969, at which time most emerged from between 0
and 4 meters depth. By the end of the summer 1969, all were
emerging from between 4 and 8 meters depth. Their 1970
emergence pattern differed greatly from the 1969 pattern in
both time and depth of emergence. The 1970 peak emergence
occurred during August, with almost no emergence before the
-------
346
Figure 99. Section Four Mayfly (Ephemeroptera) depth
distribution as percent of number during
each sampling period during the summers 1969
and 1970. Shaded histograms represent
aerated periods.
-------
50
0)
A
z
»^
o
o
0)
~
—
)—
-
>—
)-
) —
> -
s ~
)-
5-
» "
>—
)-
>—
1 -
6-15-
x=4.0
7-5-^
x=4.7
7-25-
x=5.2
8-15-
9-6-d
x=4.9
69
>9
69
69
9
ill i ii
1
l l i
i i i i
6-12-70
x=5.9
7-3-70
1
11
7-24-70
X=6.5
•
1
8-14-70
x=7.0
»*
m
9-4-70
x=8.2
mil
(III III II
,
I
11
1
1 1 1 1 1
75-
5 10 15
0
10
Depth (m)
-------
348
Figure 100- Total estimated Mayfly (Eph enter opt era)
number and wet weight in Section Four during
the summers 1969 and 1970. One standard
error is shown about each estimate. Aeration
occurred between June 16 and September 7,
1970. Totals from dredge samples only.
-------
8-
6-
0)
>s
O
3
<+-
O
k.
E
Z
4-
2-
0-
6-
E
O)
CM
O
4-
o
E
o
a 2-
x
x
O
0-
-2-
10 20 1 10 20 1 10 20 T
June July August
-------
350
end of July. The early summer emergence was entirely from
between 0 and 4 meters, but the August 1970 emergence
occurred from between 0 and 12 meters.
Two species of Amphipods were identified by T. Wayne
Porter: Hyalella azteca and Gamarus. H. azteca was by far
the most abundant. Total amphipod biomass was about the
same both years, but about 32% more individuals were col-
lected during 1970 (Table 8; Figure 101). Their depth
distributions are about the same both years (Figure 102),
with almost no specimens collected below 14.5 meters.
Four Trichoptera were identified by Glenn B. Wiggins
(Royal Ontario Museum): Mystacides spp., Oecetis spp.,
Polycentropus and Oxyethira in order of relative abundance.
Trichoptera numbers, biomass and depth distribution were
about the same both years (Table 8; Figures 103 and 104).
Leonora K. Gloyd identified six Odonates from Section
Four: Dragonflies: Gomphus spp. (probably G. spicatus) ,
G. quadricolor (or possibly G. lividus); Damselflies:
Ischnora verticallis. Enallagma hageni, Argia spp. (probably
A. fumipennis violacea) and E. ebrium (or possibly E. hageni).
Odonata numbers and biomass were about the same both years-
(Table 8) .
Heleidae (=Ceratopogonidae ) larval biomass and numbers
decreased by about 50% during 1970 compared to 1969 (Table
8; Figure 105). Their depth distributions were erratic, with
no obvious trends (Figure 106).
-------
351
Figure 101. Total estimated Amphipod number and wet weight
in Section Four during the summers 1969 and
1970. One standard error is shown about each
estimate. Aeration occurred between June 16
and September 7, 1970. Totals from dredge
samples only.
-------
•o
o
in
•o
O
Q.
CL
E
JQ
E
3
Z
9-
6-
3-
0-
E
O)
CO
2 2-1
O
E
o
OQ
-o
O
a
IE
a
E
1-
0-
- - -O
10 ' 2b i 10 ' 20
—r-
10
—I—•-
20
June
July
August
-------
353
Figure 102. Section Four Amphipod depth distribution as
percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
-------
rri i i i i i i i' i i i i i i i i
Depth (m)
-------
355
Figure 103. Section Four Trichoptera depth distribution
as percent of number during each sampling
period during the summers 1969 and 1970.
Shaded histograms represent aerated periods.
-------
0
Depth (m)
-------
357
Figure 104. Total estimated Trichoptera number and wet
weight in Section Four during the summers
1969 and 1970. One standard error is shown
about each estimate. Aeration occurred
between June 16 and September 7, 1970.
Totals from dredge samples only.
-------
0-
O>
O
I/)
O
E
o
03
a
o
4-
3-
•- 2-
1-
0-
c
June
July
10 20
August
-------
359
Figure 105. Section Four Heleidae (=Ceratopogonidae) depth
distribution as percent of number during each
sampling period during the summers 1969 and
1970. Shaded histograms represent aerated
periods.
-------
45-
30-
15-
6-15-69
x=4.1
6-15-70
7-5-69
45- x=6.4
30-
(f)
15-
7-3-70
x=7.3
7-25-69
x=9.6
g
O
0) 15-^
O.
(C
! 7-24-70
!x=4.6
45-
8-15-69
x=4.0
0) 30-1
(0
0)
I 0
18-14-70
Ifcll.l
1
45-
30-
15-
9-6-69
x=5.0
9-4-70
]x=9.8
-------
361
Figure 106. Total estimated Heleidae (=Ceratopogonidae)
number and wet weight in Section Four during
the summers 1969 and 1970. One standard
error is shown about each estimate. Aeration
occurred between June 16 and September 7,
1970. Totals from dredge samples only.
-------
-o
o
25-
20-
ju 15-
0)
I
»*- 10-
o
1 s-
0-
8-
E
D)
-------
363
Crayfish
During 1969, Section Four crayfish were only collected
between August 12th and August 30th. During this period,
the males were largely confined to shallow water, and the
females to deeper water (Figure 107). The average depth for
males was 4.4 m and 8.8 m for females. Three times as many
males were captured as females. No crayfish were collected
below 14 meters depth. Their maximum depth during 1969
corresponds closely with the 10°C isotherm. Although some
chemical stratification was present, it did not appear to be
an important barrier to crayfish depth distribution.
During early June 1970, both males and females were
largely confined to shallow water. Their average depths were
2.6m and 3.3m respectively, with no animals below 9 meters.
The lake was well-stratified thermally during this period,
but chemical stratification was not evident. As during
August 1969, their maximum depth distribution during early
June corresponds to the 10°C isotherm. After aeration began,
the crayfish very rapidly distributed to maximum depth.
Aeration began June 17, 1970 and the lake was almost com-
pletely destratified within a few days. After destratifica-
tion, the minimum temperature was always greater than 14 C.
The females' average depth between June 16th and June 30th
was 9.5 m and the males' 11.8 m. Their depth distributions
varied somewhat during the remainder of the summer, but they
were always distributed to maximum depth. No conspicuous
-------
Figure 107. Section Four crayfish depth distributions during the summers u>
1969 and 1970. Total numbers during each sample period and ^
their average depths are shown. The shaded area represents
the 1969 distributions. Aeration occurred between June 16
and September 7, 1970.
-------
5-
10
15-
10-
15-
¥,
4P
2i°
0 20
i ill
n=8
7=3.3
6-7-70
6-16-70
n=22
x=72
7-24-70
8-14-70
40
J
60 60 40
n=39
x=2.6
n=118
7= 12.0
CJ
jj
>T
n 90
x=9.0
6-16-70
6-30-70
n=31
x=9.5
8-14-70
9-4-70
Percent
2p 0 2jO 4p 6p 6(0 4p 2p 0 2p ^ 4p 6(0
L
1
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7=75
0*
n=273
x=11.8
1
J
n=52
7=8.6
6-30-70
7-24-70
n=40
x=8.8
8-12-69
8-30-69
v
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'~f '
s""*
% . ,
?
~ f. A
IT-O4
7=9.3
rf>
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£ ^ / ':
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n=120
x=4.4
-------
366
concentrations in response to environmental factors was
obvious. The sex ratio was always in favor of the males.
During 1969 this ratio was 1:3.0 and during 1970 it was
1:3.8.
From August 14, 1970 through September 4, 1970, the
distributions were much changed from the previous year.
The males were most numerous at maximum depth during 1970.
Their average depth was 11.8 m during 1970 compared to
4.4 m during 1969. The females were also distributed to
maximum depth (19.6 m) during 1970, compared to 14.0 m during
1969. Their average depth was only slightly greater during
1970; 9.5 m compared to 8.8 m.
Rainbow Trout
Rainbow trout ranged between the surface and bottom
during June 1969 (Figure 108). Later in the summer they
were found mostly below 8 meters depth. At no time were
they caught in water warmer than 19°C. The gill net samples
may give a distorted picture however, because of small sample
size. Only thirty-two 1969 stocked RBT and nineteen 1964-65
stocked RBT were caught during 1969. This low capture rate
is partly due to the small size of the 1969 stocked fish and
small population size of the 1964-65 RBT. The 1969 stocked
RBT averaged 188 mm when stocked, but fish less than 200 mm
were seldom caught in the nets. Only 10% of the 1969
stocked fish were 200 mm or larger when stocked. Section
Four fish have always had very slow growth and few attained
-------
Figure 108. Section Four rainbow trout depth distributions during 1969. w
Open squares represent fish stocked during June 1969 and o\
marked with a right-pectoral fin clip. Solid squares are ^
fish stocked during 1964-65 and lack fin clips. Each square
represents one fish.
-------
August
20
-------
369
net vulnerable size during 1969. The clear water of Section
Four Lake also contributed to low catch rates.
During early June 1970, the rainbow trout were mostly
distributed between the surface and 12 meters (Figure 109).
Soon after aeration began they distributed throughout the
lake. By early July they were mostly distributed along the
bottom of the lake. Ninety-four 1970 stocked RBT, eleven
1969 stocked RBT and eleven 1964-65 stocked RBT were cap-
tured during 1970. The increased capture rate of the 1970
stocked fish is attributed to their larger size; they
averaged 200 mm when stocked.
-------
Figure 109. Section Four rainbow trout depth distribution during 1970.
Open circles represent fish stocked during May 1970 and
marked with a left-pelvic fin clip. Solid circles repre-
send fish stocked during June 1969 and marked with a right
pectoral fin clip. Solid squares represBnt fish stocked
during 1964-65 and lack fin clips. Each symbol represents
one fish.
-------
June
10 20
July
10 20
August
10 20
-------
DISCUSSION AND CONCLUSIONS
Physical-Chemical Parameters
As discussed earlier, a lake1s oxygen and temperature
regimes are its most important parameters. In Section Four,
oxygen concentrations were generally quite high and pre-
sented no biotic distributional barrier. In fact, oligo-
chaetes and midge larvae were most abundant in the profundal
zone. Temperature exerted a greater influence than oxygen.
Artificial destratification greatly altered the temperature
regime in Section Four Lake. Although the maximum average
temperature was increased 3.6 C by destratification, maximum
bottom temperatures were increased more than 15.3°C. Since
the dominant biota live in the profundal zone, this repre-
sents a very significant alteration of their environment.
Many metabolic and other chemical processes double for every
10 C increase. This sort of temperature change could lead
to changes in species composition, growth rates, reproduc-
tive patterns and distribution within the lake. When
temperature is no longer an important barrier, the organ-
isms should distribute according to other conditions such as
substrate, light, plankton, rooted aquatic plants and pre-
dator-prey relationships. Certain coldwater species may be
372
-------
373
eliminated from the lake because of the absence of cold,
aerated water during the summer. I had expected this sort
of problem with the rainbow trout, but it did not occur.
However, this could be a serious consequence of destratify-
ing oligotrophic lakes that normally have greater surface
temperatures than Section Four.
I did not expect any great changes in the chemical
conditions in Section Four as a consequence of destratifica-
tion. Changes did occur, but they were generally not as
striking as when eutrophic lakes are destratified (Fast,
1968). Oligotrophic lakes are typified by their chemical
homogeneity. Since the water chemistry did not appear to
limit the biotas' distribution before aeration, we should
not expect much distributional change in the biota in re-
sponse to changes in the water chemistry after destratifi-
cation.
The thermal profiles and thermal stability values indi-
cate the lake was nearly isothermal after June 20, 1970.
Slight temperature gradients often occurred at the surface
as it was warmed faster than the heat could be redistributed
throughout the lake. During periods of intense heating, it
is difficult to prevent this thermal microstratification.
This is due in part to the fact that the relationship between
rate of destratification with constant air input is not
linear. The closer thermal stability is to zero, the greater
the energy required to cause a unit decrease in thermal
-------
374
stability. It may require relatively little energy to reduce
thermal stability by 75%, but much more energy to reduce it
to zero.
The destratification system used in Section Four was
much larger than necessary. This situation was purposely
arranged to assure complete mixing. As in Hemlock Lake, the
important factor was measuring the effects of this system of
mixing on the biota. We did not want to measure the effects
of partial mixing, but of complete destratification. The
proper size compressor, distribution and duration of air
input, etc. is basically an engineering problem, and one
that has not yet been adequately solved.
There were large changes in dissolved organic matter
and particulate organic matter. DOM changes may be related
to changes in primary production. These changes will be
discussed later in greater detail by R. G. Wetzel.
As with Hemlock Lake, phosphorus concentrations were
measured only during 1969. They were not continued for the
reasons given. Because of the oligotrophic condition of
Section Four, I expected even less measurable changes in
phosphorus concentrations than we expected in Hemlock.
Phosphorus concentrations before aeration were quite variable
and low.
There is usually not much economic incentive to arti-
ficially destratify an oligotrophic lake. In fact this is the
only case that I am familiar with. Destratification is usual-
ly instigated to improve water quality by oxidizing and
-------
375
otherwise eliminating anoxic conditions. This is not the
case with oligotrophic lakes. The major reason oligotrophic
lakes may be destratified is to reduce evaporation rates.
This is also an important reason for destratifying eutrophic
lakes. Destratification may reduce annual evaporation by
4 to 10 percent (Koberg, 1964, personal communications).
This is accomplished by a slight reduction in surface tempera-
tures during the summer. Surface temperatures are slightly
warmer during the cooling period, but the periods of above-
normal and below-normal surface temperatures are such that
a net evaporation reduction is realized. Although the lake's
heat budget is greatly increased by destratification, this
extra heat is lost to a greater extent by infra-red radiation
from the lake, than by evaporation. Reduced evaporation rates
can result in a substantial savings. An estimated #10,000
worth of water was saved from evaporation during one year's
destratification of El Capitan Reservoir, California (Fast,
1968). The annual cost of running the compressor, amortiza-
tion of initial investment and maintenance was only about
#3,000. These savings are most important, and most likely,
in water-starved regions such as our American southwest.
Water is in short supply, expensive, and evaporation rates
are high.
Primary Production
Because of Section Four's oligotrophic condition and
marl deposition, I did not expect much change in primary
-------
376
productivity during destratification. Although I expected
profundal sediment temperature increases to regenerate some
nutrients, I expected these nutrients to be readily bound by
the carbonate complexes and therefore effectively unavailable
for plant growth.
The evidence indicates that this did not occur. Surface
primary production potentials were about three times as
great during August 1970 compared to August 1969, and produc-
tion efficiencies were likewise increased from 1 mgC/m3/4 hrs/
In cells during August 1969 to between 3 and 4 mg during
August 1970. These changes strongly suggest that nutrients
were more available following aeration. However, as dis-
cussed for Hemlock Lake, other factors could also account for
these apparent increases.
Although production potentials and efficiencies increased
following aeration, phytoplankton standing crop did not.
Average surface values were actually lower during 1970 com-
pared to 1969. Zooplankton grazing could be flaunted as a
possible explanation for lower standing crops, but I feel
that was not the case. I believe that increased mixing rates
and increased mixing volume caused the reductions in standing
crop. This mixing in effect prevented the phytoplankton
from realising their growth potential.
During normal, stratified periods phytoplankters may
spend most or all of their time within the photic zone
(Figure 110). The ratio ti/t2 is relatively large and
-------
Figure 110. Hypothetical residence times for a passive, neutral buoyancy
object with the photic and aphotic zones of a stratified and
unstratified lake.
-------
t,
Depth of
Photic Zone
Stratified
Unstratified
-------
379
approaches infinity where tz is small. This latter situa-
tion probably occurs in a thermally stratified Section Four
because of its clarity- About 20% of the surface irradiance
was still present at 12 meters on August 11, 1969 when the
Secchi was 10.25 m (Figure 82). Although the entire lake
may lie within the photic zone, light intensity and produc-
tion rates are very low in deep water. After destratification,
phytoplankters were transported into the deep water to a
greater extent than under stratified conditions (Figure 111).
Surface/15 meter phytoplankton density ratios average 2.2
during 1969, whereas surface/16 meter densities averaged 1.5
during 1970. This indicates a more even distribution during
1970 compared to 1969 and a shift in densities from the sur-
face to deep water. A 1.0 ratio indicates equal densities
at both depths. Ratios above 1.0 represent higher densities
at the surface, and ratios less than 1.0 represent higher
bottom densities. Densities were always greater at the
surface both years, and quite variable from day to day.
