CENTRAL PACIFIC
I
RIVER BASINS
PROJECT
LIMNOLOGICAL ASPECTS OF CLEAR LAKE,
CALIFORNIA, WITH SPECIAL REFERENCE
TO THE PROPOSED DIVERSION OF EEL
RIVER WATER THROUGH THE LAKE.
BY
Charles R. Goldman
U.S.DEPARTMENT OF THE INTERIOR
Federal Water Pollution Control
Administration
Southwest Region

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REPORT
U. S. DEPARTMENT
FEDERAL WATER POLLUTION
SOUTHWEST R
TO
OF THE INTERIOR
CONTROL AD_MINITRATION
'HON
LIMNOLOGICAL ASPECTS OF CLEAR LAKE,
CALIFORNIA, WITH SPECIAL REFERENCE
TO THE PROPOSED DIVERSION OF EEL
RIVER WATER THROUGH THE LAKE.
BY
Charles R. Goldman
April, 1968
Institute of Ecology
University of California, Davis

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UNIVERSITY OF CALIFORNIA, DAVIS
BERKELEY • DAVIS • IRVINE • LOS ANCELES • RIVERSIDE • SAN DIECO • SAN FRANCISCO
SANTA BARBARA • SANTA CRUZ
INSTITUTE OF ECOLOGY .
DAVIS, CALIFORNIA 95616
April 23, 1968
Mr. Richard C. Bain
Central Pacific River Basins Comprehensive Water
Pollution Control Project
BLdg. 2G
620 Central Ave.
ALameda, California 94501
Dear Dick:
Attached is the report on limnological aspects of Clear
Lake, Lake County, California, with special emphasis on possible
diversion of Eel River.
The work continues here on the problem and I hope to
begin a more extensive research progianon nutrient regeneration,
from the sediments in the near future. In this area we badly
need more information and my report could be a good deal more
authoritative if we had it. I have appended a research pro-
posal for this work which will be submitted to a funding
agency in the very near future.
I have reviewed three drafts of your report and am in
substantial agreement with their conclusions and recommendation.
I would like to stress the importance of a total watershed
approach to the problem and some concern as to the water quality
of the Clear Lake out flow. If I can be of further assistance
please feel free to contact me.
£-1 -nr* orol v
Charles R. Goldman, director
CBG:mm
encl. 25pp

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CONTENTS
Page
I. Introduction	 1
II. Some laboratory experiments on the dilution of Clear Lake 5
cultures with Eel River water	
III. Some aspects of the water chemistry of Clear Lake in com- 8
parison with the Eel River with special reference to
copper	•	
IV. Nutrient regeneration from the Clear Lake sediments and a 12
recommendation for altering the regime	
V. Conclusions	 15
INTRODUCTION
The natural process of lake eutrophication has been discussed in the
limnological literature for many years. Since the turn of the century there
has been increased interest in cultural influences which are, with paleo-
limnological' techniques, traceable back to Roman antiquity (Cowgill and
Hutchinson 1964). The speed with which a lake can pass from oligotrophic
through mesotrophic to a eutrophic state was well documented by the tran-
sition of Lake Erie in North America and Lake Zurich in Switzerland in a
half century of domestic pollution. Attention to domestic pollution was
first directed to obvious public health problems such as typhoid epidimics.
Gradually, with the advent of better sewage treatment plants there developed
a concern for the destruction of aesthetic qualities of lakes and streams.
Although good secondary sewage treatment could produce an effluent of near
drinking water quality the content of such important nutrients for plant
growth as nitrogen and phosphorus accelerate the growth of algae in waters
receiving plant discharge.
The problem of lake eutrophication has been extensively discussed and
debated for years. It often has been reduced to a consideration of the

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importance of nitrogen and phosphorus in accelerating the eutrophication of the
lakes. Sawyer's recent analysis of eutrophication is very useful but must by
necessity be considered an oversimplification which is almost impossible to
avoid in any general discussion of lakes. Both phosphorus and nitrogen metabo-
lism by algae are influenced by a host of environmental and nutrient factors.
In a lake receiving treated sewage severe trace element limitations are not
likely, but a careful analysis may prove useful. Clear Lake is an extremely
productive lake in a rather advanced state of eutrophication..(Goldman and
Wetzel 1963). The question of the relative importance of nitrogen and phosphorus
in the lake at this point in its history are rather academic! since there is
obviously enough to sustain a nearly continuous bloom. In contrast, Lake Tahoe,
which has received increasing attention during the last five years, shows
severe nitrogen deficiency and added phosphorus iB ineffective without additional
nitrogen (Goldman and Carter 1965). The proposed diversion of Eel River water
through Clear Lake would not greatly alter the ratio of nitrogen and phosphorus
but would dilute both. Let us therefore first consider a widely accepted
generality. Most algae require about twenty times as much nitrogen as they
do phosphorus and are able to extract it from the media against a tremendous
gradient. Further, they are able to store it against "hard times". The overall
importance of the nitrogen fixing ability of some of the bluegreen algae in com-
pensating for a deficiency of fixed nitrogen has really never been determined.
We know that where phosphorus levels are high the nitrogen fixers have an
easier time, but in a lake like Crater Lake, Oregon, where there is both high P
and low nitrogen bloom conditions have not resulted despite the presence of
nitrogen fixing bluegreen algae (Hutchinson 1957, p. 847). In Brooks Lake,
Alaska, where phosphorus levels were very low, bioassays showed nitrogen to be
by far the mo&t limiting nutrient. Only in late summer did response to phosphorus

