1PA-R3-73-002
EBRUARY 1973
Ecological Research Series
Limnology of Yellowtail
Reservoir and The
Bighorn River
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL
RESEARCH series. This series describes research
on the effects of pollution on humans, plant and
animal species, and materials. Problems are
assessed for their long- and short-term
influences. Investigations include formation,
transport, and pathway studies to determine the
fate of pollutants and their effects. This work
provides the technical basis for setting standards
to minimize undesirable changes in living
organisms in the aquatic, terrestrial and
atmospheric environments.
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EPA-R3-73-002
February 1973
LIMNOLOGY OF YELLOWTAIL RESERVOIR
AND THE BIGHORN RIVER
By
John C. Wright
Montana State University, Bozeman, MT
and
Raymond A. Soltero
Eastern Washington State College
Cheney, Washington
Project 18050 DBW
Project Officer
Dr. Donald Hilden
Office of Water Programs
Environmental Protection Agency
Washington, D.C. 20460
Prepared for
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
Price $1.25 domestic postpaid or $1 QPO Bookstore
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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 Environ-
mental Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
11
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ABSTRACT
Chemically, water impounded in the reservoir, was a calcium, sodium,
sulfate, bicarbonate type. Mean salinity of the effluent was essentially
the same as that of the influents. There was a striking increase in water
clarity down the reservoir due to settling of silt.
Impoundment and deep water withdrawal displaced the maximum and
minimum temperatures and conductivities of the effluent approximately two
months behind the influent occurrance and greatly reduced the amplitude
of seasonal change.
Of the influent total carbon, nitrogen and phosphate, 24%, 25% and
86% respectively were retained in the reservoir. The major fraction
retained was the particulate fraction. Of the trace metals there was a
97% retention for iron, 86% for manganese, 40% for copper and 71% for
zinc. Particulate carbon, nitrogen, and phosphate, orthophosphate,
nitrate and trace metals were in higher concentration in the upper end
of the reservoir associated with silt.
A withdrawal created density current was evident which altered the
vertical and longitudinal distribution of physical and chemical parameters.
Volume based phytoplankton density and chlorophyll concentration
decreased down-reservoir. However, the depth of the euphotic zone in-
creased down-reservoir as silt settled out. Consequently the euphotic
zone standing crops were greatest in the mid-section of the reservoir.
Insufficient light penetration was the principal limiting factor to
primary production in the upper end of the reservoir. Decreased primary
production in the lower end of the reservoir did not appear to be due to
nutrient limitation.
111
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CONTENTS
Page
I. CONCLUSIONS 1
II. INTRODUCTION 3
III. DESCRIPTION OF THE STUDY AREA 5
IV. METHODS AM) MATERIALS 11
Influent and Effluent Waters 11
Water Chemistry 11
Temperature and Conductivity 14
Hydrology 14
Reservoir 14
Light 15
Temperature and Conductivity 16
Water Chemistry 16
Phytoplankton Standing Crop, Chlorophyll
and Primary Productivity 16
Hydrology 17
V. RESULTS 17
Influent and Effluent Waters 17
Hydrology 17
Temperature and Conductivity 19
Water Chemistry 24
Reservoir 34
Hydrology 34
Light 34
Temperature and Conductivity 41
Water Chemistry 51
Phytoplankton Standing Crop and Chlorophyll . 62
Primary Productivity 82
Relationships of Physical and Chemical
Parameters to Chlorophyll and Total Phyto-
plankton Standing Crop 87
VI. DISCUSSION 91
VII. ACKNOWLEDGEMENTS 97
VIII. LITERATURE CITED 99
IV
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LIST OF TABLES
Page
Table
Table
Table
Table
Table
II.
III.
IV.
V.
Table
VI.
Table
VII.
Table
VIII.
Table
Additional morphometric data for
Bidhorn Lake at maximum capacity
Celevation 1,115.6 m)
The date and the river where water
samples were collected C+) during the
1968 and 1969 sampling periods . . .
12
Th.e dates for each cruise and type
of cruises made during the study period
Discharge (m^/sec) for the influent
and effluent waters of Bighorn Lake
during 1968 and 1969 sampling periods .
Total monthly discharge (m /sec) for
the influent and effluent waters of
Bighorn Lake during 1968 and 1969
sampling periods
13
18
20
Range and mean of water chemistry
for the influent and effluent waters
of Bighorn Lake during 1968 sampling
periods
25
Range and mean of water chemistry
for the influent and effluent waters
of Bighorn Lake during the 1969
sampling periods
27
Discharge-weighted chemical composition
(meq/1) of the influent and effluent
waters of Bighorn Lake during 1968 and
1969
The carbon (mg/lC) nitrogen (mg/lN)
and phosphate (mg/1 PO^ balances of
Bighorn Lake for the period between 19
August 1968 and 18 August 1969
29
30
v
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Page
Table
Table
X.
XI.
Table
Table
Table
Table
XII.
XIII.
XIV.
XV.
Table
XVI.
Table
XVII.
Table XVIII.
Iron, manganese, copper and zinc (mg/1)
budget of Bighorn Lake during the
1968 and 1969 sampling periods. ....
Inflow, discharge and storage change
(X105m3) in Bighorn Lake for the
water years ending 30 September 1968,
30 September 1969 and 30 September 1970
Water exchange rates (days) in
Bighorn Lake for 1968, 1969 and 1970. .
Range and mean water chemistry at
each station of Bighorn Lake during
the study
Mean water chemistry (mg/1) of the
euphotic zone at each station of
Bighorn Lake during the study
Phytoplankton species observed from
all sampling stations of Bighorn Lake
during the study with some calculated
volumes of individual cells or colonies
Rank of the major phytoplankton
species from Bighorn Lake according
to absolute mean cell volumes (mm3/l)
based on collections from all stations
during the study
Rank of the major phytoplankton species
of Bighorn Lake according to presence
(%) as described by Curtis (1959).
Values are based upon collections from
all stations over the entire study. . .
Mean total phytoplankton standing
crop (X103mm3/m2) and chlorophyll ji
concentrations (mg/m2) at each station
during the study
31
35
37
52
59
66
68
69
71
VI
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Page
Table XIX. Variables used for multiple linear
regression analysis of chlorophyll a_
and total phytoplankton standing
crops for 1968, 1969 and 1970, Bighorn
Lake 88
VI1
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LIST OF FIGURES
Page
Figure 1. Water levels of Bighorn Lake as related
to area (X103m2) and capacity (X107m3)
with operational zones delineated
(Bureau of Reclamation Data)
Figure 2. Detailed structure of Yellowtail Dam.
Diagram was furnished through the
courtesy of the Bureau of Reclamation. ... 8
Figure 3. Map of Bighorn Lake (Bureau of
Reclamation) showing location of the
six permanent sampling stations 9
Figure 4. Monthly average of temperatures (C) for
the influent and effluent waters of Big-
horn Lake during the 1968 and 1969 samp-
ling periods (September-December values
supplied by the U.S.G.S.) 21
Figure 5. Monthly average of specific conductance
(micromhos) for the influent and effluent
waters of Bighorn Lake during the 1968
and 1969 sampling periods (September-
December values supplied by the U.S.G.S.). . 22
Figure 6. Relationship between specific conductance
(micromhos) and mean discharge (m /sec)
for the influent waters of Bighorn Lake
during the 1968 and 1969 sampling periods. . 23
Figure 7. Seasonal fluctuations of mean discharge
(m^/sec) and turbidity (Standard Jackson
Turbidity Units) for the influent and
effluent waters of Bighorn Lake during
the 1968 and 1969 sampling periods 32
Figure 8. Relationship between turbidity (Standard
Jackson Turbidity Units) and ortho-phosphate
(mg/1 POT) for the Bighorn and Shoshone
Rivers 33
viii
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Page
Figure 9. Range and mean water levels of Bighorn
Lake during 1968, 1969 and 1970 (Bureau
of Reclamation Data) 36
Figure 10. Water clarity in Bighorn Lake expressed
as the mean turbidity (Standard Jackson
Turbidity Units) and light transmittance
(% T/lOcm) at each sampling station
during the study 39
Figure 11. Relationship between turbidity (Standard
Jackson Turbidity Units) and light trans-
mittance (% T/10 cm). A point represents
a mean of all data at a given station,
Bighorn Lake 40
Figure 12. Seasonal and longitudinal distribution of
suspended sediment, utilizing transmission
data (% T/lOcm) for Bighorn Lake during
1969 42
Figure 13. Average extinction coefficients (k/m) at
each station for each year, Bighorn Lake . 43
Figure 14. Penetration of total visible light and
average extinction coefficients (k/m) for
each sampling station during 1968, 1969
and 1970, Bighorn Lake 44
Figure 15. Isotherms (C) at station 0 during 1968,
1969 and 1970, Bighorn Lake 45
Figure 16. Distribution of 1 C isotherms in Bighorn
Lake during 1968 47
Figure 17- Isolines of conductivity (micromhos) at
station 0 during 1968, 1969 and 1970,
Bighorn Lake 49
Figure 18. Distribution of 100 micromho isolines of
conductivity in Bighorn Lake during 1968 . 50
IX
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Page
Figure 19. Distribution of turbidity (Standard
Jackson Turbidity Units) with depth at
station 0 of Bighorn Lake during 1968 ... 60
Figure 20. Distribution of ortho-phosphate (mg/1
POp with depth at station 0 of Bighorn
Lake during 1968 61
Figure 21. Distribution of nitrate nitrogen (mg/1
N03-N) with depth at station 0 of Bighorn
Lake during 1968 63
Figure 22. Distribution of dissolved oxygen (mg/1
with depth at station 0 of Bighorn Lake
during 1968 64
Figure 23. Distribution of pH with depth at station
0 of Bighorn Lake during 1968 65
Figure 24. Yearly mean cell volumes (mnH/l) of the
phytoplankton at each station of Bighorn
Lake during 1968, 1969 and 1970 72
Figure 25. Monthly mean cell volumes (mm^/l) of the
phytoplankton in Bighorn Lake during
1968, 1969 and 1970 75
Figure 26. Mean relative standing crop (%) of the
eight most abundant phytoplankton species
fox all sampling stations on Bighorn
Lake during 1968 , 76
Figure 27. Mean relative standing crop (%) of the
eight most abundant phytoplankton species
for all sampling stations on Bighorn Lake
d-uring 1969 77
Figure 28. Mean relative standing crop (%) of the
eight most abundant phytoplankton species
for all sampling stations on Bighorn Lake
d-uring 1970 78
x
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Page
Figure 29. Relationship between mean total phyto-
plankton standing crop (mrn^/l) and
chlorophyll a_ concentrations (mg/m3) for
all stations during the study, Bighorn
Lake 80
Figure 30. Frequency of the ratios of chlorophyll a.
to cell volume (ug/mm^) during the study,
Bighorn Lake 81
Figure 31. Seasonal relationship between mean chloro-
phyll a_ concentration (ug/1) and algal volume
(mm3/l) for all stations during the Bighorn
Lake study. Open circles represent samples
which, contained virtually no blue-green algae
contained predominately blue-green algae.
The solid line represents a 3.42:1.00 ratio
of chlorophyll a_ to phytoplankton volume.
Month, of sample is shown by the number near
the. circle 83
Figure 32. Mean priirary productivity (g C/m2/day) at
each, station and seasonal fluctuations of
primary production during the study.
Bighorn Lake 86
XI,
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SUMMARY AND CONCLUSIONS
1. Bighorn Lake, an impoundment of the Bighorn River, has a maximum
useable capacity of 169 x 19? m-^ (1,375,000 acre-ft) and a surface area
of 700 x 1Q5 m^ (17,298 acres). The principal purposes of the reservoir
are flood control, power production, irrigation and recreation.
2. The reservoir became thermally stratified for all three years of
the study. Surface water temperatures were greater than 20 C in late
July and August. Bighorn Lake acquired an ice cover for a period of
approximately 60 days in 1969. The spring warming process began in the
upper end of the reservoir and advanced toward the dam and to greater
depths as the season progressed. The development of a distinct thermo-
cline for any given year of the study was not detectable.
3. Conductivity ranged from 430 to 1,628 micromhos. Differences in
conductivity by season and location are depicted for the 1968 sampling
periods. Reservoir regulation delayed normal trends in conductivity.
Water of minimal conductance (salinity) was discharged from the dam
between July and September, which corresponds to the periods of heavy
downstream irrigation.
4. Calcium, sodium, sulfate and bicarbonate are the most common
constituents of the dissolved solids present in Bighorn Lake. Photo-
synthetic reduction of alkalinity was not detected.
5. Turbidities were drastically reduced thus improving water quality.
A comparison of the mean turbidities for the Bighorn and Shoshone Rivers
with that of the reservoir discharge during the study reveals approxi-
mately a 60-fold decrease. A turbidity current was established at the
depth of the power penstock during 1968. Nitrate nitrogen and ortho-
phosphate maxima as well as the oxygen and pH minima were associated
with the above turbidity current.
6. It was apparent that Bighorn Lake was fertilized with nutrients
from the major tributaries. The relationships of conductivity, turbidity,
nitrogen and phosphate to the rate of tributary flow have been examined.
It does not appear that any of the determined essential ions for bio-
logical production are lacking in this reservoir.
7. Maximum phytoplankton volumes were found in the spring and early
summer months. A definite algal succession pattern was established
for all three years. Phytoplankton volumes increased from the dam to
the upper end of Bighorn Lake.
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8. Comparison of sampling periods (June-September) common to all
years of th.e study showed th.at the calculated net primary production
increased 84% in 1970 over 1968. The above increase in productivity
related well with the 44% increase of mean total phytoplankton stand-
ing crop (mm^/m2) tn 1970 over 1968 as well as the 49% increase in
mean chlorophyll a. concentrations (mg/m2) in 1970 and 33% increase
in mean phytoplankton biomass (g/m2).
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INTRODUCTION
The decline in "productivity" of newly impounded reservoirs is
almost universal (Bennett, 1971; Carlander at al., 1963; Neel, 1963).
Productivity in this context refers to the successful establishment and
maintenance of a large population of preferred fishes. The initial
high productivity has been attributed to the organic matter and nutri-
ents resulting from the flooded soil and vegetation, thus entering the
trophic cycle of the reservoir. Although the above enrichment process
may have some validity in humid regions it is rather doubtful if this
is applicable to semi-arid regions.
Whether or not this loss of fish production is related to a
decline in primary or secondary productivity, or both has not been
established.
A comprehensive investigation of the physical, chemical and
biological limnology of Bighorn Lake (formerly Yellowtail Reservoir)
and its tributaries was initiated in the fall of 1967 to determine if
a decline in primary productivity of this new impoundment would occur.
The study specifically encompassed the heat budget, salinity regime,
internal currents and biological productivity (phytoplankton) of the
reservoir.
The three-year study was undertaken to relate the physical
and chemical environment of the reservoir to primary production and
to determine what changes in the primary production took place over the
entire study. An effort was also made to assess the physical and
chemical characteristics of the influent and effluent waters of the
reservoir.
The theoretical points of the above approach to primary production
are best summarized by Findenegg (1965) as follows:
"It is a well known fact that primary production
in lakes is controlled by the interaction of many
factors which usually are divided into three groups:
(1) Physical factors originating directly or indirectly
from solar radiation, such as light conditions, tempera-
ture, mixing and turbulence by the action of the wind;
(2) The content of the nutrients in the euphotic zone
of the lakes, and (3) The interaction of the organisms
present in the plankton community which may promote or
hamper the production of certain species".
The cause(s) of the decline in reservoir fish production must
be known before formulation of better and more feasible fisheries
management (both preventive and corrective) can be applied.
-------
DESCRIPTION OF THE STUDY AREA
Bighorn Lake is a new impoundment (Yellowtail Dam) of the Bighorn
River approximately 80.5 kilometers (50 miles) southeast of Billings,
Montana, Yellowtail Dam is in Bighorn County at lat. 45°18'27", long.
107°57'26", in SW1/4 SE1/4 Sec. 18, T.6 S. and R. 31 E. At normal
operating level the reservoir extends from the dam at Fort Smith,
Montana into Wyoming for a distance of 98.4 kilometers (61 miles).
The water is used for power production, flood control, irrigation and
recreation.
Construction of the dam by the Bureau of Reclamation began in
1961 and was completed in 1967. Storage began 4 November 1965. The
reservoir has a usable capacity (Fig. 1) of 169 x 107m3 (1,375,000
acre-ft) below elevation 1,114.6 m (3,657 ft). Normal operating
capacity is 144 x 107m3 (1,097,000 acre-ft) at elevation 1,109.5 m
(3,640 ft) and minimum operating level is 60 x 107m3 (483,400 acre-
ft) at elevation 1,081.1 m (3,547 ft). Dead storage amounts to
234 x 105m3 (18,970 acre-ft) below elevation 1,005.8 m (3,296 ft).
Maximum daily content since construction occurred on 6 July 1967 with
166 x 107m3 (1,346,000 acre-ft) at elevation 1,114.5 m (3,656 ft),
while the minimum since first filling occurred on 22 May 1968 and
was 82 x 10 m3 (667,400 acre-ft) at elevation 1,093.0 m (3,586 ft).
Other morphometric data for the reservoir are given in Table I.
Details of the structure of the thin concrete-arch dam are shown
in Figure 2. Water can be discharged from the reservoir through three
outlets; (1) the spillway—elevation 1,095.1 m (3,593 ft); (2) the
power penstocks—elevation 1,051.6 m (3,450 ft), and (3) the river
outlet invert— elevation 1,005.8 m (3,296 ft). Unless it is necessary
to discharge water through the spillway or river outlet invert, all
water is discharged from the reservoir through the power penstocks.