Bottom densities were greater than surface densities in only
2 of 24 sample sets during 1970. These data indicate that
this system of artificial mixing redistributed a significant
portion of the phytoplankton population into deeper water.
Time spent in the aphotic, or at least dimly lit deep water
(t4) was much increased relative to time spent at shallow
depths (ts). Thus the time available for high production
was reduced (t3/t4 < ti/t2) by destratification. Increased
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380
Figure 111. Ratios of Section Four surface/bottom
phytoplankton concentrations during 1969
and 1970. The lake was destratified
during 1970.
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June
July
1 10 20
August
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382
nutrient availability was not adequate to compensate for
these changes and net in situ production decreased. The
above conditions are likely to occur in relatively deep,
oligotrophic lakes with a large hypolimnetic volume and
nearly complete destratification. If destratification is
not complete, but stratification persists near the surface,
production rates may remain the same or be increased. I ob-
served increased primary production rates in El Capitan
Reservoir, California following incomplete destratification.
Even with continuous air injection, the eutrophic reservoir
typically had microstratification of 2 to 3 C within the
upper few meters (unpublished data) , and almost all of the
primary production occurred within this region. Phytoplank-
ton were apparently kept within this zone, and not swept
into the dimly lit regions of the reservoir in sufficient
quantity to greatly reduce their population. This stratifi-
cation was almost always present during the yearly heating
cycle and developed because the heat input from solar irradi-
ance was greater than could be distributed throughout the
reservoir by the aeration system. This condition almost
never developed in Section Four Lake because mixing was
almost complete. The air input was actually greater than
necessary to assure a thorough mix.
Murphy (1962) hypothesized that increased mixing depths
and/or turbidity acting alone would reduce primary produc-
tion. His hypothesis predicts that increased mixing depths
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383
and turbidity such as occurred in Section Four during com-
plete destratification would lead to decreased primary
production, and that decreased mixing depths such as
occurred in El Capitan Reservoir during incomplete destrati-
fication would lead to increased production rates. His
predictions in these two cases agree with observations.
Likewise his calculated production rates agreed well with
those he observed in 33 shallow California ponds. He sug-
gests manipulating reservoir production rates by adjusting
metalimnion depths. Decreased metalimnion depths could be
achieved by epilimnion withdrawals or incomplete destratifi-
cation/ whereas increased metalimnion depths could be
achieved by hypolimnion withdrawals or air injection at some
desired depth which is less than maximum depth. Hooper et al.
(1952) increased the metalimnion depth by mixing hypolimnion
water with epilimnetic. This increased phytoplankton and
periphyton production because the hypolimnion was nutrient-
rich relative to surface waters. This nutrient increase more
than compensated for possible increased mixing depths.
Knoppert et al. (1970) found they could increase the
metalimnion depth by air injection at some intermediate
depth. Their metalimnion usually began at about 5 meters,
but was lowered to the air input level of 19 m within three
weeks. Maximum depth was over 27 m, but water below 19 m was
not upwelled by their aerator and a sharp thermal discontin-
uity developed at 19 meters. Knoppert et al. conducted
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384
another experiment to determine the effect of increased mix-
ing on plankton populations. They increased the mixing
rate of two shallow reservoirs without altering their thermal
regimes. These reservoirs did not normally stratify thermal-
ly, but they had reduced photic zones. Their results were
inconclusive, but suggest that increased mixing alone did not
greatly affect the phytoplankton.
Robinson et al. (1969) evaluated the effects of inter-
mittent destratification on two northern Kentucky reservoirs.
Total phytoplankton standing crops in these destratified
lakes responded about the same as those in a control lake.
They concluded, however, that bluegreen algae declined faster
than green algae and the number of plankton species remained
the same or increased slightly following air injection.
Bernhardt (1967) also reports a decline in the bluegreen
algae Oscillatoria rubescens during artificial destratifica-
tion of eutrophic Wahnback Reservoir, Germany. Melosira
qranulata angustissima became abundant after 0^. rubescens
disappeared. Bluegreen algae were not conspicuous in Section
Four either before or during destratification. Most signifi-
cantly, Bernhardt also found "... there was no increased bio-
production, " due to artificial destratification. Artificial
destratification was incomplete since a small thermal gradient
persisted near the surface part of the summer. This condi-
tion is similar to that discussed for El Capitan Reservoir,
California.
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385
I am uncertain how to interpret periphyton events. In
contrast to the phytoplankton, they were not swept out of
the surface waters by the currents. Increased turbidity
could have deleteriously affected their growth, but increased
nutrient availability should have promoted periphyton growth.
Likewise, increased water currents due to air injection
should have favored periphyton growth. Short-term periphyton
accumulations do show significant increases, but the long-
term accumulations are about the same both years. This sug-
gests that colonization and the early "successional" stages
were accelerated by destratification but the maximum accumu-
lation levels were not affected. In contrast, both short-
term and long-term periphyton accumulations were increased
in Hemlock Lake. I have no good suggestions to explain
these differences in Section Four Lake.
Zoobenthos
The most obvious response to the Section Four zoobenthos
to destratification appears to be a reduction in numeric
and biomass standing crops. Oligochaetes (microdriles)
and Chironomid larvae had especially large reductions in
standing crop as well as average sizes during 1970 (Table 8).
All organisms except the Oligochaete megadriles, Chironomid
pupae and Odonates were smaller during 1970, and all the
minor species, except the Heleids were numerically more
abundant during 1970.
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386
Although reduction in oligochaete standing crop appears
directly related to destratification, Chironomid standing
crop reduction could be due to emergence. Midge emergence
during the summer 1969 was closely related to periods of
rapid heating. The spring 1970 temperatures appear to have
been warmer than during the spring 1969. For example, the
early June 1970 surface temperature was 19.5 C compared to
16°C the previous June. These higher temperatures could have
promoted a greater emergence rate prior to my sampling and
resulted in lower standing crops during June 1970. This
could account for lower standing crops during June 1970,
but not necessarily during the remainder of the summer since
reproduction and growth should have occurred.
The most likely explanation for the observed zoobenthos
reductions in standing crop is that destratification resulted
in a reduction, or at best no change in primary production
and an increased heat budget. The surface phytoplankton
standing crop appears less concentrated during most of the
summer 1970 (Figure 82), and total accumulated periphyton
was about the same both years. Total phytoplankton standing
crop may actually have been greater during 1970 than during
1969 since aeration could have distributed it more uniformly
throughout the lake; but this cannot be accurately demon-
strated from the data. In any case, phytoplankton surface
concentrations were less during 1970. An increased heat
budget should have resulted in greatly accelerated metabolic
rates for certain organisms such as the oligochaetes.
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387
Almost all of the oligochaetes and a large percent of the
Chironomid larvae were found below 14 meters both years.
These deep-dwelling individuals experience maximum tempera-
ture increases of about 15°C due to destratification. Many
biochemical reactions were doubled by every 10°C temperature
increase. Increased catabolic rates without a commensurate
increase in anabolism should result in decreased biomass,
as observed. Put more simply, respiration was increased by
temperature increases, but synthesis either remained the
same or decreased due to an unchanged or decreased food
supply. The net result was "negative growth," i.e., a de-
crease in standing crop. If we agree that this is deleteri-
ous, then we could say that artificial destratification of
Section Four caused thermal pollution of the lake, although
the results were not obvious to the casual observer.
Unlike Hemlock Lake, the Section Four's sediments were
well oxidized and contained sparse organic matter prior to
artificial aeration (Figure 14). Oxygen concentrations were
always high over the sediments and decomposition was probably
almost complete. Aerobic decomposer microbes, as well as
larger detritivores undoubtedly worked over these sediments
to a large degree. Consequently, destratification probably
did not greatly affect nutrient regeneration from, or
decomposition of, these sediments. The availability of
organic debris to the zoobenthos was probably likewise un-
changed by destratification. These conditions differ
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388
greatly from the profundal conditions of eutrophic lakes
where decomposition is retarded by anaerobiosis and organic
debris is unavailable to the detritivores for long periods.
Reductions in average sizes of most organisms during
1970 is most puzzling. It is generally agreed that smaller
organisms have greater metabolic rates. If this is true of
aquatic invertebrates, and the aforementioned changes occurred
in the metabolic rates, then I would expect larger species
or individuals to be favored during destratified periods.
In fact, this does not appear to be the case.
Although production rates were not measured for any
species, midge emergence may be considered a rough estimate
of midge production. The reduction in total emergence sug-
gests that total midge production was decreased by destratifi-
cation. Production per individual may have actually in-
creased, however, since total midge emergence decreased 10%
between 1969 and 1970, but number of midge larvae collected
decreased 54% during these same periods.
I was surprised by the almost indiscernible effect of
destratification on the zoobenthos depth distributions.
Midge pupae and emergence depth distributions were most
affected, but not as much as expected. Although oxygen and
presumably most other chemical parameters were not limiting,
I expected temperature to represent a real barrier to certain
organisms (e.g., see discussions of fish and crayfish depth
distributions). I had expected a net movement of Ghironomids,
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389
mayflies, amphipods and possibly other taxa into deep water
and a net movement of oligochaetes into shallow water. The
absence of these changes suggests that other conditions such
as sediment conditions, attached vegetation, and light are
more important factors. Oligochaetes were almost entirely
limited to shallow water by anoxia in eutrophic El Capitan
Reservoir, California (Fast, unpublished data). When this
lake was destratified the oligochaetes distributed evenly
throughout the entire lake even though large differences
existed between sediment conditions at different depths and
at different points in the lake (Fast, 1968). I had expected
a similar net movement of oligochaetes into shallow water
after Section Four was mixed, but only a few individuals
moved into, or remained in shallow water after destratifica-
tion.
Crayfish
Factors influencing Orconectes virilis depth distribu-
tions within lakes are not well understood. Momot (1967)
and Momot and Cowing (1970) found that both sexes of
0. virilis, in nearby lakes were mostly found in shallow
water during May and June. Adult females moved to deeper
water first, followed by young females and males as they
reached sexual maturity. By August 70% of the adult females
were below 6.0 m and were concentrated at 7.6 m. During
this same period, 65% of the yearling males and females were
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390
between 3.0 m and 6.0 m, while over 85% of the adult males
were above 6.0 m. The lowermost extent of the metalimnion
during August was 9.1 m with a 13 C temperature. Oxygen
and other chemical concentrations were not presented. The
crayfishes' maximum depth distribution coincided with the
bottom of the metalimnion. These authors feel that the
migration to deeper water is related to sexual maturation.
Aiken (1968) also showed that mature 0_. virilis in an Alberta,
Canada stream also moved to deeper water in late summer.
The females preceded the males. (This migration contributed
to overwinter survival of the species.) He also believes
the migration is related to sexual maturation since matura-
tion is related to photoperiodism and temperature (Aiken,
1969) .
Section Four 0_. virilis depth distributions during 1969
coincide well with those described by Momot (1967) and Momot
and Cowing (1970). During August the males were in shallow
water and the females were much deeper. By June 1970, both
sexes were concentrated in shallow water. Both seasons
their lowermost limit was related to the 10°C isotherm and
not other chemical factors. However, almost immediately
after Deration began during June 1970, both sexes distributed
throughout the lake. Although they were not aged, there was
no conspicuous size distribution of either sex as a function
of depth. By early July and thereafter, the males always
had a greater average depth than the females. Both sexes
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391
were about evenly distributed throughout the lake after
destratification. This even distribution seems to mitigate
against the sexual maturation hypothesis. If light intensity
is important for maturation, then the mature females and
recently mature males and females still should have preferred,
and concentrated in, deep water. The mature males distribu-
tion should have remained about the same. If cold water is
the important factor affecting their depth selection, then
an even distribution of the females could be expected; since
the lake was isothermal, they should have randomly searched
for cold water. This does not necessarily explain the even
distribution of the mature males, however, since the surface
temperatures were about as warm as during the preceding
summer. If the males were independent of temperature above
10°C, then their distribution should have been about the
same both years.
I would like to suggest that O. virilis depth distribu-
tions are not directly related to maturation, but when other
factors such as oxygen are not limiting, mostly to water
temperature, social aggression of the mature male, and
maturation of the mature female and yearlings. The mature
males are highly aggressive and are known to repel the smaller
males and females (Abrahamsson, 1966; Camougis and Hichar,
1959). These authors also suggest that the adult males con-
centrate in shallow water because this zone offered the best
conditions for food and shelter. I suggest that the mature
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392
males usually select shallow water because this is the zone
with the highest temperature. Although 0. virilis functions
above 10°C (Momot, 1967) its metabolism should increase as
a function of acclimation temperature. If increased meta-
bolic rate is advantageous, then the crayfish should seek
warmer waters. Not all individuals successfully inhabit the
warmer water, however, since the mature males repel the
weaker, less aggressive females and yearlings into deeper,
colder water. Bovbjerg (1964) found that both (). virilis
and 0. immunis prefer the same substrate when tested sep-
arately. When tested together 0_. virilis drove
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393
individuals during this period. This is important for the
survival of the species. If growth and molting is also
related to temperature, it is important that mature females
and yearlings remain in shallow, warm water as long as pos-
sible. This will assure development of the eggs and matura-
tion of yearlings. Once these functions are complete, it
may be immaterial where these members spend the rest of the
summer, as long as there are enough available for breeding
and reproduction the following year. The newborn have
mostly left the mature females by June. This is when the
mature females migrate to deeper waters, or are driven there
by the males. The yearlings move into deeper water some-
what later than the mature females. This exposes them to
predation by the mature males for a longer period, but not
during the warmest part of the summer. The advantages of
remaining in the shallow, warm water to mature may outweigh
the detrimental influence of the mature males.
Artificial destratification greatly altered the usual
distribution patterns. Since the lake was isothermal, there
was no longer any advantage to select shallow depths. The
water was about the same temperature at all depths and all
individuals were exposed to similar thermal conditions.
Under this situation, the mature males no longer selected
the shallow depths, but distributed more or less evenly
throughout the lake. Several authors have shown that cray-
fish either have a very large home range or none at all
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394
(Abrahamsson, 1966; Hichar and Camougis, 1959; Penn, 1950)
and travel great distances in a short period. During
stratified periods, they moved randomly about the shallow
depths, limited by the cold temperature of the lower depths
and by the shore. After destratification, individuals un-
doubtedly wander throughout the entire lake. During August
1970, the entire lake was about as warm as the surface waters
were during 1969. I would therefore expect similar behavior-
al activities and metabolic rates of the mature males at
all depths. The effect of this on the females and yearlings
is unknown- Also unknown is the effect of increased tempera-
ture on the maturation and metabolism of the females and
yearlings. Increased metabolism may have permitted them to
better cope with the aggressive males. Decreased densities
following dispersal should also have lowered encounter rates.
If destratification were continued several years, densities
of mature males throughout the lake might approach former
shallow water densities and lead to low survival of females
and young crayfish.
If repulsion of females is the important factor affect-
ing their distribution during late summer, then evidence
should exist for this both years« The correlation between
male and female depth distributions during August 1969 was
-0.29 (F= 0.76, d.f.= 8). During August and September 1970,
when the lake was isothermal, the correlation was -0.52
(F= 1.89, d.f.= 5). Although neither correlation is
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395
significant at the 0.05 level, they are indicative. In both
cases low concentrations of females were associated with
high concentrations of males. During 1969 the males were
most abundant in shallow water, but during 1970 they were
most abundant in deep water. This evidence is rather weak
and indirect, but tends to substantiate the general hypothe-
sis.
Another, somewhat overlooked possibility exists to
explain the observed distributions. If the much touted
aggressive behavior of the male does greatly affect the
behavior of the female and yearlings, it is also possible
that this factor alone determines the distribution of females
and yearlings within traps. If male aggression can be
credited for altering the preferred distribution of other
individuals within the lake, it seems logical that this ag-
gression could also affect their distribution within the
traps. Traps with many mature males usually contain few
females or young crayfish. Is this because the latter are
not present in that area, or because they are driven from
or do not enter the trap? If the actual distribution of
females was exactly the same as the males at all times, but
the females avoided high concentrations of males, such as
in certain traps, then we would observe distributions such
as those discussed. Likewise, the sex ratio would on the
average be in favor of the males and female catch rates
would be much lower. These conditions are also universally
observed with (3. virilis.
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396
Rainbow Trout
During 1969, the Section Four rainbow trout ranged
between the 5°C and 19°C isotherms (Figure 108). They
exhibit no preference for the 13°C final preferendum tempera-
ture indicated by Garside and Tait (1958). Garside and Tait
conducted their laboratory experiments with 100 mm to 150 mm
length fish. Although light (Sullivan and Fisher, 1953;
Brett, 1952; Pearson, 1952), feeding activity (Brqtt, 1952;
Pearson, 1952) and social behavior (Pearson, 1952) are known
to affect fishes' temperature selection, it is uncertain
what the major factor was in Section Four. These fish had
very slow growth rates. Their stomachs were usually
empty when captured. The usual stomach contents included
periphyton, sticks, marl encrustaceons, miscellaneous detri-
tus, terrestrial insects, amphipods and cladocera. No food
item predominated. The nature of their diet and slow growth
indicate they were at near starvation levels. The 1954-65
stocked trout were very emaciated. These conditions could
lead to a general "search" behavior and thus account in part
for their scattered distribution. This distribution is in
contrast to that found by Horak and Tanner (1964) in Horse-
tooth reservoir. Horsetooth Reservoir is also oligotrophic.
