Pre-and Post-Operational Effects of a Temperature

Control Device on Physical, Chemical, and

Biological Attributes of Shasta Lake, California:

Phase 1, Spring 1995 through Fall 1997

Open File Report 98-251

U.S. Department of the Interior 

U.S. Geological Survey

science 

uses

for a changing world

Prepared in Cooperation with 

the U.S. Bureau of Reclamation
U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Pre- and Post-Operational Effects of a Temperature Control Device on Physical, Chemical, and 

Biological Attributes of Shasta Lake, California: Phase 1, Spring 1995 through Fall 1997

by

iDavine M. Lieberman, U.S. Geological Survey 

^Michael J. Horn, U.S. Bureau of Reclamation

Open-File Report 98-251 

Prepared in cooperation with the U.S. Bureau of Reclamation

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards (or with the North American Stratigraphic Code). Any use of trade, product, 

or firm names is for descriptive purposes only and does not imply endorsement by the U.S. 

Government.

!p.O. Box 25007 (D-8220), Denver, Colorado 80225 

2P.O. Box 25007 (D-8220), Denver, Colorado 80225
Abstract:

A temperature control device (TCD) was installed on Shasta Dam, California which began to 

operate in spring 1997 for the purpose of cooling downstream river temperatures to aid recovery 

of chinook salmon in the Sacramento River. This study began in spring 1995 to investigate preand post-TCD effects on the limnology of Shasta reservoir. The maximum pool of cold water 

observed was a function of runoff, as bypass operations resulted in an almost complete yearly 

depletion of the cold water pool. Maximal surface temperatures and the strongest thermocline 

occurred during the month of August. Winter mixing was confined to the upper 50 m of the water 

column. Metalimnetic and hypolimnetic oxygen minima occur yearly in summer. Degree of 

oxygen depletion was related to distance from river inflow, while rate of movement of 

hypolimnetic minima downstream was dependent on deep level withdrawals from the dam. 

Preliminary observations show the TCD affected metalimnetic temperature gradients, movement 

of riverine inflows through the reservoir, and strength of DO minima.

Secchi transparency was highest in the main lake and the Sacramento Arm and, lowest in the 

McCloud and Pit Arm, and was indicative of differences in productivity between the arms. 

Patterns of nutrient cycling within the reservoir differed between epilimnetic and hypolimnetic 

waters. Hypolimnetic nutrient maxima were related to high flow events, while epilimnetic waters 

responded more to in reservoir events, such as stratification and changes in productivity. During 

spring and summer months, TCD releases of surface to mid-level water caused the hypolimnion 

to act as a nutrient sink. Composite chl a concentrations (0 to 5 m) ranged from BDL to 30 ug/L. 

Mean composite chl a concentrations for the period 1995 to 1997 were: main lake (2 ug/L), 

Sacramento River Arm (2 ug/L), McCloud River Arm (2.7 ug/L), Pit River Arm (5.2 ug/L), and 

the Pit-McCloud confluence (3 ug/L). Diatoms, Melosira islandica and Melosira varians 

dominated the algal population. Greatest algal biovolume occurred in the Pit River Arm. 

Biovolume increased significantly from 1995 to 1997. Seasonal algal peaks occured in spring, and 

again on early fall coinciding with development and breakdown of thermal stratification. Greatest 

mean zooplankton biomass occurred in the Sacramento River Arm and was lowest in the 

McCloud River Arm. Cladocerans were the dominant zooplankton at the main lake station and 

Sacramento River Arm. Cladoceran and copepod biomass was equally distributed at other 

stations.

In Shasta and Keswick tailwaters, <25 um POM composed the greatest proportion of total POM 

contributing 90% to the total. Total POM averaged 0.8 g/m3 and 0.9 g/m3 in Shasta and Keswick 

tailwaters, respectively. In 1997, there was a significant increase in zooplankton biomass in the 

drift that was attributed to TCD operations. Copepods, cladocerans, and even rotifers increased. 

Cladocerans composed less and copepods made up more of the total zooplankton biomass. 

Releases of surface water during the most productive time of year resulted in entrainment of 

zooplankton and a significant downstream increase in biomass. As with zooplankton biomass, 

phytoplankton biovolume increased significantly (by a factor of 10) in 1997 over 1995 and 1996.
Table of Contents:

Page

List of Figures: ........................................................... iii

List of Tables: ............................................................ vii

I. Introduction: ........................................................... 1

II. Methods and Materials: ................................................... 2

1. Reservoir Sampling: .................................................. 2

2. River Sampling: ..................................................... 3

HI. RESULTS AND DISCUSSION ............................................ 4

1. Physical Limnology: .................................................. 4

A. General Trends: ............................................... 4

B. Interflows: ................................................... 7

2. Secchi Transparency: ................................................. 8

3. Nutrient Dynamics: .................................................. 9

4. Primary and Secondary Productivity: .................................... 12

A. Chlorophyll: ................................................. 12

B. Phytoplankton: ............................................... 13

C. Zooplankton: ................................................ 15

5. River Studies: Downstream Drift In Shasta and Keswick Tailwaters Below Shasta

Lake: ........................................................ 17

A. Temperatures: ............................................... 17

B. Particulate Organic Matter (POM): ............................... 18

C. Zooplankton: ................................................ 20

D. Phytoplankton and Chlorophyll: .................................. 22

IV. Post TCD Results: 22

V. Management Implications: ............................................... 24

VII. Acknowledgments: ..................................................... 25

VI. Literature Cited: 25
List of Figures:

Page

Figure 1. Seasonal patterns of inflow (cfs), discharge (cfs) and reservoir elevation (Feet above

msl) for Shasta Lake, CA, 1995-1997 ..................................... 34

Figure 2. Map of limnological sampling stations in Shasta Lake. Main lake (S6), Sacramento

River Arm (S7, S15), McCloud River Arm (S8 and S14), Pit River Arm (S9, S12, S13), 

Squaw Creek Arm (SI 1), and Pit-McCloud Confluence (S10). River stations are located 

in Shasta tailwaters (SO) and Keswick tailwaters (Kl). ......................... 35

Figure 3 a-e. Time series isopleths of dissolved oxygen (mg/L), temperature (°C) and specific

conductance (yuS/cm) for Shasta Lake sampling stations, a. S6; b. S7; c. S8; d. S9; e. S10

.................................................................. 36

Figure 4 a-e. Time series isopleths of Relative Thermal Resistance to Mixing (RTRM) coefficients 

for Shasta Lake sampling stations a. S6; b. S10; c. S9; d. S8; e. S7. .............. 41

Figure 5 a-t. Monthly isopleth description of temperature (°C ), dissolved oxygen (percent

saturation), pH, and specific conductance (/^S/cm) for the Pit River arm for 1996 and 

1997. a. February 1996; b. March 1996; c. April 1996; d. May 1996; e. June 1996; f. 

July 1996; g. August 1996; h. September 1996; i. October 1996; j. January 1997; k. 

February 1997; 1. March 1997; m. April 1997; n. May 1997; o. June 1997; p. July 1997; q. 

August 1997; r. September 1997; s. October 1997; t. November 1997. ............ 44

Figure 6 a-t. Monthly isopleth description of temperature (°C ), dissolved oxygen (percent

saturation), pH, and specific conductance (yuS/cm) for the Sacramento River arm for 1996 

and 1997. a. February 1996; b. March 1996; c. April 1996; d. May 1996; e. June 1996; 

f. July 1996; g. August 1996; h. September 1996; i. October 1996; j. January 1997; k. 

February 1997; 1. March 1997; m. April 1997; n. May 1997; o. June 1997; p. July 1997; q. 

August 1997; r. September 1997; s. October 1997; t. November 1997. ............ 64

Figure 7. Comparison of chl a concentrations (ug/L) from surface to 30m between the main lake 

(S6), Sacramento River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and the 

Pit-McCloud Confluence (S10) from August 1995 thru October 1997. ............. 84

Figure 8. Seasonal cycle of inflow temperatures for the Sacramento river at Delta, station (DLT), 

and for the Pit river at station (PMN). ..................................... 85

Figure 9. Isopleth description of 1997 flood inflow patterns using turbidity as an indicator for

October 1996, January 1997, February 1997, March 1997. ...................... 86

Figure 10 a-b. Secchi depth transparencies (m) for Shasta Lake from May 1995 thru November 

1997. a. main lake (S6) and forebay (SI6); b. Sacramento River Arm (S7) and upper 

Sacramento River Arm (SI5). ........................................... 87

in
Figure 11 a-b. Secchi depth transparencies (m) for Shasta Lake from May 1995 thru November 

1997. a. McCloud River Arm (S8) and upper McCloud River Arm (S14); b. Pit River 

Arm (S9), upper Pit (S12), upper upper Pit (S13), and Squaw Creek (SI 1). ......... 88

Figure 12. Seasonal patterns of epilimnetic and hypolimnetic nitrate-nitrogen for Shasta Lake

sampling stations from 1995-1997. ........................................ 89

Figure 13. Seasonal patterns of epilimnetic and hypolimnetic orthophospahte (SRP) for Shasta

Lake sampling stations from 1995-1997. ................................... 90

Figure 14. Seasonal patterns of epilimnetic and hypolimnetic ammonia (NH4) for Shasta Lake

sampling stations from 1995-1997. ........................................ 91

Figure 15. Seasonal patterns of epilimnetic and hypolimnetic total phosphorus (TP) for Shasta

Lake sampling stations from 1995-1997. ................................... 92

Figure 16. Seasonal patterns of epilimnetic and hypolimnetic TP/SRP ratios for Shasta Lake

sampling stations from 1995-1997. ........................................ 93

Figure 17. Seasonal patterns of epilimnetic and hypolimnetic DIN/SRP ratios for Shasta Lake

sampling stations from 1995-1997. ........................................ 94

Figure 18. Comparison of total composite chl a concentrations (ng/L) (0-5 m) between stations

from 1995 thru 1997. ................................................. 95

Figure 19 a-d. Seasonal trend of composite chl a concentrations (ng/L) (0 to 5 m) from May 1995 

thru October 1997. a. main lake (S6) and forebay (S16); b. Sacramento River Arm (S7) 

and upper Sacramento River Arm (SI6); c. McCloud River Arm (S8) and upper McCloud 

River Arm (S14); d. Pit River Arm (S9), upper Pit (S12), upper upper Pit (S13), Squaw 

Creek (SI 1), and Pit-McCloud Confluence (S10). ............................ 96

Figure 20 a-c. Seasonal trend of dominant phytoplankton groups collected from 0-30 m from the 

main lake (S6). a. June 1995 thru November 1996; b. January 1996 thru October 1996; c. 

January 1997 thru October 1997. ......................................... 98

Figure 21 a-b. Seasonal depth distribution of phytoplankton collected from 0-10 m, 10-20 m, and 

20-30 m in the main lake (S6) from June 1995 thru October 1997. a. bacillariophyta; b. 

cryptophyta. ......................................................... 99

Figure 22 a-c. Seasonal trend of dominant phytoplankton groups collected from 0-30 m in the Pit 

River Arm (S9). a. June 1995 thru November 1995; b. January 1996 thru October 1996; c. 

January 1997 thru October 1997. ........................................ 100

Figure 23 a-b. Seasonal depth distribution of phytoplankton collected from 0-10 m, 10-20 m, and 

20-30 m in the Pit River Arm (S9) from June 1995 thru October 1997. a. bacillariophyta; 

b. cryptophyta. ...................................................... 101

IV
Figure 24. Mean total copepod and cladoceran biomass (|tig/L) for for all sampling dates for the 

main lake (S6), Sacramento River Arm (S7), McCloud River Arm (S8), Pit River Arm 

(S9), and Pit-McCloud Confluence (S10) from 1995 thru 1997. ................. 102

Figure 25. Mean copepod and cladoceran biomass (ng/L) for the main lake (S6), Sacramento 

River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and Pit-McCloud 

Confluence (S10)for 1995, 1996 and 1997. ................................ 103

Figure 26 a-b. Trends in zooplankton abundance (0-30 m) in the main lake (S6) from June 1995 

thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass (|ig/L) trends. .................. 104

Figure 27 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the main lake (S6) from June 1995 thru September 1997. a. 

copepods; b. cladocerans. ............................................. 105

Figure 28 a-b. Trends in zooplankton abundance (0-30 m) for the Sacramento River Arm (S7) 

from June 1995 thru September 1997. a. Percent composition of copepods and 

cladocerans; b. Cladoceran, copepod, and rotifer total biomass (ng/L) trends. ...... 106

Figure 29 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the Sacramento River Arm (S7) from June 1995 thru 

September 1997. a. copepods; b. cladocerans. .............................. 107

Figure 30 a-b. Trends in zooplankton abundance (0-30 m) for the McCloud River Arm (S8) from 

June 1995 thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass (ng/L) trends. .................. 108

Figure 31 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the McCloud River Arm (S8) from June 1995 thru September 

1997. a. copepods; b. cladocerans ....................................... 109

Figure 32 a-b. Trends in zooplankton abundance (0-3Om) for the Pit River Arm (S9) from June 

1995 thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass(ng/L) trends. ................... 110

Figure 33 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the Pit River Arm (S9) from June 1995 thru September 1997. 

a. copepods; b. cladocerans. ............................................Ill

Figure 34 a-b. Trends in zooplankton abundance (0-30 m) for the Pit-McCloud confluence (S10) 

from June 1995 thru September 1997. a. Percent composition of copepods and 

cladocerans; b. Cladoceran, copepod, and rotifer total biomass (ng/L) trends. ...... 112

Figure 35 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals at the Pit-McCloud confluence (S10) from June 1995 thru 

September 1997. a. copepods; b. cladocerans. .............................. 113
Figure 36. Seasonal trend of rotifer biomass (^ig/L) (0-30 m) in the main lake (S6), Sacramento 

River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and the Pit-McCloud 

Confluence (S10) from June 1995 thru September 1997. ...................... 114

Figure 37. Water temperatures (°C) in Shasta tailwaters and Keswick tailwaters from April 1995 

thru November 1997. ................................................. 1 15

Figure 38 a-b. The relationship between size fractions of <25um, >25, and >505^m POM 

concentrations (g/m3) from April 1995 thru October 1997. a. Shasta tailwaters; b. 

Keswick tailwaters. .................................................. 1 1 6

Figure 39 a-c. Seasonal POM (g/m3) trnds in Shasta and Keswick tailwaters from April 1995 thru 

October 1997. a. <25^m; b. >25um; c. >505um ........................... 117

Figure 40 a-c. Composition of total particulate matter (g/m3) in Shasta tailwaters from April 1995 

thru October 1997. a. <25um; b. >25^m; c. >505um ......................... 1 18

Figure 41 a-c. Composition of total particulate matter (g/m3) in Keswick tailwaters from April

1995 thru October 1997. a. <25um; b. >25um; c. >505um ..................... 1 19

Figure 42. Mean total POM (g/m3) at Shasta and Keswick tailwaters for the period 1995 thru

1997. ............................................................ 120

Figure 43 a-b. Seasonal composition of zooplankton for 1995, 1996, and 1997 in Shasta

tailwaters. Major groups are cladocerans, copepods, and rotifers, a. biomass (^ig/L); b. 

percent composition ..................................................121

Figure 44 a-b. Seasonal composition of zooplankton for 1995, 1996, and 1997 in Keswick

tailwaters. Major groups are cladocerans, copepods, and rotifers, a. biomass (ng/L); b. 

percent composition .................................................. 122

Figure 45 a-b. Cladoceran, copepod, and rotifer biomass (^ig/L) drift from April 1995 thru

October 1997. a. Shasta tailwaters; b. Keswick tailwaters. ..................... 123

Figure 46 a-b. Total biovolume (^ig/L) of phytoplankton size fractions (<25um, >25^m, >505um) 

from April 1995 thru September 1997. a. Shasta tailwaters; b. Keswick tailwaters. ... 124

Figure 47. <25um Chlorophyll a concentration (^ig/L) in Shasta and Keswick tailwaters from

April 1995 thru October 1997. .......................................... 125

Figure 48 a-c. Percent composition of the <25um phytoplankton biovolume in Shasta and

Keswick tailwaters for the period 1995 thru 1997. a. <25^m; b. >25um; c. >505|am . 126

VI
List of Tables

Page 

Table 1. UTM coordinates of sampling stations in Shasta Lake. ........................ 28

Table 2. Phytoplankton species collected from stations S6, S7, S8, S9, and S10. ........... 29

Table 3. Zooplankton species collected from stations S6, S7, S8, S9, and S10. ............ 33

vn
I. Introduction:

Limnological research on Shasta Lake began in March 1995 as a joint effort between USGS/ 

Midcontinent Ecological Science Center (MESC), Bureau of Reclamation (BOR)/ Northern 

California Area Office (NCAO), and BOR/Technical Service Center (TSC) to investigate the 

potential changes in the biological, chemical, and physical characterisitics of the reservoir as a 

result of operating the temperature control device (TCD).