The depth of water overlying the power penstocks would be 63.1 m (207
ft) at maximum usable capacity, 57.9 m (190 ft) at normal operating
level and 29.6 m (97 ft) at minimum operating level. Discharge
through the river outlet invert would come from very deep water;
109.9 m (360 ft) at maximum usable capacity, 96.8 m (317 ft) at normal
operating level and 76.4 m (250 ft) at minimum operating level.
Six permanent sampling stations were established on the reservoir
during the course of the study (Fig. 3). Kilometer 0 (Station 0) was
located at the dam site with the remaining stations at approximately
16.1 kilometer (10 mile) intervals from each other up the reservoir
for 80.5 kilometers to station 5.
The major tributaries to the reservoir, as can be seen from
Figure 3, are the Bighorn and Shoshone Rivers. The average discharge
for the Bighorn River was 63.9 m3/sec (2,256 cfs) for a 41 year period
(U.S.G.S., 1969). The discharge normally fluctuates between a fall
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CO
or
UJ
f-
LU
UJ
>
Ld
in
<
UJ
LL)
O
m
11278
AREA (X I03m2)
16.2 24.3 32.4 40.5 48.6 56.7 64.8 72.8
1097.3-
1066.8-
1036.3-
1005.8
TOP OF DAM AND MAXIMUM WATER SURFACE
"TOP OF JOINT USE STORAGE (NORMAL OPERATING LEVEL)
TOP OF CONSERVATION STORAGE
^ 9754-
LU
LJ
944.9
TOP OF DEAD STORAGE (RIVER OUTLET INVERT)
24.6 49.2 73.8 98.4 123.0 147.6
CAPACITY (XI07m3)
172.2 196.8 221.4
Figure 1. Water levels of Bighorn Lake as related to area
(XlcP m ) and capacity (XIO^ nP) with operational
zones delineated (Bureau of Reclamation Data).
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Table I.
Additional morphometric data for Bighorn Lake at
maximum capacity (elevation 1,115.5 m).
Maximum Length
Maximum Effective Length
Maximum Width
Maximum Effective Width
Mean Width
Maximum Depth
Mean Depth
Area
Volume
Length of Shoreline
Shoreline Development
Slope of Basin
98.4 km (61 mi)
9.8 km (6.1 mi)
3.2 km (2.0 mi)
3.2 km (2.0 mi)
739 m (2,425 ft)
140 m (459 ft)
24 m (80 ft)
727 X 105 m2 (17,958 acres)
176 X 107 m3 (1,427,840 acre-ft)
206 km (128 mi)
11.8
0.14%
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Top of Exclusive
Flood Control-El. 1114.6m
Top of Joint Use
El. 1109.5m
Conservation-El. 1101.5m—
Min. W.S. for Power _
Operation-El. 1081.1m
Top of Dam-El. HI5.5m
Trashrack-
EI.I05l.6m
Top of Dead Storage
El. 1004.8 m
Axis of Dam.
El. 968.6 m
of Dam
El. 958.6m
YELLOWTAIL DAM
Figure 2. Detailed structure of Yellowtail Dam. Diagram was
furnished through the courtesy of the Bureau of
Reclamation.
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BIGHORN LAKE-YELLOWTAIL DAM
0 Kilometers 8
Figure 3. Map of Bighorn Lake (Bureau of Reclamation) showing
location of the six permanent sampling stations.
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minimum of approximately 21.2 m-Vsec (750 cfs) and a spring maximum
of 339.8 mVsec (12,000 cfs). Maximum recorded discharge was 712.7
m3/sec (25,000 cfs) on 16 June 1935 and the minimum was 5.1 m3/sec
(179 cfs) on 22 July 1934. The drainage area of this river comprises
40,831 km2 (15,765 mi2) at an elevation greater than 1,115.6 m (3,660
ft) above mean sea level.
The average discharge from the Shoshone River was 32.3 m-Vsec
(1,141 cfs) for an 11 year period (U.S.G.S., 1968). The discharge
normally fluctuates between a fall minimum of approximately 12.8 m^/
sec (430 cfs) and a spring maximum of 195.4 m-Vsec (6,900 cfs).
Maximum recorded discharge was 373.8 m^/sec (13,200 cfs) on 19
September 1961 and the minimum was 3.4 mVsec (120 cfs) on 21-23
January 1959. The drainage area of this river comprises 7,742 km2
(2,989 mi2) at an elevation greater than 1,117.9 m (3,635 ft) above
mean sea level.
Permanent sampling stations were established during the study
for each of the above tributaries. The Bighorn sampling site was
located at lat. 44°45'31", long. 108°10'51", in NW1/4 NE1/4 SW1/4
Sec 9, T. 55 N. , R. 94 W. , off the right bank and 10.5 kilometers
(6.5 miles) south of Kane, Wyoming. The location of the Shoshone
River sampling station was lat. 44°51'45" long. 108°12'30", in
E 1/2 Sec.6, T. 56 N. , R. 95 W., off the right bank, 1.6 kilometers
(1 mile) north of Kane, Wyoming and 2.4 kilometers (1.5 miles)
upstream from its mouth.
A sampling station at the base of the dam was also established
for the characterization of the effluent waters from the reservoir
during the course of the study.
10
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METHODS AND MATERIALS
Influent and Effluent Waters
Water samples and field measurements were taken at the various
river stations at biweekly intervals for 1968 and weekly intervals
for 1969, when possible, throughout the duration of this part of the
study. Table II shows the dates and the rivers which were sampled.
All samples were obtained by lowering an 8-liter polyethylene
bucket into the main current of the river. The container was rinsed
well with the surface water prior to sampling. Upon collection, two
1-liter aliquots were collected in glass-stoppered Pyrex bottles.
Immediately, one of the samples, to be used for heavy metal analyses,
was preserved with 2 ml of 50% HC1 (Rainwater and Thatcher, 1959).
All storage bottles were rinsed twice before being filled with the
water sample.
Water Chemistry
After returning to the laboratory, a portion (700 ml) of the
untreated sample was filtered through Millipore^y filters with a pore
size of 0.45 microns. After filtering, the sample was placed back
in the glass-stoppered Pyrex bottle, which had been rinsed with a
small quantity of the filtrate. The remaining unfiltered water was
placed in a 300 ml glass-stoppered Pyrex bottle and used in some of
the subsequent analyses.
Measurement of hydrogen ion concentration was determined in
the field and in the laboratory with an Orion specific ion meter
(Model 401) and a Beckman Expanded Scale pH meter (Model 76),
respectively.
Total alkalinity, chloride, fluoride, nitrate, nitrite, ammonia,
total and soluble nitrogen, total phosphate, soluble and inorganic
phosphate, sulfate, silica, calcium, magnesium, copper and turbidity
determinations were made as described by the American Public Health
Association (1965).
Total iron determinations were made according to the method of
Collins and Diehl (1960). Manganese was determined by the leuco-base
method as described by Strickland and Parsons (1968). The colori-
metric equipment used in the various analyses was either a Bausch
and Lomb "Spectronic 20" (Serial No. 4848 UB) or a Klett-Summerson
(Model 800-3) colorimeter.
Total and soluble carbon fractions were determined by employing
a Beckman Laboratory Carbonaceous Analyzer (Serial No. PI 1114).
11
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Table II.
The date and the river where water samples were
collected (+) during the 1968 and 1969 sampling
periods.
Date
1968
1969
Bighorn Shoshone
Influent Influent Discharge
Date
Bighorn Shoshone
Influent Influent Discharge
2/22 + +
3/ 7 + +
3/28 + +
4/11 + +
5/ 4 + +
5/18 + +
6/ 1 + +
6/12 + +
6/24 + +
7/15 + +
8/ 1 + +
8/19 + +
9/23 + +
10/ 7 + +
10/19 + +
III 9 + +
11/23 + +
12/ 7 + +
12/20 * +
+ I/ 3 * * +
+ 1/18 * + +
+ 2/ 1 * + +
+ 2/15 * + +
+ 3/ 1 + +
+ 3/17 + +. +
+ 3/31 + + +
+ 4/ 7 + + +
+ 4/14 + + +
+ 4/21 + + +
+ 4/28 + + +
+ 51 5 + + +
+ 5/12 + + +
+ 5/22 + + +
+ 5/28 + + +
+ 6/ 3 + + +
+ 6/10 + + +
+ 6/17 + + +
+ 6/24 + + +
11 1 + + +
11 8 + + +
7/14 + + +
7/21 + + +
7/29 + + +
8/ 5 + + +
8/11 + + +
8/18 + + +
Samples were not collected because of ice cover.
12
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Table III.
The dates for each cruise and type of cruise
made during the study period.
Cruise
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
26
1968
(Type)
(L)
(S)
(s)
(S)
(L)
(S)
(S)
(S)
(S)
(L)
(S)
(S)
(S)
(L)
(S)
(S)
(S)
(L)
(S)
(S)
(S)
(L)
(S)
(S)
(S)
(L)
Date
5/ 5
5/13
5/20
5/27
6/ 7
6/12
6/20
6/27
11 2
11 8
7/15
7/23
7/29
8/ 5
8/12
8/19
8/26
9/ 3
9/ 9
9/17
9/23
10/ 2
10/ 8
10/14
10/22
ll/ 2
Cruise
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
1969
(Type)
(L)
(S)
(s)
(S)
(L)
(S)
(S)
(S)
(S)
(L)
(S)
(S)
(S)
(L)
(S)
(S)
1970
Date
4/15
4/21
4/28
5/ 5
5/12
5/21
5/27
6/ 3
6/13
6/18
6/24
6/30
7/22
7/28
8/ 4
8/11
Cruise
43
44
45
46
47
48
49
50
51
52
53
54
55
56
Date
6/11
6/18
6/24
11 2
11 8
7/16
7/23
7/29
8/ 4
8/10
8/18
8/24
9/ 1
9/ 8
S = short cruise
L = long cruise
1.3
-------
Sodium and potassium were determined by flame emission with a
Beckman DU Flame Spectrophotometer. Zinc was determined by atomic
absorption spectroscopy employing a Perkin-Elmer Atomic Absorption
Unit (Model 303).
All of the above mentioned analyses were made within 96 hours
after collection. Total alkalinity, the various forms of carbon, the
various forms of phosphorus, total and soluble nitrogen, ammonia,
nitrate, nitrite and laboratory -pH determinations were made within
48 hours after collection.
Temperature and Conductivity
The temperature of the water sample upon collection was measured
with a Gemware bucket thermometer (No. 297WA100).
The electrical resistance of each sample was measured with a YSI
Conductivity Bridge (Model 31). An Industrial Instruments dipping
cell (Model CEL 4) was used with the above conductivity bridge. The
cell constant of the dipping cell was approximately 2.1 throughout
the study.
The specific conductance of the water at 25 C was computed from
the observed resistance and corrected for temperature and cell
resistance.
Hydrology
Discharge measurements for the Bighorn and Shoshone Rivers were
supplied by the U. S. Geological Survey. The gaging stations are
located in the same areas where water samples were collected.
Records of the total discharge from the dam were furnished by
the Bureau of Reclamation.
Reservoir
During the study all water samples and in situ measurements were
taken during one of the fifty-six cruises at each station on Bighorn
Lake. The length of the sampling season was usually five months
(Table III). This study was carried out over three years (1968,
1969, and 1970). Due to the late date of receipt of the grant award
it was not possible to sample the reservoir intensively in 1967.
When possible, sampling periods were spaced at weekly intervals.
In 1968 and 1969 both "short cruises" and "long cruises" were
made. A long cruise was made once a month and short cruises the rest
of the month. On short cruises, transmissivity, temperature and
conductivity measurements were made from the surface to the bottom
14
-------
of the reservoir at 5 meter intervals at all sampling stations.
In situ light measurements at depth intervals of 1 meter were
obtained. Water samples were collected from the surface to the
lower limit of the euphotic zone usually at 1 meter intervals.
The pH of each sample was determined. Equal volumes of the
euphotic zone samples were then composited and this composite was
used for chlorophyll, nitrate, nitrite, ammonia, ortho-phosphate,
total iron, manganese, copper, and zinc determinations. Also, a
sample was taken from the composite for phytoplankton enumeration.
Everything determined on a short cruise was duplicated on a
long cruise, but additional water samples for a more detailed
chemistry study of the reservoir were collected at 10 meter inter-
vals from the surface to the bottom of the reservoir. These samples
were taken every 16.1 km starting with station 0 and analyzed for
dissolved oxygen, pH, total alkalinity, chloride, fluoride, sulfate,
nitrite, nitrate, ammonia, ortho-phosphate, silica, turbidity, po-
tassium, sodium, calcium, and magnesium concentrations.
In 1970, transmissivity, temperature and conductivity were
determined as for preceding years. Sampling procedures in the
euphotic zone were similar to that of 1968 and 1969, but pH, oxygen,
ortho-phosphate, nitrate, nitrite and ammonia concentrations were
determined from the surface to the bottom of the reservoir at 10
meter intervals for all stations on all cruises.
Vertical profiles of light attenuation were obtained by measur-
ing in situ light intensities with a Gemware Photometer (Model No.
268WA310). This instrument included a gimbal-mounted deck photocell
and an underwater photocell (both had matched photocells). Light
intensity was measured from the surface and at 1 meter intervals until
a depth at which only 1% of the total surface radiation was obtained.
A number of field and laboratory studies have shown that the
compensation point for various phytoplankton organisms is reached
at light intensities of about 1% total surface radiation (Verduin,
1964). Therefore, by definition the compensation point sets the
lower limit of the euphotic zone.
The mean vertical extinction coefficients were computed as
described by Hutchinson (1957). The extinction coefficient units
are common log units per meter (k/m).
Light transmission was measured at 5 meter intervals from the
surface with 1 meter and/or 10 centimeter Hydro Products trans-
missometer columns.
15
-------
Kimball's (1928) tables of average radiation data for selected
dates and latitudes were used in the calculations of primary
productivity.
Temperature and Conductivity
Vertical in situ measurements for conductivity and temperature
were made with~a Beckman RB3-3341 Solu Bridge, calibrated for use
with conductivity cell CEL-S02-VH20-KP-X9. The latter incorporates
a thermistor which serves a dual function as a component of an
automatic temperature compensator for all conductivity ranges and
as a primary element for temperature measurement.
Water Chemistry
A 3-liter Van Dorn Bottle was used to collect all water samples.
All storage containers were rinsed with sample prior to filling.
dD
One-liter samples were filtered through Millipore^ filters with
a pore size of 0.45 microns. After filtering, the samples were
placed back in the storage containers, which were rinsed with a small
quantity of the filtrate.
The methodology for the chemistry of the reservoir was the same
as that used in characterizing the influent and effluent waters. A
YSI Model 54 Oxygen Meter was used to the determination of dissolved
oxygen. The instrument was calibrated by allowing the electrode
system to equilibrate in a sample of known oxygen content.
Phytoplankton Standing Crop, Chlorophyll and Primary Productivity
The total cell volume per unit volume of water (mm^/liter) was
determined for each, taxon in the phytoplankton community as follows.
A 125 ml sample of the euphotic zone composite was preserved with
Lugol's solution. Later in the laboratory, the algae were uniformly
suspended in the solution, and a 10 ml settling chamber was filled
with the phytoplankton sample. After 24 hours the sediment was
examined with a Zeiss-Winkel inverted microscope. Morphological units
representing each taxon were counted and linear dimensions measured
with a Whipple micrometer disk. By assuming an appropriate geometri-
cal shape, (i.e, sphere, prolate spheroid, etc.), the average cell
volume per morphological unit was computed. A series of ratios
involving sample volume, magnification and the number of fields count-
ed were used to compute the cell volume per liter (Schwoerbel, 197Q)
Lund et al. (1958) have discussed the statistical validity of such
direct count methods.
16
-------
Identification of the phytoplankton was carried out to the
species level where possible, but in some cases only generic
designations were made. Algae were identified from both living
and preserved material using the keys of Smith (1950), Prescott
(1962), Hustedt (1930), Tiffany and Britton (1952) and Drouet (1959).
Fresh algal, weight, in mg, was considered to be equivalent to
cell volume in mm3 (Strickland, 1960).
Chlorophyll a concentrations were determined by filtering (0.45
micron Millipore(^filters) a known volume (usually 500 ml) of the
euphotic zone composite water. The membrane was then dissolved in
5 ml of 90% acetone and allowed to stand in the dark for 24 hours.
The solution was then centrifuged and the optical density of the
supernatant was measured at 665 millimicrons using the Bausch and
Lomb "Spectronic 20" colorimeter. The milligrams of chlorophyll a_
per cubic meter were calculated according to Odum et^ _al. (1958).
The method of Ryther and Yentsch (1957) as modified by Martin
(1967) was used to estimate primary productivity. This method
assumes an average ratio between chlorophyll and productivity at
light saturation and requires data on: (1) the average chlorophyll a_
concentration of the euphotic zone; (2) total solar radiation;
(3) the extinction coefficient of the water column; and (4) average
temperature of the euphotic zone for that day.
Hydrology
Stage, net inflow, total discharge and storage records for the
reservoir were supplied by the Bureau of Reclamation.
Water exchange rates for the reservoir were computed by dividing
the mean storage for a month by the mean monthly outflow.