As in Section Four, oxygen, pH, carbon dioxide and alkalinity
gradients apparently did not present barriers to the rainbow
trouts' depth distribution. Nevertheless, the Horsetooth
Reservoir trout preferred water between 18.9°C and 21.1°C.
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397
Over 93% were found in or above the metalimnion. The pre-
dominant factor affecting their distribution in Horsetooth
Reservoir appeared to be food distribution. The trout pre-
dominantly fed on cladocera, and cladocera were most abundant
in the epilimnion. We did not measure cladocera depth dis-
tribution in Section Four, but trout food analysis indicates
they were not a major item.
The intensity of the thermal gradient could be an
important factor. In Section Four this gradient was rela-
tively weak. This is typical of sheltered lakes. Using a
definition of the metalimnion as a change of 1 C/m depth
increase, the metalimnion begins at the surface on some dates
(Figure 72) and extended to near the bottom. Although no one
has clearly described rainbow trout responses to different
temperature gradients, other organisms react abruptly to
strong thermal gradients. Beeton (1960) found that vertical-
ly migrating Lake Michigan Mvsis relica would not penetrate a
thermal gradient of 1.67°C to 2.0 C/m, but some temporarily
penetrated a 0.66°C to 0.94 C/m gradient. During isothermal
periods they would migrate uninterrupted from the bottom to
the surface. Harder (1968) found many marine zooplankters
reacted to discontinuities in stratified laboratory cylinders.
These discontinuities included density gradients due to
temperature, salinity and density without temperature and
salinity gradients. Burbige (1969) found that American smelt
(Osmerus mordax) would not penetrate strong thermal gradients
in the metalimnion.
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398
Although trout were not captured near the surface after
early July 1969, they were seen to feed at the surface after
that period. Likewise, terrestrial insects and surface
living insects were found in their stomachs. This indicates
that they avoided prolonged periods in shallow water„ They
appeared to reside mostly in the deeper water with feeding
excursions into shallow water. Because of the water clarity,
they could undoubtedly see surface disturbances from some
depth.
I was especially interested in the effects of artificial
destratification on the survival and distribution of the
trout. Since artificial destratification increases the
lake's heat budget, and eliminates the deep, cold water, this
poses a threat to the trout (Fast, 1968; Fast and St. Amant,
in preparation). Although trout can withstand 26.7 C tempera-
tures for a few days, prolonged temperatures above 24°C lead
to high mortalities (Eipper, 1960), During a summer of con-
tinued aeration the entire lake will become about as warm as
the surface waters during a summer of normal stratification.
If the surface waters normally attain 26 C or more during the
summer, the entire lake may become this warm. Normally
Section Four's maximum epilimnetic temperature is between
23 C and 25 C. With continuous air injection during 1970,
the entire lake was over 23°C for about two weeks during
August. No trout mortalities were observed during this
period, nor did the fish appear otherwise adversely affected.
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399
The temperature increase apparently was not great enough
to be detrimental.
Although they were distributed throughout the lake dur-
ing artificial destratification, they showed a preference
for the bottom. Before aeration began during early June,
they were found mostly between 1 and 12 meters, but soon
after aeration began, they were most abundant in the 17 to
19.6 meter interval. Food does not appear to be an important
factor affecting this distribution, since their diet was
essentially the same as during 1969. It could be a thwarted
attempt to seek cooler water, since before aeration cooler
water could be found by swimming downwards.
Many trout concentrated in the rising air bubbles.
Fast '(1971) describes this same response of threadfin
shad (Dorosoma petenense) in a southern California reser-
voir. In the shad case, their aggregation was thought to
be a rheotactic response which was reinforced, or rewarded,
by high food concentrations in the rising water. If zoo-
plankton concentrated along the bottom of Section Four,
this rising water undoubtedly contained higher concentra-
tions than the surface waters.. Trout aggregated in the
rising water might thus be exposed to higher food concen-
trations than other surface-dwelling trout.
From the fisheries standpoint, artificial destratifica-
tion of oligotrophic lakes is generally not advisable, since
such mixing will increase their heat budgets and eliminate
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400
the lakes' cold water. Such heating can lead to the elimi-
nation of coldwater species such as trout. Oligothrophic
lakes with borderline surface temperatures, such as Section
Four, are possible exceptions. Destratification of these
lakes may increase fish food and trout production. There
is no evidence that artificial destratification of Section
Four was eithsr beneficial or detrimental for the rainbow
trout. No obvious increase in mortality was observed, nor
did their growth or general condition appear to improve.
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AERATION TO PREVENT WINTERKILL
Winterkill conditions often develop in small eutrophic
lakes subject to extensive periods of ice and snow cover
(Greenbank, 1945; Cooper and Washburn, 1946). These lakes
are typically shallow with a high BOD. The ice cover pre-
vents absorption of atmospheric oxygen, while the snow cover
limits photosynthetic oxygen production. As a consequence,
oxygen may be depleted below concentrations necessary for
fish and other biota and mass mortalities occur.
There are basically two solutions to the winterkill
problem: (1) Snow removal to promote photosynthesis. This
procedure should be started early and continued most of the
winter; and (2) Artificial aeration of the water. Several
techniques for artificial aeration have been developed.
Merna (1965) and Flick (1968) pumped water onto the ice and
allowed it to drain back into the lake through holes chopped
in the ice. This procedure melted the snow cover and in-
creased oxygen concentrations within the lake to acceptable
levels. Rasmussen (1960) and Wood (1961) injected air under
the ice from perforated air lines. This technique melted
large areas of the ice cover and greatly increased the oxygen
concentrations. Patriarche (1961) unsuccessfully used a
401
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402
perforated air line system in a shallow southern Michigan
lake. His system circulated the water over high BOD sedi-
ments which removed oxygen from the water. His air input
was not great enough to compensate for this loss and the
total oxygen content decreased. Halsey (1968) effectively
prevented winterkill conditions by artificially aerating
before an ice cover formed. His lake usually did not
thoroughly mix following the fall overturn. Consequently,
oxygen concentrations, especially in deep water, were low
when ice covered the lake. Snow cover compounded this situ-
ation and led to near zero oxygen concentrations by spring.
By aerating before ice formed, he raised oxygen concentra-
tions throughout the lake to near saturation, oxidized much
of the organic matter and thus prevented oxygen depletion.
As part of my study, I was especially interested in
what effect summertime aeration has on winter oxygen concen-
trations. As we have seen, primary production and plant
standing crops were greatly increased in both Hemlock and
Section Four Lakes by aeration* These materials use oxygen
when they decompose and could contribute to winterkill con-
ditions. Tanner (1952) greatly reduced winter oxygen con-
centrations in these two lakes by summertime artificial
fertilization. Fertilization increased primary production
and the rate of oxygen consumption. Both summer and winter
oxygen concentrations were greatly reduced by this practice.
During the winter following fertilization, the depth where
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403
oxygen fell below 2.0 mg/1 decreased from 6.8 to 3.4 meters
in Hemlock lake, and from over 15 meters to 1.2 meters in
Section Four Lake. Ball (1948) also reports the winterkill
of fish and invertebrates following artificial fertilization.
Ball used much higher fertilizer concentrations and thereby
produced anaerobic conditions throughout the entire lake
during the winter.
After a summer of normal stratification Section Four
had more than 5 mg/1 at all levels on January 24, 1970
(Figure 112). About 37 cm of powdery snow and 31 cm of ice
covered the lake. This much snow reduced light penetration
by more than 99%. The dates of ice cover formation are not
known, but were thought to be during early December both
winters. Winter oxygen concentrations were greatly reduced
following fertilization in 1949 and 1950. Most of the lake
had less than 2.0 mg/1 by February 26, 1951 (Tanner, 1952).
The increased oxygen concentration by 1969 suggests that
the effects of fertilization were not long lasting. The
nutrients presumably were tied up in the sediments and
essentially non-cycling.
On January 22, 1971, following a summer of artificial
destratification, Section Four had more than 7.0 mg/1 oxygen
at all depths. Oxygen concentrations were from 1.0 to 2,0
mg/1 greater at all depths than during the previous year.
Snow and ice cover were less during January 22, 1971; 19 cm
and 16 cm respectively. This indicates that snow and ice
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404
Figure 112. Section Four oxygen profiles during January
1970 and 1971. The 1970 profile is after a
summer of normal stratification, while the
1971 profile is after a summer of artificial
aeration.
-------
Oxygen (mg/l)
0 24 6 8 10
a
a>
a
12-
16-
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406
cover was not as great as during the previous year, and
could account in part for the higher oxygen concentrations.
Nevertheless, the increased productivity during artificial
aeration apparently did not deleteriously affect the winter
oxygen concentrations. I believe that the decomposition
rates were also greatly accelerated by destratification,
and the increased plant biomass was more completely oxidized
before winter stratification began. Destratification in-
creased the lakes' average summer temperature, as well as
oxygen concentration. Both of these conditions should pro-
mote rapid decomposition.
Hemlock Lake has a much greater oxygen demand than
Section Four. On December 21, 1969, levels above 12 meters
were well oxygenated, but no oxygen was observed below 13
meters (Figure 113) . Snow and ice cover were 18 cm and 12
cm respectively. By January 24, 1970, no oxygen was present
below 8 meters and only 3.5 mg/1 were present just under the
ice. Snow and ice cover were 37 cm and 31 cm respectively.
Conditions undoubtedly became worse before the spring turn-
over, but no appreciable winterkill occurred. Many rainbow
trout overwintered without any known ill effects.
After a summer of artificial aeration, oxygen levels
were much greater at all levels. About 4 cm of ice and
scant snow covered Hemlock on December 12, 1970. Oxygen
concentrations were about 8.0 mg/1 at all levels. This
represents a large increase in oxygen content compared to the
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Figure 113. Hemlock Lake oxygen profiles during December 1969 and 1970,
and January 1970 and 1971. The December 1969-January 1970
profiles are after a summer of normal stratification, while
the December 1970-January 1971 profiles are after a summer
of artificial aeration.
-------
Oxygen (mg/l)
a
0)
a
4-
8-
12-
2
i
468
I i i i I i i I LL
XII-21-69
XII-12-70
16-
I 1 I I I
6
i
' 1-24-70
1-22-71,
8
I
-------
409
previous winter. By January 22, 1971, oxygen values ranged
from 4.5 mg/1 at the bottom to 7.5 mg/1 at the surface.
Snow and ice cover were 15 cm and 25 cm respectively.
Although less stringent climatic conditions could account
for some of the increased oxygen, they probably do not
account for much of it. I attribute this large increase in
winter oxygen concentrations to summertime aeration of
Hemlock. Although more plant biomass was produced during
the summer 1970 compared to the summer 1969, I believe it was
more completely decomposed because of the well-aerated condi-
tions. These conditions, plus increased temperatures, per-
mitted more efficient decomposition and oxidation of materi-
als before the onset of winter stratification. The oxygen
concentration was not only increased by aeration, but the
BOD was undoubtedly lowered by continuous summertime aera-
tion.
After the samples were collected January 22, 1971, I ran
the aerator almost continuously for two days (Figure 114).
This was done to determine its ability to aerate under the
ice. Before aeration began, oxygen concentrations at the
lake's center ranged from 4.5 mg/1 at the bottom to 7.5
mg/1 just under the ice (Figure 115J. Oxygen isopleths were
not horizontal, indicating nonuniform rates of oxygen con-
sumption and/or convection currents. Oxygen concentrations
were above 4.5 mg/1 at all locations however. On January
23rd, after 23 hours of air injection, not less than 6.5 mg/1
-------
*>•
Figure 114. Artificial aeration of Hemlock Lake during January 1971. H
The compressor was towed onto the lake and run for two
days. A rubber air line leads to the aeration tower.
-------
-------
412
Figure 115. Effects of artificial aeration on the oxygen
regime during January 1971. The January 22nd
figure shows the oxygen profiles before
winter aeration began, but after a summer of
artificial aeration. The January 23rd profile
is after 24 hours of air injection and the
January 24th profile is after 48 hours of air
injection.
-------
Pistance From Aerator (m)
80 70 60 50 40 30 20 10
a
41
a
-------
414
oxygen was present at all locations. A maximum concentra-
tion of 7.7 mg/1 was observed. Air and water leaked through
the tower walls under the ice. After four hours of aeration,
the ice was completely melted around the tower. This melted
region measured about 20 meters by 10 meters after one day
of aeration. The ice was melted from below by upwelled
water, since water did not flow onto the surface of the ice.
On January 24th, after about 46 hours of aeration,
oxygen concentrations ranged between 6.5 mg/1 and 8.3 mg/1.
Oxygen concentrations inside the aerator were 9.3 mg/1 at
the top.
These data indicate that this hypolimnion aerator can
be used to aerate under the ice. If it had not leaked air
and water through its walls, I would expect the ice around
the tower to remain intact and not melt. In most situations
it is desirable to prevent melting since open water or weak
ice is a hazard. Although the under-the-ice oxygen values
were increased substantially, the relative increase would
have been even greater if conditions had been comparable to
January 1970. Oxygen absorption is much more efficient when
the concentration is near zero, than when it is near satura-
tion.
-------
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-------
APPENDIX
-------
Table A-l.
Ilerilock Lake 17 day peri nhyton weights during 1969
and .1970. Samples were incubated on plastic slides
durinp June,'.July and August each year. Four slides
were incubated at each of" five depths. Ash-free dry
weight is shown for each sanple.
0.0
0.9
Date Collected
0.0140
0.0106
0.0132
0.0103
0.0184
0.0159
0.0155
0.0068
Date Collected
0.0062
0.0075
0.0091
0.0112
0.0118
0.0186
0.0122
0.0133
Date Collected
0.0122
0.0145
0.0146
0.0305
0.0159
0.0213
0.0305
0.0214
Date Collected
0.0254
0.0317
0.0206
0.0225
0.9366
0.0496
0.0489
0.0318
DEPTHS IN METERS
1.8 2.7
7-2-69
0.0177
0.0144
0.0161
0.0172
7-19-&9
0.0141
0.0108
0.0149
0.0072
7-28-69
0.0223
0.0277
0.0282
0.0219
8-5-69
0.0341
0.0440
0.03S 2
O.Gv-'+O
0.0116
0.0114
0.0126
0.0103
0.0176
0.0132
0.0172
0.0165
O.C176
0.1451
0.0470
0.0167
O.C236
o.o '319
0.0394
O.C437
Date Collected 8-12-69
0.0553
0.0811
0.0604
0.0620
0.0416
0.0541
0.0472
0.0671
0.0337
0.0289
0.0345
0.0327
0.0467
0.0564
0.0713
0.0581
3-7
Date Set
0.0090
0.0084
0.0125
0.0115
Date Set
0.0027
0.0035
0.0100
0.0091
Date Set
0.0187
0.0152
0.0098
0.0231
Date Set
0.0061
0.0134
0.0108
0.0143
Date Set
0.0340
0.0465
0.0341
0.0 '507
4.5
6-15-69
0.0059
0.0043
0.0068
0.0091
7-2-69
0.0039
0.0063
0.0031
0.0059
7-9-69
0.0033
0.0063
0.0040
0.0047
7-19-69
0.0095
0.0172
0.0159
0.0110
7-28-69
0.0495
0.0140
0.0217
0.0263
-------
Table A-l (Continued)
0.0
DEPTHS IN
0.9 1.8
METERS
2.7
Date Collected 8-22-69
0.0374
0.026?