Shasta Lake is located 12 miles north of Redding in northern California, and is part of the Central 

Valley Project (CVP), a federal water project operated by the Bureau of Reclamation. Shasta 

Dam, a 602-foot high curved concrete gravity structure with a crest elevation of 1077 feet above 

mean sea level (MSL) was completed in 1945 forming the largest reservoir in California. The 35 

mile long reservoir has 365 miles of shoreline, a surface area of 29,500 acres, a maximum depth of 

157 m, and contains 4.5 million acre-feet of water at full pool. Limnologically the reservoir is 

characterized as monomictic, however, it does not turn over completely, and remains ice-free in 

the winter. The reservoir receives the majority of its water during the rainy season from the end 

of December through March each year (Fig. 1). The reservoir supports a two-level fishery with 

salmon and trout providing a cool water fishery, and a variety of Centrarchids, notably spotted 

bass, providing the warm water portion.

A temperature control device (TCD) was installed on Shasta Dam and began to operate on March 

13, 1997 for the purposes of controlling downstream river temperatures to aid recovery of the 

endangered winter run chinook salmon, and to minimize loss of generating capacity as a result of 

releasing deeper, colder water through low level outlet works in order to meet downstream 

temperature criteria. Prior to operation of the TCD, late summer water temperatures in the 

Sacramento River were too warm for successful spawning of salmon. Proper operation of the 

TCD allows surface waters to be released in the spring and early summer, conserving the pool of 

cold water. As the season progresses withdrawals move deeper into the hypolimnion, and if need 

be, deeper than the old penstock intakes. Historically, Shasta was operated as a hypolimnetic 

deep release reservoir. In 1987, however, bypass releases were instituted as a conservation 

measure for chinook salmon. With the exception of surface withdrawl capabilities, TCD 

operations are meant to mimic bypass releases.

The current limnological study began in spring 1995, two years prior to operation of the TCD. 

The objectives of the study are to: 1) Compare pre- and post-operational changes on the physical, 

chemical, and biological attributes of Shasta Lake and tailwaters; 2) help develop better 

operational guidelines for the TCD in order to minimize negative impacts to Shasta Lake while 

providing optimum water temperatures downstream for chinook salmon spawning; and 3) apply 

limnological, fisheries, and modeling results to existing and planned TCD facilities.

We will test several hypotheses that address potential effects from operation of the TCD on the 

limnology of Shasta Lake. These include 1) increased winter mixing due to lower temperature 

gradient as a result of depleting the deep cold water pool in late fall; 2) delay of thermal 

stratification due to surface withdrawals during spring months; 3) increased degree of thermal
stratification due to shifts in withdrawal patterns; 4) lower summer primary and secondary 

productivity due to increased stratification; 5) increased hypolimnetic nutrient levels during spring 

and summer as a result of a shift to surface withdrawals; 6) potential decreased zooplankton 

biomass and increased algal production due to spring surface withdrawal; and 7) shifts in quantity 

and/or quality of downstream organic drift, potentially influencing riverine fish production.

II. Methods and Materials:

1. Reservoir Sampling:

Beginning April 1995, the reservoir was sampled monthly except during the months of OctoberDecember 1995, December 1996 and December 1997. Five stations were established at the 

beginning of the study: main lake (S6), Sacramento River Arm (S7), McCloud River Arm (S8), 

Pit River Arm (S9), and Pit-McCloud Confluence (S10). The sampling program was expanded in 

February 1996 to include 6 additional stations: Squaw Creek (SI 1), upper Pit (S12), upper upper 

Pit (S13), upper McCloud (S14), upper Sacramento (S15), and forebay (S16) (Fig. 2, Table 1). 

Stations SI 1 to SI6 were only sampled for water temperature (°C), conductivity (uS/cm), 

dissolved oxygen (mg/L), pH, turbidity (NTU), surface and composite chl a (ng/L), and secchi 

disk transparency (m). Stations were sampled at the deepest point on the thalweg of the historic 

river channel.

Water column profiles for water temperature (°C), dissolved oxygen (mg/L), specific conductance 

(nS/cm), pH, and turbidity (NTU) were completed at each station using a Hydrolab Surveyor 3® 

connected to an H20® sonde unit. Data was collected at one meter intervals through the 

thermocline then every two to five meters thereafter until the bottom was reached. At each depth 

readings were allowed to stabilize before data was recorded. The sonde unit was calibrated 

according to Hydrolab specifications at the beginning of each sampling trip.

Nutrient samples (500 mL) were collected from surface, middle, and bottom depths through the 

summer of 1996 for total phosphorus (TP) (detection limit 0.002 mg/L), soluble reactive 

phosphorus (SRP) (detection limit 0.001 mg/L), dissolved nitrate and nitrite nitrogen (NO3 + 

NO2) (detection limit 0.002 mg/L), and ammonia (NH4) (detection limit 0.003 mg/L). Middle 

depths were initially selected based on conductance (an identifier of riverine interflow). Surface 

and bottom samples were Om and 85 m (if station depth allowed). Nutrient sampling protocols 

were changed in the summer of 1997 to reflect a better representation of the whole water column. 

From summer 1997 to present 0 m and 85 m collections remained constant, however, one middepth sample was added and the collection depths fixed at 10 m and 20 m. Total kjeldahl nitrogen 

(TKN) (detection limit 0.035 mg/L) and total suspended solids (TSS) (detection limit <1 mg/L) 

were collected only during the first few months of the study. Water samples were kept 

refrigerated until analyzed. Nutrient analyses were performed by the University of California, 

Davis.

Secchi transparency was measured using a standard 20 cm secchi disk and View Scope®. The
secchi disk was lowered in the water column until it disappeared, then brought up until visible, 

and lowered again until it disappeared. Secchi disk transparency was recorded at the point of 

disappearance.

Replicate zooplankton tows were collected from three depth intervals: 0-10 m, 10-20 m, and 20- 

30m with a 64 |iim birge-style closing net. Samples were stored in 125 mL amber bottles, and 

preserved with Acid Lugols solution. Samples were identified to species and enumerated by Dr. 

John Beaver, BSA, Beachwood Ohio. Biomass was calculated based on enumerated samples and 

individual species bio-volume estimates provided by Dr. Michael Brett (UC Davis, U. 

Washington).

Phytoplankton samples were collected from discrete depth intervals using a electric water pump 

and composited for analysis. Samples were collected from 0, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 

28, 30 m. At each depth, duplicate 1-gallon containers were filled and composited into 5 gallon 

buckets. Composited samples were 0-10 m, 10-20 m, and 20-30 m. 250ml of composited sample 

from each bucket was preserved in Lugols and later identified to species and enumerated and 

converted to biovolume. Dr. John Beaver, BSA, Beachwood, Ohio identified and enumerated 

samples and individual species bio-volume estimates were provided by Dr. Michael Brett (UC 

Davis, U. Washington).

Duplicate water samples for chlorophyll a ( chl a) pumped from discrete depths were collected in 

a similar manner as phytoplankton except depth intervals used were 0, 5, 10, 15, 20, 25, and 30 

m. Duplicate composite samples were additionally collected from 0-5 m using a pool hose 

lowered into the water column to a depth of 5 m. For analysis from 150 to 250 ml of sample was 

filtered onto Whatman GF/C filters (47 mm). Filters were kept frozen until analyzed. Samples 

were extracted with methanol and analyzed flourometrically by the UC Davis. Chl a 

concentrations were corrected for phaeophytin.

2. River Sampling:

Two river sites on the Sacramento River, one below Keswick Dam and the other below Shasta 

Dam, were sampled on a monthly basis (Fig. 2). The Keswick station was located approximately 

14 km downstream from Shasta and about 0.8 km downstream of Keswick Dam. The Shasta site 

is about 0.8 km downstream of Shasta Dam.

Particulate organic matter (POM) samples were collected and fractionated into three sizes (>505 

^im, >25 ^im, and <25^m) using a series of plankton nets; all samples were collected in triplicate. 

>505 ^im POM samples were collected using a 505 ^im net 3 m in length with a 0.5 m diameter 

mouth. The 505 ^im net was deployed in the current 3-4 minutes. A calibrated flow meter 

mounted across the mouth of the net was used to determine volume of water filtered. During 

extreme high flow events >505 ^im samples were not collected. Three liters were collected for 

each <25 ^im POM replicate by filtering water pumped from the river through a 25 ^im plankton 

net into a 5 gallon bucket and collecting the filtrate. The >25 \im size fraction was obtained by
filtering 96 L through a 25 jum plankton net. All samples were stored chilled until processed. 

Samples were filtered through ashed, pre-weighed Gelman 47 mm glass fiber A/E filters. Filters 

were oven-dried at 75 °C for 24 hrs, weighed for dry weight, ashed at 500 °C for one hour, and 

weighed for ash weight. Dry weight (seston), ash weight, and ash-free dry weight (POM) were 

calculated as g/m3 according to Strickland and Parsons (1968).

Four chlorophyll samples were collected from each river station. Two samples were collected as 

grab samples from the river surface, and two collected from the portion of water representing the 

<25 (urn size fraction (as described above). Duplicate water samples for phytoplankton were 

collected and separated into >505 jum (500 mL), >25 jum (125 mL), and <25 jum (1 L) size 

fractions, according to the above netting protocols for POM. Duplicate zooplankton samples 

were collected from the >25 jum size fraction as described for POM above. Nutrients (NO3 + 

NO2, NH4, TKN, TP, SRP) were collected at each station 0.5m below the surface. Chlorophyll, 

plankton and nutrient samples were processed following the same guidelines as those outlined for 

reservoir samples. Water temperature, pH, specific conductance, dissolved oxygen, and turbidity 

were taken 0.5 m below the water surface.

ID. RESULTS AND DISCUSSION

1. Physical Limnology: 

A. General Trends:

Physical data indicated Shasta Lake is monomictic, however, the reservoir did not turn over 

completely during this study and mixing was confined to the upper 50m of the water column. 

Thermal stratification extended from late April through the end of September (Fig. 3a-e). 

Duration of stratification was driven by ambient temperatures and amount of solar input, thus the 

length of time the reservoir stratified for was variable from year to year. Bypass operations 

probably had no significant impact on the timing of, or extent of, thermal stratification of the 

epilimnion. However, we do not have data to indicate whether bypass operations of the last 10 

years differ in their effect from that of historical reservoir operations. Once stratification occurred 

typical reservoir and bypass operations generally withdrew water from well below the 

thermocline, and as such, should have had no real impact on epilimnetic heat budgets during 

summer months. Bypass operations did, however, as will be shown, affect thermal structure and 

water movement patterns, such as interflows, of hypolimnetic waters. Decrease in hypolimnetic 

cold water pools over the course of the summer was a direct consequence of bypass operations. 

Replenishment of the cold water pool in winter and spring was a function of runoff rate and 

temperature of inflow.

Figures (4a-e) indicate relative thermal resistance to mixing (RTRM) for each station by date, and 

provide a pictorial representation of stratification patterns that occurred within the reservoir. 

Graphs do not show true values for the large peaks due to the smoothing function of the graphical 

technique, but never the less indicated time periods and depths of greatest relative resistance to
mixing. RTRM was calculated as the difference in density of water due to temperature at two 

different depths standardized to the difference in density of water between 4 and 5°C. Salinity 

differences were not incorporated into the resistance coefficients due to minimal contributions to 

density based on observed water column specific conductance values. The larger the RTRM 

coefficent (such as at the thermocline), the greater the density (temperature) gradient and thus a 

correspondingly larger amount of energy that is needed to mix water across the gradient.

Stratification developed in April, and the thermocline established at a depth range of 10-15 m 

(Figs. 3a-e, 4a-e). Maximal surface temperatures and the strongest thermocline occurred in 

August of the three years of this study (Figs. 5g,q, 6g,q). Maximal surface temperatures were 27- 

28 °C. Productivity decreases and nutrient declines during the summer were associated with the 

development of the thermocline, and increased RTRM. Fall disappearance of a strong 

thermocline was fairly rapid and by September lake surface temperatures had dropped 4-5 °C 

from the previous month (Fig. 4a-e). With the drop in temperatures there was gradual erosion of 

the thermocline as it was pushed deeper into the metalimnion. The time period of a weakening 

thermocline and greater potential mixing coincided with fall algal blooms each year of this study.

The metalimnetic zone in the reservoir represented a transition zone beginning at the thermocline 

(1 °C/m) and extending to the hypolimnion. This zone showed fairly consistent temperature 

change (<1 °C/m), though not to the degree of the thermocline. Early in the season the 

metalimnion was narrow, such as during April to May when the cold water pool in the reservoir 

was near maximum. As the reservoir warmed through surface heating, increases in inflow water 

temperature, and as hypolimnetic releases began removing the cool water pool, the metalimnetic 

zone thickened. RTRM indicated a fairly shallow metalimnion in April which deepened over the 

course of the summer to a maximal depth of about 50 m toward the end of September; this 

pattern was consistent for both 1995 and 1996. Below the metalimnion RTRM coefficients 

remain low and relatively constant, an indication of the hypolimnetic zone where temperatures 

changed little.

Metalimnnetic oxygen minima developed seasonally within the reservoir, tending to be most 

severe upstream with almost complete anoxia developing at some sites (Figs. 3a-e, 5g,q, 6g,q). 

Minima began developing in July and become strongest during peak stratification in August. 

Metalimnetic minima developed at the thermocline, and immediately above and extending into the 

high conductivity water of the interflow region at all reservoir stations. Minima develop from 

several causes. As inflow waters and their associated organic load move as interflow through the 

reservoir, respiration rates due to bacterial decomposition result in oxygen depletion. Upstreamdownstream gradients occurred due to decreasing amounts of organic matter available for 

decomposition the further into the lake the interflow extends from the source. Secondly, as dead 

algal material settles out of the epilmnion settling rates slow as material encounter the denser 

water associated with the thermocline allowing more time for decompositional activity and 

consequently lowered oxygen levels. Plankton respiration in this zone may further be an important 

contributor to oxygen depletion. Sediment oxygen demand, at least early in the year is likely not 

an important contributor to the metalimnetic minima; it is, however, probably important in
development of hypolimnetic minima at upstream sites. All factors act together to some degree in 

the reservoir.

The upper portion of the metalimnion was important to reservoir productivity during summer 

months. Chl a peaked at the thermocline and measurable levels extended into the upper 

metalimnion. During summer, surface waters were depleted of nutrients quickly and productivity 

in near surface waters was low (Fig. 7). The 1% light level extended down to around 20-25 m 

during the summer, which represents the lower limit of active algal photosysnthesis. There was 

thus a 10-15 m band in the upper metalimnion suitable for algal growth. At least early in the 

development of the metalimnion each year, this zone contained higher nutrient levels than surface 

waters and there were correspondingly higher chl a concentrations (Fig. 7). As summer 

progressed nutrient levels decreased due to an ever thickening metalimnion with the temperature 

gradient acting to limit the degree of continued mixing.

Below the metalimnion, hypolimnetic temperatures remained relatively stable to the bottom of the 

reservoir. There was a slow decrease in temperature with depth (Fig. 3a-e), however, 

temperature changes were subtle enough that RTRM coefficients were relatively constant and 

small throughout this region (Fig. 4a-e). RTRM plots were used to determine the break between 

the metalimnion and hypolimnion, as even in the hypolimnion temperature change still occurred 

with depth. Hypolimnetic oxygen depletion developed over the course of the summer, significant 

declines began appearing in July with the severest depletion occurring during the months of 

September-November (Figs. 5h,i,r,s,t, 6h,i,r,s,t). Oxygen depletion was severest near the bottom 

sediments with levels gradually recovering towards the surface, and was a function of bacterial 

decomposition and associated sediment oxygen demand. Similar to metalimnetic responses, 

severest depletion occurred at upstream sites where organic load was highest.

Hypolimnion volume was near maximal in late winter to early spring, coincident with the end of 

the rainy season. Deep hypolimnetic temperatures varied slightly from year to year, though the 

range for the past four years is less than one degree, ranging from a low of 6.7 °C to a high of 7.5 

°C. Minimal hypolimnetic temperatures were a function of inflow temperature (Fig. 8). During 

the three seasons of study to date, the hypolimnion has not mixed completely with the rest of the 

water column during winter mixing. Thorough mixing occurred to between 50 and 60 m 

consistently, though there was some exchange with deeper layers.