RESULTS
Influent and Effluent Waters
Hydrology
Fluctuations in the discharge for the Bighorn River are more
apparent than for the Shoshone River (Table IV). The natural flow
of the Shoshone is regulated by Buffalo Bill reservoir while the
Bighorn receives some regulation by Boysen reservoir. Both rivers
are affected by diversions for irrigation and return flow from
irrigated areas.
17
-------
3
Table IV. Discharge (m /sec) for the influent and effluent
waters of Bighorn Lake during 1968 and 1969
sampling periods.
Date
2/22
3/ 7
3/28
4/11
51 4
5/18
6/ 1
6/12
6/24
7/15
8/ 1
8/19
9/23
10/ 7
10/19
ll/ 9
11/23
12/ 7
12/20
Bighorn
Influent
59.4
79.2
68.2
63.4
53.8
59.7
92.5
20535
181.4
47.5
35.9
82.9
58.9
58.9
64.2
66.5
70.8
73.0
42.5
1968
Sho shone
Influent
22.6
24.1
32.3
30.0
15.6
20.7
23.0
49.0
20.2
19.7
20.7
58.6
37.1
27.7
25.7
35.7
24.2
35.4
28.9
Discharge
114.5
148.6
107.8
98.1
86.8
167.8
141.3
300.7
154.0
91.1
59.4
46.3
113.2
97.7
87.5
94.7
111.8
113.8
110.4
Date
H 3
1/18
2/ 1
2/15
3/ 1
3/17
3/31
4/ 7
4/14
4/21
4/28
5/ 5
5/12
5/22
5/28
6/ 3
6/10
6/17
6/24
11 I
11 8
7/14
7/21
7/29
8/ 5
8/11
8/18
Bighorn
Influent
42.5
42.5
56.6
76.4
76.4
79.0
74.1
74.7
78.4
65.1
78.4
77.0
57.7
62.3
91.4
44.1
60.6
65.6
71.3
169.8
101.3
62.3
52.6
43.0
23.2
22.1
25.0
1969
Sho shone
Influent
25.5
25.5
22.6
17.0
24.1
34.2
27.3
31.7
26.3
22.6
28.3
15.6
16.8
24.9
25.5
19.9
65.7
43.0
20.2
28.9
20.4
19.4
18.2
18.6
24.9
47.3
70.8
Discharge
129.8
95.9
92.5
102.5
133.9
139.4
95.4
79.0
76.9
39.4
48.4
70.1
43.4
62.7
36.7
50.7
44.4
56.4
50.1
122.8
168.3
165.6
145 . 3
104.3
110.4
102.5
97.0
13
-------
During 1968 and 1969, the Bighorn River had a mean monthly
discharge of 2,191 m3/sec, (77,342 cfs) while the discharge for the
Shoshone River was 941 m3/sec (32,158 cfs). Winter months usually
had the lowest flows, whereas peak streamflows occurred in the spring
(Table V). The peak inflows during June accounted for 13-19% of the
total net inflow to the reservoir. The Bighorn River made up approxi-
mately 70% of the net inflow.
The major portion of the discharge from the dam was released
through the power penstocks. Greater quantities of water were dis-
charged during 1968 than any of the other years.
Temperature and Conductivity
The mean monthly temperatures for the influent and effluent
waters are given in Figure 4. The cycle of temperature in the
discharge water lagged behind the influent water temperature.
Temperatures of the influent streams were at or near freezing
through most of December, usually all of January and most of February.
From the latter part of February there was a rise in temperature
until maximal temperatures were attained in July and August. The
highest recorded temperature was 28.2 C for the Bighorn River on
5 August 1969.
In contrast, the effluent water temperature never reached freez-
ing. Minimum temperatures appeared in March and April (2.5 C) follow-
ed by a maximum in September (16.0 C, 1968; 12.5 C, 1969).
The effect of impoundment and deep water withdrawal was to
displace the maximum and minimum temperatures two to four months
behind the influent temperatures and to increase the minimum tempera-
tures above those of the influents.
Figure 5 compares the conductivity of the influent waters with
that of the discharge. Conductivity of the Bighorn River never
exceeded 1,250 micromhos while 1,500 micromhos was the high recorded
for the Shoshone River.
Extremely large fluctuations in conductivity were noted for the
Shoshone River whereas most of the values for the Bighorn River were
around 900 micromhos. Values were minimal in the Bighorn River
during periods of high streamflow in May and June. Maximal conduc-
tivity values for the Bighorn River occurred in late summer and early
fall periods. The relationship between specific conductance and
discharge is illustrated in Figure 6.
19
-------
Table V. Total monthly discharge (m /sec) for the influent
and effluent waters of Bighorn Lake during 1968
and 1969 sampling periods.
Month
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec
Bighorn
Influent
1,572
1,873
2,214
1,851
1,848
5,582
1,791
1,918
2,02.3
1,780
2,014
1,818
1968
Sho shone
Influent
753
591
888
808
670
983
609
1,325
1,035
874
973
1,025
Discharge
4,714
3,434
3,820
3,064
3,589
7,010
2,405
1,905
3,110
2,997
3,445
3,425
Month
Jan
Feb
Mar
Apr
May
June
July
Aug
Sept
Oct
Nov
Dec
Bighorn
Influent
1,373
2,018
2,370
2,085
2,102
2,918
2,206
741
937
2,935
3,665
2,969
1969
Sho shone
Influent
880
640
739
751
485
1,200
1,148
527
692
1,598
1,386
1,292
Discharge
3,136
2,943
3,665
1,846
1,492
2,605
4,233
3,135
2,739
2,838
2,635
3,292
20
-------
Bighorn River
Shoshone River
// \ \ Discharge
J FMAMJ JASON DJ FMAMJ JASOND
0
1968
1969
Figure 4. Monthly average of temperatures (C) for the influent
and effluent waters of Bighorn Lake during the 1968
and 1969 sampling periods (September - December values
supplied by the U.S.G.S.).
-------
I400i
1200
O
o 1000
t 800-
o
o
§ 600
o
o
400-
Bighorn River
Shoshone River
J F M
J J
1968
0
~Or~t*r~Qr
1969
Figure 5. Monthly average of specific conductance (micromhos)
for the influent and effluent waters of Bighorn Lake
during the 1968 and 1969 sampling periods (September
December values supplied by the U.S.G.S.)-
-------
1500-
1400-
1300-
g 1200-
2 1100-
o
o 1000
2
- 900
H 800
700
600
500
400
-300
I-
O
.
O
o
10
Bighorn River
Trend
o o ,
Shoshone R iver
Trend
50 100 500 10 50 100
DISCHARGE (m3/sec)
Figure 6. Relationship between specific conductance (micromhos)
and mean discharge (nr/sec) for the influent waters
of Bighorn Lake during the 1968 and 1969 sampling
periods.
-------
The two to four month lag is again evident between minimum and
maximum values of conductivity when influent waters (particularly
the Bighorn River) and the discharge are compared (Fig. 5).
Water Chemistry
The composition of the influent waters is what would be expected
from rivers draining sedimentary rocks under semi-arid conditions
(Hem, 1959). The range and mean water chemistry are presented in
Tables VI and VII. The cations in highest concentration, calcium and
sodium, were approximately equal in concentration followed by
magnesium and potassium. Sulfate was the anion in highest concen-
tration followed by bicarbonate and chloride.
Discharge-weighted means (for 1968 and 1969) of the major ions
of the influent streams and the discharge are given in Table VIII.
Discharge-weighted means were computed by multiplying the discharge
for a given sampling period by the concentrations of individual
constituents for the period and dividing the sum of the products
by the sum of the discharges. Overall, water discharge from the dam
was slightly lower in dissolved solids than the weighted average of
the influents. Sodium, potassium, chloride and sulfate appeared to
behave in a conservative manner. The downstream decrease in concen-
tration of these ions, particularly sodium, probably was due to
dilution by rainfall and/or run-off from snow-fed tributaries. In
1969, there was a decrease in calcium concentration in the discharge
compared to an increase in magnesium, but a decrease in both ions
occurred in 1968. These elements were determined using a complexo-
metric titration which, because of the inherent errors of the method
(A.P.H.A., 1965), could possibly account for the different results
between the two years.
Table IX presents values of the various carbon, nitrogen and
phosphorus fractions averaged from 22 samples collected between 19
August 1968 and 18 August 1969 from the influent and effluent waters.
Of the total amount of nitrogen that entered the reservoir 75%
was discharged. A large decrease in particulate nitrogen was evident
from a comparison of influent and effluent concentrations. The
concentration of total inorganic nitrogen leaving the reservoir was
essentially the same as that entering. More nitrate was discharged
than entered, which indicates nitrification and nitrogen fixation were
in excess of nitrogen assimilation and denitrification.
Only 14% of the phosphorus that entered the reservoir was dis-
charged. The greatest loss was in particulate phosphorus.
24
-------
Table VI.
Range and mean of water chemistry for the
influent and effluent waters of Bighorn Lake
during the 1968 sampling periods.
Bighorn Shoshone
Influent Influent Discharge
Ca++ (meq/1)
Mg (meq/1 )
Na (meq/1)
K+ (meq/1)
1.45-4.66
3.66
0.49-5.17
2.09
1.12-4.75
3.35
0.06-0.27
1.40-7.62
4.76
1.34-3.84
2.42
1.72-6.84
4.84
0.09-0.22
2.00-4.98
3.82
0.91-2.60
1.86
1.99-4.25
3.23
0.08-0.42
HCO~ (meq/1)
Cl= (meq/1)
SO^ (meq/1)
F" (meq/1)
Soluble Organic C (mg/l)
Particulate C (mg/l)
NO" -N (mg/l)
NO" -N (mg/l)
NH -N (mg/l)
Soluble Organic NH -N (mg/l)
Particulate NH -N (mg/l)
Ortho-P0~ (mg/l)
Soluble Organic P0~ (mg/l)
Particulate PO? (mg/l)
0.14 0.15 0.15
1.92-3.82 3.24-4.76 2.81-3.97
3.03 3.90 3.18
0.12-0.57 0.13-0.52 0.20-0.41
0.35 0.30 0.29
1.04-8.28 3.75-13.54 5.25-7.42
5.95 8.35 6.17
0.02-0.11 0.02-0.11 0.02-0.10
0.04 0.05 0.04
1.2 -14.2 1.5- 11.4 0.0 -10.3
7.7 6.7 6.4
0.8 -31.7 0.3 - 7.4 0.0 - 3.9
7.0 3.7 2.0
0.09-0.79 0.08-1.67 0.25-0.83
0.35 0.85 0.54
0=003-0.028 0,003-0.029 0.001-0.017
0.008 0.011 0.005
0.00-1.36 0.00-0.66 0.00-0.50
0.35 0.28 0.1.7
0.00-0.95 0.02-1.49 0.00-1.50
0.33 0.52 0.47
0.00-1.88 0.00-0.45 0.00-1.18
0.34 0.06 0.09
0.00-0.40 0.00=0.64 0.00-0.16
0.11 0.12 0.04
0.00-0.35 0.00-1.10 0.00-0.16
0.04 0.06 0.02
0.00-3.39 0.00-2.08 0.00-0.21
1.90 0.47 0.04
25
-------
Table VI.(Gont'd)
Turbidity (J.T.U.)
Silica (mg/1)
Total Iron (mg/l)
Mn++ (mg/l)
Bighorn
Influent
30-4,900
816
6.3-12.9
9.4
0.004-0.885
0.138
0.004-0.119
S ho shone
Influent
36-2,220
434
7.6-18.5
13.8
0.016-0.440
0.129
0.001-0.077
Discharge
4-30
13
6.7-14.0
10.0
0.003-0.022
0.009
0.000-0.009
0.021 0.025 0.004
Cu (jig/1) 0.70-3.80 0.80-2.80 0.80-1.70
1.60 1.40 1.10
Zn (mg/l) 0.007-0.232 0.010-0.260 0.006-0.258
0.094 0.084 0.057
Conductance (micromhos) 412-1,125 818-1,684 669-932
837 1,062 870
pH Range 7.49-8.55 7.78-8.46 6.98-8.10
26
-------
Table VII.
Range and mean of water chemistry for the
influent and effluent waters of Bighorn Lake
during the 1969 sampling periods.
Bighorn Shoshone
Influent Influent Discharge
Ca++ (meq/1)
Mg (meq/1)
Na (meq/1)
K+ (meq/1)
HCO~ (meq/1)
J
Cl" (meq/1)
SO? (meq/1)
H-
F" (meq/1)
Soluble Organic C (mg/1.)
Particulate C (mg/l)
N0~ -N (mg/1)
j
NOT -N (mg/1)
/,
NH0 -N (mg/1)
o
Soluble Organic NH0-N (mg/l)
j
Particulate NH,-N (mg/l)
j
Ortho-PO? (mg/l)
4
Soluble Organic P0~ (mg/l)
_ M-
Particulate PO? (mg/l)
M-
2.08-5.48
3.43
0.49-2.80
1.69
1.77-6.80
3.51
0.06-0.17
0.12
1.41-3.45
2.52
0.17-0.56
0.35
2.42-7.50
5.03
0.02-0.05
0.03
4.4 -20.0
9.6
0.0 -39.6
10.5
0.12-0.78
0.40
0.002-0.011
0.005
0.04-0.71
0.25
0.00-0.87
0.19
0.04-2.18
0.67
0.00-1.55
0.11
0.00-0.04
0.00
0.00-3.22
0.68
1.82-4.67
3.76
0.86-2.73
1.95
2.19-6.20
4.16
0.06-0.16
0.12
1.81-4.60
3.15
0.14-0.69
0.31
3.10-8.44
5.83
0.02-0.06
0.04
4.8 -24.9
9.7
0.0 -27.0
8.1
0.00-1.53
0.79
0.000-0.019
0.011
0.07-0.71
0.26
0.00-0.87
0.26
0.00-2.24
0.46
0.00-0.28
0.08
0.00-0.12
0.00
0.00-1.30
0.55
2.88-4.43
3.71
1.46-3.38
2.02
2.73-4.50
3.53
0.06-0.16
0.12
2.25-3.70
3.05
0.27-0.45
0.34
4.33-6.21
5.47
0.02-0.06
0.04
5.3 -23.0
9.5
0.0 -30.8
5.0
0.00-0.74
0.55
0.000-0.015
0.004
0.02-0.55
0.21
0.01-0.56
0.18
0.00-0.75
0.21
0.00-0.17
0.04
0.00-0.14
0.00
0.00-0.16
0.05
27
-------
Table VII.(Cont'd)
Bighorn
Influent
Shoshone
Influent
Discharge
Poly-P0~ (mg/1)
Turbidity (J.T.U.)
Silica (mg/1)
Total Iron (mg/1)
Mn++ (mg/1)
Cu++ (ng/1)
Zn++ (mg/1)
Conductance (micromhos)
pH Range
0.00-0.43 0.00-0.18 0.00-0.35
0.02 0.05 0.05
59-3,600 22-2,540 0-36
631 371 10
6.3-19.4 8.3-17.6 6.0-12.8
9.1 13.8 10.5
0.001-4.015 0.001-3.900 0.000-0.463
1.290 1.390 0.052
0.000-2.145 0.001-0.560 0.000-0.300
0.265 0.182 0.030
0.5-22.0 0.5-21.0 0.0-6.0
3.1 2.6 1.3
0.000-0.178 0.004-0.169 0.004-0.058
0.048 0.038 0.022
427-1,247 507-1,315 692-971
826 941 877
7.33-8.63 7.35-8.56 6.81-8.31
28
-------
Table VIII . Discharge-weighted chemical composition (meq/l)
of the influent and effluent waters of Bighorn
Lake during 1968 and 1969.
1968
Ca Mg Na K HC03 Cl SO^ F Sum
Bighorn (B.H.) 3.64 2.10 3.22 0.13 2.94 0.33 5.37 0.04 17.77
Shoshone (Shos.) 4.69 2.32 4.72 0.15 3.91 0.30 8.00 0.04 24.13
Weighted Average
of B.H. & Shos. 3.94 2.17 3.65 0.14 3.22 0.33 6.12 0.04 19.61
Discharge 3.89 1.91 3.27 0.14 3.18 0.30 6.11 0.03 18.83
Percent change -1.3 -11.9 -10.4 0.0 -1.3 -9.1 -0.2 -25.0 -4.0
1969*
Ca Mg Na K HCO Cl SO F Sum
Bighorn (B.H.) 3.80 1.90 3.61 0.10 2.94 0.37 5.65 0.02 18.39
Shoshone (Shos.) 4.02 2.06 3.87 0.11 3.62 0.33 5.83 0.03 19.87
Weighted Average
of B.H. & Shos. 3.87 1.95 3.69 0.11 3.16 0.36 5.70 0.03 18.87
Discharge 3.74 2.05 3.70 0.11 3.14 0.31 5.79 0.03 18.87
Percent change -3.4 +4.9 +0.3 0.0 -0.6 -13.9 +1.6 0.0 0.0
* September-December data supplied by the U.S.G.S.
29
-------
Table IX, The carbon (rag/1 G), nitrogen (mg/1 N) and phosphate (mg/1 P0=) balances
of Bighorn Lake for the period between 19 August 1968 and 18 August 1969,
OJ
o
Bighorn (B.H,)
Shoshone (Shos,)
Weighted Average
of B.H. & Shos.
Discharge
Percentage change
Bighorn (B.H.)
Shoshone (Shos. )
Weighted Average
of B.H. & Shos.