0.0337
0.0416
0.0426 0.0349
0.0514 0.0491
0.0460 0.0429
0.0576 0.0416
0.0378
0.0414
0.0462
0,0528
Date Collected 8-29-69
0.0522
0.0411
0.0321
0.0362
0.0618 0.0461
0.0365 0.0428
0.0450 0.0491
0.0324 0.0375
0.0390
0.0435
0.0474
0.0328
3.7
Date Set
0.0479
0.0466
0.0407
0.0486
Date Set
0.0318
0.0267
0.0258
0.0285
4.5
8-5-69
0.0253
0.0275
0.0365
0.0301
8-12-69
0.0226
0.0198
0.0198
0.0245
-------
Table A-l (Continued)
0.0
D3PTHS IN METERS
0.9 1.8 2.7
Date Collected 7-2-70
0.0096
0.0138
0.0194
0.0124
0.0172 0.0091
0.0119 0.0164
0.0102 0.0118
0.0070 0.0094
0.0123
0.0166
0.0038
0.0048
Date Collected 7-19-70
0.0462
0.0385
0.0444
0.0452
0.0503 0.0161
0.0306 0.0161
0.0347 0.0188
0.0337 0.0213
0.0449
0.0691
0.0861
0.0658
Date Collected 7-26-70
0.0366
0.0374
0.0387
0.0422
0.0338 0.0273
0.0326 0.0353
0.0297 0.0287
0.0371 0.0290
0.3219
0.2668
0.1658
0.2223
Date Collected 8-5-70
0.0534
0.0526
0.0510
0.0439
0.0514 0.0740
0.0597 0.0583
0.0550 0.0575
0.0296 0.0498
0.0800
0.1037
0.0918
0.1063
Date Collected 8-12-70
0.0581
0.0639
0.0520
0.0578
0.0564 O.OS13
0.0579 0.0560
0.0619 0.0608
0.0572 0.0622
O.Of^07!
0.0654
0.0727
0.0639
3.7
Date Set
0.0229
0.0029
0.0030
0.0021
Date Set
0.0393
0.0426
0.0367
0.0467
Date Set
0.1157
0.1083
0.1187
0.0660
Date Set
0.0345
0.0591
0.0422
0.0363
Date Set
0.0333
0.0323
0.0367
0.0404
4.5
6-15-70
0,0033
0.0015
0.0016
0.0040
7-2-70
0.0219
0.0266
0.0109
0.0203
7-9-70
0.1451
0.0808
0.1168
0.0816
7-19-70
0.0241
0.0240
0.0286
0.0221
7-26-70
0.0192
0.0290
0.0270
0.0138
-------
Table A-l (Continued)
0.0
DEPTHS IN
0.9 1.8
METERS
2.7
Date Collected 8-21-70
0.0669
0.0636
0.0714
0.0748
0.0645 0.0626
0.0664 0.0645
0.0648 0.0698
0.0650 0.0662
0.0902
0.0789
0.0851
0.0745
Date Collected 8-29-70
0.0492
0.0559
0.0643
0.0431
0.0648 0.0718
0.0676 0.0669
0.0653 0.0669
O.C520 0.0878
0.0429
O.C493
0.0595
0.0455
3.7
Date Set
0.0612
0.0578
0.0642
0.0592
Date Set
O.OR14
0.0893
0.0883
0.0926
4.5
8-5-70
0.0482
0.0358
0.0398
0.0463
8-12-70
0.1153
0.1256
0.1282
0.0897
-------
Table A-2.
Hemlock Lake accumulative periphyton weights
during 1969 and 1970. Samples were incubated
starting June 15 each year and a portion was
retrieved at different times during the summer.
Samples were incubated on plastic slides. These
slides were incubated at each of five depths.
Ash-free dry weight is shown for each sample.
0.0
0.9
DEPTHS II
1.8
T METERS
2.7
3.7
4.5
Date Collected 7-19-69
0.0142
0.0549
0.0278
0.0474
0.0383
0.0322
0.0518
0.0463
0.0338
0.0216
0.0198
0.0301
Date Set 6-15-69
0.0224
0.0179
0.0104
0.0136
0.0069
0.0122
Date Collected 3-5-69
0.0859
0.0494
0.0354
0.1486
0.1127
0.0809
0.1652
0.1179
0.0899
0.0953
0.0712
0.0822
Date Set 6-15-69
0.0685
0.0340
0.0245
0.0282
0.0282
0.0423
Date Collected 8-22-69
0.1773
0.0841
0.0982
0.1855
0.1427
0.2042
0.1902
0.1217
0.1257
0.1266
0.2471
0.1032
Date Set 6-15-69
0.0790
0.0898
0.0748
0.0722
0.0506
0.0849
-------
Table A-2 (Continued)
0.0
DEPTHS IN METERS
0.9 1.8 2.7
Date Collected 7-19-70
0.0861
0.0953
0.0619
0.07^6 0.0753
0.0785 0.0410
0.0626 0.0890
0.0497
0.1180
0.1491
Date Collected 8-5-70
0.0631
0.0706
0.0571
0.1425 0.1187
0.1338 0.1072
0.1460 0.1511
0.1571
0.1464
0.1301
Date Collected 8-21-70
0.244-9
0.2262
0.2066
0.2712 0.2796
0.2598 0.2360
0.2806 0.2515
0.2468
0.2351
0.1801
3.7
Date Set
0.0338
0.0527
0.1237
Date Set
0.0532
0.0690
0.0874
Date Set
0.1200
0.1110
0.1202
4.5
6-15-70
0..0217
0.0480
0 . 0424
6-15-70
0.0393
0.0473
0.0337
6-15-70
0.0949
0.0851
0.1043
-------
Table A-3.
Section Four Lake 17 day periphyton weights durinp
1969 and 1970. Samples were incubated on plastic
slides durinp June, July and Aupust each year. Four
slides were incubated at each of five depths. Ash-
free dry weight is shown for each sample.
0.0
DEPTHS IN METERS
1.8 3.7 5.4
Date Collected 7-2-69
0.0110
0.0120
0.0118
0.0155
O.C1J3 0.0220
0.01 £-9 0.0173
0.0137 0.0199
0.0129 0.0135
0.0118
0.0141
0.0075
0.0075
Date Collected 7-19-69
0.0129
0.0108
0.0107
0.0226
0.0061 0.0235
0.0123 0.0129
0.0112 0.0107
0.0145 O.OC83
0.0103
0.0177
0.0202
0.0210
Date Collected 7-28-69
0.0066
0.0114
0.0078
0.0095
0.0105 0.0090
0.0109 0.0114
0.0105 0.0137
0.0084 0.0168
0.0079
0.0118
0.0150
0.0103
Date Collected 8-6-69
0.0060
0.0070
0.0074
0.0161
0.0103 0.0118
0.0117 0.0122
0.0127 0.0069
0.0101 0.0079
0.0077
0.0101
0.0144
0.0098
Date Collected 8-12-69
0.0071
0.0070
0.0066
0.0119
0.0065 0.0102
0.0147 0.0125
0.0095 0.0089
0.0275 0.0099
0.0235
0.0142
0.0115
0.0191
7.3
Date Set
0.0074
0.0058
0.0103
0.0083
Date Set
0.0186
0.0190
0.0177
0.0196
Date Set
0.0068
0.0084
0.0039
0.0087
Date Set
0.0084
0.0137
0.0057
0.0087
Date Set
0.0063
0.0017
0.0052
0.0157
9.3
6-15-69
0.0092
0.0072
0.0049
0.0072
7-2-69
0.0111
0.0114
0.0127
0.0180
7-9-69
0.0104
0.0081
0.0016
0.0088
7-19-69
0.0080
0.0086
0.0092
0.0107
7-28-69
0.0027
0.0045
0.0061
0.0197
-------
Table A-3 (Continued)
DEPTHS IN METERS
0.0 .1..8 3.7
Date Collected 8-22-69
5.4
7.3 9.3
Date Set 8-6-69
0.0020
0.0145
0.0030
0.0064
0.0057
0.0180
0.0152
0.0112
0.0217
0.0175
0.0094
0.0179
0.0184
0.0108
0.0047
0.0146
0.0099
0.1176
0.0071
0.0125
0.0084
0.0102
0.0088
0.0088
Date Collected 8-29-69
0.0100
0.0059
0.0146
0.0207
0.0070
0.0109
0.0034
0.0042
0.0162
0.0147
0.0194
0.0160
.Date Set 8-12-69
0.0145
0.0167
0.0127
0.0141
0.0157
0.0120
0.0198
0.0093
0.0114
0.0084
0.0046
0.0071
-------
Table A-3 (Continued)
0.0
1.3
DEPTHS IN METERS
5-7 5.4
7.3
9.3
Date Collected 7-2-70
0.0031
0.0017
0.0046
0.0018
0.0056 0.0025
0.0091 0.0061
0.0066 0.0063
0.0049 0.0084
0.0075
0.0083
0.0077
0.0078
Date Collected 7-19-70
0.0068
0.0076
0.0062
0.0069
0.0149 0.0172
0.0196 0.0252
0.0201 0.0305
0.0165 0.0207
C.0198
0.0242
0.0166
0.0290
Date Collected 7-26-70
C.0141
0.0103
0.0120
0.0150
O.C305 0.0980
0.0285 0.0334
0.0254 0.0415
0.0667 0.0378
0.0244
0.0307
0.0276
0.02^6
Date Collected 8-5-70
0.0121
0.0182
0.0179
0.0154
0.0230 0.0195
0.0228 0.0219
0.0258 O.G280
0.0242 C.0191
0.0210
0.0177
0.0269
0.0138
Date Collected 8-12-70
0.0114
0.0118
0.0155
0.0189
0.0300 0.0344
0.0339 0.0111
0.0192 0.0194
0.0339 0.0130
0.0203
0.0399
0.0279
O.C181
Date Set
0.0078
0.0094
0.0124
0.0135
Date Set
0.0268
0.0178
0.0201
0.1231
Date Set
0.0195
0.0291
0.0187
0.0281
Date Set
0.0243
0.0193
0.0159
0.0169
Date Set
0.0189
0.0246
C.021C
0.0210
6-15-70
0.0070
0.0044
0.0041
0.0054
7-2-70
0.0133
0.0178
0.0168
0.0110
7-9-70
0.0259
0.0233
0.0247
0.0123
7-19-70
0.0114
0.0126
0.0110
0.0136
7-26-70
0.0155
0.0156
0.0162
0.0167
-------
Table A-3 (Continued)
0.0
1.8
DEPTHS IN METERS
3.7 5.4
7-3
9-3
Date Collected
0.0192
0.0196
0.0177
0.0268
0.0270
0.0310
0.0246
0.0272
Date Collected
0.0148
0.0153
0.0182
0.0145
0.0287
0.0359
0.0381
0.0378
8-21-70
0.0246
0.0241
0.0262
0.0269
8-29-70
0.0288
0.0229
0.0336
0.0253
0.0272
0.0251
0.0210
0.0221
0.0352
0.0356
0.0369
0.0189
Date Set
0.0178
0.0208
0.0180
0.0183
Date Set
0.0268
0.0277
0.0346
0.0286
8-5-70
0..0110
0.0101
0.0144
0.0084
8-12-70
0.0141
0.0166
0.0140
0.0199
-------
Table A-4.
Section Four Lake accumulative periphyton weiphts
during 1969 and 1970. Samnles were incubated
starting June 15 each year and a portion was retrieved
at different times during the summer. Samples were
incubated on plastic slides. These slides were incu-
bated at each of five depths. Ash-free dry weiqht is
shown for each sample.
0.0
1.8
DEPTHS IN METERS
3.7 5.4
7-3
9.3
Date Collected
0.
0.
0.
0393
0152
0107
0.
0.
0.
0252
0185
0228
Date Collected
0.
0.
0.
0318
0356
0304
0.
0.
0.
0482
0536
0606
Date Collected
0.
0.
0.
153^
0299
2914
0.
0.
0.
0757
1378
1517
7-19-69
0.
0.
0.
8-6-69
0.
0.
0.
8-22-69
0.
0.
0.
Date Set
0166
0253
0184
0.
0.
0.
0184
0228
0111
0.
0.
0.
0204
0141
0185
Date Set
0472
0735
0390
0.
0.
0.
0327
0282
0357
0.
0.
0.
0247
0335
0657
Date Set
1010
2195
0683
0.
0.
0.
0575
2635
0511
0.
0.
0.
0315
0335
0304
6-15-69
0
0
0
.0120
.0178
.0139
6-15-69
0
0
0
.0237
.0264
.0283
6-15-69
0
0
0
.0311
.0304
.0303
-------
Table A-4 (Continued)
0.0
D3PTH3 IN METERS
1.8 3-7 5.4
Date Collected 7-19-70
0.0142
0.0107
0.0092
0,0323 0.0355
0.0366 0.0453
0.0309 0.0332
0.0383
0.0429
0.0425
Date Collected 8-5-70
0.0291
0.0325
0.0293
0.0630 0.0648
0.0652 0.0427
0.0633 0.0701
0.0575
0.0564
0.0577
Date Collected 8-21-70
0.0^90
0.0536
0.0535
0.1083 0.1256
0.1214 0.1090
0.0890 0.1355
0.1000
C.0653
0.1278
7.3
Date Set
0.027«
0.0301
0.0015
Date Set
0.0277
0.0425
0.0350
Date Set
0.0969
0.0748
0.0772
9.3
6-15-70
0.0583
0.0433
0.0281
6-15-70
0.0195
0.0211
0.0404
6-15-70
0.0405
0.0340
0.0558
-------
Table A-5. Hemlock l,a-ke loobenthos collected with an Fl-.man dredpe durinc I960 and 197n. Numbers
and wet weights for the seven most abundant taxa are *hown in this table for each
samnle. 125 sannles were collected each simmer. The less abundant taxa are listed
in Table A-6, Tn verify the total orpanisms for a piven sample, consult both tables.
llenth is in meters and weipjit is in
Sample
Number
6-13-69
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
7-4-69
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
Depth
15.6
16.0
15.5
15.1
15.5
14.4
14.2
13.5
12.8
12.2
10.5
9.6
7.5
9.2
8.3
6.9
6.2
4.6
6.4
4.6
3.0
2.3
1.6
1.0
0.3
16.5
16.9
16.0
15.5
15.5
14.4
13.2
12.3
13.5
11.4
10.7
10.1
8.7
9.4
7.8
7.1
6.0
5.7
5.0
Oligochaeta
No. Wt.
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
o o.nooooo
0 0.000000
0 0.000000
0 0.000000
0 0.000000
o o.nooooo
0 0.000000
1 0. 000807
1 0. 1101200
0 0.000000
0 0.000000
0 0.000000
Chironomid L.
No. Kt.
0
0
0
0
0
0
0
0
0
0
0
2
23
14
32
14
41
22
5
19
14
14
9
17
51
n
0
0
0
0
0
0
1
0
1
4
1
0
0
0
8
1
0
74
0.000000
0.000000
0.000000
0.00(1000
0.000000
0.000000
0.000000
0.000000
0.000000
n. oooooo
0.000000
0.001062
0.004367
0.003997
0.009144
0.007068
0.040451
0.008452
0.001444
0.008793
0.003842
0.004136
0.005714
0.002697
0.004725
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000164
0.000000
0.00049S
0.001055
0.000160
0.000000
n. oooooo
0.000000
0.004809
0.000563
0.000000
0.020104
Chironomid P.
No. Wt.
0
0
n
0
0
0
n
0
0
0
0
0
0
0
0
0
0
0
0
0
0
i
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
n
0
2
0.000000
0.000000
n. oooooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000194
0.000000
0.000000
0.000088
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0,000204
Mayflies
No. Wt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
1
4
1
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000798
0.000000
0.000560
0.001520
0.000629
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000348
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
o.oooono
0.000000
Chaoborus L.
No. Wt.
6
3
3
9
8
1
14
11
18
29
40
2
20
10
4
10
14
18
1
8
0
0
0
0
0
11
11
9
11
3
2
15
16
3
8
15
5
9
12
5
13
5
4
1
0.002399
0.002742
0.002443
0.007949
0.009722
0.000418
0.010680
0.007672
0.011638
0.017525
0.024427
0.002856
0.015112
0.007879
0.003355
0.006468
0.006407
0.011059
0.000316
0.005127
0.000000
0.000000
0.000000
0.000000
0.000000
0.007579
0.009043
0.008026
0.008793
0.003142
0.001055
0.010921
0.012084
0.002552
0.006492
0.013125
0.004211
0.009479
0.011695
0.003100
0.009874
0.003972
0.002097
0.000613
Chaoborus P.
No. Wt.
2
1
0
1
0
0
1
1
0
2
10
0
6
3
2
2
4
11
1
.3
1
0
0
0
0
2
2
0
1
0
0
0
0
0
0
0
1
1
1
0
1
0
n
i
0.013074
,0.001037
0.000000
0.000945
0.000000
0.000000
0.000874
0.001240
0.000000
0.002777
0.009640
0.000000
0.010270
0.005007
0.002676
0.003642
0.012160
0.013505
0.000976
0.002355
0.000730
0.000000
0.000000
0.000000
0.000000
0.002270
0.002203
0.000000
0.000653
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001246
0.000969
0.001175
0.000000
0.000845
0.000000
0.000000
0.000709
Heleidae
No. Wt.
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
2
0
2
1
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
1
2
10
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001182
0.000000
0.000912
0.000342
0.000000
0.002971
0.000653
0.002524
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000558
0.000214
0.000608
0.003064
0.000000
-------
Table A-S (Tont inueil ]
Sample
Number
120
121
122
123
124
125
7-25-69
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
8-15-69
301
302
303
304
305
306
307
308
309
310
311
312
Depth
4.3
3.7
2.3
2.9
1.4
0.7
17.8
16.5
16.5
16.0
15.3
14.2
13.7
13.2
12.8
12.2
10.5
8.7
9.6
7.8
8.5
7.3
6.9
6.0
5.0
4.6
3.2
2.7
1.8
1.4
0.7
17.8
16.9
16.9
16.5
16.2
14.6
13.7
13.2
12.6
12.0
10.1
9.6
Oligochaeta
No. Kt.