Mixing may have been influenced by operational patterns. Typical early winter releases were 

through the penstocks (el. 815), and given reservoir elevations for the same time period, what 

may be occurring is penstocks were not tapping the upper levels of the reservoir, while cold 

inflows in the range of 5-8 °C are replenishing the bottom waters up to the level of the penstocks. 

Cold inflows occurred from late December through March. As an example there was a fairly 

rapid break at about 45 m in February 1996 where water temperature drops from 10 °C down to 

about 8 °C. A depth of 45 m corresponded to a reservoir elevation of about 885 ft. This upper 

limit may represent the upper zone of influence of penstock releases (Tracy Vermeyen, USBR, 

Denver, Co. Pers. Comm.). During the three years of this study the level was fairly stable.
Without complete mixing the upper portion of the reservoir was unaffected by typical release 

patterns. During high flow events where upper bypass tubes were operated more of the surface 

layer was released. As such, the lowest temperatures observed for surface waters were influenced 

more by ambient weather conditions than inflow waters. Support for limited mixing was further 

provided by water column turbidity profiles conducted during winter and early spring 1997 (Fig. 

9). A large flow event (Fig. 1) provided a turbid inflow into the reservoir that was monitored for 

several months. Initial movement was rapid, and within days inflow had reached the dam. One 

month later this plume had mixed fairly well. Surface turbidity indicated some mixing, but the 

majority of high turbidity water remained deep, with a well defined break at about 40 m (Fig. 9).

Bypass operations, with release target temperature near 9 °C in late summer, resulted in a gradual 

depletion of the hypolimnetic cold water pool over the course of late summer and fall. The 

maximum pool of cold water observed for the past three years was a function of runoff. Average 

inflow temperatures were below the 9 °C level for 3-4 months depending on the year. For 

example, in 1995-96 there was about a 110 day period of average 9 °C or lower, with inflow for 

the period being approx 2.8 million acre feet, during this time approximately 1 million acre feet 

was discharged, leaving an excess of approximately 1.8 million acre feet of 9 °C or cooler water in 

the reservoir.

B. Interflows;

The Sacramento and Pit Rivers provided the majority of inflow, with the Pit providing close to 

two-thirds (69% vs. 18%) of the total. Sacramento River water had lower specific conductance 

than water entering from the Pit river arm due to characteristics of the drainage basin. This 

provided the ability to distinguish the fate of the two rivers as they travel through the reservoir. 

Movement of riverine water through the reservoir was a function of both release depth, volume of 

releases at the dam, amount of inflow entering the reservoir and inflow density, primarily as a 

function of temperature. Pre-TCD upstream downstream patterns of water movement through the 

reservoir were similar from year to year. Variation existed in exact timing of events due to 

seasonal differences in flow rate and temperature of inflows. When warm temperatures demanded 

higher bypass releases, flow changes occurred at a faster rate in the reservoir because more water 

was being moved. As examples of water movement patterns, this report will focus on 1996 data 

as representative of typical bypass conditions for the Sacramento and Pit river arms.

Run-off temperatures were at or near their lowest in January -February (Fig. 8). For both rivers 

inflows were typically in the 7-9 °C range; similar to deep hypolimnetic temperatures. Surface 

temperature never dropped below 9-10 °C, thus river inflow always entered as interflow or 

underflow. A plunge point existed near the upstream end of each arm above which all water was 

river water and downstream of which was an isolated pool of lake water. During the spring as 

runoff increased, a shift in thermal structure could be seen in upstream sites, where cooler water 

was shallower than further downstream (Figs. 5a, j, 6a, j). This represented the wedge shapecl 

mass of water sliding under the plunge zone and flowing down the narrow channel. As it moved 

downstream and the channel widened water dispersed to an equilibrium depth. Pit River inflow at
this time of the year moves along the bottom of the reservoir, and essentially functioned to 

replenish the cold water pool of the hypolimnion and pushed the warmer layers of water upward 

(Fig. 5b). The Sacramento river followed a similar pattern though tending to ride above the inflow 

from the Pit arm (Fig. 6b). Whereas the Pit river followed the bottom, the Sacramento river 

intrusion was most prominent in the 50-70 m depth range.

From March into April the interflows from both rivers elevated into the water column and by May 

stabilized at 10-20 m in depth, riding just under the thermocline, in the upper metalimnion. The 

Sacramento river plume was less visible in summer due to low inflows and conductivity more 

similar to average reservoir conditions. Effects of shallow interflows extended into the forebay of 

Shasta Lake, though not as prominently as at upstream sites (Figs. 5d,h, 6d,h). Inflows dispersed 

as a narrow band in the lake. This was attributed to the fact that releases were below this level and 

the plume is not pulled through the lake as when intrusions are near penstock depths (Figs. 5,6). 

As this intrusion band thickened through August it remained prominent but dispersal was 

evidenced by conductivity gradients of upper metalimnetic waters (Figs. 5,6). Beginning in 

September, as inflow temperatures declined at a rate more rapid than reservoir temperatures, 

interflows began settling in the water column (Figs. 5,6).

An upstream downstream gradient of oxygen depletion in the hypolimnion developed soon after 

the plume elevated off the bottom for both river arms. This bottom layer was isolated from 

further input until the plume descended in the fall. Since it was below the photic zone and there 

was no freshwater input, dissolved oxygen was not replenished and decompositional processes 

gradually utilized remaining dissolved oxygen. As typical with most reservoir systems, depression 

of dissolved oxygen levels was first apparent at upstream sites, gradually extending down 

reservoir. There was a one-month time lag between the Pit arm (S9) and the main lake (S6) in the 

appearance of severest DO depletion. Slow downstream movement in the summer, was a result 

of deep bypass withdrawals moving water through the reservoir. At upstream sites low DO water 

was associated with bottom sediments, however, further downstream the low DO center elevates 

into the water column and about mid-October can be observed in the main lake (S6) at about 100 

m during 1995 and 1996, and at about 80 m during 1997, which approximate low-level bypass 

elevations, and indicate a possible cause-effect relationship.

2. Secchi Transparency:

Secchi transparency is a function of light absorption characteristics of water due to dissolved and 

particulate matter, either organic such as plankton, or inorganic such as suspended sediments. It 

reflects both the seasonal thermal structure and plankton productivity in the reservoir. Secchi 

transparency was highest in the main lake (Fig. lOa) and Sacramento Arm (Fig. lOb) and, lowest 

in the McCloud (Fig. 1 la) and Pit Arm (Fig. 1 Ib), and was indicative of differences in 

productivity between the arms. Secchi transparencies, reached a maximum in May, and again in 

October or November, and coincided with time of minimal algal productivity. Greater secchi 

depths in early summer were a result of decreased mixing, on-set of thermal stratification, 

subsequent depletion of nutrients and consequently a decrease in algal productivity. Secchi depth
transparency was lowest during the winter-spring rainy season, during spring algal blooms, and 

during late summer-early fall drawdown of the reservoir. During these times suspended sediment 

as a result of rains and/or reservoir drawdown and algal material caused a decrease in water 

clarity.

Secchi depth transparency trends were similar for 1995 and 1996, while 1997 data show some 

differences that reflected hydrology unique to 1997. Secchi transparencies for all stations were 

below 0.5 m from the beginning of January through March 1997 (Figs. 10-11). Torrential rains 

and severe flooding in northern California produced extremely turbid conditions and chocolate 

brown waters throughout the reservoir in 1997. The reservoir began clearing April and shortly 

after significant algal blooms occurred. Secchi transparency increased to about 2 m at all stations, 

lower readings were recorded in the upper reaches of river arms primarily due to greater 

concentration of suspended sediment. Following the April algal bloom, water clarity increased as 

a result of algal die-off from nutrient depletion and settling of sediments. In early summer 1997 

secchi depths were greater than the two previous years during the same period (Figs. 10-11). 

Secchi transparency remained high until August, then decreased. Water were more turbid in late 

summer-early fall 1997 compared to 1995 and 1996 due to resuspension of particulate material in 

the water column as the reservoir was drawn down to its lowest level in three years. Draw down 

had a pronounced effect on water clarity, but at the same time may have brought in additional 

nutrients through resuspension which contributed to algal blooms throughout the reservoir in 

August 1997, particularly in the Pit river arm (S9).

3. Nutrient Dynamics:

Epilimnetic and hypolimnetic nutrient pools within the reservoir showed distinct spatial and 

seasonal patterns. There were, however, differences in cycling unique to each pool of water. 

Epilimnetic peaks were dependent on winter mixing whereas flow events and runoff played a 

more important role in the hypolimnion. Variation between years was likely driven by large scale 

climate responses that resulted in higher or lower inflows, shifts in outflow release patterns and 

variation in degree and duration of thermal stratification and resultant reservoir mixing. Spatial 

separation of nutrient levels within reservoir arms was related to distance from inflow and may be 

affected by contributions from exposed sediments due to changing reservoir levels, and local 

events such as algal blooms. All stations showed similar long-term patterns though there were 

substantial short term differences. Extremes for nutrient levels ranged from below detection limits 

(BDL) -160 //g/L for nitrite-nitrate, BDL to slightly over 30 //g/L for ammonia, BDL-60 //g/L for 

orthophosphate and BDL-100 //g/L for total phosphorus. Hypolimnetic values were typically 

higher than epilimnetic values for all nutrient parameters.

Nitrate and SRP (orthophosphate) levels reached epilimnetic seasonal peaks at all stations in 

January-February, during the time of maximal reservoir mixing (Figs. 12-13). Patterns of increase 

were similar between the two, however, SRP increased in surface waters prior to measurable 

increases in nitrate. For both nutrients increases began in October-November. Increases were a 

combination of both biological and physical dynamics. As the reservoir cooled and stratification
began to break down both nutrients were cycled into the surface waters, however, the reservoir 

tended to be more nitrogen limited, and nitrogen may be sequestered more rapidly than 

phosphorus during fall algal blooms. As such there was an apparent fall surplus of phosphorus. 

Some of the increase in phosphorus may be attributed to reservoir levels that were continually 

dropping during this time. Reservoir turbidity tended to increase in late summer due to wave 

action introducing fine sediments from a formerly inundated shoreline. As fall progressed, 

continued cooling, shortened day-length and greater mixing rates finally suppressed these blooms 

and both nutrient levels then increased.

Although runoff associated with winter storms began in mid-winter, winter nutrient peaks did not 

appear correlated with runoff events (Figs. 1,12,13). Peaks occurred at the time of greatest 

potential mixing, as indicate by reservoir temperatures. Chl a levels increased significantly 

beginning in February and were fairly uniform through at least the top 30m of the water column, 

an indication of the mixing going on (Fig. 7). Although February reservoir temperatures were 

similar or even cooler then in January, lengthened photoperiod probably triggered the start of 

algal growth. As spring progressed nutrient levels decreased as algal production increased. 

Although nutrient levels appeared similar in different reaches of the reservoir, it may be somewhat 

misleading because higher algal abundance in the upper arms probably sequestered any new 

nutrients made available, or resulted in faster turnover times of available nutrients.

With few exceptions nutrient levels decreased and remained low through the summer due to 

biological uptake. Epilimnetic minima typically occur around April to May, though the minima 

for nitrogen occurs sooner in more productive areas such as at S9 and S10 (Figs. 12-13). Strong 

stratification within the reservoir prevented mixing, and once depleted, nutrients were not 

replenished until fall turnover. Algal production still occurred, but tended to be deeper and 

associated with the thermocline and upper metalimnion where their was increased availability of 

metalimnetic nutrients.

In surface waters nitrate-nitrogen was the dominant nitrogen form when nutrient levels were high, 

as during spring, and winter mixing. In late spring to early summer there were periods where 

epilimnetic ammonia spikes occurred. Spikes occurred at all stations, but were higher at upstream 

sites (Fig. 14). Occurrence times of spikes was not similar among stations. Chlorophyll levels 

were usually low when they occurred and ammonia spikes may represent an algal crash where 

there is a short peak due to decomposition. Other influences such as weather and periodic mixing 

may have also caused short-term peaks in ammonia

Hypolimnetic nutrient levels were on average greater than epilimnetic levels, and appeared to be 

driven more by hydrodynamic events. Though there was substantial variation within and between 

sites there were several emergent patterns. The beginning of winter runoff brings in nutrient laden 

water and a lot of detrital material, notably woody debris. Sudden changes in nutrient levels 

corresponded to changes in the hydrograph, and are apparent at all stations almost simultaneously 

(Figs. 12,13,15). Under normal operations (bypass) nutrient levels reached peak values at roughly 

the same time high flow events enter the reservoir though this may be an artifact of sampling

10
frequency. With only once per month sampling, we may miss time-lags associated with 

interflows from flood events. Using turbidity measurements as a marker for a high flow event in 

January, 1997 mass water movement was extremely rapid through the reservoir taking a week or 

less (Fig. 9). Inflows of greater than 100,000 acre/feet per day were recorded, reducing whole 

reservoir turnover time to less than 40 days. Ammonia and SRP levels showed large increases 

following high runoff events, due to high levels often associated with rain driven inflows. Change 

in TP at this time was due to contribution from SRP. Nitrate in contrast decreased during high 

flow events. The highest nutrient spikes occurred February-March 1996 and in early January for 

1997, and corresponded to the two highest flow events. As reservoir waters warmed, effects were 

most noticeable in the hypolimnion due to underflow of riverine input. The epilimnion, except in 

extreme cases, remained relatively isolated, as runoff entered the reservoir as underflow. The 

flood turbidity graphs further support the idea that mixing is not deep (Fig. 9), and may explain 

why hypolimnetic nutrient levels are driven more by hydrologic events than were epilimnetic 

levels.

Following cessation of winter runoff ammonia levels decreased. Ammonia is utilized quickly or 

converted to nitrate in the well oxygenated waters, and essentially remained at low levels. 

Nitrate, and phosphorus decreased at a slower rate, mirroring changes in epilimnetic nutrient 

levels. The spring decrease reflected uptake by algae during the early spring months before the 

reservoir stratified. An increase in TP/SRP ratios suggested build up of biological organisms 

during the spring at least in surface waters. Total phosphorus decreased through the spring, as a 

result of lower nutrient level water in the deep interflow, and settling out of phosphorus due to 

sediment adsorption.

SRP levels were stable through the summer months and started increasing again in early fall (Fig. 

13). Hypolimnetic nitrate increased early in summer then decreased as the season progressed. 

This may have been due to deep withdrawals. In a reservoir with epilimnetic withdrawal nutrient 

levels should increase over the summer in the hypolimnion. Deep withdrawals, however, 

constantly removed hypolimnetic water, and associated nutrients. Occasionally large ammonia 

spikes were observed, for example at S7 and S9 in October 1995 when deep layers were anoxic 

(Fig. 14).

Trends in N/P ratios in hvpolimnetic waters were most notable in up-reservoir stations. The main 

forebay exhibited a more stable pattern (Fig. 17). Although co-limitation of nutrients occurred, 

DIN/SRP ratios indicated seasonal shifts in the availability of the two nutrients. Mid-summer 

spikes in N/P were primarily due to ammonia, however, neither ammonia or SRP were 

exceptionally high. There was a spring-fall shift in ratios with low ratios in early fall indicating 

quicker build up of SRP relative to TIN. Mid-winter ratios indicated a predominance of nitrate in 

surface waters. Spring decrease indicated more rapid sequestering of SRP relative to nitrate. 

Trends in hypolimnetic ratios were more stable and exhibited a distinct seasonal cycle versus the 

multiple cycles observed in surface waters. Hypolimnetic ratios peaked in late summer following a 

build up of DIN, while SRP levels remained stable. Ratios decreased in winter as high inflow 

events increased phosphorus concentrations at a greater rate than nitrogen. TP/SRP ratios

11
remained relatively low in the hypolimnion indicating much of the hypolimnetic nutrient pool was 

composed of orthophosphate. Epilimnetic TP/SRP ratios cycled to a much larger degree. Ratios 

were high in the late summer dropping during the rest of the year. This was indicative of a higher 

proportion of phosphorus tied up in plankton biomass. Increases may be a result of resuspension 

of reservoir sediments due to dropping reservoir levels in late summer, and/or possibly 

corresponds to increases in recreational usage and changes in wave action.