Discharge
Percentage change
Bighorn (B.H.
Sho shone ( Sho s . )
Weighted Average
of B.H. & Shos.
Discharge
Percentage change
Partic-
Total ulate Soluble
Organic Organic Organic
-N =N -N
0.91 0,68 0.23
0.75 0.47 0.29
0.86 0.62 0.25
0.44 0.23 0.21
=49 -63 -16
Total
-P04
0.926
0.792
0.886
0.123
-86
Total
Organic -C
18.75
16.50
16.57
12.51
-24
NH NO NO
=N -N -N
0.30 0.006 0,40
0.28 0,01 0.89
0.29 0.007 0.55
0.23 0,004 0.61
-20 =43 +11
Particulate
-P04
0.625
0.553
0.603
0.040
-93
Particulate
Organic -C
9.82
7.20
7.22
3.79
-47
Total In- Total In=
organic organic
-N + Organic -N
0.71 1.62
1.18 1.93
0.85 1.71
0.84 1.28
-1 -25
Ortho
-P04
0.104
0.077
0.096
0.031
-68
Dissolved
Organic -C
8.93
9.30
9.27
8.72
-6
-------
Significant correlations existed between high turbidity and
high- total phosphorus for both, the Bighorn (r = 0.79; P = 0.01)
and Shoshone Q: » 0.71; P = 0.01} Rivers. A positive correlation
was also found between turbidity and total nitrogen for the Bighorn
Or = Q.66; P H 0.011, however, this relationship for the Shoshone
River was not statistically significant.
Figure 7 presents a comparison of streamflows and turbidities
for influent and effluent waters. When run-off into the reservoir
was high., especially in the case of the Bighorn River, a corresponding
increase in turbidity was observed, but turbidity for the discharge
never exceeded 30 Standard Jackson Turbidity Units.
High, values of ortho-phosphate as well as total phosphate are
associated with. high, turbidity CFig. 8). This may indicate that a
base exchange equilibrium occurred between the water and the suspend-
ed sediments, releasing ortho-phosphate from the sediments.
The most significant change in the carbon balance of the influent
and effluent waters (Table IX) was the decrease in particulate carbon.
Dissolved organic carbon was essentially the same in the discharge
as in the influent streams.
Data concerning the heavy metal analyses are given in Table X.
There was a decrease in concentration of these elements in the dis-
charge compared to the influent streams. The greatest decrease was
in iron followed by manganese. Copper appeared to be the most mobile
of all the heavy metals. The. ratio of iron to manganese was less in
the discharge than in the influents. The ratio of copper to zinc was
higher in the discharge than in the influent water. The major cause
of decrease in concentration of these metals was attributed to the
settling out of suspended sediments that were carried into the
reservoir.
Table X.
Iron, manganese, copper and zinc (mg/1) budget of
Bighorn Lake during the 1968 and 1969 sampling periods.
Fe
Mn
Fe/Mn
Cu
Zn
Cu/Zn
Bighorn (B.H.)
Shoshone (Shos.)
Weighted Average
of B.H and Shos.
Discharge
Percentage Change
1.052
1.000
1.036
0.034
-97
0.
0.
0.
0.
152
124
144
022
-86
6.
8.
7.
1.
92
67
19
55
0.
0.
0.
0.
0025
0023
0024
0015
-40
0.
0.
0.
0.
086
067
080
023
-71
0.
0.
0.
0.
03
03
03
07
31
-------
I
LJ
C9
CC
<
X
o
CO
o
200-
150
100-
50-
0.
3000-
5 2500-
^ 2000-
£ 1500-
m I000^
rr
H 500-
Bighorn River
Shoshone River
Discharge
FMAMJ JASONDJ FMAMJJA
Figure 7. Seasonal fluctuations of mean discharge (m-Vsec) and
turbidity (Standard Jackson Turbidity Units) for the
influent and effluent waters of Bighorn Lake during
the 1968 and 1969 sampling periods.
-------
lOOOH
Q
CO
or
IOCH
O.t 0.2 0.3 0.4 0.5
ORTHO-PHOSPHATE (mg/l)
0.6
Figure 8. Relationship between turbidity (Standard Jackson
Turbidity Units) and ortho-phosphate (mg/l P0£) for
the Bighorn and Shoshone Rivers.
33
-------
Reservoir
Hydrology
Due to excessive inflow to the reservoir. Bighorn Lake was filled
to maximum capacity in 1967. Sixty-one percent of the total net
inflow for 1967 occurred during May, June and July. Twenty.percent
of the total discharge for the year was diverted through the spillway
in July because of the excessive run-off to the reservoir in the
preceding months. These high, discharges caused damage to the spillway
tunnel.
Inflow, discharge and storage change data for water years 1968,
1969 and 1970 are given in Table XI. Two extremes are illustrated,
with a negative storage value for 1968 and positive storage values for
1969 and 1970. The negative value in 1968 was due to the fact that
the total discharge had to be greater than the total inflow in order
to attain and maintain water levels below the spillway elevation to
facilitate repair of the spillway tunnel.
Reservoir water level fluctuations for 1969 and 1970 were fairly
constant. There was a spring rise of 20 meters (66 ft) to reach a
maximum in July followed by receding water levels to a minimum in
February and March (Fig- 9). However, the reservoir was in a filling
stage during the study and water levels were not indicative of normal
operation until 1970. ,
The annual water exchange rates for Bighorn Lake were 0.3 in
1968, 0.4 in 1969 and 0.5 in 1970 (Table XII). This illustrates that
as water levels increased, the retention time of a given mass of water
within the reservoir became greater.
The transmittance of light in Bighorn Lake ranged from 3 to 100%
T/10 cm column. The influent waters had the lowest clarity, but as
the water flowed toward the dam the clarity increased (Fig. 10). The
mean turbidity was 10 and 414 J.T.U. at stations 0 and 5, respectively,
while transmission of light was 92 and 59%.
The significant correlation (r = -0.99; P = 0.01) between trans-
mission and turbidity is evident (Fig. 11). The regression equation
between transmission and turbidity was calculated:
2
Transmission (% T/10 cm) = -20.9T + 112.1 R =0.98
where T equals the common log of the turbidity expressed as J.T.U..
34
-------
5 3
Table XI. Inflow, discharge and storage change (X10 m ) in Bighorn Lake for the
water years ending 30 September 1968, 30 September 1969 and 30 September
1970.
1968
Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Total
Net
Inflow 2,375 2S580 2,466 2,329 2,628 2,853 2,408 2,490 6,542 2,354 2,794 2,686 34,505
Total
Discharge 2,240 2,703 3,835 4,064 2,960 3,268 2,638 3,094 6,043 2,074 1,643 2,681 37,243
Storage
Change +135 -123 -1,369 -1,735 -332 -415 -230 -604 +499 +280 +1J.51 +5 -2,738
w 1969
Ln .
Oct Nov Dec Jan Feb Mar Apr May June -July Aug Sept Total
Net
Inflow 2,662 25840 2,483 2,034 2,389 2,861 2,625 2,615 4,018 3,320 1,561 1,837 31,245
Total
Discharge 2,587 2,970 2,953 2,704 2,537 3,159 1,592 1,286 2,266 3,157 2,703 2,361 30,275
Storage
Change +75 -130 -470 -670 -148 -298 +1,033 +1,329 +1,752 +163 -1,142 =524 +970
1970
Oct Nov Dec Jan Feb Mar Apr May June July Aug Sept Total
Net
Inflow 23407 2,334 1,880 1,719 2,286 2,439 1,945 3,448 5,863 3,643 1,334 1,906 31,204
Total
Discharge 2,450 2,272 2,838 2,919 2,487 1,453 795 1,681 3,856 5,032 1,781 1,383 28,947
Storage
change -43 +62 -958-1,200 -201 +986+1,150+1,767+2,007-1,389 -447 +523+2,257
-------
1127.8
UJ
CD
< CO n I O Q.
LI n- III^.O-
UJ
UJ
Ul
UJ
O 1097.3
CD _J
< UJ
z §
r- 1082.1
UJ
1066.8
'J 'J'A'S'O'N'DIJ'F'M'A'M'J'J'A'S'O'N'DIJ'F'M'A'M'J'J'A'S'O'N'D
1968 1969 1970
Figure 9. Range and mean water levels of Bighorn Lake during
1968, 1969 and 1970 (Bureau of Reclamation Data).
-------
Table XII,
Water exchange rates (days) in Bighorn Lake
for 1968, 1969, and 1970.
Month
January
February
March
April
May
June
July
August
September
October
November
December
Mean
Monthly
Annual
January
February
March
April
May
June
July
August
September
October
November
December
Mean
Monthly
Annual
Average
Storage
(X106 m3)
1,071.7
982.7
952.4
922.9
877.1
866.9
927.8
968.7
1,053.1
1,043.9
1,046.8
1,027.4
951.5
921.5
882.8
917.8
1,044.2
1,175.9
1,298.8
1,198.4
1,105.5
1,091.3
1,085.6
1 , 049 . 5
1968
Average
Discharge
(X106 m3/day)
13.1
10.2
8.7
8.8
10.0
20.1
6.9
5.5
8.9
8.3
9.9
9.5
1969
8.7
9.1
10.2
5.3
4.1
7.5
11.8
8.7
7.9
7.9
7.6
9.1
Exchange
Rate
(days)
81.9
96.4
109.4
105.0
88.0
43.1
134.5
177.2
118.1
125.5
105.9
108.0
107.8
3.6
0.3
109.3
101.9
86.8
173.3
252.2
156.0
110.5
137.7
140.7
138.5
143.6
114.9
138.8
4.6
0.4
37
-------
Table XII. (Cont'd)
Month
January
February
March
April
May
June
July
August
September
October
November
December
Mean
Monthly
Annual
Average
Storage
(X106 m3)
925.8
865.2
875.9
1,022.4
1,152.7
1,323.2
1,346.1
1,281.3
1,281.3
1,332.9
1,331.6
1,296.6
1970
Average
Discharge
(X106 m3/day)
9.4
8.9
4.7
2.6
5.4
12.8
16.2
5.7
4.6
6.2
7.5
9.3
Exchange
Rate
(days)
98.5
97.6
187.2
386.5
213.0
103.1
83.1
223.5
278.5
215.9
177.3
139.0
183.6
6.1
0.5
38
-------
E
o
O
CO
CO
CO
2
<
QL
10-
20-
30-
40-
60-
70-
80-
90-
•Turbidity
- Transmission
414
0
2 3
STATION
-90
80
-70
-60
-50 >-
-40
-30
-20
-10
o
CD
cr
Figure 100 Water clarity in Bighorn Lake expressed as the mean
turbidity (Standard Jackson Turbidity Units) and light
transmittance (% T/10 cm) at each sampling station
during the study.
39
-------
500-
20 40 60 80 100
TRANSMISSION (%T/IOcm)
Figure 11. Relationship between turbidity (Standard Jackson
Turbidity Units) and light transmittance (% T/10 cm)
A point represents a mean of all data at a given
station. Bighorn Lake.
40
-------
It has been pointed out by many workers, including Neel jst_ al.
(1963), that because of impoundment there is a striking reductiorT^of
turbidity as the water mass flows through the reservoir. More detailed
patterns of water clarity, utilizing transmission data for 1969, are
depicted in Figure 12. Turbidity for the influent streams was signifi-
cantly reduced within the upper 32.2 km (20 mi) of the reservoir.
Seasonal changes in the clarification process are given with peak in-
flow occurring in June, and minimal inflow during August.
Figure 13 gives the average euphotic zone extinction coefficients
of total visible light measured at each station for each year of
sampling. It is noted that stations 0, 1, 2, 3 and 4 have coefficients
ranging between 0.35 and 1.50, but the range between stations 4 and
5 is of a greater magnitude for all years except 1970. Station 5
consistently attenuated light at a much greater rate than any of the
other sampling stations.
A t-test was used to compare the average extinction coefficients
of the six stations. Between 13 and 25 degrees of freedom were
available for each test between each of the possible 12 pairs of
stations within a given year. The statistical analyses showed a
significant difference in the average transparency conditions among
all stations, except for stations 2, 3 and 4 during 1970.
A t-test was also used to compare the 1968, 1969 and 1970 average
transparencies for all stations. Between 178 and 250 degrees of
freedom were available for each test. A significant difference was
found between the mean extinction coefficients for all years except
between 1969 and 1970.
When all the data (n= 336) are used, the correlation (r = -0.19;
P = 0.01) between extinction and reservoir stage indicated that as
water levels rose, light extinction became less.
A summary of underwater light conditions at all sampling stations
during the study is presented in Figure 14.
Temperature and Conductivity
Figure 15 shows the thermal regime at station 0 during the 1968,
1969 and 1970 sampling periods. In general, spring temperatures
were lower during 1969 than on comparable dates for 1968 and 1970.
Mid-summer surface temperatures for all years were greater than 21.0 C.
On 5 May 1968, the surface temperature was 7.8 C. Only slight
thermal stratification was evident as the temperature declined with
depth to 3.3 C at elevation 1,025. Below 995 meters there was an
increase in temperature near the bottom attributed to heat exchange
-------
Figure 12. Seasonal and longitudinal distribution of suspended
sediment, utilizing transmission data (% T/10 cm) for
Bighorn Lake during 1969.
-------
4.CH
e
v.
-* 3.5
!if 3.0
o
u.
QJ
8 25
2.0
o
1.0
.5
12.2
1— 1968
1969
1970
0
3 4
STATION
Figure 13. Average extinction coefficients (k/m) at each station
for each year, Bighorn Lake.
43
-------
co
-------
APRIL MAY JUNE JULY AUG
Figure 15. Isotherms (C) at station 0 during 1968, 1969 and 1970,
Bighorn Lake.
-------
with. the. bottom of the reservoir. Warmer water was also found on
the bottom of the reservoir from the latter part of April to the
end of June in 1969.
A rapid spring warming of the reservoir was evident for all
three years. During 1968 this- process occurred until 27 June,
after which, the isotherms were horizontal and there was a tempera-
ture difference of 14.4 C between the surface and the bottom.
Although thermally stratified through November, a sharply defined
thermocline was not evident. After 29 July, there was a gradual
cooling of the upper portion of the reservoir and by 2 November
thermal stratification was greatly weakened.
The degree of thermal stratification that occurred during
1970 was stronger than that of 1969. Again the development of a
sharply defined thermocline for either of the above years was not
evident.
A significant fact was the change of temperature at the depth
of the power penstocks Q.,051 meters). During 1968, from 5 May to
27 June the temperature increased at this depth from 4.4 to 13.0 C.
A much, slower increase of temperature followed reaching 16.8 on 7
September. After 7 September, temperature at the power penstock
elevation decreased, attaining a value of 12.0 on 2 November.
Similar trends in temperature fluctuations at the penstock elevation
were observed for the 1969 and 1970 sampling periods, although they
were not as well defined as in 1968.
Figure 15 also illustrates the fact that the greatest rate of
temperature decline with, depth, was in the stratum of water immedi-
ately above and below the power penstock. For 1968 this occurred
from 20 June through. 10 September.
Longitudinal and seasonal changes in temperature for 1968 are
portrayed in Figure 16. The warming process began in the upper end
of Bighorn Lake and then advanced downstream and to greater depths
during the summer. By 5 May, the 4.0 C isotherm had advanced to the
dam and the 13.0 C isotherm was in th.e upper end of the reservoir.
By 7 June, the surface waters at station 3 had warmed to 18.0 C
and the 4.0 C isotherm had almost disappeared. The cell of cold water
at station 4 was attributed to run-off into the reservoir from a
small, snow-fed tributary in that area.
On 8 July, the entire surface was at or above 20.0 C and the
22.0 C isotherm had started to develop in the upper end. By 3
September, a rather distinct stratification developed between ele-
vations 1,060 and 1,035.
46
-------
I 105- -
Figure 16. Distribution of 1 C isotherms in Bighorn Lake
during 1968.
47
-------
By 2 October, the surface water was 17.0 C or lowfr and a
14.0 C isotherm had developed in the upper end. As of 2 November,
no temperature greater than 14.0 C was evident.
The above discussion illustrates the effectiveness of Bighorn
Lake as a heat trap. Because of deep water withdrawal, summer
influent temperatures are consistently warmer than those of the
effluent. Therefore, during the summer the reservoir stored ad-
vected heat in addition to heat absorbed from solar radiation.
Isolines of conductivity at station 0 are portrayed in Figure
17. On 5 May 1968, a slight degree of chemical stratification was
evident ranging from 900 micromhos at the surface to 1,120 micromhos
at the bottom. Above elevation 1,070 a marked change in conductivity
occurred after 3 July as flood water flowing along the surface layers
of the reservoir' reached this station. A drop in conductivity from
850 to less than 650 micromhos occurred between 3 and 25 July.
Water of conductivity between 650 and 600 micromhos persisted at the
surface from 25 July to 27 September following which the conductivity
increased to 760 micromhos on 2 November. This increase in conduc-
tivity was partly due to down-reservoir flow of higher conductive
water associated with low flow conditions and partly due to mixing
with the deeper water of higher conductivity as a result of the
breakdown of thermal stratification.
The most striking aspect of the 1968 data was the tongue of
water between elevation 1,070 and 1,035 exhibiting a conductivity
minimum from 18 June to 7 September. The centerline through the
tongue occurred at the depth of the power penstock. Wright (1969)
showed that the position of the tongue of low conductive water was
similar in position to a well defined density layer.