0 0.000000
o n.nooono
0 0.000000
0 0.000000
o o.oooooo
o o.oooono
o o.oooooo
0 0.000000
o o.onoooo
0 0.000000
0 0.000000
o o.oooooo
n n. oooooo
o o.onoooo
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0'. OOOOOO
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
o o.nooooo
0 0.000000
o o.ooooon
o o.onooon
0 0.000000
0 0.000000
0 0.000000
Cbironomid I..
So. Kt.
i:
20
1
3(1
89
90
n
0
0
c
0
n
n
n
0
0
2
->
0
1
n
4
5
13
17
4
23
6
39
39
0
n
0
0
0
0
0
0
s
r)
n
n
n. 004593
0. 004953
0. 000626
0.003803
0. 010616
0. 008971
0.000000
o.ooooon
o.oooooo
0.000000
o.oooooo
0.000000
0.000000
o.oooooo
n. oooooo
0.000000
0.000574
0.00676S
0.000000
0.000030
0.000000
0.0037RS
0.001082
0.00236T
0.002(129
0.005782
0.000218
0.001429
0.000253
0.002314
0.003501
1.000000
O.OOOOnn
O.OOOOOn
1.000000
n.oononr
o.oooooo
0.000000
o.oonoon
0.001162
0.001494
0.000000
n. oooooo
Chironomid P.
No. Wt.
0
1
0
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
0
3
4
0
0
0
n
0
0
0
0
0
0
0
0
0.000000
0.000283
0.000000
0.000123
0.000060
0.000190
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000073
0.000000
0.000066
0.000000
0.000000
0.000000
0.000267
0.000276
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
Mayflies
No. Wt.
0
0
0
1
4
19
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
43
0
0
0
0
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000791
0.002167
0.013419
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
o.ooonoo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000051
0.002655
0.017489
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
Chaoborus L.
No. Wt.
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
2
1
0
1
2
0
0
0
0
0
0
0
0
4
2
2
1
3
1
9
6
7
4
13
6
0.000365
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000767
0.002268
0.000436
0.000000
0.000762
0.000754
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.003367
0.000769
0.001700
0.001494
0.003742
0.000940
0.009658
0.006078
0.007245
0(003729
0.015894
0.005475
Chaoborus P.
No. Wt.
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
0
5
2
0
1
1
3
0
0.000570
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000885
9. OOOOOO
0.000000
0.000000
0,000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001791
0.000000
0.000000
0.000000
0.000000
0.006079
0.002257
0.000000
0.001325
0.001514
0.004065
0.000000
Heleidae
No. Wt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
3
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
o.eooooo
0.000000
0.000000
0.000117
0.000000
0.002063
0.000000
0.000000
0.000000
0.000039
0.000120
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
-------
Table A-5 (Continued)
Sample
Number
313
314
315
316
317
318
319
320
321
322
323
324
325
9-6-69
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
6-12-70
1001
1002
1003
1004
1005
Depth
8.7
8.3
7.3
7.3
6.9
6.0
5.0
4.8
3.2
2.S
1.8
0.9
0.5
17.8
17.4
17.1
16.5
15.8
14.6
12.8
13.7
12.0
11.4
10.5
7.8
8.7
9.4
8.7
6.9
7.3
5.0
6.0
4.3
3.4
2.1
1.8
0.9
0.5
0.0
0.0
17.4
16.5
16. n
Oligochaeta
No . Wt .
0 0.000000
0 0.000000
1 0.000442
0 0.000000
n o.oooooo
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 O.OCOOOO
0 0.000000
0 0.000000
o o.nooooo
ft 0.000000
0 0. 000(100
0 0.000000
0 0.000000
o o.oonooo
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
1 0.001023
0 0.000000
0 0.000000
n o.oooooo
P 0.000000
o o.ooonoo
0 0.000000
0 0.000000
n n. oooooo
n o.oooooo
0 0.000000
0 0.000000
0 0.000000
0 0.000000
o o.noonoo
Chironomid L.
No. Wt.
2
28
30
5
4
0
21
26
11
14
4
63
64
0
0
0
0
0
0
2
0
8
7
3
17
5
8
6
48
34
18
1
20
15
16
9
152
29
0
0
0
0
0
0.001487
0.018956
0.012203
0.001011
0.000812
0.000000
0.008194
0.007209
0.00'2274
0.001255
0.000538
0.005374
0.006092
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000574
0.000000
0.006546
0.001930
0.000613
0.011584
0.003208
0.006087
0.002373
0.004146
0.005071
0.002413
0.000147
0.001984
0.001502
0.001885
0.000913
0.008952
0.002256
0.000000
0.000000
0.000000
0.000000
0.000000
Chironomid P.
No. Wt.
0
0
1
0
0
0
2
3
0
0
0
0-
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
3
0
0
1
2
0
0
0
0
0
0
0.000000
0.000000
0.000192
0.000000
0.000000
0.000000
0.004295
0.001834
0.000000
0.000000
0.000000
0.000000
0.000182
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001935
0.000000
0.000000
0.000000
0.010601
0.000000
0.000000
o.ooonn
0.018306
0.000000
0.000000
o.nooooo
o.oonooo
o.oooooo
o.ooonoo
Mavflies
No. Wt.
0
0
0
0
0
0
0
0
0
1
2
9
3
0
n
0
0
0
0
0
0
n
0
0
0
0
0
0
0
0
0
n
1
4
n
0
17
0
0
0
n
0
0
o.oooono
0.000000
o.oooopo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000103
0.000505
0.001182
0.001010
0.000000
0.000000
0.000000
0.000000
P. OOOOOO
0.000000
0.000000
n. oooooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
o.oooooo
n. "oooooo
n. 000176
n. 000405
0.000000
n. oooooo
0.001671
0.000000
o.onnooo
0.000000
o.ooonoo
0.000000
o.ooonon
Chaohorus L.
No. Wt.
3
1
1
4
6
0
1
0
0
0
0
0
0
1
3
3
1
2
3
3
4
1
6
20
2
2
14
1
0
0
0
0
n
n
p
p
n
0
0
0
3
2
1
0. 002953
0.000479
0. 000594
0.001634
0.003496
0.000000
0.000746
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000923
0.002929
0.001823
0.000718
0.000844
0.001230
0.002643
0.002263
0.000903
0.006074
0.013576
0.000752
0.001923
0.007097
0.000687
o.oonooo
0.000000
0.000000
o.noooon
0.000000
0.000000
O.OOOhOO
0.000000
0.000000
0.000000
n. oooooo
n.nnonno
n. 001574
0.001630
n. 001161
Chaoborus P.
No. Wt.
3
3
1
1
2
0
0
0
0
0
0
0
0
0
0
2
0
0
1
0
0
0
0
0
0
0
1
1
0
n
0
0
0
0
0
0
n
n
n
n
0
0
0
0.003871
0.004301
0.002051
0.002074
0.002404
0.000000
0.000000
0.000000
0.000000
0.000000
o.nooooo
0.000000
0.000000
0.000000
0.000000
0.001660
0.000000
0.000000
0.003538
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001228
0.001728
0.000000
0.000000
n. oooooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
O.ROOOOO
o.ooooon
n.onnooo
0.000000
0.000000
o.oo.nono
Heleidae
No . Kt .
0
2
0
31
0
0
6
7
2
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
2
5
0
7
0
0
2
0
0
0
0
p
0
0
n
0.000000
0.000442
0.000000
0.018306
0.000000
0.000000
0.005091
0.007542
0.000165
0.000000
0.000000
0.000082
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000316
0.000000
0.000000
0.000608
0.001536
o.ooooon
0.005464
O.OOQOOO
0.000000
0.000228
0.000000
o.oooooo
0.000000
0.000000
0.000000
0.000000
P. OOOOOO
o.ooooon
-------
Tnble A-S (Continued)
Sample
Number
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
7-3-70
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
Depth
0.0
13.2
0.0
0.0
12.0
11.0
10.5
10.1
8.7
7.8
7.3
6.9
5.3
4.6
3.9
3.2
1.8
1.4
0.5
0.3
17.8
17.4
16.7
16.0
15.8
14.6
13.7
13.5
12.6
12.0
11.0
10.3
9.6
8.0
8.5
7.1
6.9
4.6
5.0
4.3
3.2
2.5
1.6
0.9
0.3
Oligochaeta
No. Wt.
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
JO 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
4 0.001083
88 0.018548
7 0.001453
2 0.000124
0 0.000000
0 0.000000
4 0.004159
2 0.003062
0 0.000000
0 0.000000
2 0.000259
0 0.000000
n o.oooooo
0 0.000000
1 0.000160
Chironomid L.
No. Kt.
0
0
0
0
4
4
6
11
3
6
22
3
48
52
24
15
12
9
10
5
1
0
0
0
0
0
1
0
0
1
7
28
1
11
2
12
13
36
20
42
10
Q
53
131
260
0.000000
0.000000
0.000000
0.000000
0.000457
0.001170
0.005489
0.006766
0.001525
0.003202
0.011157
0.001426
0.028546
0.016277
0.003680
0.002233
0.002606
0.001168
0.000553
0.000328
0.000193
0.000000
0.000000
0.000000
0.000000
0.000000
0.000606
0.000000
0.000000
0.000564
0.004382
0.012183
0.000214
0.01063!)
0.000999
0.008927
0.007622
0.039185
0.017539
0.008507
0.003254
0.000729
0.002923
0.006770
0.012253
Chironomid P.
No. Wt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
3
5
o.oooono
o.onoooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001078
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
o.oooono
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001110
0.000000
0.000000
0.000000
0.001110
0.000000
0.000000
0.000000
0.000000
0.000000
0.000150
0.000378
M
No.
n
0
0
0
0
0
0
0
0
]
0
0
1
1
3
1
19
5
6
11
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
2
6
J
13
avflies
Wt.
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000050
0.000000
0.000000
0.000066
0.000275
n. 000075
0.000257
0.005706
0.000942
0.001575
0.001661
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000666
0.000551
0.002970
0.002788
0.003023
Chaoborus L.
No. Wt.
n
i
0
0
2
1
4
7
9
3
3
13
0
0
0
0
0
0
6
0
0
2
3
3
5
0
1
1
4
0
1
4
8
4
3
5
3
6
8
6
0
0
0
0
0
0.000000
0.000535
0.000000
0.000000
0.002212
0.002586
0.002576
0.006233
0.006715
0.002793
0.001824
0.001685
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.004714
0.000000
0.000000
0.000986
0.002013
0.000163
0.000234
0.000000
0.000043
0.000132
0.001263
0.000000
0.000136
0.000524
0.004832
0.001427
0.000113
0.000788
0.000343
0.001083
0.000787
0.001461
0.000000
0.000000
0.000000
0.000000
n. 000000
Chaoborus P.
No. Wt.
0
0
0
0
0
1
0
1
0
1
2
1
2
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
4
1
6
1
9
1
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000852
0.000000
0.001118
0.000000
0.000774
0.001939
0.000928
0.001822
0.000000
0.000000
0.000000
0.000000
0.000000
0.000559
0.000000
0.000000
0,000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000810
0.000000
0.000000
0.000000
0.000000
0.003438
0.000819
0.004837
0.000701
0.005280
0.000388
0.000000
0.000000
0.000000
0.000000
Heleidae
No . Kt .
0
0
0
0
0
0
0
1
1
0
9
0
2
0
1
2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
0
4
0
0
0
1
1
2
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000222
0.000062
0.000000
0.001004
0.000000
0.000388
0.000000
0.000037
0.003432
0.000215
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000341
0.000000
0.001010
0.000000
0.000000
0.000000
0.000267
0.000359
0.000617
0.000000
0.000000
0.000000
0.000000
0.000000
-------
Table A-5 (Continucdl
Sample
Number
7-24-70
3001
30(12
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
8-14-70
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4P15
40J6
4017
4018
4019
Depth
18.1
17.6
16.7
16.7
16.2
14.6
14.2
12.3
11.4
12.6
11.0
10.5
9.6
7.8
8.5
7.3
6.7
5.0
5.5
4.1
3.4
1.8
2.5
0.9
0.3
18.1
17.4
16.9
16.1
15.1
14.6
13.7
12.6
11.7
i:.o
11. n
9.6
8.7
10.1
S.3
" . 3
6.9
5.3
4.6
OliRnchaeta
No. Kt.
0
0
0
0
0
0
0
6
2
0
2
1
7
0
0
1
2
1
0
0
1
0
0
0
0
0
0
0
0
n
0
c
11
n
7
5
2
4
1
n
1
p
r
n
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001384
0.000337
0.. 000000
0/000457
0.001051
0.004039
0.000000
0.000000
0.000117
0.002728
0.000240
0.000000
0.000000
0.000074
0.000000
0.000000
0.000000
0.000000
r. oooooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.002900
o.oooono
0.002178
0.003687
0.000776
0. 003144
0.000141
o.oonooo
n. 000934
O.OPPPOO
O.noooon
o.onooon
Chironomid 1, .
No. Wt.
0
1
0
0
0
0
0
4
6
0
10
11
0
~l
10
45
31
1
15
45
172
17
73
78
147
0
1
0
0
5
1
1
M
5
8
^
27
4
10
13
C4
SR
31
60
0.000000
0.000113
0.000000
0.000000
0.000000
0.000000
0.000000
n. 000885
0.005058
0.000000
0.004102
0.005610
0.000000
0.000931
0.004292
0.011427
0.014501
0.001617
0.001494
0.004718
0.018816
0.000701
0.008740
n. 007059
0.012557
n. OOOOOO
0.000159
0.000000
0.000000
0.000993
0.000494
0.000192
0.023224
0.004328
0.010667
0.000587
n. 010915
n. 002437
0.005115
o.oioooi
n. 003236
n. 003820
0.006249
n . 0 0 4 4 3 1
Chironomid P.
N'o. >Vt.
0
0
0
0
0
0
0
1
0
0
-)
0
0
0
0
2
0
0
0
4
3
0
10
4
7
0
0
0
0
1
0
0
1
1
3
0
3
0
2
n
2
0
0
i
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000107
0.000000
0.000000
0.000306
0.000000
0.000000
0.000000
0.000000
0.000347
0.000000
0.000000
0.000000
0.000860
0.000296
0.000000
0.001464
0.000855
0.000509
0.000000
0.000000
0.000000
0.000000
0.002072
0.000000
0.000000
0.000330
n.oooson
0.006105
0.000000
0.001004
0.000000
0.000973
0.000000
0.000246
0.000000
0.000000
0.000159
Mavf lies
No. ' Wt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
2
.2
7
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000074
n. oooooo
0.000563
0.000312
0.001542
0.000000
0.000000
o.oooeoo
0.000000
0.000000
0.000000
0.000000
0.000000
P. OOOOOO
0.000000
0.000000
0.000162
0.000000
P.OPOOOO
0.000000
O.OOPOOO
0.000000
0.000000
O.OPOOOO
Chaobnrus L.
No. Wt.
18
15
31
21
45
14
34
43
25
21
100
46
16
68
48
33
31
25
66
4
6
1
0
0
0
26
15
31
45
11
35
26
10
7
6
21
8
13
16
11
5
12
3
2
0.002534
0.002945
0.007430
0.002454
0.006981
0.002142
0.007453
0.007448
0.004476
0.004675
0.016980
0.008715
0.004008
0.011200
0.010063
0.007372
0.010005
0.005735
0.018560
0.000440
0.001905
0.000530
0.000000
0.000000
0.000000
0.003743
0.004067
0.005504
0.010303
0.002567
0.007870
0.005705
0.002281
0.002226
0.002014
0.004824
0.001388
0.002659
0.005156
0.002385
0.000915
0.001997
0.000799
0.000303
Chaohorus P.
No. Wt.