4. Primary and Secondary Productivity: 

A. Chlorophyll:

Chl a is the predominant photo synthetic pigment in planktonic algae, and can be used to estimate 

total algal biomass. Chl a is often used to determine productivity and as a comparison with other 

aquatic systems to determine trophic status (Likens, 1975). Oligotrophic lakes range from 0.3 to 

3.0 (ig/L chl a, mesotrophic lakes from 2 to 15 ng/L chl a, and eutrophic lakes from 10 to 500 

(ig/L chl a. Composite chl a concentrations (0 to 5m) in Shasta Lake ranged from undetectable to 

30 (ig/L. Mean composite chl a concentrations for the period 1995 to 1997 were: main lake (2 

Hg/L), Sac River Arm (2 ng/L), McCloud River Arm (2.7 ng/L), Pit River Arm (5.2 ng/L), and 

the Pit-McCloud River Arm (3 (ig/L) (Fig. 18). Based only on chl a Shasta Lake falls into the 

mesotrophic category.

Chl a tracked seasonal algal trends well. There were two well defined chl a peaks, one in spring 

and the other in late summer to early fall (Fig. 19 a-d). Chl a was highest at all stations as 

stratification began developing in the spring, and in the fall as stratification began breaking down. 

Spring peaks were usually highest, due to greater availability of nutrients in the reservoir from 

spring run-off and winter mixing. Development of spring chl a blooms was likely triggered by 

photoperiod, and a stabilizing water column. The spring chl a peak was not recorded in 1997 due 

to data loss because of a faulty spectrophotometer (i.e. used to analyze chlorophyll). If the chl a 

peak had been recorded it probably would have been greater than the March 1996 maxima, based 

on algal biovolume present at the time (Fig. 20 a-c). Once stratification fully developed, limiting 

mixing of nutrients, algal production utilized remaining nutrients and chl a levels decreased and 

remained low through the summer. Fall increases in chl a were generally associated with 

breakdown of thermal structure in the reservoir. Peak chlorophyll values in 1997, however, 

occurred in August during the time of greatest stratification. It is possible nutrient resuspension in 

surface waters due to reservoir drawdown and mixing of hypolimnetic waters contributed to this 

increase. Increased turbidity as a result of suspended sediments was an indication of potential 

nutrient influx. Chl a decreased from late fall into winter due to shortened photoperiod, cooling 

reservoir temperatures, and increase in mixing rates.

Spatially, chl a levels were higher uplake than downlake, particularly in the Pit River Arm (S9) 

and McCloud River Arm (S8) (Fig. 19c,d). The lowest composite chl a concentrations were 

reported in the main lake (S6), typical of a finger shaped reservoir. Kimmel et al. (1988) found 

that spatially, phytoplankton biomass and productivity generally decreased downstream within

12
reservoirs, reflecting uplake-to-downstream decreases in nutrient availability. Chl a values ranged 

from about 0 to 8.1 \ig/L (Fig. 19a). Composite chl a productivity of the lower Sacramento River 

Arm (S7) was similar to the main lake (S6) (Fig. 19b). The upstream station on the Sacramento 

River Arm (SI5) showed similar seasonal trends but had consistently higher chl a concentrations 

due to greater nutrient availability. The McCloud River Arm (S8) was yet more productive than 

the Sacramento Arm (S7) or the main lake (S6). Chl a in the upper McCloud River Arm (SI4) 

was significantly greater than the lower arm only during August 1997 (Fig. 19c). The Pit River 

Arm (S9, S10, SI 2, SI 3) and Squaw Creek (SI 1) were the most productive sections of the 

reservoir in terms of chlorophyll production (Fig. 19d). The lowest secchi disk transparencies 

occurred at these stations due to greater algal productivity and suspended sediments in the water. 

Composite chl a concentrations ranged from about 0 ng/L to about 30 ng/L in the upper section 

(SI 3) of the Pit River Arm. Typical peaks were observed in spring, summer, and fall similar to 

other stations, although the amplitude of the peaks were significantly greater at these stations.

Vertical gradients of chl a were also apparent (Fig. 7). Highest chl a concentrations occurred 

below the top 5 m of water during summer months following development of the thermocline. 

Greatest algal biovolume was lower in the water column during the summer months as warmer 

surface temperatures, photoinhibition, and lack of nutrients may limit diatoms, the dominant 

species group in the reservoir. For example, in the Pit Arm (S9), the greatest percentage of 

bacillariophyta were collected from 10 to 30 m from May through October, while diatoms 

avoided the upper 10m of water. The 1% light level for minimum photosynthetic activity was at 

20 to 25 m in summer, while thermocline depth was 10-15 m. As such the majority of production 

was at or near the thermocline, extending into the upper metalimnion. This zone contained higher 

nutrients than surface waters yet still had adequate light for photosynthesis. This was reflected in 

the Pit River Arm (S9) and Pit-McCloud confluence (S10) during late summer when greater 

concentrations of chl a were found below 10m (Fig. 7).

Flooding in January 1997 had a pronounced effect on chlorophyll production in the reservoir. 

Flood waters entering the headwaters of the reservoir made the arms extremely turbid. Chl a 

concentrations were very low at upper arm stations and probably light limited. During this time, 

however, there was production in the main lake (S6) which was clearer. By February, mixing of 

the water column had introduced enough turbidity that even in the main lake algal productivity 

stalled. The waters began to clear in March, and in April there was a tremendous bloom in 

diatoms resulting from the high nutrient load from the floods.

B. Phvtoplankton:

A total of 134 phytoplankton species were collected from the main lake (S6) and Pit River Arm 

(S9) stations (Table 2). The algal community of Shasta Lake was dominated by diatoms, and 

occasionally by cryptomonads. The dominant diatom species were Melosira islandica and 

Melosira varians. Melosira sp. is one of the most ubiquitous of algal genera, and is widely 

distributed in all types of water bodies. Rhodomonas minuta var. nannoplanctica and 

Rhodomonas minuta were the primary cryptomonads. Cryptomonads (cryptophyta) were only

13
dominant from June through September 1995. Cryptophytes (Fig. 21b) were collected at all times 

but represented a significant proportion of the total phytoplankton only when diatom biovolume 

was low. Since 1995, diatoms (bacillariophyta) have remained the dominant group through 1997 

(Fig. 2la). Blue-green and green algae were never common in the main lake (S6). There were 

occasional blue-green blooms (Anabaena spp.), as during January 1996 (Fig. 20b), however, lowlevels of nutrients in Shasta Lake typically do not favor the dominance of blue-green 

assemblages.

Spring blooms peaked in March or April at the on-set of thermal stratification when nutrients 

were abundant and became available to phytoplankton (Figs. 20b-c). In May, as stratification 

intensified mixing ceased, and algal blooms crashed as nutrients were depleted from the 

epilimnion. Phytoplankton biovolume remained low from early to mid summer. In late summer 

biovolume increased and a fall algal bloom occurred. Biovolume increases during August or 

earlier may have been due to drawdown of the reservoir. As reservoir levels dropped wave action 

resuspended sediment and may have released nutrients. Fall blooms coincided with the 

breakdown of thermal stratification and circulation of nutrients from the metalimnion. Plankton 

populations began developing again in January or February. In the main lake (S6) the majority of 

diatom biovolume was concentrated in the top 10m of the water column during the spring bloom. 

Phytoplankton moved downward in the water column into the 10-20 m, and 20-30 m depth 

interval (Fig. 2 la) as the summer season progressed. Downward movement of phytoplankton may 

have been from settling and the preference of cooler water temperatures found deeper. 

Cryptophyta biovolume remained low throughout the year. Cryptomonads are known to adapt to 

low light levels (Wetzel 1975) and were collected in all 3 depth intervals (Fig. 21b).

Algal biovolume in the main lake (S6) increased significantly from 1995 to 1997 (Fig. 20a-c). In 

the main lake (S6), biovolume increased to 45,000 ^g/L during April 1997. This was an increase 

of almost 10 fold from the maximum algal peak in March 1996 (4700 ng/L). The increase may 

have been caused by influx of nutrients from winter floods. In January and February following 

flooding, algal production developed in the main lake. By February flood waters had circulated to 

the point that the entire reservoir was turbid and suppressed production. Secchi disk transparency 

decreased to less than 0.5 m. When the main lake began to clear, the secchi disk transparency 

increased to about 2 m and algal blooms reached a maximum in April. The reservoir became 

thermally stratified in May, algal blooms collapsed, and secchi disk transparency reached a 

maximum.

There was greater algal biovolume in the Pit River Arm (S9) than in the main lake (S6). During 

September 1995, algal biovolume was dominated byMelosira varians in the Pit River Arm (S9) 

and biovolume reached 12,000 ^g/L (Fig. 22a). In 1996, spring blooms peaked in April, one 

month later than in the main lake (Fig. 22b). Diatom biovolume reached 17,000 ng/L. The lowest 

biovolume occurred in June, then increased from July through October. In the spring of 1997 

maximum biovolume was 38,000 ng/L, but did not exceed the bloom (45,000 ^g/L biovolume) at 

S6 during the same period. Diatoms were concentrated in the upper 10m of the water column 

only during early spring (Fig. 23a) when light and temperature were limiting at greater depths.

14
The rest of the year, diatoms were collected from deeper in the water column below 10m, due to 

deeper light penetration, cooler water temperatures, and greater nutrient concentrations in the 

metalimnion. Cryptomonad biovolume was greater in the Pit River Arm than in the main lake 

station. Biovolume was evenly distributed throughout the water column (Fig. 23b) and occurred 

throughout the season, but cryptomonads were never dominant in the Pit River Arm (S9).

There was greater phytoplankton biovolume during 1997 compared to the two previous years 

(Fig. 22a-c). The bloom in April 1997 was significantly greater than blooms occurring in 1995 or 

1996. Zooplankton biomass significantly decreased during the same period indicating less 

cropping of phytoplankton, and therefore larger algal blooms. Phytoplankton biovolume increased 

in late summer to 30 |^g/L (0 to 5 m) from reintroduced nutrients from reservoir drawdown and 

again in the fall from reservoir turnover.

C. Zooplankton:

A total of 33 Zooplankton species were collected from all stations: 8 cladocera, 3 copepoda, and 

22 rotifera species (Table 3). The dominant cladocerans were Daphniapulex and Daphnia laevis 

which are herbivorous zooplankters. The dominant copepod species were the cyclopoids, 

Leptodiaptomus ashlandi and Limnocalanus macrurus. Cyclopoids for the most part are 

carnivorous. Numerous species of rotifers were present throughout the year (Table 3) but were 

not a significant proportion of total Zooplankton biomass. Greatest mean Zooplankton biomass 

occurred in the Sacramento River Arm (S7) and the least zooplankton biomass in the McCloud 

River Arm (S8) for the sampling period, 1995 to 1997 (Fig. 24). Cladocerans were the dominant 

zooplankton at the main lake station (S6) and Sacramento River Arm (S7). Cladoceran and 

copepod biovolume was equally distributed at other stations (Fig. 25).

In 1995, total zooplankton biomass reached about 1200 j^g/L in the Sacramento River Arm (S7) 

and Pit River Arm (S9). Zooplankton biomass was about 400 |^g/L in the McCloud River Arm 

(S8). Total zooplankton biomass at all stations decreased in 1996 (Fig. 25b). Zooplankton 

biomass in the Pit River Arm (S9) and Pit-McCloud Confluence (S10) decreased more than 50 

percent from the previous year. There was a further decrease in biomass in 1997 in the main lake 

(S6) and the Sacramento River Arm (S7). Total zooplankton biomass in the McCloud (S8), Pit 

(S9), Pit-McCloud Confluence (S10) did not significantly change in 1997. Overall, a significant 

reduction in zooplankton biomass has occurred at all stations since this study began in 1995. One 

possible explanation may be greater fish densities (i.e. threadfin shad) in the reservoir as compared 

to 1995 that are feeding on zooplankton. As a result of fewer zooplankton, phytoplankton 

biovolume has increased dramatically in the main lake (S6) and Pit (S9) since 1995, particularly 

during 1997 (Lieberman 1996).

Cladocerans were dominant in the main lake (S6) from spring through mid summer. The rest of 

the year copepods dominanted. Cladoceran and copepod springtime blooms sometimes occurred 

at the same time, although the copepod blooms were not as large as cladoceran blooms. 

Cladocerans composed as much as 85 percent of the total zooplankton biomass during the spring

15
bloom (Fig. 26 a). In 1995, we missed the spring bloom because we began sampling in June. 

Cladoceran biomass reached a maximum in June, followed by a copepod peak in August in the 

main lake (Fig. 26 b). In 1996, cladocerans and copepods bloomed simultaneously in April. In 

1997, copepods bloomed in April followed by a cladoceran bloom in May. Blooms usually 

coincided with algal peaks. Following spring algal blooms, nutrients were depleted, phytoplankton 

died off and cladocerans populations decreased. This was followed by copepod dominance. 

Cladocerans and copepods were collected down to 30 m, although the majority of the 

zooplankton were in the upper 20 m of the water column (Figs. 27 a,b). Net tows from surface to 

bottom during a field sampling trip were used to determine if we were missing zooplankton by 

only collecting to 30 m. Significant numbers of zooplankton below 30 m were not collected in the 

tows. Zooplankton often exhibit diel migration throughout the water column to escape fish 

predation or for energetic reasons. At Lake Powell, Utah-Arizona, Bureau of Reclamation and 

USGS scientists have observed daily migration of zooplankton down to depths of 30 m in the 

water column (M.Horn, personal observation). At Shasta Lake, during a hydroacoustic fishery 

survey in April 1997, we observed some movement of zooplankton with hydroacoustic 

equipment. Zooplankton were concentrated at about 20 to 30 m early in the evening but at about 

5 m after dark. The zooplankton may not be moving through the water column as freely as 

observed in some other reservoirs. In mid-summer zooplankton moved to below 10m when the 

thermocline began to decline in the water column (Fig. 27 a,b). Early in the season during 

cladoceran-copepod blooms the majority of plankton were collected from the top 10m down to 

30m.

Seasonal zooplankton trends in the Sacramento River Arm (S7) were similar to the main lake 

station (Fig. 28 a,b). In fact, the Sacramento River Arm (S7) was similar to the main lake in 

secchi depth transparencies, nutrient concentrations, and chl a concentrations. The main lake (S6) 

and the Sacramento River Arm (S7) were not as productive as the Pit River Arm (S9) in terms of 

chl a and algal production although there was greater zooplankton biomass. Specifically, 

cladoceran biomass was higher in the Sacramento River Arm (S7) and we speculate this may be 

due in part to lower fish abundance in this section of the reservoir. Hydroacoustic surveys of the 

lake were conducted and data will be helpful in answering these questions in regard to location 

and biomass offish. The majority of copepods (Fig. 29a) were collected in the upper 20 m of the 

water column. For example, during blooms in August 1995 and April 1996 the greatest biomass 

of copepods were collected from 10 to 20 m. Cladoceran (Fig. 29b) blooms during the same time 

were concentrated in the upper 20 m of the water column.

Similar seasonal trends were observed in the McCloud River Arm (S8), although at this station 

the cladoceran and copepod peaks usually did not coincide (Figs. 30 a,b). Competition for food 

may be a probable reason. Copepods generally dominated except during major cladoceran 

blooms. This was the only station where the cladoceran bloom (125 ug/L biomass) in May 1997 

was greater than in the two previous years. The zooplankton bloom was still lower than in the 

main lake (S6) and Sacramento River Arm (S7). It is significant to note that in 1997, cladocerans 

were dominant for a greater period of time (May to July) compared to previous years. A similar 

trend was observed in the Pit River Arm (S9) and Pit-McCloud confluence (S10). The distribution

16
of zooplankton throughout the water column is illustrated in Fig. 31 a,b.

Overfall, the Pit River Arm (S9) was the most productive. The Pit River Arm (S9) had the 

greatest concentration of chl a and algal biovolume, and lowest secchi depth transparencies. 

Total zooplankton biomass has decreased since 1995. Copepods dominated in both 1995 and 

1996. In 1997, from April through September, cladocerans dominated (Fig. 32a) and composed at 

least 50 percent of the total zooplankton biomass. This general trend towards cladoceran 

dominance was observed at all stations. The increase in percent composition of cladocerans was 

due to increase in biomass (Fig. 32b) and the general decrease in copepod biomass during the 

1997 spring and summer months. Zooplankton were collected deeper in the water column as the 

season progressed (Fig 33 a,b). The Pit-McCloud Confluence (S10) was most similar to the Pit 

River Arm (S9) in productivity. Cladocerans were dominant from March through September 

1997 (Fig. 34 a,b). Most zooplankton were concentrated in the upper 30m of water (Fig. 35 a,b).