During 1969 and 1970 there appeared to be a progressive increase
in conductivity from the surface to the bottom. Chemical stratifi-
cation was observed for both years, but the development of low con-
ductivity water masses at the power penstock elevation was less
distinct.
Longitudinal and seasonal changes in conductance are presented
in Figure 18. On 5 May 1968, water of conductivity less than 900
micromhos was overriding water of higher conductivity from stations
2 to 3. The downward bending of the 900 and 950 micromho isolines
between stations 1 and 0, in contrast to the horizontal isoline of
1,000 micromhos, indicates that penstock withdrawal of water was
occurring above elevation 1,032.
By 7 June, peak runoff had begun and water of conductivity rang-
ing from less than 500 micromhos to 900 hicromhos had filled the upper
48
-------
to
CC
UJ
UJ
>
UJ
tu
o
CD
5
UJ
1100'
1080
1060
I04O-
1020-
1000-
980
AUG. SEPT. OCT. 'NOV.
1968
Figure 17. Isolines of conductivity (micromhos) at station 0
during 1968, 1969 and 1970, Bighorn Lake.
49
-------
Figure 18.
Distribution of 100 micromho isolines of conductivity
in Bighorn Lake during 1968.
50
-------
end of the reservoir. Water of conductance higher than 1,000 micro-
mhos, that occupied the bottom at the upper end, had been displaced
down-reservoir to almost station 2.
By 8 July, water having a conductivity above 800 micromhos had
been;split into two separate masses. One mass occurred as a discrete
body between the dam and 9.6 km (6 mi) from the dam and above the
power penstock elevation. The other mass occupied the lower portion
of the reservoir below the power penstock elevation. By the above
date large inflows had diminished and water of higher conductivity
had entered the upper end of the reservoir displacing the 600 micromho
water downstream by 32.2 km (20 mi).
On 5 August, it was evident that the water of greater conductance
had been separated into two masses above and below the power penstock
elevation. As a result of withdrawal and the influx of higher
conductive water associated with low stream flow, water having a
conductivity of less than 600 micromhos had been isolated at elevations
1,085 and 1,055 between stations 1 and 3.
By 2 October, the pattern described above had been eliminated
and water of conductivity between 800 and 900 micromhos was being
discharged. Influent water of higher conductance flowed along the
bottom, instead of surface or sub-surface because of the cooler
water temperatures at this time of year.
On 2 November, as a result of vertical mixing due to breakdown
of thermal stratification, there had virtually been an elimination of
vertical chemical stratification.
Water Chemistry
Concentrations of the major cations and anions found in Bighorn
Lake are given in Table XIII. This table gives the range and mean
of a given element for the complete strata of water sampled at the
indicated sampling station for that year.
Calcium, magnesium, sodium and potassium, as well as bicarbonate,
sulfate and chloride have previously been demonstrated to act in a
relatively conservative manner (Table VIII). A comparison of the
mean concentration of a given element at any station gives additional
evidence to support this fact. In general, the vertical and horizon-
tal distribution of each of the above constituents stayed relatively
homogeneous as indicated by the similar seasonal averages for each
station (Table XIII). Comparisons by means of a t-test for paired
observations showed that there was no significant difference in the
mean concentrations of these elements for any pair of stations during
1968 and 1969.
51
-------
Table XIII.
Range and mean water chemistry at each station of Bighorn Lake
during the study.
Station
1968
Maximum Mean Minimum
Ca++ (meq/1)
Mg (meq/1)
Na (meq/1 )
K+ (meq/1)
HCO" (meq/1)
Cl" (meq/1)
S0° (meq/1)
F" (meq/1)
NO~-N (mg/1)
NO~-N (mg/1)
NH -N (mg/1)
Ortho-P0° (mg/1)
Turbidity (J.T.U.)
Silica (mg/l)
Dissolved Oxygen (mg/l)
Conductance (micromhos)
pH
9.05
4.66
4.15
0.15
4.53
0.38
8.35
0.19
0.90
0.035
0.25
0.80
22
12.4
11.6
1300
8.77
4.38
2.13
3.34
0.11
3.21
0.29
5.74
0.05
0.51
0.006
0.07
0.08
11
9.9
5.6
866
2.74
0.84
2.10
0.03
2.00
0.17
2.67
0.01
0.22
0.000
0.00
0.00
4
6.4
0.6
600
7.55
Maximum
4.64
2.40
4.25
0.15
3.80
0.41
7.25
0.06
0.79
0.013
0.60
0.15
12
15.8
10.0
1064
8.70
1969
0
1970
Mean Minimum Maximum Mean Minimum
4.08
1.96
3.59
0.12
3.27
0.35
5.66
0.04
0.50
0.004
0.20
0.04
8
10.4
6.4
918
3.12
1.19
2.46
.08
2.55
0.25
3.92
0.02
0.14 0.79 0.57
0.001 0.059 0.005
0.00 0.15 0.02
0.00 0.14 0.05
4
5.8
4.2 10.9 6.4
685 1282 942
7.53 8.80
0.01
0.000
0.01
0.00
3.4
692
7.50
-------
Table XIII. (Cont'd)
Ui
LJ
Station
Ca (meq/l)
Mg (meq/l)
Na (meq/l)
K+ (meq/l)
HCO~ (meq/l)
Cl" (meq/l)
S0~ (meq/l)
F~ (meq/l)
NO~-N (mg/1)
NO~-N (mg/1)
NH -N (mg/1)
Ortho-P0~ (mg/1)
Turbidity (J.T.U.)
Silica (mg/l)
Dissolved Oxygen (mg/l)
Conductance (micromhos)
pH
Maximum
8.26
4.33
4.40
0.27
4.55
0.37
8.83
0.18
0.89
0.051
0.00
0.63
44
14.6
10.7
1000
8.78
1968
Mean Minimum
3.99
2.10
3.14
0.11
2.97
0.26
5.62
0.05
0.52
0.008
0.08
0.08
17
10.2
6.2
798
2.55
0.75
1.90
0.07
2.09
0.17
2.83
0.00
0.11
0.000
0.33
0.00
8
6.7
1.4
540
7.65
Maximum
4.49
3.84
4.40
0.13
3.40
0.41
6.75
0.06
0.76
0.043
0.46
0.10
12
13.4
10.8
1050
8.63
1969
Mean
3.86
1.98
3.59
0.11
3.05
0.33
5.54
0.04
0.49
0.006
0.21
0.04
8
10.0
7.3
880
1
Minimum
2.99
1.12
2.50
0.08
2.36
0.22
4.12
0.03
0.23
0.001
0.01
0.00
4
5.4
4.7
590
7.90
1970
Maximum Mean Minimum
0.74 0.56 0.08
0.065 0.007 0.001
0.08 0.03 0.01
0.14 0.07 0.00
9.1 6.0 3.6
1077 916 566
8.65 7.00
-------
Table XIII. (Cont'd)
Station 2
Ca++ (meq/1)
Mg (meq/1)
Na (meq/1)
K+ (meq/1)
HCO~ (meq/1)
Cl" (meq/1)
SO^ (meq/1)
F~ (meq/1)
NO"-N (mg/1)
NO~-N (mg/1)
NH -N (mg/1)
Ortho-PCC (mg/1)
Turbidity (J.T.U.)
•Silica (mg/1)
Dissolved Oxygen (mg/l)
Conductance (micromhos)
pH
Maximum
7.28
3.81
4.65
0.18
3.52
0.36
8.64
0.16
0.95
^0.038
0.31
0.85
68
14.7
11.2
1370
8.74
1968
Mean Minimum
4.00
1.99
3.18
0.12
2.93
0.25
5.50
0.05
0.52
0.009
0.08
0.15
24
10.6
6.8
816
2.18
0.81
1.50
0.06
1.29
0.13
3.00
0.00
0.11
0.000
0.00
0.00
4
7.3
2.5
430
7.61
1969
1970
Maximum Mean Minimum Maximum Mean Minimum
5.76
2.44
4.65
0.13
3.50
0.44
7.21
0.08
0.15
0.019
0.31
0.13
16 -
14". 6
11.1
1298
8.70
3.87
1.79
3.69
0.11
2.92
0.32
5.52
0.04
0.49
0.006
0.25
0.05
10
10.2
7.3
869
2.92
1.08
2.40
0.08
2.22
0.18
3.12
0.03
0.12
0.001
0.00
0.00
4
6.7
4.1
531
7.61
0.88 0.53 0.05
0.039 0.009 0.001
0.07 0.03 0.01
0.30 0.09 0.00
9.8 5.1 0.5
526 799 1092
8.65 7.00
-------
Table XIII. (Cont'd)
Ui
Lrt
Station 3
1968
Maximum Mean Minimum
Ca++ (meq/1)
Mg (meq/1)
Na (meq/1)
K+ (meq/1)
HCO" (meq/1)
Cl" (meq/1)
SO" (meq/1)
F~ (meq/1)
NO~-N (mg/1)
NO~-N (mg/1)
NH3-N (mg/1)
Ortho-PO? (mg/l)
Turbidity (J.T.U.)
Silica (mg/1) - -
Dissolved Oxygen (mg/l)
Conductance (micromhos)
pH
8.83
2.32
4.25
0.18
3.49
0.33
7.94
0.15
0.83
0.033
0.66
0.78
217
17.6.
10.0
1320
8.75
4.11
2 -.01
3.11
0.12
2.86
0.24
5.57
0.06
0.49
0.011
0.08
0.10
49
-10.5
7.3
828
2.74
0.92
1.95
0.08
2.08
0.14
2.65
0.01
0.10
0.001
0.00
0.00
4
7.6
3.1
450
7.40
Maximum
4.24
2.32
4.78
0.13
3.45
0.40
6.89
0.06
1.46
0.043
0-.44
0.18
34
12.4
9.9
1628
8.56
1969
1970
Mean Minimum Maximum Mean Minimum
3.73
1.76
3.63
0.11
2.84
0.31
5.46
0.04
0.52
0.011
0.25
0.07
18"
10.2
7.4
843
3.13
0.92
2.50
0.07
2.32
0.20
3.62
0.02
0.21 0.80
0.003 0.065
0.13 0.44
0.00 0.77
6
8.3
5.2 10.3
531 1105
7.91 8.80
0.51 0.08
0.012 0.003
0.04 0.01
0.11 0.00
5.0 0.5
729 143
7.05
-------
Table XIII. (Cont'd)
1968
Maximum Mean Minimum
Ca (meq/l)
Mg (meq/l)
Na (meq/l)
K+ (meq/l)
HCO" (meq/l)
Cl" (meq/l)
SO* (meq/l)
F~ (meq/l)
NO~-N (mg/l)
NO~-N (mg/l)
NH.-N (mg/l)
Ortho-P0~ (mg/l)
Turbidity (J.T.U.)
Silica (mg/l)
Dissolved Oxygen (mg/l)
Conductance (micromhos)
pH
8.92
4.82
4.30
0.14
3.54
0.34
7.87
0.14
0.66
0.029
0.76
1.00
350
13.9
9.6
1300
8.80
4.38
1.96
3.24
0.12
3.02
0.24
5.63
0.04
0.44
0.009
0.12
0.11
67
10.7
7.9
858
2.92
0.19
0.90
0.06
2.12
0.07
2.75
0.00
0.09
0.001
0.00
0.00
12
8.2
5.4
405
7.57
S
tation
1969
4
Maximum Mean Minimum Maximum
4.16
2.40
4.95
0.14
3.55
0.44
7.37
0.07
0.72
0.018
0.5.3
0.21
83
12.8
10.7
1369
8.58
3.64
1.64
3.59
0.11
2.82
0.34
5.57
0.04
0.47
0.013
0.35
0.10
40
10.6
7.7
818
2.96
0.84
2.90
0.08
2.39
0.16
3.02
0.03
0.29 0.74
0.004 0.046
0.18 0.39
0.00 0.25
16
9.0
6.0 11.8
407 1199
7.90 8.75
1970
Mean Minimum
0.44 0.10
0.019 0.005
0.05 0.03
0.11 0.00
5.8 2.9
711 511
7.00
-------
Table XIII.(Cont«d)
Station
Ca (meq/l)
Mg (meq/l)
Na (meq/l)
K+ (meq/l)
HCO° (meq/l)
Cl" (meq/l)
S0~ (meq/l)
F" (meq/l)
NO~-N (mg/1)
NO°=N (mg/1)
NH3=N (mg/1)
Ortho-PO" (mg/1)
Turbidity (J.T.U.)
Silica (mg/1)
Dissolved Oxygen (rng/l)
Conductance (micromhos)
pH
Maximum
8.96
4.75
4.55
0.18
3.38
0.35
7.54
0.17
0.73
0.030
0.22
0.72
3350
12.9
12.6
1070
8.72
1968
Mean Minimum
4.62
2.13
3,50
0.13
3.10
0.27
6.39
0.06
0.44
0.011
0.06
0.18
558
11.4
8.3
882
3.48
0.52
1.97
0.11
2.16
0.14
3.54
0.00
0.13
0.004
0.00
0.00
44
9.8
6.2
460
8.10
Maximum
4.01
2.00
5.05
0.13
3.00
0.39
6.25
0.06
0.89
0.023
0.49
0.24
875
14.4
13.0
1133
8.71
1969
5
1970
Mean Minimum Maximum Mean Minimum
3.66
1.56
3.42
0.11
2.77
0.30
5.42
0.04
0.44
0.011
0.42
0.16
211
11.2
9.3
833
3.18
'1.31
2.11
0.08
2.41
0.25
4.25
0.03
0.02 0.72 0.50
0.010 0.029 0.019
0.31 0.12 0.04
0.16 0.30 0.11
36
9,2
6.4 12.1 6.7
697 1008 731
8.31 8.90
0.09
0.007
0.01
0.00
3.7
500
7.55
-------
Concentrations of nitrogen, phosphate, silica, dissolved oxy-
gen and hydrogen ion are highly non-conservative and rather large
fluctuations in the concentration of these elements were often
observed (Table XIII). Silica was never recorded less than 5.4
mg/1, which is well above the minimum requirements for most diatoms
(Lund, 1954; 1964).
The greatest vertical range of dissolved oxygen was from 0.6
to 11.6 mg/1 at station 0. The lower oxygen values were observed
in the hypolimnetic waters during summer stagnation, while the higher
values were usually associated with periods of large phytoplankton
standing crop.
The mean concentrations of certain elements occurring in the
euphotic zone are presented in Table XIV. Total inorganic nitrogen
(primarily nitrate nitrogen), ortho-phosphate, iron, manganese and
zinc were usually in higher concentrations at station 5 than any
other station; but no significant differences in concentration were
found between stations 0, 1 and 2. These higher concentrations were
attributed to the larger amount of suspended sediment at station 5
carried into the reservoir by the Bighorn and Shoshone Rivers.
Euphotic zone pH ranged from 7.60 to 8.88 during the study.
The majority of the higher pH values occurred during the summer.
In relation to average natural waters, the content of total in-
organic nitrogen and inorganic phosphate in Bighorn Lake is rela-
tively high. Mackenthun (1965) showed that nuisance blooms of algae
may be expected when inorganic phosphate and nitrogen reach average
concentrations exceeding 0.01 mg/1 and 0.30 mg/1, respectively. The
above levels were usually exceeded in Bighorn Lake.
The complex interaction of thermal stratification, density flow
and seasonal inflow and outflow not only exhibited an effect on the
distribution of conductivity, but also altered the depth distribution
of nitrate, ortho-phosphate, dissolved oxygen, pH and turbidity
concentrations during 1968. The distribution of turbidity with depth
at station 0 is portrayed in Figure 19. From the end of June through
the middle of October there was a turbidity maximum present at the
power penstock elevation. This turbidity maximum was associated with
water of minimum conductivity characteristic of the high flow con-
ditions in June. Apparently a current was established that was strong
enough to retain some of the suspended silt that entered the reservoir
in June.
There was also an ortho-phosphate maximum (Fig. 20) present
during August of 1968 at the penstock elevation. This sub-surface
maximum of phosphate was attributed to the phosphate being associated
with the sediment washed into the reservoir by the heavy run-off in
58
-------
Table XIV.
Mean water chemistry (mg/1) of the euphotic zone
at each station of Bighorn Lake during the study.
Station
1968
pH Range
N03-N
N02-N
NH3-N
Ortho-PO.
4
1969
pH Range
N03-N
NOjJ-N
NH3-N _
Ortho-PO A
Total Iron
Mn++
Cu++
Zn++
1970
pH Range
N03-N
NOg-N
NH3-N
Ortho-PO
0
7.80-8.69
0.35
0.009
0.09
0.08
0
8.03-8.70
0.40
0.008
0.19
0.06
0.030
0.013
0.001
0.011
0
8.00-8.70
0.34
0.010
0.02
0.03
1
8.02-8.75
0.30
0.007
0.08
0.07
1
8.05-8.73
0.38
0.008
0.20
0.04
0.030
0.014
0.001
0.010
1
8.15-8.60
0.30
0.011
0.03
0.06
2
8.01-8.78
0.37
0.008
0.09
0.08
2
8.15-8.86
0.32
0.007
0.19
0.04
0.038
0.013
0.001
0.008
2
7.60-8.65
0.28
0.010
0.03
0.07
3
8.16-8.81
0.40
0.012
0.09
0.13
3
8.23-8.88
0.35
0.008
0.20
0.07
0.050
0.007
0.001
0.009
3
7.90-8.80
0.25
0.010
0.04
0.08
4
8.00-8.70
0.50
0.011
0.12
0.09
4
8.17-8.75
0.39
0.007
0.25
0.04
0.086
0.015
0.001
0.009
4
7.85-8.50
0.30
0.014
0.04
0.10
5
8.00-8.72
0.59
0.014
0.16
0.15
5
8.17-8.79
0.49
0.009
0.34
0.09
0.135
0.036
0.001
0.020
5
7.55-8.75
0.44
0.018
0.05
0.10
59
-------
CT-
O
CO
cr
LJ
LJ
>
LJ
LJ
CO
<
LJ
LJ
O
00
g
<
>
LJ
_l
LJ
105
1085
1065
- Power
IO45
1025
1005
985
965
May
June
July Aug.