1
0
1
0
0
0
0
0
1
1
2
0
1
0
1
0
1
2
4
2
1
0
0
0
0
2
1
1
0
1
5
0
0
2
0
2
3
3
0
2
0
3
1
P
0.000960
0.000000
0.000614
0.000000
0.000000
0.000000
0.000000
0.000000
0.000513
0.000645
0.001046
0.000000
0.001062
0.000000
0.000515
0.000000
0.000607
0.001276
0.002521
0.001779
0.000736
0.000000
0.000000
0.000000
0.000000
0.001387
0.0001D9
0.000453
0.000000
0.000119
0.002344
0.000000
0.000000
0.001099
0.000000
0.001167
0.001304
0.001169
0.000000
0.001001
o.nooooo
0.001381
0.000580
0.000000
Heleidae
No. Kt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
7
2
0
3
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
2
0
0
8
0
1
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
O.OOOtJOO
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000269
0.000406
0.000586
0.000000
0.001106
0.000000
0.000000
0.000000
0.000000
0.000161
0.000113
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000322
0.000000
0.000000
0.000832
0.000000
0.000615
-------
Table A-5 (Continued)
Sample
Number
4020
4021
4022
4023
4024
402S
9-4-70
S001
5002
S003
5004
5005
5006
5007
5008
5009
5010
5011
5012
5013
5014
5015
5016
5017
5018
5019
5020
5021
S022
5023
5024
5025
Depth
3.9
3.0
2.1
1.6
1.2
0.3
18.3
17.8
16.9
16.2
15.1
13.9
12.6
11.4
12.0
12.8
11.0
9.8
9.2
8.0
8.3
6.9
5.7
4.6
4.8
3.7
3.0
2.1
1.4
0.7
0.3
Oligochaeta
No. Wt.
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
1 0.000198
0 0.000000
74 0.055148
3 0.000632
4 0.002107
1 0.010180
3 0.001317
3 0.003327
8 0.006156
0 0.000000
6 0.002028
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
Chirononid L.
No. Wt.
136
6
18
8
42
59
2
0
4
3
1
1
10
3
6
5
3
2
14
13
9
1
17
38
12
40
41
24
9
IS
63
0.011041
0. 000450
0.000760
0.000886
0.002043
0.002828
0.003847
0.000000
0.002151
0.001267
0.002180
0.000089
0.007225
0.001256
0.005148
0.002651
0,000768
0.001666
0.004711
0.002222
0.003552
0.000037
0.000786
0.001862
0.000332
0.003022
0.002620
0.001584
0.000151
0.010543
0.003172
Chironomid P.
No . Wt .
8
1
2
0
0
1
0
0
0
1
0
0
0
0
0
1
0
0
0
1
0
1
0
0
0
1
0
0
0
1
4
0.000747
0.000086
0.000176
0.000000
0.000000
0.000119
0.000000
0.000000
0.000000
0.000249
0.000000
0.000000
0.000000
0.000000
0.000000
0.000932
0.000000
0.000000
0.000000
0.000046
0.000000
0.000030
0.000000
0.000000
0.000000
0.000150
0.000000
0.000000
0.000000
0.000049
0.000179
Mavflies
No . Wt .
0
0
2
0
1
9
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
2
0
(1
3
0.000000
0.000000
0.000151
0.000000
0.000150
0.000683
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000-00
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000084
n. oooooo
0.000000
0.000118
0.000090
0.000000
n.onoooo
0.000292
Chaoborus L.
No . Wt .
4
0
0
0
0
0
10
25
90
16
12
0
2
6
3
6
4
0
3
3
6
5
0
0
1
0
0
n
0
i
0
0.000321
0.000000
0.000000
0.000000
0.000000
0.000000
0.001336
0.005454
0.029378
0.004247
0.002245
0.000000
0.000319
0.001675
0.000418
0.000927
0.000900
0.000000
0.000473
0.000424
0.001338
0.000947
0.000000
0.000000
0.000155
0.0t)0000
0.000000
0.000000
0.000000
0.000307
0.000000
Chaoborus P.
No. Wt.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000366
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
Heleidae
No. Wt.
4
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
1
10
14
2
2
1
2
0
0
2
0
0
1
0.002745
0.000000
0.000000
0.000000
0.000000
0.000025
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001240
0.001430
0.002777
0.000399
0.000601
0.000831
0.000743
0.000000
0.000000
0.000524
0.000000
0.000000
0.000020
-------
Table A-6.
Hemlock Lake zoobenthos collected during 1969 and
1970. The less abundant organisms are listed in
this table. To obtain a total for a given sample,
add the values for each sample (check each organism)
to the values for that sample piven in Table A-5.
Wet weights are shown.
Sample
Number
Amphipods
224
325
424
1024
1025
2004
Dragonf lies
22
23
24
124
125
223
225
321
324
325
424
425
1022
2024
2025
3025
4022
4025
5020
5025
Damselflies
118
424
425
1025
4002
5025
Depth
On)
1.37
0.46
0.92
0.46
0.23
16.02
2.29
1.60
0.92
1.37
0.69
1.83
0.69
3.20
0.92
0.46
0.92
0.46
1.83
0.92
0.23
0.23
2.06
0.23
3.66
0.23
5.72
0.92
0.46
0.23
17.40
0.23
Date
7-25-69
8-15-69
9- 6-69
6-12-70
6-12-70
7- 3-70
6-13-69
6-13-69
6-13-69
7- 4-69
7- 4-69
7-25-69
7-25-69
8-15-69
8-15-69
8-15-69
9- 6-69
9- 6-69
6-12-70
7- 3-70
7- 3-70
7-24-70
8-14-70
8-14-70
9- 4-70
9- 4-70
7- 4-69
9- 6-69
9- 6-69
6-12-70
8-14-70
9- 4-70
Number
1
1
1
1
1
1
1
2
1
1
1
1
5
1
1
1
1
1
2
1
2
1
2
3
1
2
4
9
2
1
1
1
Weight
CRN)
0.000148
0.000058
0.000229
0.000012
0.000454
0.000220
0.043686
0.076687
0.008999
0.020766
0.057300
0.169671
0.055579
0.225487
0.000118
0.152927
0.000233
0.022SS7
0.151958
0.081826
0.005540
0.049046
0.003524
0.079121
0.202513
0.400948
0.004010
0.004751
0.001369
0.003350
0.000409
0.000038
-------
Table A-6 (Continued)
Sample
Number
Trichoptera
115
5022
Tabanid
5022
Leeches
323
5017
Depth
(m)
7
2
2
1
5
.78
.06
.06
.83
.72
7 _
9-
9-
8-
9-
Date
4-
4-
4-
15-
4-
69
70
70
69
70
Number
28
1
1
1
1
Weight
(Rm)
0.
0.
0.
0.
0.
016076
000082
000243
546294
029607
-------
Section Pour Lake inobenthos collected with an Fkman dredce during 1969 and 1970.
Numbers and weinhts for the seven most abundant taxa are shown in this table for
each sample. 125 samples were collected each summer. The less abundant taxa are
lisli:.' iii T.ible A-S. To verifv thr toL.'l irmnisms for a oivcn s.innlo, consult
both tables. Depth is in neters and wciclit is in °rams.
Sample
Number
6-15-69
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
7-5-69
151
15?
151
ZS4
155
156
157
158
159
160
161
162
163
164
165
166
167
168
Depth
18.7
17.8
14.6
16.9
16.0
13.0
13.7
12.3
12.8
11.7
11.7
8.9
7.8
7.5
9.2
6.4
3.7
4.6
6.2
5.0
3.2
2.5
2.1
0.9
1.4
19.7
19.2
18.3
17.4
16.0
14.2
13.0
12.8
12.3
11.2
10.1
8.3
8.3
9.2
8.5
5.0
5.0
4.8
Oli^ochaeta
No. Wt,
12S 0.
263 0.
216 0.
112 0.
20 0.
35 0.
29 0.
6 0.
34 0.
3 0.
2 0.
1 0.
6 0.
16 0.
0 0.
9 0.
4 0.
18 0.
4 0.
10 0.
1 0.
11 0.
0 0.
11 0.
4 0.
398 0.
358 0.
156 0.
32 0.
45 0.
6 0.
70 0.
30 0.
18 0.
3 0.
0 0.
2 0.
7 0.
2 0.
20 0.
2 0.
5 0.
4 n.
037484
129977
113488
036015
006093
008992
022968
001411
004647
000785
000589
000207
001358
016207
000000
001384
000680
003336
000558
002172
OOOS41
001344
000000
003405
001753
394441
469270
055653
028483
010068
,- --750
017975
006122
005887
000272
000000
000782
005178
001123
018710
000^25
002251
001672
Chironomid L.
No . Wt .
0
2
11
40
53
8
1
5
4
1
8
22
51
258
53
84
89
164
72
225
142
112
184
205
200
0
0
54
59
77
13
39
32
17
9
183
78
180
119
192
132
57
155
0.000000
0.001303
0.001349
0.030825
0.007247
0.007369
0.000102
0.001807
0.000495
0.000510
0.001563
0.002000
0.005433
0.030392
0.006443
0.006158
0.004919
0.008330
0.005483
0.012618
0.000500
0.006432
0.010559
0.012364
0.042538
0.000000
0.000000
0.134584
0.092093
0.012093
0.001*33
0.014097
0.012732
0.007923
0.003595
0.056019
0.015103
0.038387
0.007244
0.027144
0.017560
0.012130
0.012R60
Chironomid P.
No. Wt.
0
0
1
1
1
1
0
1
0
0
0
1
1
53
1
23
4
7
9
8
3
2
3
11
16
0
0
0
1
2
0
0
0
i
0
4
1
0
4
3
3
3
7
0.000000
0.000000
0.000062
0.000286
0.000124
0.000091
0.000000
0.000146
0.000000
o.oooooo
0.000000
0.000163
0.000099
0.006324
0.000088
0.002117
0.000139
0.000670
0.001031
0.000728
0.000597
0.000214
0.000112
0.000540
0.002381
0.000000
0.000000
0.000000
0.000920
0.000389
n. Trioooo
0.000000
0.000000
0.000406
o.ooaooo
0.001597
0.003525
o.oononn
o.ooii,,:
0.00162S
0.000601
0.00052R
0.001003
Amphinoda
No. ' Wt.
1
0
2
0
-------
Table A-7 (Continued)
Sample
Number
169
170
171
172
173
174
T - :
7-25-69
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
8-15-69
351
352
353
354
355
356
357
358
359
360
361
362
Depth
4.1
3.7
2.7
2.3
3.0
1.2
•".7
19.7
18.7
19.4
18.5
17.4
13.2
13.7
12.0
11.0
11.4
10.3
9.2
8.3
9.2
8.3
7.3
5.5
4.8
5.0
4.3
3.2
3.7
2.3
1.2
0.5
19.7
19.7
19.4
18.5
16.5
14.2
11.0
11.0
11.2
11.0
S.7
9.2
01 igochaeta
No . Wt .
1 0.000604
13 0.005265
3 0.001496
3 0.002026
3 0.001165
22 O.OOS603
2 1.000874
1123 0.947312
480 0.259524
438 0.587135
286 0.154376
16 0.002096
46 0.005866
33 0.020125
17 0.009033
1 0.000531
1 0.000570
0 0.000000
3 0.002475
17 0.006339
0 0.000000
1 0.000080
0 0.000000
0 0.000000
0 0.000000
o o.ooooon
0 0.000000
0 0.000000
0 0.000000
1 0.000415
0 0.000000
0 fl. 000000
360 0.346086
280 0.341950
146 0.078877
112 0.085044
493 0.495488
74 0.013434
0 0.000000
0 0.000000
o o.ooooon
o o.onnon.i
5 0.003183
o o.ooonon
Chironomid L.
No. Wt,
153
109
43
58
81
228
93
3
2
14
375
109
30
381
185
150
324
52
150
33
24
46
43
13
13
4
8
110
26
7
21
19
1
20
62
128
147
349
18-1
52
25
15
30
72
0.018628
0.025384
0.003544
0.010751
0.007529
0.019800
0.006263
0.003898
0.002852
0.067439
0.049310
0.011697
0.001467
0.051125
0.040806
0.028433
0.026003
0.007057
0.026280
0.008026
0.006246
0.009995
0.006635
0.003826
0.001632
0.000855
0.003904
0.012074
0.006374
0.001342
0.003564
0.002602
0.001577
0.007445
0.148463
0.160487
0.087398
0.087005
0.050390
0.015136
0.005971
0.003621
0.009534
0.008541
Chironomid P.
No. Wt.
12
14
4
4
4
18
4
0
1
0
1
0
1
0
0
0
1
0
0
1
0
0
5
3
5
1
1
2
1
0
1
0
0
0
0
0
0
1
4
1
0
0
0
3
0.002326
0.002677
0.000595
0.000586
0.000629
0.001913
n.0006"-!
0.000000
0.000215
0.000000
0.000481
0.000000
0.000322
0.000000
0.000000
0.000000
0.000120
0.000000
0.000000
0.000160
0.000000
0.000000
0.000868
0.000441
0.000431
0.000091
0.000591
0.000471
0.000114
0.000000
0.000099
0.000000
o.nooooo
0.000000
0.000000
0.000000
0.000000
0.001065
0.000941
0.00018(1
o.ooooon
0.000000
0.000000
0.000412
Anphipoda
No. Wt.
0
11
1
1
0
11
-1
0
0
0
0
0
0
2
0
0
0
0
0
1
1
0
5
1
1
3
0
8
5
0
0
9
0
1
0
0
0
15
1
0
0
0
0
0
0.000000
0.007166
0.001035
0.001208
0.000000
0.009274
0 . 0 0 2 1 8 5
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.002589
0.000000
0.000000
0.000000
0.000000
0.000000
0.000836
0.000291
0.000000
0.004608
0.016308
0.000672
0.001130
0.000000
0.001677
0.002387
0.000000
0.000000
0.001688
0.000000
0.000407
0.000000
0.000000
0.000000
0.019278
0.000520
0.000000
0.000000
0.000000
0.000000
0.000000
Mavflies
No. Wt.
1
2
2
0
1
1
1
0
0
0
0
0
1
0
0
0
0
0
1
0
0
0
0
2
3
1
0
1
2
0
1
0
0
0
0
0
0
0
0
0
0
0
n
0
0.000204
0.003410
0.004788
0.000000
0.000340
r. "00655
0.000803
0.000000
0.000000
0.000000
0.000000
0.000000
0.000159
0.000000
0.000000
0.000000
0.000000
0.000000
0.000252
0.000000
0.000000
0.000000
0.000000
0.000709
0.002148
0.000173
0.000000
0.001265
0.001160
0.000000
0.000921
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
llelcidae
No. Wt.
7
1
1
0
0
0
7
0
0
0
0
0
1
0
4
1
2
0
1
0
0
3
0
0
0
0
0
0
2
0
1
0
0
0
1
0
0
0
0
0
0
0
1
0
0.002687
0.000476
0.000602
0.000000
0.000000
0.000000
o.ooime
0.000000
0.000000
0.000000
0.000000
0.000000
0.000010
0.000000
0.001830
0.000214
0.000149
0.000000
0.000077
0.000000
0.000000
0.001206
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000447
0.000000
0.000165
0.000000
0.000000
0.000000
0.000424
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000114
0.000000
Trichoptera
No. Wt.
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0.000446
0.000000
0.000000
0.000000
0.000000
o.oooono
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.004088
0.005864
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001711
0.000637
0.000000
0.000000
0.000000
0.000000
-------
TaMc V7 fCniitiiiucUl
Sample
Number
363
364
365
366
367
368
369
370
371
372
373
374
375
9-6-69
475
474
473
472
471
470
469
468
467
466
465
464
463
462
461
460
459
458
457
456
455
454
453
452
451
6-12-70
1051
1052
1053
1054
1055
Depth
8.3
7.5
9.2
6.9
6.0
5.3
4.6
3.9
3.2
2.5
1.2
1.6
0.5
20.1
19.9
18.1
19.7
IB. 3
11.4
11.4
12.2
12.2
12.2
10.5
10.1
9.2
9.6
8.0
6.4
6.0
4.1
6.0
5.3
2.7
1.4
1.4
2.7
0.3
20.1
20.1
19.4
18.5
16.7
Oliqochaeta
No. Wt.
15 0.007483
2 0.000960
4 0.002165
3 0.000369
0 0.000000
0 0.000000
1 0.000154
1 0.000013
0 0.000000
0 0.000000
0 0.000000
0 0.000000
0 0.000000
512 0.411180
342 0.775198
88 0.025160
219 0.632133
137 0.070083
0 0.000000
4 0.002229
32 0.004395
28 0.014446
34 0.005916
0 0.000000
0 0.000000
1 0.001245
1 0.000552
0 0.000000
1 0.000406
0 0.000000
0 0.000000
o o.onoooo
0 0.000000
1 0.000632
0 0.000000
o o.ooonon
0 0.000000
1 0.002280
433 0. H3696
476 (1.394387
124 O.OS7330
125 O.H37617
195 n. 048141
Chirnnomid L.
No. Wt.
76
30
153
35
13
5
46
77
23
12
38
51
35
0
2
71
57
44
57
16
68
218
29
75
17
19
17
12
12
3
23
14
f.
3
30
6
7
21
1
2
11
5
40
0.016883
0.007216
0.017192
0.005275
0.005913
0.000202
0.003389
0.005515
0.001465
0.000751
0.1)03347
0.002407
0.001618
0.000000
0.003283
0.073864
0.019344
0.053595
0.017942
0.010740
0.021900
0.064953
0.014170
0.032766
0.004612
0.007020
0.003493
0.004235
0.002295
0.000148
0.006938
0.002253
0.002592
(1.000446
0.005540
'•-. 000798
0.003316
O^-'l'S:
0.000235
0.000279
0.018985
0.000480
0.008197
Chironomid P.