There were twenty-two species of rotifers collected. The maximum biomass of rotifers was 

collected from the Pit River Arm (S9) (Fig. 36). In Shasta, rotifer biomass composed less than 0.5 

percent of the total zooplankton. The highest biomass (0.33 |ag/L) occurred at the Pit in August 

1995. Often times, rotifers are associated with more eutrophic conditions meaning the more 

productive a body of water, the greater the rotifer biomass (Lieberman, 1986). Most stations had 

less than 0.05 jag/L biomass of rotifers. Seasonal trends for rotifers showed spring and summer 

maxima followed by fall and winter minima. Similar trends were observed for cladocerans and 

copepods and may be why rotifers were not dominant in the reservoir. Rotifers cannot compete 

for food with larger zooplankton (Lieberman, 1986) but at the same time are not inhibited by 

larger algae and high bacterial densities that may exist in a reservoir during the summer months 

(Orcutt and Pace, 1984).

Significant decreases in zooplankton have occurred since 1995, particularly in the main lake (S6) 

and Sacramento River Arm (S7). Compounding factors that may have affected the zooplankton 

include the January 1997 floods, TCD operations that began in March, and grazing of 

zooplankters by possible increase in fish abundance. The floods of January and February 1997 

flushed the reservoir and zooplankton may have been flushed downstream. When the reservoir 

inflows entered on January 1, 1997 at greater than 200,000 cfs flushing rate of the reservoir 

decreased to approximately 8-10 days. Hayward and Van Den Avyle (1986) observed residence 

times of at least 50 to 250 days were needed to allow establishment of plankton populations that 

reflected the productive potential as well as effects of species interactions in the reservoir. Brook 

and Woodward (1956) found that the water exchange rate had to be greater than 18 days for 

significant development of zooplankton, and Johnson (1964) demonstrated that when the mean 

flushing rate was less than 15 days, the effect on development was not linear. Cowell (1967) 

found that high flushing rates of 8-10 days caused little in situ zooplankton production.

5. River Studies: Downstream Drift In Shasta and Keswick Tailwaters Below Shasta Lake: 

A. Temperatures:

17
Temperatures in the Sacramento river showed similar seasonal trends in both Shasta and Keswick 

tailwaters (Fig. 37). Water temperatures in Keswick tailwaters were slightly warmer. River 

temperature increased from April through October and decreased from October through March. 

The TCD began to operate on March 13, 1997 and upper and mid gates were opened in various 

combinations. In April, upper gates were open, and warmer water was released from the top layer 

of the reservoir, producing river temperatures higher than those recorded in April 1995 and 1996. 

In May, the mid gates were opened following reservoir stratification and temperatures dropped in 

the river because cooler metalimnetic water was being released. In June, upper and mid gates 

were used in combination and temperatures increased over what was recorded for the two 

previous years. Opening and closing the top and middle gates changed downstream water 

temperatures significantly. In general, there may be warmer temperatures in Shasta and Keswick 

tailwaters with the TCD operating during winter and spring than in previous years. Cooler 

temperatures will occur in the river during the late summer and early fall due to release of 

hypolimnetic waters. This shift may mean species changes in macroinvertebrate and plankton 

downstream.

B. Particulate Organic Matter (POM):

POM supports the base of the food web in many aquatic systems and is one of many factors 

determining the nature of biotic communities in a riverine ecosystem. Composition of POM is 

diverse and includes living and dead, whole and fragmented plant and animal material. POM 

provides the trophic connection between microbial assemblages and macroconsumers. It is the 

particulate fraction that is directly available to filter feeders whereas the dissolved fraction is not. 

The dissolved fraction usually is present in greater concentrations but not useable as food by 

freshwater filter-feeding zooplankton. If these compounds were made available by becoming 

particulate they could represent an important source of carbon in suspension. Detrital material is 

an important part of the food web and provides energy for bacterial and aquatic fauna and is 

commonly found to be the major proportion of stomach contents of many fish species, particularly 

salmonids. Microbial maceration and animal consumption can convert relatively large sized POM 

to finer sizes which dominate the organic matter pools. Usually the plankton only composes a 

small fraction of the POM except during the spring when plankton productivity is high in the 

reservoir. When limnoplankton is discharged from the reservoir it becomes an important part of 

the POM in the river.

The <25 um POM composed the greatest proportion of total POM (Fig. 38 a,b) and contributed 

about 90% to the total POM in Shasta and Keswick tailwaters. <25 um POM levels were higher 

in Keswick tailwater than at Shasta (Fig. 39a). The >25 um and the >505 um size fraction 

contributed the remainder. Detrital and small plankton fragments composed the majority of the 

<25 um size fraction. The <25 um size fraction has been broken down from the coarse POM and 

contributes greatly to the food base. Numerous investigators have reported that this smallest size 

fraction dominates in streams both natural and manmade (Maciolek, 1966; Fisher and Likens, 

1973; Naiman and Sedell, 1979; Webster et al., 1979; Vannote 1980; Lieberman and Burke, 

1993). <25 um POM was greatest in Shasta tailwaters during the spring (March 1996 and April

18
1997) which coincided with algal blooms in the reservoir. The <25 jam size fraction also increased 

during the winter floods of February 1997. The <25 jam size fraction reached 1.5 g/m3 in Shasta 

tailwaters and 2.0 g/m3 in Keswick tailwaters.

Maximum POM concentrations are often associated with storm events such as flash floods (Fisher 

and Minckley, 1978) when stream bank erosion and sediments can contribute detrital material 

(Bilby and Likens, 1979). Detrital material associated with flooding at Shasta included large 

amounts of logs and woody debris washed from upstream into the reservoir. There was no 

correlation between discharge and <25um POM. POM tended to fluctuate from month to month 

with greater concentrations occurring during spring time and flood events.

The <25 jam PIM (particulate inorganic matter) (Fig. 40a) also fluctuated significantly during the 

start of the rainy season, flood events, and rising water levels which increased channel sediment 

resuspension and decreased the proportion of particulate organic matter in suspended material. 

The majority of inorganic drift was in the <25 um size fraction and the majority of the <25 jam 

size fraction was inorganic material (Fig. 40a). In February 1997, PIM increased to 12 g/m3 in 

Shasta tailwaters and to 16 g/m3 in Keswick tailwaters (Fig. 4la). During this period turbidity 

levels in the reservoir increased dramatically and much of the resuspended sediment was flushed 

downstream contributing to muddy river waters. PIM concentrations in Keswick tailwaters were 

higher than in Shasta tailwaters.

The >25 jam POM was composed of larger plankton and detrital material. This size fraction 

contributed the smallest proportion of POM to the total. The Keswick station was a good 

example of how downstream POM in the >25 jam size fraction fluctuated independently of Shasta 

tailwaters (Fig. 39b). During February 1996 >25 jam POM increased to a maximum of 0.08 g/m3 

at Keswick whereas POM upstream did not increase. Tributaries entering the Sacramento River 

above Keswick Dam added detrital material, producing spikes in Keswick tailwaters that did not 

appear at Shasta. The >25 jam PIM in Shasta and Keswick tailwaters peaked in March 1997 (Fig. 

40b. 41b), one month later than the <25 jam PIM (Fig. 40a). By March, the reservoir began to 

clear and turbidity levels decreased considerably. The >25 jam size fraction contributed very little 

to the total PIM in Shasta tailwaters because the reservoir tended to act as a sediment trap except 

during flood events (Fig 40b). Downstream the inorganic matter increased in Keswick tailwaters 

(Fig. 41b) from suspended sediment brought in from the river bank.

The >505 jam size fraction made up a greater proportion of the total POM than the 25 jam to 

505 jam size fraction. It was composed of green algae (Cladophora strands) and larger 

zooplankton. The <25 jam and the >25 jam size fractions were almost always greater downstream 

in Keswick than in Shasta tailwaters whereas the >505 jam size fraction (Fig. 39b) showed 

greater concentrations upstream in Shasta tailwaters. Since March 1996, the >505 jam POM has 

been greater in Shasta tailwaters. Increases in 1996 were possibly due to more cladophora 

collected in the 505 jam nets from surrounding cladophora beds and not due to increased 

zooplankton biomass. Increases in >505 urn POM during 1997 were due to increases in 

zooplankton biomass caused by operation of the TCD. The peak in April 1997 was due to

19
increased copepod biomass and the June, 1997 peak to increased cladoceran biomass. Upper 

gates were opened April 1997 during the copepod bloom and again in June when cladocerans 

were dominant.

Many investigators have found that both living and non-living plankton released from reservoirs 

provide support to large populations of filter feeding macroinvertebrates downstream. POM 

significantly decreased 14 km downstream in Keswick tailwaters due to settling out of plankton. 

Travel time between Shasta and Keswick was a matter of hours depending on flows. 

Limnoplankton decreased over this stretch and smaller size fraction detrital material increased. 

The total >505 ^m size fraction (Figs. 40c, 41c) in Shasta and Keswick tailwaters was dominated 

by the organic portion. PIM did not increase during the flood event of 1997 as observed with the 

two smaller size fractions. The majority of silt and sediment coming out of Shasta was in the <25 

\im size fraction. Larger size fraction sediments settle out quickly because of hydrdynamic 

changes at the head of the reservoir and are not transported through the reservoir. Increases in 

PEVI in Keswick tailwaters during February 1996 was due to increased sediment flow from above 

Keswick dam and not an influence from Shasta lake since there was not an increase observed at 

Shasta tailwaters during this time. Depending on the timing and location of reservoir releases, 

paniculate content of outflows may vary considerably. However, if released waters are rich in 

particulate matter, macroinvertebrate populations of Trichoptera, Ephemeroptera, and Diptera 

may be substantially enhanced.

Overall, total POM in Keswick tailwaters was higher than in Shasta tailwaters (Fig. 42) for the 

sampling period from 1995 to 1997. Ward (1975) found POM concentrations increased with 

distance downstream from Cheesman Lake on the South Platte River, Colorado. Total POM 

averaged 0.8 g/m3 and 0.9 g/m3 in Shasta and Keswick tailwaters, respectively. This was 

comparable to results found by other investigators in other 6th and 7th order streams in the western 

USA (Webster et al. 1979). Lieberman and Burke (1993) reported that the mean total POM 

concentration was 0.80 g/m3 below Davis Dam on the lower Colorado River. Birge and Juday 

(1934) reported mean POM concentrations for 57 northern Wisconsin natural lakes as 0.83 g/m3 .

C. Zooplankton:

Zooplankton composed a portion of the total particulate organic matter. Zooplankton identified 

were in the >25 ^m and >505 ^m size fractions. Zooplankton breaks down into detrital material 

in the river and may contribute to the <25 ^m POM. There was a significant increase in 

zooplankton biomass in 1997 compared to the previous years in Shasta and Keswick tailwaters 

(Figs. 43a, 44a). Copepods, cladocerans, and rotifers showed increases. Rotifers were found for 

the first time as significant biomass in Shasta tailwaters (Fig. 43a). There was a change in the 

percent composition of major zooplankton groups from 1995 and 1996, to 1997 (Figs. 43b and 

44b). Cladocerans composed less and copepods made up more of the total zooplankton biomass.

Changes in zooplankton drift were attributed to operation of the TCD in early spring. Releases of 

epilimnetic water during the most productive time of year resulted in entrainment of zooplankton

20
and a downstream increase in biomass. Hypolimnetic withdrawals in previous years introduced 

little zooplankton biomass to Shasta tailwaters due to deeper level releases. Upper bypass intakes 

did discharge water from an upper depth of about 20 m, but upper most surface waters were not 

withdrawn. In 1995 and 1996 there were greater spring zooplankton blooms in the main lake (S6) 

compared to 1997 but this was not reflected in downstream drift (Fig. 45 a) because withdrawals 

occurred below the depth of greatest zooplankton production. Zooplankton biomass blooms in 

the main lake (S6) significantly decreased in spring 1997 whereas the zooplankton drift in the 

river significantly increased. This was a direct result of TCD operation. The upper most strata of 

water was discharged downstream through the TCD when the reservoir was at full pool.

There was a increase in zooplankton biomass in Shasta tailwaters during April 1997 as the top 

gates of the TCD were open. Copepods increased to 18 ug/L, dominated by the adult cyclopoid 

Leptodiaptomus ashlandi, immature cyclopoids, and copepodids. Cladocerans increased and were 

dominated by Daphniapulex. Rotifers significantly increased in April. In May, a combination of 

mid and top gates were used and the zooplankton biomass for all three groups decreased. During 

June, top gates were opened once again and cladocerans increased in the tailwater drift. Copepod 

biomass in Shasta tailwaters was greater for July and August than in the two previous years.

Increase drift of zooplankton biomass affects POM composition. Release of limnoplankton from 

the reservoir may shift the composition of POM from detrital to limnoplankton based during the 

most productive times of the year. During the summer of 1997 the top and middle gates of the 

TCD were open until August. With operation of the TCD, organic matter was being expelled 

from the reservoir as drift. Epilimnetic releases favored living and dead limnoplankton as observed 

in 1997 whereas hypolimnetic releases contributed nutrients to downstream communities. Dance 

(1981) listed the presence of lakes/impoundments as an important factor controlling the 

concentration of POM being transported through a river system. A number of investigators have 

reported reservoirs trap POM coming into them, thereby modifying and disrupting the natural 

downstream drift (Maciolek, 1966; Armitage 1977; Goldman and Kimmel, 1978), although 

Lieberman and Burke (1993) did not find this to be true of the Lower Colorado River reservoirs.

There was a decrease in zooplankton biomass from upstream in Shasta tailwaters to downstream 

in Keswick tailwaters (Fig. 45b) and has been observed in other studies (Lieberman and Burke, 

1993; Soballe and Bachmann, 1984). The change from a lentic environment in the reservoir to a 

lotic environment in the river does not favor reservoir produced plankton. Travel time from 

Shasta to Keswick was short, a matter of hours, as compared to the residence time in the 

reservoir of over one year. Even though limnoplankton decreased from upstream to downstream 

the detrital content increased as material was broken down. Total POM concentration in Keswick 

tailwaters was greater than in Shasta tailwaters, but zooplankton biomass was lower. Grazing, 

sedimentation, and mechanical destruction, as well as filtering, may have effected the decrease in 

numbers.

Lentic zooplankton were affected most severely by the change to lotic conditions, and rapidly 

decreased in numbers downstream. Ward (1975) found that copepods dominated the zooplankton

21
in the South Platte River below Cheesman Lake, Colorado but within 5 km of the dam the rotifers 

were the most abundant organisms. Importantly, Ward (1975) demonstrated that the persistence 

of zooplankton, downstream from a lentic source, was primarily related to their size and form (in 

terms of their exoskeletal components). The larger organisms, having a smaller surface: volume 

ratio, sink more rapidly, become entangled more easily, and be more vulnerable to mechanical 

destruction and fragmentation, than the smaller ones.

D. Phvtoplankton and Chlorophyll:

Three size fractions of phytoplankton corresponding to POM size fractions were identified and 

enumerated. The <25 fim size fraction composed the greatest phytoplankton biovolume in Shasta 

and Keswick tailwaters (Figs. 46 a,b). As with zooplankton biomass, phytoplankton biomass 

increased significantly in 1997 following operation of the TCD. In April 1997 there was a large 

diatom bloom in the main lake (S6) and this was reflected in a 10-fold biovolume increase in the 

tailwaters of both stations. The top gates of the TCD were open in April allowing for surface 

releases from the reservoir. Most of the phytoplankton in the reservoir were concentrated in the 

upper 20 m of the water column. Chl a in the river was generally greater downstream in Keswick 

than in Shasta tailwaters (Fig. 47). Chl a ranged from about 1.1 jig/L to 2.7 jig/L but was often 

below 1.0 |ig/L. Chl a at Shasta tailwaters exceeded chlorophyll concentration at Keswick during 

February 1997.

Phytoplankton biovolume was higher in Shasta tailwaters than in Keswick tailwaters. 

Phytoplankton released from Shasta Lake during algal blooms (i.e. April 1997) appeared to fall 

out of the drift quickly and did not always reach Keswick tailwaters in the form of algal material. 

Reservoirs provided an important source of phytoplankton for downstream reaches, although the 

lentic species may be selectively eliminated by filtering, sedimentation, and destruction during 

transport by the river. Hynes (1970) found that diatoms and blue-green algae survived 

downstream transport better than green algae and desmids , although in the Sacramento River 

drift that did not always appear to be true.