1968
Sept.
Oct.
Nov.
Figure 19. Distribution of turbidity (Standard Jackson
Turbidity Units) with depth at station 0 of
Bighorn Lake during 1968.
-------
UJ
965
Oct.
Nov.
Figure 200 Distribution of ortho-phosphate (mg/1 PO^) with depth
at station 0 of Bighorn Lake during 1968.
-------
June. Being below the euphotic zone it was not utilized by phyto-
plankton and thus was discharged through the penstock. It will be
noted that there was phosphate depletion in the surface layers of
the reservoir from May to August. Slightly increased values of
phosphate in surface waters during August and September were also
associated with low conductivity water that originated from high
flow conditions again in June.
A similar pattern is shown in nitrate (Fig. 21) with a tongue
of high nitrate nitrogen water at the power penstock elevation from
June to September. From September to November water of lower nitrate
content was at this elevation. In contrast to phosphate, there was
no decline in nitrate in the euphotic zone; instead, the concentrations
increased during September and October.
Figure 22 presents data for oxygen and Figure 23 for pH. It is
evident that a layer of water with minimum oxygen and pH was at the
power penstock elevation. The low oxygen and hydrogen ion concen-
trations were probably due to respiratory processes. However, it
does not seem possible that respiration in situ was responsible for
the decreased oxygen and pH values as the water mass moved downstream
away from the bottom. It will be noted that the oxygen and pH values
both are similar to those of the stagnant bottom water at station 0.
This suggests that oxygen depletion and carbon dioxide increase
occurred while the water was on the bottom of the reservoir upstream
from station 0 and the water mass preserved these characteristics as
it moved down the reservoir toward the power penstock.
If a line perpendicular to the dam (parellel to the water's
surface) is drawn from the power penstock elevation upstream from the
dam, this line would intersect the bottom of the reservoir approxi*-
mately 48.3 km (30 mi) from the dam.
Phytoplankton Standing Crop and Chlorophyll
Table XV lists all the phytoplankton taxa identified from the
composited euphotic zone samples. This list of the Bighorn Lake flora
contains 51 genera and 58 species of algae.
It is important to remember that from year to year the early and
late sampling periods do not coincide and there may exist a built-in
bias in the presentation of the phytoplankton data.
The Bacillariophyceae were the dominant class of phytoplankton
comprising 58.8, 71.5 and 42.9% of the total cell volume during 1968,
1969 and 1970, respectively. Fragilaria crotonensis was the most
important organism of the phytoplankton on a cell volume basis
(Table XVI), but ranked fourth according to presence (Table XVII).
62
-------
1105
LO
UJ
965
May
June
July Aug.
1968
Sept.
Oct.
Nov.
Figure 21. Distribution of nitrate nitrogen (mg/1 NO^-N) with
depth at station 0 of Bighorn Lake during 1968.
-------
105
CO
cr 1085
LJ
I-
LJ
LJ
>
UJ
LJ
CO
1065
1045
< 1025
LJ
LJ
I 1005
LJ
_1
LJ
965
May
June
July Aug.
1968
Sept.
Oct.
Nov.
Figure 22. Distribution of dissolved oxygen (mg/1) with depth
at station 0 of Bighorn Lake during 1968.
-------
1105
LJ
96
May
June
July Aug.
1968
Sept.
Oct.
Nov.
Figure 23. Distribution of pH with depth at station 0 of
Bighorn Lake during 1968.
-------
Table XV. Phytoplankton species observed from all sampling
stations of Bighorn Lake during the study with
some calculated volumes of individual cells or
colonies.
DIVISION GHLOROPHYTA (Green Algae)
Class Chlorophyceae
Actinastrum Hantzschii Lagerheim. 213
Ankistrodesmus Braunii (Naeg. ) Brunnthaler. 200
Anki strode sinus f alcatus (Corda) Ralfs. 35
Carteria sp. Diesing. 68
Characium sp. A. Braun. 252
Chlamydomonas sp. Ehr. 41
Chlorella spp. Beijernick.
Closterium sp. Nitzsch. 2,312
Cosmarium subcostatum Nordstedt.
Crucigenia sp. Morren. 34
Pandorina mo rum Bory. 132
Pediastrum duplex Meyen. (Col.) 44,792
Oocystis sp. Naegeli. 403
Scenedesmus acuminatis (Lag.) Chodat. 362
Scenedesmus quadricauda (Turp.) deBrebisson. 152
Schroederia setigera (Schroed.) Lemmermann. 321
Staurastrum paradoxum Meyen. 11,521
Stichpcoccus bacillaris Nageli. 31
Tetraedron sp. Kutz.
Westella botryoides (W.West) deWildemann.
Westella linear is Cr. M. Smith.
DIVISION CRYSOPHYTA (Yellow-green Algae)
Class Bacillariophyceae (Diatoms)
Achnanthes lanceolata Breb. 171
Asterionella f o rmo s a Hassall. 761
Caloneis amphisbaena (Bory) Cleve. 23,024
Cocconeis spp. Ehr.
Cyclotella spp. Kutz.
Cymbella affinis Kutz. 3,717
Diatoma elongatum Agardh. 875
Diatoma hiemale (Lyrigbye) Heiberg. 2,985
Diatoma vul gare Bory. 974
66
-------
Table XV. (Co:?t d)
i Diatomel la Ba 1 fou.riana_ Greville. 1 ,006
Eur.otla sp. Ehr. 295
Fragi 1 aria capaci^.a Desmazieres. 385
FragLiaria crotonensis Kitton. 1,057
Gomphorema spp. Agardh.
Gyrosigma Speg_c_e_rij_ (W, Smith) Cleve. 16,896
Hannea.e_ areas (Ehr. ) Patr, 1 ,414
Melosira ^rarail^ata (Ehr.) Ralfs. 492
Melosira italtea (Ehr.) Kiitz. 520
Navicu La spp. Bory.
Nltzschia spp. Hassall.
S tephar-.od i s cus niagarae Ehr. 41, 700
Surirella ovata Kutz. 7,120
Synedra ulna (Nitzsch) Ehr. 9,567
Class Chrysophyceae
Chrysococcas sp. K1eb s. 25
Dinobryon sertularia Ehr. 1,236
Class Xanthophyceae (Heterokontae)
Botryococcus sudeticus Lemmermann. 263
DIVISION CYANOPHYTA (Blue-green Algae)
Class Myxcphyceae
Anabaena sp. Bory. (1 mm) 12,570
Aphatiizomenon flos=aquae (L.) Ralfs. (l mm) 12,570
Coelosphaerium Nagelianum linger, (col.) 177,500
Coccochloris peniocystis Sprengel. 11
Merismopedia punctata Meyen.
Microcystls aeruginosa Kuetz. (col.) 25,695
DIVISION PYRRHOPHYTA (Dinoflagellates)
Class Dinophyceae (Dinokontae)
Geranium hirundinella (O.F.M.) Schrank. 108,307
Peridiaium sp. Ehr. 2,340
DIVISION CRYPTOPHYTA (Blue and Red Flagellates)
Class Cryptophyceae
Cryptomonas c^vata Ehr. , 2,473
Rhcdomcnas lacastris Pasch. & Ruttn. 65
67
-------
Table XVI.
Rank of the major phytoplankton species x'rom
Bighorn Lake according to absolute mean cell
volumes (mm /l) based on collections from all
stations during the study.
Rank
1.
2
3
4
5
6
7
8
9
10
11
12
13
14
Taxon
Fragilaria crotonensis
Cryptomonas ovata
Stephanodiscus niagarae
Asterionella formosa
Aphanizomenon flos-aquae
Melosira granulata
Cyclotella spp.
Pediastrum duplex
Rhodomonas lacustris
Ceratium hirundinella
Navicula spp.
Microcystis aeruginosa
Melosira italica
Diatoma vulgare
Synedra ulna
Cell Volume
1.222
0.658
0.518
0.513
0.487
0.173
0.165
0.143
0.105
0.088
0.087
0.087
0.073
0.060
0.052
68
-------
Table XVII. Rank of the major phy to plank ton. species of Bighorn
Lake according to presence (7o) as described by
Curtis (1959). Values are based upon collections
from all stations over the entire study.
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Taxon
Rhodomonas lacustris
Cryptomonas ovata
Asterionella formosa
Fragilaria crotonensis
Stephanodiscus niagarae
Cyclotella spp.
Navicula spp.
Ankistrodesmus falcatus
Aphanizomenon flos-aquae
Oo'cystis spp.
Melosira italica
Scenedesmus quadricauda
Melosira granulata
Diatoma vulgare
Schroederia setigera
Pandorina mo rum
Scenedesmus acuminatis
Ankistrodesmus Braunii
Anabaena sp.
Synedra ulna
Diatoma elongatum
Presence
85.4
84.8
53.9
52.7
36.3
33.7
32.7
31.3
30.9
26.8
25.9
25.7
23.5
20.6
18.8
17.9
15.5
14.6
12.2
12.2
10.7
69
-------
Presence is the number of stands of occurrence of a species expressed
as a percentage of the total number of stands examined. Throughout
the study, Asterionella formosa contributed more to the total cell
volume than either Stephanodiscus niagarae or Melosira granulata. In
1970, S_. niagarae and M. granulata had similar total cell volumes,
but in 1968 and 1969, S_. niagarae contributed four times the volume
that M. granulata did to the total standing crop. Diatoma vulgare,
Navicula spp. „ Cyclotella spp. and Melosira italica at times contrib-
uted large cell volumes even though presence was low compared to the
previously mentioned diatoms. Synedra ulna and Diatoma elongatum
were encountered in the samples but contributed little to the cell
volume.
The Chlorophyceae were not an important class on a cell volume
basis as they only contributed 6.4, 4.2 and 7.5% of the total cell
volume of phytoplankton for 1968, 1969 and 1970, respectively. The
green algae were represented by many genera, none of which showed a
dominance in cell volume except Pediastrum duplex, a large colonial
form (Table XVI). Ankistrodesmus falcatus ranked the highest accord-
ing to presence of the chlorophytes (Table XVIII), but contributed
little to the cell volume. OiJcystis sp. , Scenedesmus quadricauda,
Schroederia setigera, Pandorina morum, Scenedesmus acuminatis and
Ankistrodesmus Braunii were also frequently encountered.
The class Myxophyceae comprised 13.3, 6.4 and 17.5% of the total
cell volume in 1968, 1969 and 1970, respectively. The blue-greens
appeared in July and were present the remainder of the sampling
season. Aphanizomenon flos-aquae was the most important represent-
ative of this class on a presence and cell volume basis. Other
important members of this group were Anabaena sp. according to
presence and Microcystis aeruginosa according to cell volume.
The dinoflagellates, Dinophyceae, were represented by Ceratium
hirundinella and Peridinium sp. , but C_. hirundinella distinctly
dominated this class on a cell volume basis (Table XVI).
Of the Cryptophyceae, Rhodomonas lacustris was the more fre-
quently occurring phytoplankter (Table XVII). However, Cryptomonas
ovata contributed most of the cell volume of this class as can be
seen from Table XVI. The Cryptophyceae comprised 14.4, 14.9 and 28.6%
of total cell volume in 1968, 1969 and 1970, respectively.
Chrysococcus sp. and Dinobryon sertularia, the only represent-
atives of the Chrysophyceae, appeared in trace amounts as did
Botryococcus sudeticus, the only representative of the Xanthophyceae.
The longitudinal phytoplankton distributions during the study
are portrayed in Figure 24. The total standing crops of Chlorella sp.,
70
-------
Table XVIII.
Standing Crop
Chlorophyll a^
Mean total phytoplankton standing crop (X10 mm /
nr) and chlorophyll a_ concentrations (mg/m2) at
each station during the study.
1968
Station
012345
13.55 20.46 21.46 24.40 15.19 4.82
31.0 34.9 42.8 37.9 38.3 13.5
1969
0
Standing Crop
Chlorophyll _a
32.73 39.59 32.60 42.61 25.93 16.90
30.4 30.5 43.3 41.8 42.1 25.4
1970
0
Standing Crop
Chlorophyll _a
31.65 56.37 39.90 37.15 26.54 22.39
34.5 40.7 56.1 60.0 59.7 43.2
71
-------
9
8-
7-
^ 6
E
E
LJ 5
^
0 4
_J
UJ 3
O
2
1
1968
1969
^
1 *\
Total Phyloplanklon ' *
, 1 1 Individual Classes , \
/
/'
d
/
4^L_L^_.J
\
1970
c
//
/
/
I f
A>
/
/
"'
1 . r
1L^
x~.
I
ill
p
y
v'r
_^
,1.
/
'
;
/
/
/
/
/
'
/
d
, 1
,i. .
1 1
1L^_
CD1^-
--
Bocillanophyceae
mop yceoe
1 p '
an hop yceae
Microplonkton
^_i.
i .1
II
A
,
/
1
1
I
1
I
1
1
1
!
d
=\v
^x
\
\^
__!_
1
^
,^
v"
J
^J — i
0 I 2345
012345
STATIONS
2345
Figure 24. Yearly mean cell volumes (mm-^/1) of the phytoplankton
at each station of Bighorn Lake during 1968, 1969 and
1970.
-------
Tetraedron sp., Chlamydomonas sp., Stichococcus bacillaris, Carteria
SP•> Coccochloris peniocystis, Merismopedia punctata and Chrysococcus
sp. appear under the title of "Microplankton". This consolidation was
necessary because distortion of cells, caused by preservation, made
positive identification impossible much of the time and many of the
above taxa were only encountered in a few samples.
In general, phytoplankton cell volumes increased from the dam
to the upper end of Bighorn Lake and larger standing crops were
observed in 1970 than in 1968 (Fig. 24).
The 1968 distribution of phytoplankton was represented by
relatively small cell volumes at stations 0, 1 and 2 while stations
3, 4 and 5 were higher and had annual means of 4.90, 3.85 and 4.80
mm3/ls respectively. The progressive increase in cell volume from
stations 0 and 3 is evident with station 0 having an annual mean
cell volume of 1.33 mm3/l (Fig. 24).
The longitudinal distribution pattern of phytoplankton in 1969
was similar to that of 1968. The progressive increase in cell volume
from station 0 to station 3 was again evident, but station 2 was
almost equal in cell volume to station 3. Stations 2, 3, 4 and 5 all
had cell volumes between 7.10 and 8.80 mm3/l whereas station 0 had
an annual mean cell volume of 2.79 mm3/l.
In 1970, the cell volumes were higher at stations 1 and 2 with
volumes of 7.65 and 7.40 mm^/l respectively, whereas station 0
exhibited the lowest volume of 3.48 mm3/l (Fig. 24).
It is also apparent from Figure 24 that the Bacillariophyceae
were the major contributors to the estimated cell volumes at each
station during the study. However, in 1970 the Cryptophyceae were
of equal or of greater importance in their contribution to the cell
volumes at stations 4 and 5. The Myxophyceae are another class of
organisms that accounted for substantial volumes at stations 2, 3 and
4 during 1968 and 1969, and stations 0, 1 and 2 during 1970.
Matched t-tests at the 95% confidence level demonstrated that
there was a significant difference in the amount of phytoplankton at
any particular station versus the phytoplankton volume at any adjacent
station, except for stations 2 and 3 for 1969, and stations 3 and 4
for 1970. A significant difference in the mean phytoplankton volumes
was found between all years except for 1969 and 1970.
The seasonal distribution of the monthly mean phytoplankton
standing crops is depicted in Figure 25. Again the progressive
increase in cell volumes from 1968 to 1970 was evident. Overall,
the larger standing crops on a volume basis were observed in the
earlier part of the sampling season.
73
-------
In 1968, the phytoplankton reached the seasonal peak in July
with Fragilaria crotonensis accounting for 26.8% by volume of the
total cell volume during this month. Stations 1 and 2 exhibited
the highest mean cell volumes of 2.96 and 3.67 mm-Vl, respectively.
As the season progressed the amount of phytoplankton diminished to
1.05 mm^/l, with the Bacillariophyceae becoming minimal in September
corresponding to a maximum in the Myxophyceae. The Cryptophyceae
and Dinophyceae both reached maxima in June and July.
It should be noted that the cell volumes of the Dinophyceae
may be misrepresented. Ceratium hirundinella contributed primarily
to this class and accurate volume determinations are difficult be-
cause of its large and irregular shape.
The amount of phytoplankton in April of 1969 was the recorded
low (5.82 mm^/1) for the season but increased to the seasonal peak of
7.65 mm^/l in May (Fig. 25). Asterionella formosa dominated the
plankton during this peak. From May, the phytoplankton decreased
and then increased to a second peak in July when Fragilaria croton-
ensis, Melosira granulata and Stephanodiscus niagarae were dominant.
The Bacillariophyceae were maximal in May, then progressively de-
creased through the season as the Myxophyceae reached peak volumes
in August.