No. Wt.
6
3
1
3
0
1
2
7
1
2
4
6
5
0
0
0
0
0
0
0
2
8
0
3
6
2
1
0
0
0
n
0
0
1
i
n
0
2
0
0
n
i
i
0.000394
0.000390
0.000043
0.000456
0.000000
0.000138
0.000279
0.000335
0.000064
0.000086
0.000100
0.000222
0.000526
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000379
0.001723
0.000000
0.001103
0.001557
0.001755
0.000276
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000561
0.000194
n. oooooo
o.o'ooooo
0.000283
0.000000
n. oooooo
n. oooooo
n. 000144
0.002021
Amphipoda
No. Wt.
1
2
11
1
4
2
1
5
1
1
0
2
37
0
0
0
0
0
0
0
0
0
0
0
1
1
0
3
20
0
8
18
5
1
5
0
3
89
0
0
0
1
0
0.000577
0.001673
0.016288
0.000245
0.001816
0.000952
0.000279
0.000396
0.000093
0.000096
0.000000
0.000241
0.003858
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000391
0.000173
0.000000
0.000804
0.004973
0.000000
0.003159
0.005197
0.001814
0.000212
0.001433
0.000000
0.000975
0.016186
0.000000
0.000000
0.000000
0.001444
0.000000
Mayflies
No. Wt.
1
0
0
2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
2
2
0
0
0
0
0
1
0
0
0
0
0
0.001607
0.000000
0.000000
0.008254
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000482
0.000000
0.001926
0.000728
0.000000
0.000000
0. OOOOOO
0.000000
o.onorno
0.000106
0.000000
0.000000
0.000000
0.000000
0.000000
Heleidae Trichoptera
No. Wt. No. Wt.
0
0
0
0
1
0
6
1
1
0
8
4
1
0
0
0
1
0
0
0
0
1
1
0
0
0
0
0
0
0
1
0
1
1
2
2
4
0
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000388
0.000000
0.000649
0.000134
0.000091
0.000000
0.000994
0.000126
0.000076
0.000000
0.000000
0.000000
0.0003S3
0.000000
0.000000
0.000000
0.000000
0.000470
0.000316
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000501
0.000000
0.000145
0.000156
0.000675
0.000376
0.000805
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0
0
1
0
0
1
2
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
0
0.000000
0.000000
0.000037
0.000000
0.000000
0.000289
0.000289
0.000708
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000200
0.000227
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
-------
Table A-7 (Continued!
Sample
Number
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
7-3-70
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
Depth
12.3
12.6
12.0
11.2
11.0
10.5
9.8
8.9
8.0
8.0
6.2
7.3
3.7
4.1
4.6
2.5
1.8
2.7
1.4
0.7
19.7
19.9
19.4
18.5
17.6
12.0
11.9
11.9
11.9
11.7
10.1
8.7
9.6
8.5
7.3
5.7
6.0
4.8
4.1
4.6
3.7
2.7
1.8
0.9
0.3
Oligochaeta
No. Wt.
17 0.003504
17 0.002013
10 0.003760
0 0.000000
4 0.000696
0 0.000000
9 0.001766
0 0.000000
5 0.003505
1 0.001205
1 0.000895
0 0.000000
2 0.000806
0 0.000000
0 0.000000
0 0.000000
9 0.003465
1 0.000938
4 0.000771
1 0.000378
473 0.249827
476 0.363800
205 0.095493
142 0.029062
40 0.012842
11 0.000745
4 0.000672
5 0.000961
2 0.000164
16 0.002047
20 0.003617
11 0.006321
7 0.002160
21 0.001965
6 0.002499
5 0.002070
9 0.002428
0 0.000000
4 0.000880
2 0.000270
24 0.011530
3 0.001-19
3 0.000253
15 0.010221
10 0.004249
Chironomid L.
No. Wt.
2
10
5
17
37
14
11
10
30
48
125
30
27
SI
13
32
188
8
33
78
26
62
42
58
62
7
17
21
1
3
46
78
14
100
39
60
25
6
11
27
9
14
6
40
113
0.000969
0.003160
0.000595
0.002336
0.005432
0.002232
0. 002148
0.002073
0.006840
0.005799
0.007423
0.001600
0.004981
0.006111
0.001755
0.001492
0.011150
0.000257
0.002726
0.005612
0.002114
0.003808
0.005442
0.010911
0.002948
0.000830
0.003580
0.005144
0.000590
0.000199
0.006423
0.009408
0.001321
0.009743
0.005367
0.004884
0.007207
0.000314
0.000563
0.002702
0.0015V:
0.001804
0.000441
0.006086
0.009120
Chironomid P.
No. Wt.
1
0
1
0
0
2
0
3
0
1
6
1
0
1
0
4
11
2
4
4
0
0
0
0
0
0
0
1
0
0
0
2
0
0
3
2
1
0
1
0
0
1
0
0
15
0.000344
0.000000
0.000145
0.000000
0.000000
0.000403
0.000000
0.000374
0.000000
0.000254
0.000924
0.000210
O.OOOPfi'T
n. ''00153
0.000000
0.000334
0.000767
0.000007
0.000713
0.000171
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000110
0.000000
0.000000
0.000000
0.000150
0.000000
0.000000
0.000370
0.000299
0.000103
o.ooonoo
O.OOOOS4
0.001000
0.000000
0.000038
0.000000
0.000000
0.000760
Amphinoda
No . Wt .
0
1
0
0
0
0
0
4
0
2
16
5
6
9
30
4
4
4
3
13
0
0
0
0
0
0
1
0
0
0
2
2
0
2
3
11
0
4
1
6
0
0
0
3
23
0.000000
0.000407
0.000000
0.000000
0.000000
0.000000
0.000000
0.001489
0.000000
0.000711
0.006418
0.001497
0.002295
0.003694
0.009409
0.001379
0.001945
0.001667
0.001094
0.006169
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000717
0.000000
0.000000
0.000000
0.000823
0.000738
0.000000
0.000831
0.001214
0.005259
0.000000
0.002023
0.000405
0.002639
O.ooonnn
0.000000
0.000000
0.000930
0.006811
Mayflies
No . Wt .
0
0
0
0
0
0
0
1
0
1
1
0
1
1
3
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
5
0
0
0
0
0
0
0
0
1
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000322
0.000000
0.000738
0.000178
0.000000
0.000841
0.000408
0.002254
0.000000
0.000000
0.000253
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000068
0.000000
0.006054
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000990
Helcidae
No . Wt .
0
0
0
0
0
0
0
0
1
4
3
0
2
9
6
0
7
1
1
0
0
0
0
0
1
0
1
0
0
0
2
4
0
5
1
2
1
0
0
0
4
0
0
1
1
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000550
0.001591
0.000556
0.000000
O.OOOS2J
0.002798
0.001183
0.000000
0.001382
0.000116
0.000166
0.000000
0.000000
0.000000
0.000000
0.000000
0.000169
0.000000
0.000151
0.000000
0.000000
0.000000
0.000497
0.001607
0.000000
0.001738
0.000328
0.000630
0.000139
0.000000
0.000000
0.000000
0.001189
0.000000
0.000000
0.000159
0.000025
Trichoptera
No. Wt.
0
0
0
0
0
1
0
2
2
0
1
2
n
0
2
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
2
0
1
1
0
2
0
0
0
0
0
0.000000
0.000000
0.000000
0.000000
0.000000
0.000396
0.000000
0.000210
0.001863
0.000000
0.000132
0.000158
0.000000
0.000000
0.001456
0.000321
0.000000
0.000025
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.000000
0.001685
0.000000
0.000676
0.000462
0.000000
0.000238
0.000071
0.000000
0.002582
0.000000
0.000000
0.000000
0.000000
0.000000
-------
Table A-7 (Continued)
Sample
Number
7-14-70
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
30fh
3067
•3068
3069
3070
3071
3072
3073
3074
3075
8-14-70
/•OS 3
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
Depth
19.9
19.9
19.7
18.7
18.3
11.2
11.2
11.4
12.0
11.7
9.6
8.9
8.7
7.5
6.4
fi.2
5.5
5.0
5.5
3.7
3.2
2.5
2.5
0.7
0.3
20.1
19.7
19.7
19.0
18.1
11.0
11.4
11.2
12.0
11.0
10.1
8.9
9.6
7.8
8.7
7.3
Oligochaeta
No . Wt .
217 0.
468 0.
108 0.
474 0.
177 0.
10 0.
24 0.
12 0.
2 0.
14 0.
17 0.
12 0.
12 0.
8 0.
17 0.
6 Q!
10 0.
0 0.
2 0.
5 0.
2 0.
1 0.
4 0.
2 0.
178 0.
63 0.
140 0.
537 0.
18 0.
8 0.
32 0.
22 0.
1 0.
6 0.
4 0.
19 0.
5 0.
2 0.
2 n.
1 n.
146485
261606
033697
161224
059882
00145!)
003274
004448
000116
001423
004405
002601
004418
001540
008398
00
-------
Table A-7 (Continued)
Sample
Number
4067
4068
4069
4070
4071
4072
4073
4074
4075
9-4-70
5051
5052
5053
5054
5055
5056
5057
5058
5059
5060
5061
5062
5063
5064
5065
5066
5067
5068
5069
5070
5071
5072
5073
5074
5075
Depth
4.1
6.:
5.0
4.3
3.7
2.5
2.1
1.2
0.3
19.9
20.1
19.7
19.0
18.1
12.6
12.0
11.0
12.3
11.4
10.1
8.5
8.9
7.5
8.7
8.0
6.0
6.9
4.6
4.3
3.2
0.5
2.1
1.4
0.9
Oligochaeta
No . Wt .
3 0.001033
2" C. 004225
4 0.000682
8 0.001202
2 0.000064
3 0.000714
3 0.000726
7 0.001158
S 0.000992
318 0.318906
168 0.181866
186 0.181879
121 0.163979
103 0.121870
3 0.000588
6 0.001020
1 0.000018
5 0.000627
18 0.001878
0 0.000000
10 0.005546
12 0.002072
0 0.000000
6 0.001848
8 0.0012C2
12 0.003628
5 0.001647
4 0.002513
0 0.000000
0 0.000000
0 0.000000
0 0.000000
1 0.001053
21 0.-OOS237
Chironomid L.
No . Wt .
43
3
35
16
30
18
22
57
31
36
S3
57
43
69
3
0
14
18
9
10
52
19
18
6
13
1
9
16
i:
21
13
0
21
42
O.OCS801
0.000701
0.002083
0.000893
0.003245
0.001111
0.902142
0.004818
0.004376
0.013950
0.005296
0.009009
0.017090
0.008579
0.000702
0.000000
0.000707
0 . 0 0 0 6 S 9
0.000648
o . o n 7 ^ : '
0.002848
0.002122
O.nil] 112
0.000605
0.001^11
0.000072
0.000520
0.000043
0.0018?"
0.001947
0.00156'
o.ooopon
0. 00132 c
0.001393
Chironomid P.
No. Wt.
1
0
n
0
0
1
1
3
2
2
1
3
3
0
0
0
2
1
3
n
1
1
0
1
0
0
0
0
1
1
0
0
2
2
o.nooo?0
o.nooonn
o.oooooo
o.nnoooo
0.000000
0.000013
0.000126
0.000139
0.00012R
0.000609
0.000295
0.009677
0.000600
0.000000
0.000000
0.000000
o.onoi] 7
0.000121
0.000178
-.nni'ooo
0.000212
0.000089
0.000000
n. 000115
0.000000
0.000001
0.000000
0.000000
0.000171
n. onoois
0.000000
0.000000
0.000092
o.nnoo69
Amphipoda
No . Wt .
1
g
1
19
0
S
40
1R
0
0
0
0
0
0
0
10
0
27
1
18
15
91
1]
32
9
IP
S
in
14
69
0
14
0
.nni236
0.000037
0.000630
0.000754
0.004432
0.000000
0.002548
0.007304
0.002500
0.000000
o.onooon
o.noooon
0.000000
0.000000
0.000000
o.nnoooo
O.n04700
0.000000
0.025896
0.002827
0.002550
0.025109
0.005985
0.003880
0.006377
0.003883
0.002522
0.00200?
0.002782
n . o n 4 9 8 .1
o . o n s o 3 n
o.ooooon
0.003675
o.onnooo
Mayflies
No . Wt .
2
n
n
0
0
0
i
n
i
0
0
0
0
n
0
0
i
0
4
2
4
2
4
1
0
0
2
1
1
4
0
0
0
0
0.001773
o.onnoon
0.000000
0.000000
0.000000
0.000000
0.000064
0.000000
o.ooooso
0.000000
0.000000
n. oooooo
n. oooooo
0.000000
0.000000
0.000000
n. 000082
0.000000
0.000179
n. 000058
0.000145
0.000076
0.000491
0.000013
0.000000
0.000000
0.000459
0.000091
0.000059
0.000135
0.000000
0.000000
0.000000
0.000000
Heleidae
No . Wt .
1
0
0
0
0
0
0
0
0
0
0
0
1
0
2
0
0
3
1
0
0
0
0
0
0
1
0
2
1
0
1
0
0
0
o.opnrv
0.000000
o.onoooo
0.000000
0.000000
0.000000
o.oooooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000878
0.000000
0.000208
0.000000
0.000000
0.000026
0.000038
o.ooooon
0.000000
o.oooono
0.000000
0.000000
0.000000
0.000073
0.000000
0.000202
0.003446
o.ooonnn
O.OOOOR5
n.oonooo
0.000000
o.onoooo
Trichoptera
No. Wt.
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
1
0
2
I
1
0
2
3
2
0
0
1
1
1
0
0
1
0
P. OOOOOO
0.000000
0.000000
0.000000
0.000000
0.000222
o.ooooon
0.000000
o.ooooon
0.000000
o.oonooo
0.000000
0.000000
0.000000
0.000000
0.000000
0.000153
0.000000
o.ooisir,
o.-nf-nss
0.000259
0.000000
0.000410
0.006150
0.001937
0.000000
0.000000
0.000739
0.002432
0.000595
0.000000
0.000000
0.001209
o.ooooon
-------
Table A-8.
Section Four Lake zoobenthos collected during 1969
and 1970. The less abundant organisms are listed
in this table. To obtain a total for a given sample,
add the values for each sample (check each organism)
to the values for that sample given in Table A-7.
Wet weights are shown.