Composition of the <25 |um biovolume in Shasta tailwaters was 90 percent bacillariophyta 

(diatoms) (Fig. 48a). The dominant diatom collected in the tailwaters wasMelosira varians. At 

Keswick tailwaters composition was 90 percent diatoms, 5 percent green algae, 2 percent bluegreens, and 3 percent other algae. At Keswick other algal species were introduced into the river 

upstream from the dam from allochthonous sources other than Shasta Lake. The >25 jim 

biovolume was 87 percent diatoms in Shasta and 96 percent diatoms in Keswick tailwaters (Fig. 

48b). The >505 |um size fraction was composed of about 70 percent diatoms and 27 percent green 

algae in Shasta and 95 percent diatoms and 3 percent green algae in Keswick (Fig. 48 c). The >25 

|um and >505 |um size fractions were represented by fewer diatoms in Shasta tailwaters while the 

opposite was true of Keswick. This was a good example of how the drift composition in Shasta 

and Keswick tailwaters were somewhat different.

Mean phytoplankton biovolume increased significantly in the drift during 1997 after TCD

22
operations began. As observed with zooplankton drift, the two factors that contributed to greatest 

biovolume increases downstream were surface withdrawal and withdrawal during peak 

production from the reservoir. In support of this statement are past data that show little 

downstream drift when withdrawals were made through bypasses, below 20 m in the water 

column.

IV. Post TCD Results:

As of this report the TCD has been in operation for one season. The following represent some 

preliminary observations of potential changes that have occurred. Physical limnology of the 

reservoir shows several significant changes to patterns of water movement through the reservoir. 

Approximately 20 km upstream in the river arms were affected by TCD operations (Hanna et al. 

1998). It is difficult to determine if onset of stratification was delayed by TCD operations simply 

due to annual variability in the onset of stratification. Once stratified, however, thermal gradients 

were much sharper. This was a direct result of how the TCD withdrew mid-level water. 

Dissolved oxygen minima were more intense upstream, and there was a delay in the timing of the 

minima moving downstream until low level releases were used in late summer, moving this body 

of water downstream.

In spring and summer operations of the TCD caused the reservoir hypolimnion to act as a nutrient 

sink. Previously, hypolimnetic waters had been discharged throughout the season and nutrient 

levels did not build to the level observed this last year. With surface releases there may be 

additional accumulation of nutrients available during fall turn-over from hypolimnetic waters for 

algal production. Fewer nutrients were transported downstream during the spring and early 

summer when surface waters are released with TCD operations. More nutrients left the reservoir 

later in the season, late summer and fall, when bottom gates were opened and hypolimnetic 

(coolest waters) released downstream. Some questions that remain to be answered are; 1. Will 

there be residual (carryover) effects from the previous year and an accumulation of nutrients in 

the reservoir because of epilimnetic releases? 2. Will shifts in timing of nutrient releases affect 

downstream biota? All of these questions come to mind when thinking about how the TCD may 

affect and change the nutrient budget of the reservoir and at the same time may cause increased 

algal production in the reservoir, if in fact, additional nutrients become available in the upper 

strata of the water column. Paulson (1981) showed that epilimnetic rather than hypolimnetic 

releases of water from Hoover Dam would enhance productivity of the reservoir by reducing 

NO3 -N losses from the reservoir. At Shasta, selective withdrawal allowed for a combination of 

releases to occur during the spring-summer months.

During this first season of TCD operation there were larger algal blooms in the main lake during 

the period of surface withdrawals than previously observed. Downstream, diatoms increased 

dramatically in tailwaters due to surface water releases during the most productive time of year, 

and from the depth of greatest algal production. Generation time of algae is extremely short (a 

few days), and even after a flood as observed in the data, algae recovered rapidly. If flushing rate 

does not exceed mean doubling time of phytoplankton, increased inflow may enhance

23
phytoplankton productivity by increasing nutrient availability (Carmack et al. 1979).

We observed significant decreases in the zooplankton biomass in the reservoir and at the same 

time zooplankton drift has significantly increased in downstream tailwaters. During March 1997 

the upper gates of the TCD were open before the zooplankton bloomed. In April, at the main lake 

station (S6) copepods were at maximum biomass when the top gates were open, obviously 

effecting the upper strata of the water column where zooplankton were most abundant (as 

discussed above). We hypothesized that POM would increase in the Sacramento river with 

operation of the TCD and discharge of upper strata of water during spring months. In the 

downstream drift there were significant increases in copepods. In May, both the top and middle 

gates were open during the same time when cladocerans were at a maximum and zooplankton 

decreased in the river, but then in June only the top gates were open once again and zooplankton 

increased in the river. We have observed an increase in the zooplankton from our plankton 

collections in the river immediately after the TCD began operation this past spring. The increase 

in zooplankton in the drift was directly related to depth of withdrawal and time or season of 

withdrawal. Zooplankton were most concentrated in the upper 30 m of water and most 

productive during the spring months.

The decrease of zooplankton in the reservoir at all stations may be linked to upper strata of water 

being released during the most productive time of year. Lower zooplankton biomass means a loss 

of food for fish. Zooplankton entrainment and cropping of zooplankton may be occurring 

simultaneously. It is difficult, however, to show whether reservoir fish have increased since 1995 

because of the lack of data from Shasta Lake. After the reservoir stratified, the algal production 

decreased because of nutrient depletion and the zooplankton biomass naturally decreased during 

mid summer due to food limitation. At Hungry Horse reservoir, Montana (Brian Marotz, pers. 

comm, 1998) downstream loss of zooplankton through the dam was predicted to increase as 

warm epilimnetic waters were released. An engineering modification to the structure has allowed 

simultaneous release of water from two elevations to reduce zooplankton entrainment because it 

was deemed detrimental to the reservoir fishery.

V. Management Implications:

Studying the TCD on Shasta will provide other investigators with valuable information on 

selective withdrawal and how operations may effect the physical, chemical, and biological aspects 

of a reservoir. Currently, selective withdrawal systems are functioning on Hungry Horse Dam, 

Montana; Libby Dam, Montana; Cachuma Dam, California; Casitas Dam, California; Folsom 

Dam, California; and Flaming Gorge Dam, Utah. There has been considerable research on the 

physical aspects of these systems. In the future, a TCD is being planned for one of the largest 

reservoirs in the country, Lake Powell in Utah (Glen Canyon Dam). Additional research is needed 

on the biological effects from TCD operations in these reservoirs and downstream. At Hungry 

Horse Dam researchers are examining zooplankton entrainment from the selective withdrawal 

structure on Hungry Horse Dam. On Hungry Horse there were shutter gates that were added to 

the original design to reduce zooplankton entrainment while still meeting the target discharge

24
temperature (Brian Marotz, pers. comm.). On Lake Powell one of the primary concerns is 

whether TCD operations would alter the thermal structure of the reservoir. Thread-fin shad are 

the primary forage fish in Lake Powell. Currently winter minimum temperatures in the reservoir 

approach the thermal minimum for shad. If the TCD results in lower water temperatures, shad 

will likely die-off and the recreational fishery will be substantially reduced.

Our results on Shasta Lake and tailwaters have shown some effects from operating the TCD on 

Shasta Lake that include: 1) Cooler water tailwater temperatures during the summer months; 2) 

Significant algal blooms in April 1997 over the two previous years; 3) Significant decrease in 

spring zooplankton blooms; 4) Increase in algal biovolume in Shasta and Keswick tailwaters; 5) 

Significant increase in zooplankton biomass in Shasta and Keswick tailwaters; 6) Change in 

composition and increase in particulate organic matter in Shasta and Keswick tailwaters; 7) Shift 

in water movement patterns through the reservoir.

The goal of this project and in our continued investigation of the limnological aspects of Shasta 

was to identify potential water quality or biological problems that might arise within Shasta Lake 

due to TCD operations; identify changes in downstream drift and nutrient release that may 

potentially influence fish production and; allow for optimal use of the TCD to achieve specified 

downstream temperature requirements for chinook salmon. Though the primary use of the TCD 

was to provide benefit for one particular endangered species, its effects could negatively impact 

other species such as recreational fishes or endangered species that might use the reservoir. A 

good limnological understanding of the reservoir will allow proper operations that minimize 

impacts to all species of interest.

VII. Acknowledgments:

This study was funded through U.S. Geological Survey and U.S. Bureau of Reclamation. We are 

grateful to Clair Stalnaker, USGS, Midcontinent Environmental Science Center, for all of his 

meticulous assistance in keeping this project on track. We thank Craig Sarsfield, BOR, Northern 

California Area Office for technical support and sound advice on the temperature control device. 

Thanks to Shawn Dufify for phytoplankton data entry and Janet Martin for providing help 

collecting data on Shasta reservoir.

VI. Literature Cited:

Armitage, P.D. 1977. Invertebrate drift in the regulated river Tees, and an unregulated tributary 

Maize Beck, below Cow Green dam. Freshwater Biol. 7:167-183.

Bilby, R.E. and G.E. Likens. 1979. Effects of hydrologic fluctuations on the transport of fine 

particulate organic carbon in a small stream. Limnol. Oceanogr. 24:69-75.

Birge, E.A. and C. Juday. 1934. Particulate and dissolved organic matter in inland lakes. Ecol. 

Monogr. 4:440-474.

25
Brook, A.J. and W.B. Woodward. 1956. Some observations on the effects of water inflow and 

outflow on the plankton of small lakes. Journal of Animal Ecology. 25: 22-35.

Carmack, B.C., C.B. Gray, C.H. Pharo, and RJ. Daley. 1979. Importance of lake-river interaction 

on seasonal patterns in the general circulation of Kamloops Lake, British Columbia. Limnol. 

Oceanogr. 24:634-644.

Cowell, B.C. 1967. The copepoda and cladocera of a Missouri river reservoir: a comparison of 

sampling in the reservoir and the discharge. Limnology and Oceanography. 12:125-136.

Dance, K.W. 1981. 'Seasonal aspects of transport of organic and inorganic matter in streams' in 

Lock, M. and D. Williams (Ed.). Perspectives in Running Water Ecology. Plenum Press, New 

York. pp.69-96.

Fisher, S.G. and Likens, G.E. 1973. Energy flow in Bear Brook, New Hampshire, an integrative 

approach to stream ecosystem metabolism. Ecol. Monogr. 43:421-439.

Fisher, S.G. and W.L. Minckley. 1978. Chemical characteristics of a desert stream flash flood. J. 

Arid Environ. 1:25-33.

Goldman, C.R. and Kimmel, B.L. 1978. 'Biological processes associated with suspended 

sediment and detritus in lakes and reservoirs'in Cairns, J., Jr., E.F. Benfield, and R. Webster 

(Ed.). Current Perspectives on River-Reservoir Ecosystems. North American Benthological 

Society, Springfield, Illinois, pp. 19-44.

Hanna, B., J. Bartholow, L. Saito, and J. Sandelin. 1998. Results of mock Shasta TCD operations 

on in-reservoir and discharge water temperatures using CE-QUAL-W2. U.S. Geological Survey.

USGS/MESC/3302.

Hayward , R.S. and M.J. Van Den Avyle. 1986. The nature of zooplankton spatial heterogeneity 

in a nonriverine impoundment. Hydrobiologia. 131: 261 -271.

Hynes, H.B.N. 1970. The ecology of running waters. University of Toronto Press, Toronto.

Johnson, W.E. 1964. Quantitative aspects of the pelagic, entomostracan zooplankton of a 

multibasin lake system over a 6-year period. Verhandlungen der Internationalen Vereingung fuer 

Theoretische und Angewandte Limnologie. 15:1119-1125.

Kimmel, B.L., D.M. Soballe, S.M. Adams, A.V. Palumbo, C.J. Ford, and M.C. Bevelhimer. 1988. 

Inter-reservoir interactions: Effects of a new reservoir on organic matter production and 

processing in a multiple-impoundment series. Verh. Internat. Verein. Limnol. 23: 985-994.

Lieberman, D.M. 1996. Use of silver carp (Hypophthalmichthys molotrix) and bighead carp

26
(Aristichthys nobilis) for algae control in a small pond: changes in water quality. Journal of 

Freshwater Ecology. ll(4):391-397.

Lieberman, D.M. 1986. Variation in the crustacean and rotifer plankton of riverine and 

nonriverine lower Lake Havasu, Arizona. M.S. thesis.

Lieberman, D.M. and T.A. Burke. 1993. Particulate organic matter transport in the lower 

Colorado River, South-Western USA. Regulated Rivers: Research and Management. 8:323-334.

Likens, G.E. 1975. Primary productivity of inland aquatic ecosystems. In: Lieth, H. and R.H. 

Whittaker (ed.). Primary Productivity of the Biosphere. Springer-Verlag, New York. pp. 185-

202.

Maciolek, J.A. 1966. Abundance and character of microseston in a California mountain stream. 

Verh. Int. Ver. Limnol. 16:639-645.

Naiman, R.J. and Sedell, J.R. 1979. Characterization of particulate organic matter transported by 

some cascade mountain streams. J. Fish. Res. Board Can. 36:17-31.

Orcutt, J.D. Jr. and M.L. Pace. 1984. Seasonal dynamics of rotifer and crustacean zooplankton 

populations in a eutrophic, monomictic lake with a note on rotifer sampling techniques. 

Hydrobiologia. 119:73-80.

Paulson, L.J. 1981. Nutrient management with hydroelectric dams on the Colorado River system. 

Lake Mead Limnol. Res. Cen. Tech. Rept. 8. Univ. Nevada, Las Vegas, NV. 39pp.

Soballe, D.M. and R.W. Bachmann. 1984. Influence of reservoir transit on riverine algae 

transport and abundance. Can. J. Fish. Aquat. Sci. 37:130-137.

Strickland , J.D.H. and T.R. Parsons. 1968. A Practical Handbook of Seawater Analysis. 

Fish.Res. Board of Canada, Ottawa, Canada.

Vannote, R.L., Minshall, G.W., Cummins, K.W., Sedell, J.R. and Gushing, C.E. 1980. The river 

continuum concept. Can. J. Fish. Aquat. Sci. 37L130-137.

Ward, J.V. 1975. Downstream fate of zooplankton from a hypolimnial release mountain reservoir. 

Verh. Int. Ver. Limnil. 19:1798-1804.

Webster, J.R., Benfield, E.F., and Cairns, J., Jr. 1979. 'Model predictions of effects of 

impoundments on particulate organic matter transport in a river system' in Ward, J.V. and 

Stanford, J.A. (Eds). The Ecology of Regulated Streams. Plenum Press, New York. pp. 339-364.

Wetzel, R.G. 1983. Limnology. W.B.Saunders Co. New York.

27
Table 1. UTM coordinates of sampling stations in Shasta Lake.

Station Description UTM Coordinates

S6

S7

S8

S9

S10

Sll

S12

S13

S14

S15

S16

Main Lake

Sacramento

McCloud

Pit

Pit-McCloud

Squaw Creek

Upper Pit

Upper Upper Pit

Upper McCloud

Upper Sacramento

Forebay

05503 16E

0552009E

0559229E

0562344E

0557367E

0568062E

0568825E

0574026E

0564616E

0551101E

0549686E

4510493N

4518078N

4515403N

4512933N

4512563N

4515311N

4510733N

4513335N

4525048N

4523261N

4508330N

28
Table 2. Phytoplankton species collected from stations S6, S7, S8, S9, and SIO.

Phytoplankton Species Division

Achnanthes spp 

Amphora ovalis 

Amphora spp 

Asterionella formosa 

Asterionella spp 

Caloneis limosa 

Cocconeis placenta 

Cocconeis placentula 

Cocconeis spp 

Cy dote I la bodanica 

Cyclotella meneghiniona 

Cyclotella operculata 

Cyclotella spp 

Cyclotella stelligera 

Cymatopleura elliptica 

Cymatopleura solea 

Cymatopleura spp. 

Cymbella lanceolata 

Cymbella minuta 

Cymbella spp 

Cymbella tumida 

Diatoma spp. 

Diatomella spp 

Diploneis smithii 

Epithemia spp. 

Eunotia pectinalis 

Eunotia spp 

Fragilaria construens 

Fragilaria crotonensis 

Fragilaria spp 

Gomphonema constrictum 

Gomphonema olivaceum 

Gomphonema spp 

Gyrosigma spp. 

Melosira granulata 

Melosira islandica

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta

29
Melosira italica 

Melosira spp 

Melosira varians 

Meridian circulare 

Navicula cryptocephala 

Navicula radiosa 

Navicula spp 

Nitzschia acicularis 

Nitzschia denticula 

Nitzschia linearis 

Nitzschia sigmoidea 

Nitzschia spp 

Opephora spp 

Pinnularia obscura 

Pinnularia spp. 