The monthly mean cell volume in June of 1970 was 4.95 mm^/l and
followed by an increase to the seasonal high of 8.45 mm^/l in August.
June to August was dominated by the Bacillariophyceae and Crypto-
phyceae. The Myxophyceae were at a maximum in August (2.28 mm^/1)
then decreased to 1.63 mm^/l in September.
The phytoplankton successions observed during the course of the
study are presented in Figures 26, 27 and 28. The indicated organisms
comprised 64.1, 85.3 and 84.6% of the total cell volume during 1968,
1969 and 1970, respectively. Species succession was similar for all
three years with a larger part of the standing crop made up of diatoms
found in the spring and early summer. The latter was somewhat followed
by the flagellates, Cryptomonas ovata and Rhodomonas lacustris.
The flagellates were succeeded by the blue-greens, with Aphanizomenon
flos-aquae reaching "bloom" proportions in September. Another diatom
maximum in the fall was less distinct.
In summary, conditions of phytoplankton standing crop and species
succession were similar for all years. The same species shown in
Figures 26, 27 and 28 became dominant and declined as demonstrated by
the above figures. Minor variations were found with respect to the
dates and absolute values of standing crop attained.
As previously shown (Fig. 24), phytoplankton standing crop
expressed on a volume basis (mm-Vl), decreased downstream from station
74
-------
9-
8
7-
-
rS-^~*
E
E
"" 5
bJ
5
1 «
>
-1 3-
LU
(J
2
1
1968
1969
Total Phytoplankton Bacillariophyceoe A
^
~~-~
^
/ xv
/
/
i
j
'
A ,
x
•>!
1
>v
\
V
\
^
, 1
I
\
\
1
Individual Classes Q
i-ry rgpnyveuw o
thlorop y eae
/ s\ iviyxopnyceae u
'
/
\
\
\
\
, , I 1, . i, i ,
\ ., , L. "
\ icropo
/
tf
\ 1
Ll_a_
ll .
1
1970
/ 1
/ \
t .
i
i '
/ (
/ i
/ j
' \
i \
d I
i
I
l
\
t
c
i i
1 ll
May June July Aug. Sept. Oct Nov
April May June -July Aug.
June July Aug Sept.
Figure 25 . Monthly mean cell volumes (mnrVl) of the p-hy top lank ton
in Bighorn Lake during 1968, 1969 and 1970.
-------
AUG. SEPT. OCT. NOV.
MAY
1968
Figure 26. Mean relative standing crop (%) of the eight most
abundant phytoplankton species for all sampling
stations on Bighorn Lake during 1968.
76
-------
APR.
MAY JUNE
1969
JULY
AUG
Figure 27. Mean relative standing crop (%) of the eight most
abundant phytoplankton species for all sampling
stations on Bighorn Lake during 1969.
-------
50-
JUNE
JULY
AUG.
SEPT.
1970
Figure 28. Mean relative standing crop (%) of the eight most
abundant phytoplankton species for all sampling
stations on Bighorn Lake during 1970.
78
-------
5 to station 0. When standing crop was expressed as the volume under
a square meter of reservoir surface to a depth at which light was
sufficient for photosynthesis the picture was altered. Table XVIII
shows that standing crop increased down-reservoir reaching a maximum
at station 3 for 1968 and 1969 and station 2 for 1970.
A similar pattern was observed with chlorophyll a concentrations
(Table XVIII). Chlorophyll ji (mg/m^) increased down-reservoir and
attained a maximum at station 2 for 1968 and 1969, and station 3
for 1970.
Chlorophyll _a concentrations (mg/m3) in the euphotic zone during
the study are given in Table LXVI of Appendix C. These values repre-
sent the mean chlorophyll a. concentration of the profile taken through
the euphotic zone assuming a homogeneous vertical distribution of
phytoplankton. In general, chlorophyll concentrations (mg/m3) were
highest at the upper end of the reservoir and decreased downstream to
station 0. Mean daily chlorophyll ji concentration was 8.3 mg/m3 in
1968 and 1969, and 10.1 mg/m3 in 1970, or 21.6% greater in 1970.
The maximum concentration of chlorophyll ji was 77.0 mg/m3 on
9 September 1968, 39.7 mg/m3 on 4 August 1969 and 34.5 mg/m3 on 29 July
1970, and occurred during a period of large standing crops of
Aphanizomenon for 1968 and 1969.
Figure 29 presents the relationship between average chlorophyll ji
concentrations and total cell volumes in the euphotic zone during the
study. Chlorophyll a_ concentrations followed phytoplankton volumes
and the correlation coefficients were r = 0.28 (P = 0.01) for 1968,
r = 0.37 (P = 0.01) for 1969, r = 0.12 (P =>0.05) for 1970 and r =
0.27 (P = 0.01) for all years taken together.
The regression equation using mean chlorophyll a. concentrations
and total standing crops at each station for each year was calculated:
Chlorophyll (mg/m3) = 0.97V + 3.47 R2 = 28%
where V equals the mean phytoplankton standing crop (mm3/!). The
equation indicates that the relationship between chlorophyll and cell
volume was non-linear.
The histograms portrayed in Figure 30 show the frequency at
which certain ratios of chlorophyll a_ and total cell volume occurred
during the sampling periods for the indicated year. Over 57% in 1968,
88% in 1969 and 69% in 1970 of the ratios occurred within the interval
0-4 ug chlorophyll a_/mm3 of cells. The mean ratios, medians and modes
of p% chlorophyll a/mm3 of cells are given in Figure 30. On the basis
of the presented data, the average relationship between chlorophyll _a
79
-------
25
Chlorophyll o_ (mg/ m3
Cell Volume (mm3/!)
CO
O
MAY
JUNE^JULY
AUG. ' SEPT."" OCT
APR. MAY
1968
JUNE' JULY '
1969
JUNE JULY AUG.
1970
Figure 29. Relationship between mean total phytoplankton standing
crop (mnrVl) and chlorophyll a. concentrations
for all stations during the study. Bighorn Lake.
-------
30-
20-
10-
0-
v 30-
UJ
S 20^
cc
LL.
10-
20-
10
1968
1969
1970
Mean 5.1
Median 5.5
Mode 1.5
Mean 2.3
Median 5.5
Mode 0.5
Mean 2.9
Median 5.5
Mode 0.5
2 3 4 5 6 7 8 9 10 >IO
jjg CHLOROPHYLL a /mm3 CELLS
Figure 30. Frequency of the ratios of chlorophyll a. to cell
volume (ug/mm3) during the study, Bighorn Lake.
81
-------
and cell volume would be 3.4 pg chlorophyll a. is equivalent to 1.0
mm3 of cells. Similar values were obtained by Martin (1967), Peterka
and Knutson (1970) and Wright (1959).
Although the average ratio (ug chlorophyll a/mmS of phytoplankton)
was 3.4, ratios differed somewhat depending upon the season in which
the samples were taken (Fig. 31). The ratio of chlorophyll/phyto-
plankton volume of the samples collected from April to July primarily
composed of diatoms, was 3.8. The ratio for the samples taken in
July composed primarily of diatoms and flagellates, was 3.1. The
ratio of samples taken from August to November when Aphanizomenon was
dominant, was 4.5 /ig chlorophyll a/mm^ of cells.
The multiple linear regression equation, utilizing mean euphotic
zone data over each- year at each station, best explaining the observed
variations in the ratio of chlorophyll a_ to total phytoplankton stand-
ing crop during the study is:
Chlorophyll a/total phytoplankton standing crop (ug/mm^) =
6.13 - 0.07E + 0.26N + 7.76P - 0.01R R2 = 74%
where E = euphotic zone depth, (m)
N = nitrate nitrogen (mg/1)
P = ortho-phosphate (mg/1)
R = solar radiation (g cal/cm2)
The most significant variables, in decreasing order of signifi-
cance, were ortho-phosphate (r = 0.80; P = 0.01) solar radiation
r = -0.66; P = 0.01), euphotic zone depth (r = 0.53; P = 0.05) and
nitrate nitrogen (r = 0.48; P = 0.05).
Primary Productivity
Accurate daily photosynthesis predictions based on environmental
factors cannot be made because of the unpredictable fluctuations in
these factors from day to day. However, averaging of these factors
over longer periods of time reduces fluctuations and permits their
use in calculating photosynthesis.
The method of Ryther and Yentsch (1957) uses the equation:
P = | x C x 3.7 (1)
where P is the productivity in grams carbon per square meter per day,
R is a variable, relative rate of photosynthesis — the value of which
is fixed by the amount of solar radiation, k is the extinction
coefficient of the water column, C is the average chlorophyll concen-
tration and 3.7 is an average assimilation ratio at light saturation —
82
-------
.100
JE
Lul
ID
O
10-
a.
o
x
a.
O.I-L
10 15 20
CHLOROPHYLL .a (pg/l)
25
Figure 31. Seasonal relationship between mean chlorophyll a.
concentration (pg/l) and algal cell volume (mm^/l)
for all stations during the Bighorn Lake study.
Open circles represent samples which contained
virtually no blue-green algae while closed circles
represent samples which contained predominately
blue-green algae. The solid line represents a
3.42:1.00 ratio of chlorophyll a to phytoplankton
volume. Month of sample is shown by the number near
the circle.
83
-------
the units of which are grams carbon per gram chlorophyll per hour.
The weakest point of this method was the fixed average assimilation
ratio of 3.7.
Curl and Small (1965) obtained better comparisons between the
chlorophyll-light method and C^ measured values by using a locally
obtained ratio.
Wright (1959) replaced the constant in equation (1) with vari-
ables characterizing the local situation. The resultant equation
was:
P = ^- xFxTxCxR (2)
k opt
where 4.6/k sets the lower limit of the euphotic zone, F is the ratio
of photosynthesis at light saturation to total euphotic zone photo-
synthesis, T is the number of hours of photosynthesis, C is chloro-
phyll concentration and Ropt i-s tne assimilation ratio at light satu-
ration.
Martin (1967) demonstrated that over a wide range of light
conditions the assimilation ratio at light saturation is independent
of the amount of sunlight falling on the water surface. There was
also the relationship between the assimilation ratios obtained by
both gross 02 and C^ fixation measurements, and average temperature
of the euphotic zone.
Utilizing the observed relationship between temperature and
assimilation ratios, Martin modified equation (1) as follows:
P = | x C x Afc (3)
where all variables are the same as in equation (1) and At is the
temperature dependent assimilation ratio.
Peterka and Reid (1968) made an attempt to show the influence
of various environmental factors that significantly influenced photo-
synthetic rates in Lake Ashtabula, North Dakota. A multiple linear
regression analysis of their data revealed that chlorophyll, water
temperature and Secchi disk transparency were the only significant
variables affecting photosynthesis. Chlorophyll and water tempera-
ture together explained 65% of the variation in photosynthesis.
The methods of Wright (1959) and Martin (1967) appear to be
approaches in the right direction. Wright's method takes into account
seasonal variation in the vertical productivity profiles and Martin's
method utilizes a variable assimilation ratio based on knowledge of
the euphotic zone temperature.
84
-------
Mean values of net primary productivity (calculated by using
Martin's method of prediction) at each station and seasonal fluctu-
ations of primary production during the study are presented in
Figure 32. A photosynthetic quotient (PQ) of unity was assumed in
converting carbon measurements into units of oxygen. Ryther (1956a)
and Strickland (1960) have reviewed a number of experiments designed
to determine PQ of various planktonic algae and found values ranging
from less than unity to 1.6 or greater in a nitrate containing medium.
Average daily primary production was 0.51 g C/m2/day (1.36 g 02),
0.55 g C/m2/day (1.46 g 02) and 1.42 g C/m2/day (3.78 g 02) for 1968,
1969 and 1970, respectively. Maximum production occurred on 29 July
1970, 6.96 g C/m2/day (18.51 g 02).
An attempt was made to determine how much of the variation in
the predicted production rates was accounted for by the various para-
meters used in the calculations. A multiple linear regression equa-
tion was calculated using the means of all data at each station for
each year. The equation expressing the relationship is:
Primary Productivity (g C/m^/day) =
-3.8 - 0.04E + 0.02C + 0.01R + 0.14T R2 = 90% (4)
where E = mean extinction coefficient of the euphotic zone (k/m)
C = mean chlorophyll concentration of the euphotic zone (mg/nP)
R = solar radiation incident to the reservoir surface (g cal/cm^)
T = mean temperature of euphotic zone (C)
The above equation (4) demonstrates that the linear regression
equation accounted for most of the observed variation in the mean
production rates calculated using a non-linear combination of inde-
pendent variables, equation (3).
In the future, it would be desirable to make actual primary
production estimates (preferably using C1^) and sample the euphotic
zone for the parameters needed to predict primary production. A
complete multiple correlation and regression analysis of the collected
data would not only reveal the degree of similarity between estimates,
but would strengthen (or possibly weaken) the assumptions made in the
many models of predicting primary productivity.
Many authors (Manning and Juday, 1941; Edmondson, 1955; Ryther,
1956b) have observed a rather constant relationship between chlorophyll
a and photosynthesis. By using the mean euphotic zone data at each
station for each year, it was found that chlorophyll _a (mg/m2)
accounted for 67% of the calculated variation in primary productivity,
while phytoplankton standing crop (X10Jmm3/m2) only accounted for 21%
of the observed variation in the calculated production rates during
the study.
85
-------
O
ID
Q
O
a:
a.
oc
a:
a.
2.0-
1,5-
c^ i,(M
\
O
o>
~ 0.5-
0-
2,5-
2,0-
1.5-
1,0-
0.5-
1968-
1969-
1970-
0
2 3
STATION
1968-
1969-
1970
Apr. ' May ' June ' July ' Aug. ' Sept. ' Oct. ' Nov.
Figure 32. Mean primary productivity (g C/m /day) at each station
and seasonal fluctuations of primary production during
the study, Bighorn Lake,,
-------
Relationships of Physical and Chemical Parameters to Chlorophyll and
Total Phytoplankton Standing Crop
Multiple linear regression analysis was used to predict standing
crops of chlorophyll a. and phytoplankton using 14 independent vari-
ables (Table XIX). Chlorophyll a_ and total phytoplankton standing
crop were not used as independent variables, because they are strongly
interrelated. The various multiple regression equations were calcu-
lated using mean euphotic zone data over each year at each station.
The equation best expressing the observed variation in chlorophyll
a_ on an areal basis during the study is:
r\
Chlorophyll ji (mg/m ) =
24.26 - 95.62N + 1.66T + 0.28K R2 = 65% (5)
where N = nitrate nitrogen (mg/1)
T = temperature (C)
K = conductivity (micromhos)
The most significant variables, in decreasing order of signifi-
cance, were nitrate nitrogen (r = -0.74; P = 0.01), conductivity (r =
-0.67; P = 0.01) and temperature (r = 0.58; P = 0.05). Therefore, it
can be shown that 44% (0.67 X 0.65) of the observed variation in the
calculated mean primary productivity can be accounted for by the above
environmental variables.
The equation best expressing the variations observed for phyto-
plankton standing crop on an areal basis is:
Total phytoplankton standing crop (X103 mm3/m2) =
-34.24 - 80.54N - 4.30P + 0.23R + 0.03K R2 = 65% (6)
where N = nitrate nitrogen (mg/1)
P = ortho-phosphate (mg/1)
R = solar radiation (g cal/cm2)
K = conductivity (micromhos)
The most significant variables, in decreasing order of signifi-
cance, were nitrate nitrogen (r = -0.67; P = 0.01), solar radiation
(r = 0.60; P = 0.01), ortho-phosphate (r = 0.57; P = 0.05) and
conductivity (r = -0.43; P = 0.05). Phytoplankton standing crop and
the above environmental factors would only account for 14% (0.21 X
0.65) of variation in the calculated mean primary productivity.
Variations in chlorophyll a^ (mg/m3) observed during the course
of the study are best expressed by the following equation:
87
-------
Table XIX. Variables used for multiple linear regression
analysis of chlorophyll _a and total phytoplankton
standing crops for 1968, 1969 and 1970, Bighorn
Lake.
Dependent variables:
3
1. Chlorophyll a_ (mg/m )
2
2. Chlorophyll _a (mg/m )
3
3. Total phytoplankton standing crop (mm /I)
3 32
4. Total phytoplankton standing crop (X10 mm /m )
Independent variables:
1. Euphotic zone depth (m)
2. Extinction coefficient (k/m)
3. Nitrate nitrogen (mg/1 NO -N)
4. Nitrite nitrogen (mg/1 NO~-N)
5. Ammonia nitrogen (mg/1 NH -N)
6. Total inorganic nitrogen (mg/1 N)
7. Ortho-phosphate (mg/1 P0£)
8. Ortho-phosphate to nitrate nitrogen ratio
9. Total iron (mg/1)
10. Manganese (mg/1 Mn )
11. Copper (mg/1 Cu++)
12. Zinc (mg/1 Zn++)
13. Temperature (C)
14. Conductivity (micromhos)
-------
o
chlorophyll a_ (mg/m ) =
13.03 - 1.381 - 2.48N + 9.56P + 0.23T R2 = 93% (7)
where E = euphotic zone depth (m)
N = nitrate nitrogen (mg/1)
P = ortho-phosphate (mg/1)
T = temperature (C)
The most significant variables, in decreasing order of signifi-
cance, were euphotic zone depth (r = -0.94; P = 0.01), ortho-phosphate
(r = 0.59; P = 0.01), nitrate nitrogen (r = 0.38; P = > 0.05) and
temperature (r = 0.32; P = > 0.05).