Sample
Number
OliEOchaetes
(Megadriles)
55
57
58
59
60
158
161
252
256
466
1056
1057
3061
3067
4071
5057
Dragonflies
71
73
170
173
174
369
374
1068
2075
4060
4067
4069
4070
4074
4075
5066
5074
Depth
On)
16.02
13.73
12.36
12.82
11.67
12.82
10.07
18.77
13.28
12.13
12.36
12.59
9.61
5.49
3.66
11.90
3.20
2.06
3.66
2.98
1.14
4.58
1.60
3.66
0.23
10.99
4.12
5.04
4.35
1.14
0.23
8.01
1.37
Date
6-15-69
6-15-69
6-15-69
6-15-69
6-15-69
7- 5-69
7- 5-69
7-25-69
7-25-69
9- 6.-60
6-12-70
6-12-70
7-24-70
7-24-70
8-14-70
9- 4-70
6-15-69
6-15-69
7- 5-69
7- 5-69
7- 5-69
8-15-69
8-15-69
6-12-70
7- 3-70
8-14-70
8-14-70
8-14-70
8-14-70
8-14-70
8-14-70
9- 4-70
9- 4-70
Number
1
11
2
2
4
1
1
1
1
3
2
5
1
1
1
2
2
4
i
i
i
1
1
1
2
1
1
1
1
1
2
2
1
1
Weight
(pm)
0.004690
0.229702
0.020609
0.029082
0.821241
0.053231
0.314032
0.037648
0.018359
0.013296
0.070588
0.091363
0.346751
0.533722
0.209138
0.942075
0.045291
0.00295.5
0.001424
0.011425
0.023480
0.006573
0.004726
0.018994
0.028874
0.000113
0.000409
0.000445
0.000168
0.097749
0.015670
0.001060
0.001092
-------
Table A-8 (Continued)
S amp 1 e
Number
Damself lies
58
63
65
161
163
266
268
363
364
365
368
369
461
457
456
453
1065
1067
1070
2066
2070
3070
3072
4063
4064
4066
4067
4070
4071
5058
5060
5062
5064
5066
5068
165
5069
5070
5072
5074
Depth
(m)
12.36
7.78
9.16
10.07
8.24
7.33
4.81
8.24
7.55
9.16
5.27
4.58
8.01
5.95
5.27
1.37
8.01
7.33
4.58
5.72
4.58
3.66
2.52
9.61
7.78
7.33
4.12
4.35
3.66
10.99
11.45
8.47
7.55
8.01
6.87
8.47
4.58
4.35
0.46
1.37
Date
6-15-69
6-15-69
6-15-69
7- 5-69
7- 5-69
7-25-69
7-25-69
8-15-69
8-15-69
8-15-69
8-15-69
8-15-69
9- 6-69
9- 6-69
9- 6-69
9- 6-69
6-12-70
6-12-70
6-12-70
7- 3-70
7- 3-70
7-24-70
7-24-70
8-14-70
8-14-70
8-14-70
8-14-70
8-14-70
8-14-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
7- 5-69
9- 4-70
9- 4-70
9- 4-70
9- 4-70
Number
1
1
1
2
2
1
1
1
2
">
*_,
1
1
1
2
9
1
2
1
1
1
1
2
]
2
1
1
2
1
3
1
1
3
2
1
1
2
1
1
1
1
Weipht
(gni)
0.001010
0.001154
0.000705
0.005000
.0.003253
0.002526
0.001913
0.000041
0.001018
0.001315
0.000148
0.000684
0.000173
0.000908
0.008156
0.003337
0.004232
0.002547
0.002735
0.002653
0.000677
0.010770
0.000063
0.000390
0.000444
0.000885
0.001389
0.003097
0.002754
0.000003
0.000004
0.005000
0.001896
0.006620
0.002077
0.000771
0.000695
0.000290
0.000046
0.000973
-------
Table A-8 (Continued)
Sample
Number
Chaoborus
Pupae
1067
Clams
161
1060
2057
2062
4058
4060
4065
4071
Tabanids
371
373
374
375
451
1065
2074
3067
3068
3070
3072
3073
3074
4067
4072
4073
4074
5066
5068
5070
5072
5074
5075
Depth
0")
7.33
10.07
10.99
10.99
8.70
11.22
10.99
8.70
3.66
3.20
1.14
1.60
0.46
0.23
8.01
0.92
5.49
5.04
3.66
2.52
2.52
0.69
4.12
2.52
2.06
1.14
8.01
6.87
4.35
0.46
1.37
0.92
Date
6-12-70
7- 5-69
6-12-70
7- 3-70
7- 3-70
8-14-70
8-14-70
8-14-70
8-14-70
8-15-69
8-15-69
8-15-69
8-15-69
9- 6-69
6-12-70
7- 3-70
7-24-70
7-24-70
7-24-70
7-24-70
7-24-70
7-24-70
8-14-70
8-14-70
8-14-70
8-14-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
9- 4-70
Number
1
1
1
1
2
1
1
1
1
1
1
2
1
2
1
4
1
1
1
8
5
3
1
1
2
1
1
1
4
2
5
3
Weipht
(flro)
0.000749
0.033548
0.004714
0.004614
0.007890
0.001932
0.003084
0.022210
0.007647
0.000580
0.002152
0.001375
0.006476
0.013576
0.001660
0.000255
0.000652
0.008910
0.000661
0.000643
0.001622
0.001811
0.001217
0.000527
0.001474
0.001771
0.004368
0.003284
0.011280
0.004249
0.011580
0.008520
-------
Table A-8 (Continued)
Sample
Number
Megaloptera
452
3060
3063
3075
4056
4067
Depth
Cm)
2.75
11.67
8.70
0.23
10.99
4.12
Date
9- 6-69
7-24-70
7-24-70
7-24-70
8-14-70
8-14-70
Number
1
1
1
1
1
1
Weight
Om)
0.002803
0.000092
0.000083
0.000070
0.000411
0.000526
-------
Table A-9.
Area-capacity table for Hemlock Lake based
on January 1957 survey of the lake.
Max.
Depth
(m)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
?•*
L.o
IN 5
5.0
5.5
6.0
6.5
7.0
7.5
3.0
3.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.S
13.0
13.5
lk.0
UN*
15.0
15.5
16.0
16.5
17.0
17.5
18.0
18.5
19.0
19.5
20.0
Area
(m2)
0
555
1110
1665
2220
2775
32^.6
3638
U030
4^22
^313
5205
&6?
55<6
56)12
572Q
5816
5902
6161
6782
7^03
8025
36k6
9267
9851
10 3 Ol|
10758
11220
11723
12225
12733
13280
13826
111390
1511^6
15903
16659
17ij-l6
18172
18928
19685
Volume
(m3)
0
0510
1010
1520
2030
25UO
3860
5950
flolj.0
101^0
12220
1^320
16720
19570
22l|20
25260
28110
30960
3ljl!.iO
38030
IJ.1920
1+5810
19690
53^0
5776o
62920
68090
73330
70260
85150
911^0
97810
lO^QO
111260
119020
126780
13^.0
li+2300
150060
157830
165590
Max.
Depth Area Volume
(m) (m2) (ra3)
20.5 20l|.ljl 173350
21.0 21198 131110
21.5 21954 188870
22.0 22711 196630
22.5 23l|67 20!|1)00
-------
Table A-10
Area-capacity table for Section Four Lake
based on January 1957 survey of the lake.
Max.
Depth
(m)
0.0
i.'o
1.5
2.0
2.5
3.0
3.5
5.0
5.5
5.0
?•*
6.0
6.5
7.0
7.5
8.0
3.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
lfj.0
15.5
15.0
*%•*
16.0
16.5
17.0
17.5
18.0
18.5
19.0
19.5
20.0
Area
0
4U
832
1323
1764
2206
2610
2979
3343
3717
4o36
4455
4712
ij8i2
4912
5012
5112
5212
5371
5653
5935
6217
61(99
6762
7062
745 2
7303
314?
8409
8672
8932
9174
95-17
9060
9989
10311
10633
10955
11277
11599
11922
Volume
(m3)
0
0400
08 10
1210
1610
2020
3110
k86o
6600
3350
10090
11340
13890
16370
13860
21350
23330
26320
23990
32050
35110
38170
41230
44290
475io
512QO
55070
58930
63190
67440
71750
76390
8io4o
85710
90780
95850
100910
105980
111040
116110
121170
Max.
Depth Area Volume
(rn) (m2) (ra3)
20.5 12244 126240
21.0 12555 131300
21.5 12338 136370
22.0 13210 i4i44o
22.5 13532 146500
-------
Table A-ll
Hemlock Lake calcium, sodium, potassium, magnesium, dissolved organic
matter (D.O.M.) and particulate organic matter (P.O.M.) collected during
1970. Samples were collected from six depths seven times during the
summer. The mean concentration for the entire lake is shown. These
analyses were made by R.G. Wetzel.
0.0
2.8
6.5
Depth (m)
10.1 12.8
14.6
15.6
Mean
Calcium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
Sodium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
38.4
38.7
36.8
33.3
33.8
55.3
49.5
1.75
1.55
1.50
1.70
1.90
2.07
2.07
43.2
39.2
38.3
34.5
37.2
57.8
50.3
1.45
1.50
1.65
1.72
1.98
2.08
2.05
46.8
47.2
44.0
46.3
44.0
59.3
50.3
2.12
2.05
2.00
2.08
2.09
2.05
2.07
46.7
45.8
55.2
49.0
45.0
52.0
50.9
2.08
2.14
2.14
2.05
2.14
2.07
2.05
57.9
47.1
55.5
49.1
44.9
50.4
50.3
2.22
2.14
2.15
2.11
2.15
2.05
2.14
102.5
111.0
57.0
48.9
44.9
50.9
50.9
2.57
3.00
2.22
2.12
2.11
2.11
2.11
— —
47.7
44.9
41.8
40.8
55.4
50.3
1.90
1.87
1.92
2.04
2.07
2.07
-------
Table A-ll (Continued)
Depth (m)
Potassium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
Magnesium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
D.O.M.
VI-7-70
VI-13-70
VI-18-70
VII-17-70
VIII-15-70
IX-5-70
0.0
0.60
0.58
0.52
0.60
0.85
1.00
0.96
8.0
9.1
9.3
8.4
9.7
10.5
10.3
7.12
7.04
6.17
8.84
6.82
10.32
2.8
0.63
0.55
0.52
0.70
0.90
1.00
0.96
8.8
9.2
9.8
8.7
9.8
10.7
10.3
7.33
6.56
6.54
8.51
6.74
11.02
6.5
0.78
0.68
0.85
0.95
1.02
1.07
0.96
10.5
11.3
11.7
11.4
9.8
10.7
10.0
6.99
7.24
6.36
7.91
6.48
10.29
10.1
0.80
0.75
1.18
1.00
1.02
1.03
0.99
11.3
11.7
13.5
11.1
10.3
10.2
10.0
7.63
6.93
5.99
9.28
6.67
10.21
12.8
1.05
0.75
1.19
1.02
1.03
1.05
1.05
12.3
11.9
13.2
11.6
10.6
11.0
10.2
7.99
6.73
6.26
8.72
6.21
9.42
14.6 15.6
1.78
2.62
1.23
0.97
1.01
1.05
1.00
14.5
15.9
12.6
10.6
1003
10.9
10.6
8.39
9.14
6.53
9.24
4.68
10.89
Mean
_ .
0.78
0.81
0.84
0.96
1.03
0.98
_ _
10.8
11.3
10.1
10.0
10.6
10.2
„ _
7.04
6.33
8.60
6.49
10.46
-------
Table A-ll (Continued)
P.O.M.
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
0.0
Depth (m)
2.8 6.5 10.1 12.8
287.6
857.0
642.5
1619.1
693.2
148.3
591.1
756.2
893.3
1287.0
1915.6
993.4
156.2
444.8
981.6
759.9
641.3
1963.1
819.2
207.6
765.1
916.3
1580.1
1100.9
1635.9
566.4
128.5
377.6
1345.3
1408.6
1026.8
1774.3
554.5
164.1
319.7
14.6
2627.4
15.6
Mean
3661.1
1161.4
1774.3
643.5
243.2
1195.7
972.9
1818.3
776.7
170.0
306.4 513.2
-------
Table A-12. Section Four Lake calcium, sodium, potassium, magnesium, dissolved organic
matter (D.O.M.) and particulate organic matter (P.O.M.) collected during
1970. Samples were collected from six depths seven times during the summer,
The mean concentration for the entire lake is shown. These analyses were
made by R.G. Wetzel.
0.0
3.7
7.4
Depth (m)
11.0 14.6
17.4
18.2
Mean
Calcium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
Sodium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
51.5
53.0
55.0
55.7
55.0
52.8
52.8
2.88
2.95
3.04
3.15
2.81
3.17
3.16
55.0
56.5
55.6
56.0
53.4
52.6
52.6
3.25
3.05
3.00
3.15
3.20
3.10
3.15
58.4
58.0
55.6
56.0
54.5
53.2
52.8
3.28
3.22
3.06
3.13
3.20
3.11
3.17
57.5
56.5
55.7
57.0
54.8
49.8
51.6
3.20
3.08
3.13
3.15
3.09
3.17
3.21
57.5
58.0
58.8
56.9
55.0
52.8
52.8
3.08
3.16
3.22
3.17
3.23
3.08
3.17
57.5
58.2
58.5
56.2
55.0
52.8
53.2
3.20
3.18
3.13
3.13
3.21
3.12
3.13
— —
56.0
56.0
56.2
54.4
52.3
52.6
— —
3.09
3.07
3.15
3.12
3.12
3.17
-------
Table A-12 (Continued)
Potassium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
Magnesium
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
D.O.M.
VI-7-70
VI-13-70
VI-18-70
VII-17-70
VIII-15-70
IX-5-70
0.0
0.58
0.63
0.67
0.59
0.57
0.60
0.60
15.2
15.1
16.0
13.9
10.3
10.3
10.4
6.63
3.45
3.09
3.49
3.15
6.75
3.7
0.69
0.63
0.63
0.60
0.58
0.60
0.62
16.4
15.7
16.5
12.9
10.1
10.3
10.2
2.57
2.77
2.80
3.78
2.53
5.81
7.4
0.64
0.64
0.63
0.57
0.57
0.60
0.60
18.7
17.0
14.9
11.9
10.3
9.2
9.9
2.42
2.48
2.67
3.34
3.09
6.93
Depth (m)
11.0 14.6
0.65
0.64
0.64
0.57
0.57
0.58
0.60
17.2
16.4
14.6
11.3
9.9
9.2
10.3
2.43
2.79
2.80
3.49
2.47
4.76
0065
0.65
0.69
0.59
0.64
0.57
0.61
18.7
16.0
15.1
11.1
8.9
9.3
10.6
2.20
2.68
2.56
3.54
2.32
6.90
17.4 18.2
0.65
0.64
0.64
0.58
0.55
0.59
0.59
16.8
15.9
14.1
10.4
9.2
10.3
10.4
2.57
2.23
2.42
3.66
2.90
6.26
Mean
_ _
0.64
0.65
0.58
0.58
0.59
0.61
_ _
16.0
15.5
12.3
10.0
9.8
10.2
._
2.79
2.78
3.55
2.74
6.18
-------
Table A-12 (Continued)
Depth (m)
P.O.M.
VI-7-70
VI-13-70
VI-18-70
VI-27-70
VII-17-70
VIII-15-70
IX-5-70
0.0
140.4
140.4
310.4
417.1
128.5
259.0
148.3
3.7
168.0
136.4
381.6
405.3
81.0
176.0
199.7
7.4
156.2
172.0
405.3
440.9
132.4
235.3
211.5
11.0
247.1
215.5
385.5
452.7
140.4
187.8
259.0
14.6 17.4
227.4 345.0
144.3
425.0
480.4
124.6
203.6
148.3
18.2
_ _
191.8
322.2
531.8
132.4
160.1
191.8
Mean
•» •>
161.4
378.0
436.2
117.1
207.4
198.0
-------
465
Figure A-l. Length histograms of hatchery reared rainbow
trout at time of stocking in Hemlock Lake dur-
ing June 6, 1969 and June 25, 1970. Only one
lot of fish were stocked during 1969, whereas
four lots were stocked during 1970,. Each lot
received a separate fin clip. Total numbers
(n) , average fish lengths (x\. and fin clips
for each lot are shown.
-------
0-
5--
O-.r
10+
c
i 5:~-
a, -
0-
5--
0-
10-
1969
R. Pel.
n.= 1002
X= 7,3
^JTf
1970
Anal
n = 540
7=8.1
1970
R.Pec.
n=605
x=8.0
rn rT
1970
L. Pec.
= 8.1
11iii r j i i i i i j ii i i i
6.3 6.9 7.5 8'.1
Length (inches)
1970
L.Pel.
Jl=560
x= 8.1
fe
8.7
9.3
9.9
-------
467
Figure A-2. Length histograms of hatchery reared rainbow
trout at time of stocking in Section Four
Lake during June 6, 1969 and May 23, 1970.
One lot was stocked each year. Total numbers
(n) , average fish-lengths (3c) and fin clips
for each lot are shown.
-------
10-
5-
«**
c
0)
s°-
0,)
p. -
10-
~
5^
0 "
-i_
-
-
1969
—i
R. Pec.
™
n = 1000
7=73
TKn
1 rrK-^-f-i_ „
1970
L.Pel.
n=1071
x-7.9
TTh-i^
6-3 6i9 7.5 8.1 6.7
Length (inches)
9.3
9.9
-------
ACKNOWLEDGEMENTS
The advice and assistance of my graduate committee is
much appreciated. Drs. R. C Ball, W. E. Cooper, K. W.
Cummins, G. E. Guyer and N. R. Kevern served on this commit-
tee.
The Michigan Department of Natural Resources generously
supported this project through its loan of equipment, facili-
ties, records, hatchery fish and personnel. This project
could not have been conducted on the scale it was without
their help. Dr. Gerald Cooper, Jerry Myers, Bob Barber and
Dr. Carl Latta were especially helpful.
Several students assisted me with the work. I cannot
say enough about their enthusiasm and support. They in-
cluded: Larry Waterworth, Bob Hoffman, Mike Coney, Tawn
Jarvis, Kathy Hunter, Cheryl Bowden, Scott Mosiman and Bob
McConnel.
Dr. R. G. Wetzel assisted with water chemistry.
Dr. Brian Moss analyzed the phytoplankton. Drs. Frank D'ltri
and Marvin Stevenson advised on water chemistry and engineer-
ing aspects of the project respectively. The help of all
these people is appreciated.
1+69
-------
Martha L. Past assisted with much of the work. Her
assistance is also greatly appreciated.
Ivan Borton fabricated much of the equipment used in
the study and gave valuable advice. Here again, this
project could not have been conducted on as large a scale
as it was without his valuable assistance.
We acknowlege the support of the Water Quality Office
of the Environmental Protection Agency for supporting much
of the work through Grant 16010 EXE.
My personal support was through a Predoctoral Fellowship
5-F1-WP-26-292-01,03.
Additional support was through the Michigan Agricultural
Experiment Station, Project 64.
14-70
U. S. GOVERNMENT PRINTING OFFICE : 1972 O - 456-249
------- |