Pleurosigma delicatulum 

Rhoicosphenia spp 

Rhopalodia gibba 

Rhopalodia gibber a 

Rhopalodia gibberula 

Stephanodiscus hantzschii 

Stephanodiscus spp 

Surirella angustata 

Surirella ovalis 

Surirella ovata 

Surirella robusta 

Surirella spp 

Synedra delicatissima

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta 

Bacillariophyta

Synedra delicatissima var. angustissima Bacillariophyta

Synedra pulchella 

Synedra spp 

Synedra ulna 

Tabellaria fenestrata 

Tabellaria floccu losa 

Tabellaria spp 

Unidentified centric diatom 

Unidentified pennate diatom 

Ankistrodesmus spp. 

Chlamydomonas spp. 

Cladophora spp. 

Closterium acerosum 

Closterium spp 

Coelastrum microporum

Bacillariophyta

Bacillariophyta

Bacillariophyta

Bacillariophyta

Bacillariophyta

Bacillariophyta

Bacillariophyta

Bacillariophyta

Chlorophyta

Chlorophyta

Chlorophyta

Chlorophyta

Chlorophyta

Chlorophyta

30
Dictyosphaerium pulchellum Chlorophyta

Geminella mutabilis Chlorophyta

Kirchneriella spp. Chlorophyta

Mougeotia parvula Chlorophyta

Mougeotia spp. Chlorophyta

Oocystis pusilla Chlorophyta

Oocystis spp Chlorophyta

Palmodictyon spp. Chlorophyta

Pandorina spp Chlorophyta

Pediastrum duplex Chlorophyta

Quadrigula lacustris Chlorophyta

Rhizoclonium hieroglyphicum Chlorophyta

Rhizoclonium spp Chlorophyta

Scenedesmus bernardii Chlorophyta

Scenedesmus bijuga Chlorophyta 

Scenedesmus quadricauda var. Chlorophyta 

longispina

Scenedesmus spp Chlorophyta

Schizomeris spp. Chlorophyta

Sorastrum spinulosum Chlorophyta

Sphaerocystis schroeteri Chlorophyta

Spirogyra parvula Qilorophyta

Spirogyra spp. Chlorophyta

Staurastrum longiradiatum Chlorophyta

Staurastrum paradoxum Chlorophyta

Stigeoclonium lubricum Chlorophyta

Stigeoclonium polymorphum Chlorophyta

Stigeoclonium spp Chlorophyta

Strombidium oculatum Chlorophyta

Ulothrix lubricum Chlorophyta

Ulothrix spp Chlorophyta

Unidentified coccoid green Chlorophyta

Unidentified filament Chlorophyta

Dinobryon spp Chrysophyta

Mallomonas pseudocoronata Chrysophyta

Cryptomonas spp Cryptophyta

Rhodomonas minuta Cryptophyta 

Rhodomonas minuta var nannoplancticaCryptophyta

Anabaena spp. Cyanophyta

Chroococcus spp Cyanophyta

Microcystis aeruginosa Cyanophyta

Oscillatoria spp. Cyanophyta

Stigonema spp Cyanophyta

31
Unidentified blue-green filament Cyanophyta

Euglena gracilis Euglenophyta

Euglena spp. Euglenophyta

Phacus spp. Euglenophyta

Trachelomonas spp Euglenophyta

Ceratium hirundella Pyrrophyta

Ceratium hirundinella Pyrrophyta

Glenodinium spp. Pyrrophyta

Gymnodinium spp. Pyrrophyta

Peridinium inconspicuum Pyrrophyta

Peridinium spp. Pyrrophyta

Peridinium willei Pyrrophyta

Rhodochorton spp. Rhodophyta

32
Table 3. Zooplankton species collected from stations S6, S7, S8, S9, and SIO.

Zooplankton Species Group

Biapertura affinis 

Bosmina lonirostris 

Ceriodaphnia spp. 

Chydorus sphaericus 

Daphnia laevis 

Daphnia pulex 

Diaphanasoma brachyurum 

Leptodora kindtii 

Diacyclops thomasi 

Leptodiaptomus ashlandi 

Limnocalanus macrurus 

Asplanchna girodi 

Brachionus havanaensis 

Brachionus angularis 

Colurella spp. 

Conochilodies dossarius 

Euchlanis dialata 

Filinia longiseta 

Gastropus hypotus 

Gastropus stylifer 

Hexarthra mira 

Kellicottia longispina 

Keratella cochlearis 

Keratella quadrata 

Lecane spp. 

Platyias quadricornia 

Polyarthra vulgaris 

Pompholyx sulcata 

Trichocerca spp. 

Synchaeta pectinata

Cladocera

Cladocera

Cladocera

Cladocera

Cladocera

Cladocera

Cladocera

Cladocera

Copepoda

Copepoda

Copepoda

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

Rotifera

33
Water Surface Elevation (Feet above MSL) Reservoir Inflow (CFS) Reservoir Re

U)

CO

en

CO

en

CO 

O)

CO 

O)

CO

^J 

CO

CO 

CO

CD CO

O> 00

o o

o 

o 

o

o o o

-t*. CD CO

o o o

p 'o

en 

b

0> CD

en

en

CD

en

N>

b

CD 

+

en

N>

en

CD 

+

en

N> 

o 

o 

o 

o
Figure 2. Map of limnological sampling stations in Shasta Lake. Main lake (S6), Sacramento

River Arm (S7, SI5), McCloud River Arm (S8 and SI4), Pit River Arm (S9, SI2, SI3), 

Squaw Creek Arm (SI 1), and Pit-McCloud Confluence (S10). River stations are located 

in Shasta tailwaters (SO) and Keswick tailwaters (Kl).

Sacramento River 

Arm

Shasta Lake 

Sampling Sites

McCloud River Arm

Pit River Arm

35
Depth from Surface (m)

09/27/97

!

* fe k b o 0 8 p - J - S B.P
Figure 3 cont. 

b.

Conductivity (us-cnv1)

Date

37
Figure 3 cont. 

c.

E

I

OT

I

t 

&

Conductivity (us-crrr1)

Dissolved Oxygen (mg/L)

s g

Date

38
Depth from Surface (m) c 

n>

oo
Figure 3 cont. 

e.

Conductivity (us-crrr1)

136

126

116

-120

Date

40
Figure 4 a-c. Time series isopleths of Relative Thermal Resistance to Mixing (RTRM) coefficients

for Shasta Lake sampling stations a. S6; b. S10; c. S9; d. S8; e. S7. 

a,b. S6

-20

If) u> u> to U> U> U> U>

Date

41
Figure 4 cont. 

c,d.

S9

Date

42
p '

Depth (m)

LO

oo
Figure 5 a-t. Monthly isopleth description of temperature (°C ), dissolved oxygen (percent

saturation), pH, and specific conductance (//S/cm) for the Pit River arm for 1996 and 

1997. a. February 1996; b. March 1996; c. April 1996; d. May 1996; e. June 1996; f 

July 1996; g. August 1996; h. September 1996; i. October 1996; j. January 1997; k. 

February 1997; 1. March 1997; m. April 1997; n. May 1997; o. June 1997; p. July 1997; q. 

August 1997; r. September 1997; s. October 1997; t. November 1997.

a.

Dissolved Oxygen ( % Sat.)

-5G

Conductivity (us-cm"1)

£ Temperature ( °C)

-1

10 15 20 

Distance From Dam (km)

25 30

44
Figure 5 cont. 

b.

Dissolved Oxygen (% Sat.)

-50-

Conductivity (us-crrr1)

P Temperature ( UC)

10 15 20

Distance From Dam (km)

25 30

45
Figure 5 cont. 

c.

Dissolved Oxygen (% Sat.)

-SO

Conductivity (us-cnr1)

^MWP

Temperature (°C)

-100

-so r

7.4 I

10 16 20 

Distance From Dam (km)

26 30

46
Figure 5 cont. 

d.

Dissolved Oxygen (% Sat.)

Conductivity (us-cnr1)

10 16 20 

Distance From Dam (km)

26

47
00

g

Depth from Surface (m)

8

T) 

f

o

o

0000000000->MU« 

00000
Figure 5 cont. 

f.

Dissolved Oxygen (% Sat.)

-SO-1

-100

£ -100

0> 

U

I

CO

E

0. 

0>

Q

Conductivity (us-cnv1 )

-5«t

10 15 20 

Distance From Dam (km)

49

25 30
Depth from Surface (m)

8 01 cos

0->M«» 00000
Figure 5 cont. 

h.

Dissolved Oxygen (% Sat.)

-50

Conductivity (us-cnr1)

CO Temperature (°C) 

O K- 21

10 16 20

Distance From Dam (km)

30

51
to

Depth from Surface (m)

s

iiiimiiin 

01 w w

0 0 M fr 

000
Depth from Surface (m)

_J

ere'

c

Ui

8

OOOOOOOO^MU* 

00000
3

Depth from Surface (m)

i* 8

CTQ 

I

q

io

(D

°ooooooooooiloui
8

Depth from Surface (m)

1

!- hcj 

f

oo

oooooooooo^uui

00000
3 3 '

0 o

Depth from Surface (m)

i

fDOo

(0 J J J J

§ a a o!

O^MU&OlfllNOOtO^^^^^

OOOOOOOOOO^MU*

00000
Depth from Surface (m)
00

Depth from Surface (m)

i

p aCFQ

§

ooa

5 5 0 > M U 

01 01 01 01

OJMUfrOl9S»»JJJJJ 

OOOOOOOOOO'MUA
Figure 5 cont. 

PDissolved Oxygen (% Sat.)

Conductivity (us-cnrr1)

10 16 20

Distance From Dam (km)

26 30

59
Figure 5 cont.

qDissolved Oxygen (% Sat.)

Conductivity (us-cnr1)

co Temperature (°C)

0

10 16 20

Distance From Dam (km)

30

60
Figure 5 cont. 

r.

Dissolved Oxygen (% Sat)

Conductivity (us-cnv1)

-100

10 16 20 

Distance From Dam (km)

30

61
a\ to

Depth from Surface (m)

8

t. il

BSSSSSBBBB 

B 6 M > '« B 0 M k « s s a s : 8 S 0 M M t> 0 0 « a j 0 » §

f

8

B
Figure 5 cont. 

t.

Dissolved Oxygen (% Sat)

-1

10 15 20 

Distance From Dam (km)

65
Figure 6 a-t. Monthly isopleth description of temperature (°C ), dissolved oxygen (percent

saturation), pH, and specific conductance (//S/cm) for the Sacramento River arm for 1996 

and 1997. a. February 1996; b. March 1996; c. April 1996; d. May 1996; e. June 1996; 

f. July 1996; g. August 1996; h. September 1996; i. October 1996, j. January 1997; k. 

February 1997; 1. March 1997; m. April 1997; n. May 1997; o. June 1997; p. July 1997; q. 

August 1997; r. September 1997; s. October 1997; t. November 1997.

a.

Dissolved Oxygen (% Saturation)

TOO

Conductivity (us-crrr1)

Distance From Dam (km)

64
Figure 6 cont. 

b.

Dissolved Oxygen (% Saturation)

-50-,

-100-1

Conductivity (us-cnr1)

(O Temperature (°C)

E 

o

8 10 12 14

Distance From Dam (km)

20

65
Figure 6 cont. 

c.

Dissolved Oxygen (% Saturation)

o> 

o

O

 s.

0>

O

Conductivity (us-cnr1)

8 10 12 14 16 

Distance From Dam (km)

18 20

66
Figure 6 cont. 

d.

Dissolved Oxygen (% Saturation)

Conductivity (us-crrr1)

-50

pH '

f .t>

7.4

7.6- 

 74 --jr^»-^ I »F . -^^

1 i

I

Distance From Dam (km)

67
Figure 6 cont. 

e.

Dissolved Oxygen (% Saturation)

-50-

-100

Conductivity (us-crrr1)

-1

10 12 14 

Distance From Dam (km)

16 18 20

68
Figure 6 cont. 

f.

Dissolved Oxygen (% Saturation)

-50-

Conductlvity (us-cnr1)

-1

8 10 12 14 

Distance From Dam (km)

20

69
Figure 6 cont. 

gDissolved Oxygen (% Saturation)

-50^

-100

E -'

o> 

o

I

w

E

f

o>

Q

-1

Conductivity (us-crrv1)

10 12 14

Distance From Dam (km)

16 18 20

70
Figure 6 cont. 

h.

Dissolved Oxygen (% Saturation)

-SO

-100

Conductivity (us-crrv1)

j 30

20

10

CO Temperature (°C)

o

8 10 12 14

Distance From Dam (km)

71
Figure 6 cont. 

i.

Dissolved Oxygen (% Saturation)

-50-

Conductivity (us-cnr1)

-1

8 10 12 14

Distance From Dam (km)

16 18 20

72
Figure 6 cont.

jDissolved Oxygen (% Saturation)

-100

8 

I

£

"o.

-100^

Conductivity (us-cnr1)

-100

8 10 12 14

Distance From Dam (km)

16 18 20

73
Figure 6 cent, 

k.

Dissolved Oxygen (% Saturation)

-SO

-100-!

Conductivity (us-cnr1)

-1

8 10 12 14

Distance From Dam (km)

74

16 18 20
Figure 6 cont. 

1.

Dissolved Oxygen (% Saturation)

-5(H

-10(H

8 10 12 14 

Distance From Dam (km)

18 20

75
Figure 6 cont. 

m.

Dissolved Oxygen (% Saturation)

-50-

Conductivity (us-orrr1)

6 8 10 12 14 16

Distance From Dam (km)

76

18
Figure 6 cont. 

n. Dissolved Oxygen (% Saturation)

-50-

-100

Conductivity (us-cm-1)

8 10 12 14

Distance From Dam (km)

77

16 18
Figure 6 cont. 

o.

Dissolved Oxygen (% Saturation)

-5CH

Conductivity (us-cnr1)

-1

8 10 12 14 

Distance From Dam (km)

18 20

78
Figure 6 cont. 

PDissolved Oxygen (% Saturation)

Conductivity (us-crrr)

-1

8 10 12 14 

Distance From Dam (km)

16 18 20

79
Figure 6 cont.

qDissolved Oxygen (% Saturation)

Conductivity (us-crrr1)

-1

8 10 12 14 16 

Distance From Dam (km)

18 20

80
Figure 6 cont. 

r.

Dissolved Oxygen (% Saturation)

Conductivity (us-cnr1)

tn Temperature (°Cl

-1

8 10 12 14 

Distance From Dam (km)

18 20

81
Figure 6 cont.

s.

Dissolved Oxygen (% Saturation)

-50^

-100

o> 

u

I 

CO

o

Conductivity (us-cm-1)

-50 ~

-100

8 10 12 14 

Distance From Dam (km)

16 18 20

82
Figure 6 cont. 

t.

Dissolved Oxygen (% Saturation)

Conductivity (us-cnr1)

U -''

o Temperature ( UC)

6 8 10 12 14 

Distance From Dam (km)

83
Figure 7. Comparison of chl a concentrations (ug/L) from surface to 30m between the main lake 

(S6), Sacramento River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and the 

Pit-McCloud Confluence (S10) from August 1995 thru October 1997.

MoCi^ud fiflyer Arm (S8)

-3O

10/28/96 2/6/96 5/16/96 8/23/96 11/30/96 3/11/97 6/19/97 9/27/97

Date

84
Figure 8. Seasonal cycle of inflow temperatures for the Sacramento river at Delta, station (DLT), 

and for the Pit river at station (PMN).

D

CDCD"

CO 

CD

Oi

CD 

O)

CO

CO 

O)

CO

-xl

Oi

CO 

-J

CD 

CD

CO 

CO

CO O

Temperature ( C)

NJ -(»> O) CO

IV) 

IV)

85
Figure 9. Isopleth description of 1997 flood inflow patterns using turbidity as an indicator for 

October 1996, January 1997, February 1997, March 1997.

October 1996

-ior>

16 20 

Distance from Dam (km)

86
Figure 10 a-b. Secchi depth transparencies (m) for Shasta Lake from May 1995 thru November 

1997. a. main lake (S6) and forebay (SI6); b. Sacramento River Arm (S7) and upper 

Sacramento River Arm (SI5).

A

12

10--

8--

Main Lake (S6)

----v--- 

Forebay(S16)

M J J 

1995

SON J F M 

1996

A M J J A S O J F M

1997

AMJ JASON

F M A M 

1997

J JASON

87
Figure 11 a-b. Secchi depth transparencies (m) for Shasta Lake from May 1995 thru November 

1997. a. McCloud River Arm (S8) and upper McCloud River Arm (S14); b. Pit River 

Arm (S9), upper Pit (S12), upper upper Pit (S13), and Squaw Creek (SI 1).