The equation best explaining the observed variations in phyto-
plankton standing crop on a volume basis during the study is:
o
Total phytoplankton standing crop (mm /l) =
-16.10 - 0.52E - 2.65N + 0.06R R2 = 76% (8)
where E - euphotic zone depth (m)
N f= ammonia nitrogen (mg/1)
R = solar radiation (g cal/cm2)
The most significant variables, in decreasing order of signifi-
cance, were solar radiation (r = 0.63; P = 0.01), euphotic zone depth
(r = -0.57; P = 0.05) and ammonia nitrogen (r = 0.34; P = 0.05).
Equations (71 and (8) point out that light appears to be the
major variable controlling ths density of organisms. It is also
apparent by comparing equations (5) and (6) with (7) and (8) that
the measured independent variables are much more efficient pre-
dictors on a volume basis than on an areal basis.
89
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DISCUSSION
The chemical budget of the major ions (Table VIII) demonstrated
that there was a slight decrease in the total dissolved solids
Csalinity) as the water moved down-reservoir. Hence, the reservoir
was acting as a salinity trap. Because of the extensive development
of irrigation projects and reuse of water along a series of impound-
ments, salinity often poses a major pollution problem.
Neel, Q-963) found with the impoundment of the Missouri River
by Fort Randall Dam, the water quality of the reservoir was consider-
ably altered by carbonate precipitation, resulting in the increased
ratio of sodium to calcium. In Bighorn Lake, the above ratio was
essentially the same for the weighted average of the influent streams
versus that of the reservoir discharge for both 1968 and 1969. Since
these ratios were of the same magnitude, it was concluded that bio-
genie precipitation of calcium was not evident.
The entrance of flood waters into reservoirs created currents
which vary in magnitude due to the physical and chemical parameters
found in the reservoir (Wiebe, 1938, 1939, 1940, 1941; Lyman, 1944;
Anderson and Pritchard, 1951). The 1968 Bighorn Lake data reveal
that a turbidity current was established in the reservoir due to sub-
surface withdrawal through the power penstocks (Fig. 19). The
development of the current was attributed to the excessive withdrawal
of water from the reservoir during 1968 and was thought to extend
most of the length of the reservoir. This current was not detectable
during the 1969 and 1970 sampling periods.
A tongue of ortho-phosphate (Fig. 20) and nitrate nitrogen
(Fig. 21) rich water, which was associated with the turbidity current,
developed in Bighorn Lake at station 0 during the summer and early
fall of 1968 at the elevation of the power penstock. The discharge
of such nutrient rich water should have had a marked influence on
downstream production (downstream eutrophication). Neel (1963) dis-
cusses several cases of greatly increased downstream production
following impoundment.
Also at the depth of the power penstock during 1968, a layer
of water with minimum oxygen content (Fig. 22) and pH (Fig. 23)
developed. Kittrell (1959) cites several cases in which effluents
of low oxygen content from dams have resulted in problems (i.e.,
oxygen concentrations are low enough that downstream biochemical
oxygen demand cannot be met).
Deep water withdrawal in a reservoir tends to deplete the
reservoir system of nutrients since the effluent will be carrying
91
-------
away the nutrients that would otherwise tend to accumulate in the
deep water of a natural lake during summer stagnation (Ruttner,
1963). However, for Bighorn Lake it has been shown that some of
the nutrients that entered the reservoir were retained (Table IX).
Of the total nitrogen that entered the system, 75% was discharged.
The largest inorganic nitrogen loss was in ammonia, while an 11%
increase of nitrate nitrogen occurred. Only 14% of the total
phosphorus that entered the reservoir was discharged from it. A
32% decrease in ortho-phosphate was observed.
It was apparent that when streamflows were high for the Bighorn
and Shoshone Rivers, the reservoir was fertilized with the nutrients
associated with the suspended sediments.
Important nutrients in many natural waters are often limiting
to phytoplankton production (Hutchinson, 1957; Fogg, 1965; Lund et
al., 1963). Various workers have discussed the concentrations of
nitrogen and phosphorus that are needed for an algal bloom. The
National Technical Advisory Committee on Water Quality (Anon., 1968)
suggests that a concentration of at least 0.015 mg/1 of phosphorus
is necessary for algal growth. Hutchinson (1957) states that Asterion-
ella can take up phosphorus where it is present at less than 0.001 mg/1.
Mackenthun (1965) showed that nuisance blooms of algae may be expected
when inorganic phosphate and nitrogen reach average concentrations
exceeding 0.01 mg/1 and 0.30 mg/1, respectively. Wright (unpublished
data) found from his studies on Canyon Ferry Reservoir, Montana, that
a large increase in phosphate resulted in a strikingly large increase
in blue-green populations. The above levels for nitrogen and phos-
phate were usually exceeded at all stations of Bighorn Lake and were
not considered limiting to algal growth.
Wright (I960) suggested carbon dioxide to be limiting in reser-
voirs during dense phytoplankton blooms. Tailing (1960b) found little
reduction of the nutrient in relation to natural rates of photo-
synthesis. Lewin (1962) discusses various other elements (e.g., iron,
manganese, etc.) and their importance to phytoplankton productivity.
In general, the concentration of these nutrients in Bighorn Lake are
high enough to be considered non-limiting.
The steady depletion of nutrients from the epilimnion during the
summer leaves two alternatives of replenishment of nutrients for
continued algal growth: (1) nutrients must be added from external
sources or (2) the nutrients present must be rapidly recycled.
There was an ortho-phosphate depletion of the surface waters
of the reservoir from May to August during the 1968 sampling periods
at station 0 (Fig. 20). This loss of phosphate was attributed to
uptake by phytoplankton. Slightly increased concentrations of
92
-------
phosphate in the surface waters during August and September were
associated with low conductive water that originated from the high
flow conditions in June. The levels of phosphate observed during
the period of depletion were still above the minimal levels des-
cribed by the literature to be limiting.
Epilimnetic phosphate regeneration has also been shown to be
mediated by zooplankton. Barlow and Bishop (1965) showed that
Daphnia liberated about 80% of the assimilated phosphorus back into
the epilimnion during a period of strong stratification. Environ-
mental conditions (e.g., temperature) would affect the rate of such
a recycling process. Pomeroy et^ _al. (1963) found turnover times for
total phosphorus as low as eight days.
In contrast to ortho-phosphate there was no decline in nitrate
nitrogen in the euphotic zone (Fig. 21); instead, concentrations
increased during September and October of 1968, which corresponds
to a period of maximum development of blue-greens.
Dugdale and Dugdale (1962) have stressed the importance of
nitrogen fixation in the overall nitrogen metabolism of fresh-
waters. Most workers agree that species of Anabaena are the prin-
ciple nitrogen fixers in the phytoplankton community. However, other
authors (Krauss, 1958, Sawyer and Ferullo, 1961) have reported fix-
ation of nitrogen by Aphanizomenon, which comprised the largest stand-
ing crop of the blue-green group in Bighorn Lake.
Ryther (1956b) and Edmondson (1956) have both stressed the
importance of sunlight as a limiting factor to phytoplankton pro-
duction. The direct effect of light as it penetrates the water is
to increase the standing crop of phytoplankton assuming other
environmental factors are not limiting.
Chlorophyll a. (mg/m3) and total phytoplankton standing crops
(mm3/!) for Bighorn Lake decreased from stations 5 to 0. However,
reference to Figure 13 shows that water clarity increased down-
reservoir as the result of the settling out of silt. Therefore the
effective depths at which photosynthesis could occur increased down-
reservoir. The picture is altered when account is taken of this
factor, and chlorophyll .a and phytoplankton standing crop are
expressed as the concentrations and volumes under a square meter of
reservoir surface to a depth at which light is sufficient for photo-
synthesis. Table XVIII shows if chlorophyll a. (mg/m2) and phyto-
plankton standing crops (X103 mm3/m2) are expressed on an areal basis,
then the two measures of the phytoplankton community increased down-
reservoir and attained maximums between stations 1 and 3. More
effective light penetration is obviously important to the explanation
of this situation. The lower chlorophyll a_ (mg/m2) and phytoplankton
93
-------
standing crops (XlO^mm^/m2) at stations 1 and 0 for 1968 and 1969,
and station 0 for 1970 cannot be explained in this manner since the
water was more transparent (Fig. 14).
When nutrient conditions for all three years are compared with
the euphotic zone chlorophyll a_ concentrations (mg/m2), it will be
noted that total inorganic nitrogen and ortho-phosphate concentrations
(Table XIV) are greatest at the upper end of the reservoir, but no
significant difference was found between stations 2, 1 or 0 to explain
the decrease in chlorophyll a. (mg/m2) at the latter two stations.
Zooplankton densities must be considered as an important influ-
ence on phytoplankton standing crops and thus chlorophyll a_ concen-
trations, and may be the factor responsible for the lower phytoplank-
ton production at stations 1 and 0. Wright (1954, 1958, 1965) and
many other workers (Anderson et^ a.l_. , 1955; Comita and Anderson, 1959;
Edtnondson _eJL jil_. , 1962; Richman, 1966) have found declines in phyto-
plankton standing crops due to heavy predation by zooplankton. How-
ever, Edmondson (1962, 1965) demonstrated that zooplankton preferred
the microplankton portion of the standing crop. Tappa (1965) has
shown that Daphnia exhibits a degree of food selectivity.
It is quite possible that organisms such as Cryptomonas,
Rhodomonas and other microplankton would be heavily grazed as food
species in Bighorn Lake. The food value of such organisms as
Aphanizomenon which comprise the bulk of the phytoplankton standing
crop in late summer and early fall, is questionable. Knutson (1970)
showed that Daphnia numbers were high during almost unialgal blooms
of Aphanizomenon and concluded that Daphnia were grazing upon this
blue-green alga. He also pointed out that the frequent periods of
large rotting stands of Aphanizomenon would invite the growth of
protozoans and bacteria which could serve as food.
Blue-green algae are often the dominant algae in eutrophic lakes,
probably because they are free from grazing by zooplankters (Lund,
1969). Aphanizomenon comprised about 70% of the total phytoplankton
volume during the late summer and early fall in Bighorn Lake. Large
stands of this blue-green have been recorded for other eutrophic
lakes (Hammer, 1964; Hrbaeck, 1964; Martin, 1967; Olive j^t _aJL. , 1969).
As the concentration of algal cells increases, light penetration
decreases, so that the phytoplankters become self-shading. Inverse
correlations between plankton density and light penetration have
been described (Fogg, 1965; Javornicky, 1966), but in the field it is
usually difficult to establish the direct causal relationships due to
unknown effects of detritus and other non-algal forms of turbidity.
Tailing(196Ca) however, has reported a case of self-shading in a
field study of an Asterionella population. The appearance of Aphani-
zomenon in Bighorn Lake may have limited the growth of other algae,
94
-------
particularly Melosira granulata, Fragilaria crotonensis and Stephano-
discus niagarae (Figs. 26, 27 and 28) due to its characteristic water-
bloom and resulting shading effect (Verduin, 1951).
Temperature is considered to be a causative agent of phytoplank-
ton succession. Different species may predoinir.ate at different times
because of the interaction between prevailing temperature and other
environmental factors. Aphanizomenon development ir Bighorn Lake
started while water temperatures were about 18 C, with blooms appear-
ing shortly thereafter. Most of the summer blooms occurred at water
temperatures of 20 to 25 C, which was close to the temperature range
for Aphanizomenon waterblooms in several Canadian Lakes (Hammer,
1964).
Nutrient concentrations not only affect total phytoplankton
productivity, but also the species composition of the phytoplankton
community. The seasonal succession of phytoplankton cannot be
entirely related to the concentration of a single inorganic nutrient
nor to any combination of nutrients. However, the occurrence of
diatoms usually coincides with higher levels of nutrients present in
the spring. The position of the blue-greens in the successional
pattern is usually accompanied by low levels of nitrate nitrogen
and/or high phosphate to nitrate ratio (Hutchinson, 1967).
The spring phytoplankton peaks were dominated by Fragilaria
crotonensis, Asterionella formosa, Melosira italica and Rhodomonas
lacustris. The successional pattern for most of the above organisms
(Figs. 2~6, 27 and 28) was similar to what Lund (1965) observed for
the succession of algae in Windemere Lake.
Predicted primary productivity values fluctuated greatly from
day to day with peak production rates occurring during the summer
months. These short time variations of production are perhaps not
only the result of daily insolation changes but also the quantity and
quality of the phytoplankton standing crop and its horizontal distri-
bution in the reservoir (Rhode, 1958). Bighorn Lake is moderately-
productive with calculated mean daily net primary productivity values
of 1.36 g 02/m2/day, 1.46 g 02/m2/day and 3.78 g 02/m2/day for 1968,
1969 and 1970, respectively. Most of the above productivity rates
are low when compared to other eutrophic lakes: 3.C g 02/m2/Jay in
Canyon Ferry Reservoir, Montana (Wright, 1965), 6.9 g 02/m2/r>ay
during the summer in western Lake Erie (Verduin, 1556). Unpro-
ductive waters yielded values less than 0.3 g 02/m2/day and the most
productive saline and fresh waters may yield 1.3 to 8.0 g 02/m2/day
(Steeman-Nielsen, 1954; Rhode, 1958). Rhode (1958) arbitrarily
considered daily production rates of about 0.3 g 02/mVday as the
dividing point between oligotrophic and eutrophic lakes.
95
-------
The relationship of chlorophyll ci concentration to cell volume
was shown to be about 3.4 ug chlorophyll aYl.O mm^ of algal cells for
all data. A range of values derived from the literature is 0.5
(Strickland, 1960) to 7.6 ug chlorophyll a./mm3 of cells (Gushing,
1958).
96
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ACKNOWLEDGEMENTS
Thanks are given to Mrs. Jo Wilson and Mrs. Gail Hill for
their assistance in the laboratory. Thanks are also due to Abe
Horpestad, Dr. Ken Tuinstra, Chad Martin and John W. Wright, Jr.
for their aid in the collection of field data.
The cooperation extended by J. A. Bradley, Director, Region
6, Bureau of Reclamation, for making available the various daily
reservoir records of Bighorn Lake was greatly appreciated. The
water quality and daily discharge records supplied by F. C. Boner,
Chief, Basic Data Section, Wyoming, U.S.G.S. and G. W. Buswell,
Chief, Basic Data Section, Montana U.S.G.S. is acknowledged with
sincere thanks.
The support of this project by the Federal Water Pollution
Control Administration and Dr. D. A. Hilden, Project Officer, is
a cknowledged.
97
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Wright, J.C. 1959. The Limnology of Canyon Ferry Reservoir. II.
Phytoplankton standing crop and primary production. Limnol.
Oceanog. 4: 235-245.
V
Wright, J.C. 1960. The limnology of Canyon Ferry Reservoir. III.
Some observations on th_e density dependence of photosynthesis
and its cause. Limnol. Oceanog. 5: 356-361.
Wright, J.C. 1965. The population dynamics and production of Daphnia
in Canyon Ferry Reservoir, Montana. Limnol. Oceanog. 10: 583-590.
Wright, J.C. 1969. The limnology of Yellowtail Reservoir and the
Bighorn River. FWPCA Project 18050 DBW, Prog. Rep. (mimeographed)
53 pp.
UU.S. GOVERNMENT PRINTING OFFICE: 1973-514-154/266
105
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Accession Number
Subject Field &. Group
0 II H
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Montana State University, Bozeman
Title
LIMNOLOGY OF YELLOWTAIL RESERVOIR AND THE BIG HORN RIVER
IQ Authors)
Wright,
Soltero,
John C. , and
Raymond A.
16
21
Project Designation
FWPCA Grant 18050 DBW
Note
Environmental Protection Agency report
number EPA-R3-73-002, February 1973.
22
Citation
23
Descriptors (Starred First)
*Water Chemistry, *Impounded Waters, *Light Penetration, ^Primary Production,
*Phytoplankton, ^Withdrawal, Density stratification, Thermal stratification,
Turbidity Currents, Ammonia, Nitrates, Nitrites, Phosphates, Trace Elements,
Turbidity
Identifiers (Starred First)
27
Abstract
Impoundment and deep water withdrawal displaced the maximum and minimum tempera-
tures and conductivities of the effluent two to four months behind the influent
occurrance and greatly reduced the amplitude of seasonal change. Of the influent
total carbon, nitrogen and phosphate, 24%, 25% and 86% respectively were retained in
the reservoir. The major fraction retained was the particulate portion. A signifi-
cant correlation was found between total phosphate, orthophosphate and turbidity.
Nitrate, ortho-phosphate and trace metals were in higher concentration in the upper
end of the reservoir associated with turbid water. A withdrawal caused density current
was evident which altered the vertical and longitudinal distribution of physical and
chemical parameters. Volume based phytoplankton density and chlorophyll concentration
decreased down-reservoir. However, the depth of the euphotic zone increased down-
reservoir as silt settled out. Consequently the euphotic zone standing crops were
greatest in the mid-section of the reservoir. Insufficient light penetration was
the principal limiting factor to primary production in the upper end of the reservoir.
Decreased primary productivity in the lower end of the reservoir did not appear to be
due to nutrient limitation.
Abstractor
John C. Wright
Institution
Montana State University
WR:102 (REV. JULY 1969)
WRS1C
SEND TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON, D. C. 20240
* GPO: 1969-359-339
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