12

10--

8 --

.c "S.

6 --

4 --

2--

McCloud (S8)

__._^....

Upper McCloud (S14)

H I I I I I I I- H I I I I I I I I I I h H I I h 

MJJASONJF MAMJ JASON

1995 1996

M A M J J A S O J F 

1997

12

10 --

Pit (S9)

--v 

Upper Pit (S12)

 ---

Upper Upper Pit (S 13)

Squaw Creek (S11)

JASONJFMAMJJASOJFMAMJJASON

88
Figure 12. Seasonal patterns of epilimnetic and hypolimnetic nitrate-nitrogen for Shasta Lake 

sampling stations from 1995-1997.

160

140 -

120 -

100 -

80 -

60 -

40 -

20 -

0 -

S6

^\

 Epilimnion

 A-- Hypolimnion

O) 3 

c

O

In

"c 

<D 

o

c 

o 

O

5/1/95 9/1/95 1/1/96 5/1/96 9/1/96 1/1/97 5/1/97 9/1/97

89
Figure 13. Seasonal patterns of epilimnetic and hypolimnetic orthophospahte (SRP) for Shasta 

Lake sampling stations from 1995-1997.

50 

40- 

30 - 

20 - 

10

o H

S6

ro "c

<D

o

t= 

o 

O

Q.

a:

CO

50

40 - 

30 - 

20 - 

10 - 

0 -

S10

5/1/95 9/1/95 1/1/96 5/1/96 9/1/96 1/1/97 5/1/97 9/1/97

90
Ammonia Concentration ug/L

-> ->. to to CO co _» _» _» _» _» ro

i i i i i i i i i i i i i i i i i i i i i i i i

T to f ^* to \ to 

I co . ! ^^ oo N v -vj

>
Total Phosphorus Concentration i/g/L

to

y; o
Figure 16. Seasonal patterns of epilimnetic and hypolimnetic TP/SRP ratios for Shasta Lake 

sampling stations from 1995-1997.

5/1/95 9/1/97
Figure 17. Seasonal patterns of epilimnetic and hypolimnetic DESf/SRP ratios for Shasta Lake 

sampling stations from 1995-1997.

CO

o: 

o_ 

o:

CO

 Epihmnion

 *-- Hypolimnion

5/1/95 9/1/97
Figure 18. Comparison of total composite chl a concentrations (ug/L) (0-5 m) between stations 

from 1995 thru 1997.

o

o

CO

I

T3

ZJ

^

O 

o

hco^

o

03 

CO

CD 

CO^

(D 

*!.

m_i

'(0c

CO

(l/6rl) B

95
Figure 19 a-d. Seasonal trend of composite chl a concentrations (ng/L) (0 to 5 m) from May 1995 

thru October 1997. a. main lake (S6) and forebay (SI6); b. Sacramento River Arm (S7) 

and upper Sacramento River Arm (SI6); c. McCloud River Arm (S8) and upper McCloud 

River Arm (S14); d. Pit River Arm (S9), upper Pit (S12), upper upper Pit (S13), Squaw 

Creek (SI 1), and Pit-McCloud Confluence (S10).

a.

JASONJ FMAMJ JASOJ FMMJ JASO

b.

J F 

1997

M M

C. McCloud (S8) 

Upper McCloud (S14)

A S O J 

1997

F M M S O

96
o

o

VO

-JVO

Squaw 

Pit-McCI(SIO)

Creek (S11)

Upper Pit (S12)

Upper Upper Pit (S13)

MJJASONJ FMAMJ JASOJ FMMJJASO

1995 1996
Figure 20 a-c. Seasonal trend of dominant phytoplankton groups collected from 0-30 m from the 

main lake (S6). a. June 1995 thru November 1996; b. January 1996 thru October 1996; c. 

January 1997 thru October 1997.

1600

1200

g 800

400

1995

8000

6000

E4000

2000

50000

Cryptophyta I I

Bacillariophyta

98
Figure 21 a-b. Seasonal depth distribution of phytopiankton collected from 0-10 m, 10-20 m, and 

20-30 m in the main lake (S6) from June 1995 thru October 1997. a. bacillariophyta; b. 

cryptophyta.

50000

40000 - -

,30000--

0)

_3

§ 20000 

in

10000 - -

Bacillariophyta

0-1 Om

MAMJJASO

SON J FMAMJ J ASOJ FMAMJ J ASO 

1996 1997

99
Figure 22 a-c. Seasonal trend of dominant phytoplankton groups collected from 0-30 m in the Pit 

River Arm (S9). a. June 1995 thru November 1995; b. January 1996 thru October 1996; c. 

January 1997 thru October 1997.

12000

10000

8000

6000

4000

2000

20000

15000

100
Figure 23 a-b. Seasonal depth distribution of phytoplankton collected from 0-10 m, 10-20 m, and 

20-30 m in the Pit River Arm (S9) from June 1995 thru October 1997. a. bacillariophyta; 

b. cryptophyta.

40000

30000 - -

0)

_3

I

CD

20000 - -

10000 --

JJASONJF

1995 1996

A M J J A S O J F

1997

MAMJJASO

500

400 --

J JASONJ FMAMJ JASOJ FMAMJ J ASO

101
Figure 24. Mean total copepod and cladoceran biomass (ug/L) for for all sampling dates for the 

main lake (S6), Sacramento River Arm (S7), McCloud River Arm (S8), Pit River Arm 

(S9), and Pit-McCloud Confluence (S10) from 1995 thru 1997.

(l/Brl) ssEUJOfg uop|UE|dooz

102
Figure 25. Mean copepod and cladoceran biomass (|ig/L) for the main lake (S6), Sacramento 

River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and Pit-McCloud 

Confluence (S10) for 1995, 1996 and 1997.

1350

-S 450

main (S6) Sac (S7) McCloud (SB) Pit (S9) Pit-McCI (S10)

1350

900

-S 450

main (S6) Sac (S7) McCloud (SB) Pit (S9) Pit-McCI(S10)

1350

450

main (S6) Sac(S7) McCloud (SB) Pit (S9) Pit-McCI (S10) 

^ H cladocerans copepods

103
Figure 26 a-b. Trends in zooplankton abundance (0-30 m) in the main lake (S6) from June 1995 

thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass (ug/L) trends.

main lake (SB)

JJASONJFMAM 

1995 1996

J j A S O J F 

1997

M A M J J A S

cladocerans copepods

350

JJASONJ FMAMJJASOJ FMAMJJAS

cladocerans-*- copepods v rotifers

104
Figure 27 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the main lake (S6) from June 1995 thru September 1997. a. 

copepods; b. cladocerans.

120

100

J JASON JF MA M J J A S O J F M A M J J A S

JJASONJFMAMJJASOJFMAMJJAS

0-1 Om 10-20m 20-30m

105
Figure 28 a-b. Trends in zooplankton abundance (0-30 m) for the Sacramento River Arm (S7) 

from June 1995 thru September 1997. a. Percent composition of copepods and 

cladocerans; b. Cladoceran, copepod, and rotifer total biomass (ug/L) trends.

Sacramento River Arm (S7)

JJ 

1995

A S O N J F 

1996

J J A S O J F 

1997

M A M J J A S

cladocerans copepods

350

rsl

ASON 19^6 FMAMJJAS 0 19^? FMAMJ JAS 

 cladocerans --at- copepods --^ rotifers

106
Figure 29 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the Sacramento River Arm (S7) from June 1995 thru 

September 1997. a. copepods; b. cladocerans.

250

JJASONJ FMAMJ JASOJ FMAMJ JAS

1995 1996 1997

^H 0-1 Om ^H 10-20m """""" ;; 20-30m

300

0-1 Om 10-20m 20-30m

107
Figure 30 a-b. Trends in zooplankton abundance (0-30 m) for the McCloud River Arm (S8) from 

June 1995 thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass (ng/L) trends.

McCloud River Arm (S8)

J JASONJFMAMJJASOJFMAMJ JAS

cladocerans copepods

350

J JASON J FMAMJ JASOJ FMAMJ JAS

cladocerans -x copepods -~w rotifers

108
Figure 31 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the McCloud River Arm (S8) from June 1995 thru September 

1997. a. copepods; b. cladocerans

140

120

JJASONJFMAMJJASOJFMAMJJAS 

1995 1996 1997

 0-1 Om p'"y -l 10-20m " ^ 20-30m

J J A S O N J F M A M J J A S O JFMAMJJAS

0-1 Om

109
Figure 32 a-b. Trends in zooplankton abundance (0-30m) for the Pit River Arm (S9) from June 

1995 thru September 1997. a. Percent composition of copepods and cladocerans; b. 

Cladoceran, copepod, and rotifer total biomass(ug/L) trends.

Pit River Arm (S9)

JASONJFMAMJ JASOJ FMAMJ JAS

350

300-

JASONJ FMAMJ JASOJ FMAMJ JAS

cladocerans - * copepods --»- rotifers

110
Figure 33 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals in the Pit River Arm (S9) from June 1995 thru September 1997. 

a. copepods; b. cladocerans.

250

Pit River Arm (S9)

J J AS ONJFMAMJJASO JFMAMJJAS

0-1 Om

350

300 -

JJASONJF MA MJJASOJF M A M J J A S

0-1 Om 10-20m 20-30m

111
Figure 34 a-b. Trends in zooplankton abundance (0-30 m) for the Pit-McCloud confluence (SIO) 

from June 1995 thru September 1997. a. Percent composition of copepods and 

cladocerans; b. Cladoceran, copepod, and rotifer total biomass (ug/L) trends.

Pit-McCloud Confluence (S10)

J JASONJ FMAMJ JASOJ FMAMJ JAS

350

J JASON J FMAMJ JASO J FMAMJ JAS

cladocerans --x - copepods rotifers

112
Figure 35 a-b. Seasonal distribution of copepod and cladoceran biomass in 0-10 m, 10-20 m, and 

20-30 m depth intervals at the Pit-McCloud confluence (S10) from June 1995 thru 

September 1997. a. copepods; b. cladocerans.

200

Pit-McCloud Confluence (S10)

JJASONJ F MAM J J A S O J F M A M J J A S

1995 1996 1997

 0-1 Om 10-20m | 20-30m

300

250

J JASONJ F M A M J J A S O J F M A M J J A

0-1 Om 10-20m 20-30m

113
Figure 36. Seasonal trend of rotifer biomass (ug/L) (0-30 m) in the main lake (S6), Sacramento 

River Arm (S7), McCloud River Arm (S8), Pit River Arm (S9), and the Pit-McCloud 

Confluence (S10) from June 1995 thru September 1997. ^

CO

o

CN 

O

 CO

 <

-o

O o

Q_

N

O)' 

CO

oo 

CO

O 

o

o

ro 

CO

to 

CO

114
Figure 37. Water temperatures (°C) in Shasta tailwaters and Keswick tailwaters from April 1995 

thru November 1997.

CO

(QO )

115
Figure 38 a-b. The relationship between size fractions of <25um, >25, and >505um POM 

concentrations (g/m3) from April 1995 thru October 1997. a. Shasta tailwaters; b. 

Keswick tailwaters.

AMJJASJF AM J J A S O F MA M J J A S O 

1995 1996 1997

AMJJASJFAMJJASOFMAMJJASO 

1995 1996 1997

116
Figure 39 a-c. Seasonal POM (g/m3) trnds in Shasta and Keswick tailwaters from April 1995 thru

October^! 997. a. <25um; b. >25um; c. >505um

2.

1996

0.08

0.06 _ -

§ 0.04 - .

0.02 . .

Shasta

Keswick

A & A

1996

117
Figure 40 a-c. Composition of total particulate matter (g/m3) in Shasta tailwaters from April 1995 

thru October 1997. a. <25um; b. >25um; c. >505um

A 

16

Shasta tailwaters

<25fjm POM

£124-

S 

<5

i

E 8 --

o> 

JS 

.o

Q. 4 - -

0

AMJJASJFAMJ JASOFMAMJJASO 

1995 1996 1997

R

0.6

>25jjm POM

00

a >25]jm PIM 

"fo

-2 

JS

-| 0.2

n

Q.

5 

^

0 - jsajjretj p»i | E31 SCT | f-m | law | i^-i | BB | gm | i«-:i | |^T|_tgg|j^^yBL[j>:^^

AMJ JASJ FAMJ JASOFMAMJ JASO 

1995 1996 1997

r 

0.25

Q 2 _ _ >505jjm POM

I 0.14-

« 0.05 - - 

o

^^

AMJ JASJ FAMJ JASOFMAMJ JASO 

1995 1996 1997

118
Figure 41 a-c. Composition of total particulate matter (g/m3) in Keswick tailwaters from April 

1995 thru October 1997. a. <25um; b. >25um; c. >505um

16

Keswick tailwaters

. , ... <25um POM COE12--

Z <25iJm PIM J3 

CQ |.+

J2 

 eu

3 

o

AMJ JASJFAMJ JAS'OFMAMJ JASO 

1995 1996 1997

B 

0.6

n. .,, >25jjm POM

E

a ___

 - ' ~"~ ::: >25Kim PIM

E 

oj 

jg

u

I °-2 

o.

£ 

g

0 - . Lii I !?:> :! I t*:-H I l-:vH I M-:-M i l:-:-:-1 j m i j|K i tx:a i !: : : ! i l:-:-:-:l i l¥:-:l i l-:-:-:-l i t:-:-:-l I !: :-: ] I «_ i_ x>:. I K-:-:-l i Pmi !: : : :! i t-:-:-H i ! : : : ) i K-:-M[

AMJ JASJFAMJ JASOFMAMJ JASO 

1995 1996 1997

C 

0.25

^02-- I >505pm POM

E

a __

015 , ^ ^555TimPIM

\w

| 0.1 e

(0 

CL

I 0.05

0

AMJJASJFAMJJASOFMAMJJASO 

1995 1996 1997

119
Figure 42. Mean total POM (g/m3) at Shasta and Keswick tailwaters for the period 1995 thru 

1997.

Total POM (g/m3)

V

o 

"Co

3

Tl

o

120
Figure 43 a-b. Seasonal composition of zooplankton for 1995, 1996, and 1997 in Shasta

tailwaters. Major groups are cladocerans, copepods, and rotifers, a. biomass (ug/L); b. 

percent composition

1995 1997

cladocerans copepods rotifers

100%

o

N 20%

0%

1995 ' 1996

^^H cladocerans ^^H copepods

1997

rotifers

121
Figure 44 a-b. Seasonal composition of zooplankton for 1995, 1996, and 1997 in Keswick

tailwaters. Major groups are cladocerans, copepods, and rotifers, a. biomass (jag/L); b. 

percent composition

1997

cladocerans copepods rotifers

100%

N20%--

0%

cladocerans

122
Figure 45 a-b. Cladoceran, copepod, and rotifer biomass (ng/L) drift from April 1995 thru 

October 1997. a. Shasta tailwaters; b. Keswick tailwaters.

o 

2

ro

5--

Shasta tailwaters

cladocerans

copepods 

rotifers

AMJ JASJ FMAMJ JASOFMAMJ JASO

B

20 -i 

15--

</> </> 

ro

E

S 10

5 - -

Keswick tailwaters

cladocerans

copepods 

rotifers

X \X^'

AMJ JASJ FMAMJ JASOFMAMJ JASO 

1995 1996 1997

123
Figure 46 a-b. Total biovolume (|ug/L) of phytoplankton size fractions (<25|um, >25|um, >505um) 

from April 1995 thru September 1997. a. Shasta tailwaters; b. Keswick tailwaters.

7000

M J F M A M J J A S OFMAM J J A S

1995

7000

6000 _.

M J J A S J F M A MJJASOF M A MJ A S

<25|jm >25|jm >505|jm

124
Figure 47. <25um Chlorophyll a concentration (ug/L) in Shasta and Keswick tailwaters from 

April 1995 thru October 1997.

(-|/6rl) e mo wr1gz>

125
Figure 48 a-c. Percent composition of the <25um phytoplankton biovolume in Shasta and 

Keswick tailwaters for the period 1995 thru 1997. a. <25um; b. >25um; c. >505um

100%

0%

100%

80%--

0%

Shasta

Bacillariophyta 

Cyanophyta

Keswick

Chlorophyta 

Euglenophyta

Chrysophyta 

Pyrrophyta

Cryptophyta 

Rhodophyta

126