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develop when the environmental levels had dropped well below the limit of our
detection at the .001 ppm level (Goldman, 1960).
Unlike many lakes which show a spring and fall bloom of algae, Clear Lake
undergoes what even the casual observer must admit is a sustained phytoplankton
bloom. Obviously phosphorus and nitrogen levels, as well as the spectrum of
trace elements, remain high enough to support this condition. Any diversion of
lower nutrient water through the Clear Lake basin will reduce these levels, but
it is more likely that the reduction in nitrogen will be most significant in
lowering the rate of algal production in the lake. Our own nitrate nitrogen
analysis of Clear Lake and Eel River water with the sensitive and reliable
cadmium reduction method indicate that Eel River water contained only one fourth
as much nitrate as Clear Lake (See Section III). Bioassays of the natural Clear
Lake phytoplankton population in September have shown higher growth response
with nitrogen addition than was achieved with phosphorus addition. In July
the best growth was obtained with sulfate and nitrate in combination (Goldman
and Wetzel 1963).
Although Clear Lake is extremely turbid, its productivity can scarcely be
considered seriously light limited. Similar lakes in African Rift Valley that
have been studied by the author are even more turbid and productive than Clear
Lake, California. They are also characterized by the lack of anything more
than temporary stratification and have sufficient wind mixing to keep re-exposing
the phytoplankton population to the narrow euphatic zone. In a later section
likely benefLts to be derived from upsetting this regime are discussed.
The current eutrophication problem in Clear Lake can be summarized as a
high rate of nutrient supply and regeneration in relation to nutrients lost
from the ecosystem by harvest of plants and animals as well as those lost through
sedimentation and outflow. Altering this nutrient budget can be achieved in

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various ways. Diversion of lower nutrient Eel River water into Clear
Lake is one useful approach, but to really solve the problem of the
lake's accelerated eutrophication will require in addition, a concerted
effort to reduce the nutrient inflow from all sources on the Clear Lake
watershed.

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Some Laboratory Experiments on the Dilution
of Clear Lake Cultures with Eel River Water
Bioassay experiments utilizing 14 Carbon as sodium carbonate to measure
growth were conducted during the fall of 1967. In these experiments fresh
Clear Lake water was collected offshore at Lakeport and diluted with Eel River
water collected at the same time. The general bioassay proceedure was that
reported by Goldman, 1963, where the entire culture was labeled with 14 Carbon
and subsamples of the algae were collected on Millipore filters. There have
been a number of sophisticated experiments to demonstrate the equivalence of
14 C uptake and increase in particulate organic carbon (Antia et al. 1963,
Ryther and Menzel 1965). Because pigments may vary diurnally and cells may
divide by simply splitting their organic material the 14 Carbon method of
measuring growth has much to recommend it.
In the first experiment (Figure 1) additions of Eel River water covered
the low range of .001% to 1% dilution of Clear Lake cultures. In all cases
there was slight stimulation to carbon assimilation until 60 hours when the
growth rate fell off below the 0.11% dilution level. Possible implications of
the slight (probably well below the level of detection of any method except
14 Carbon uptake) stimulation is discussed in Section III in relation to
copper toxicity.
The second culture experiment extended the dilution to 50%. The results
for a short term experiment (Figure 2) are in general agreement with the first
experiment and show the overall decrease'in growth to be expected with a 50%
dilution. These short term growth experiments support the results of batch
experiments at the FWPCA laboratory in Alameda. The lower nutrient content
of Eel River water reduces the algal growth potential of Clear Lake water.

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i-"
3
700*
cts sec"1
4t)0
1600
Figure 1. Cultures of Clear Lake water with various
percentage by volume dilutions with Eel River
water.

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-7-
50%
25%
10%
50.
01%
50-
001%
p.poi%
2200
4 bo
100
700
1000
1300
1600
Activity in cTsVaec
Figure 2. Cultures of Clear Lake water with various
percentage by volume dilutions with Eel River
water.

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Some Aspects of the Water Chemistry of Clear Lake in Comparison
with the Eel River with Special Reference to Copper
On 6 October a comparative analysis of Clear Lake and Eel River water
was made at the limnological laboratory in the Institute of Ecology (Table 1).
Clear Lake was found to have significantly higher levels of all elements
measured except iron and calcium. There are four times as much nitrate
nitrogen in the Clear Lake water and over twelve times as much copper. It
is probable that mining activities and the extensive use of copper as a
dormant ispray in the orchards surrounding the lake are responsible for the
high environmental levels. The extremely high copper level in the sample was
surprising and a laboratory culture experiment utilizing the natural Clear
Lake phytoplankton population was established on 2 Nov. 1967. The object of
the experiment was to determine how close the copper is to inhibiting levels
in Clear Lake at the present time (Figure 3).
Copper was added at 1.25, 1.50 and 1.75 times the natural Ca level. All
additions were inhibiting to photosynthesis of the natural phytoplankton
population over a sixty hour period with 110 parts per billion essentially
stopping growth. In one culture container a copper specific chelator was added
which, after initially depressing photosynthesis slightly, increased photo-
synthesis slightly over the control after thirty-six hours. It is obvious
that algal control with copper sulfate might be less expensive in areas of Clear
Lake than in other environments and that addition of Eel River water will be
expected to lower the copper levels. This experiment is more suggestive of
additional work on the algal growth in the lake than conclusive of present
copper toxicity. There may be considerable variation in the copper levels
at various points in the lake. It may well be related to the Clear Lake

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10/6/67 COMPARATIVE ANALYSIS OF CLEAR LAKE AND EEL RIVER
COLLECTED ON 6 OCTOBER 1967
ELEMENT
Mn
Fe
Ca
Mg
no3-n
Na
Cu
Mo
Ca/Mg
CLEAR LAKE
27 ppb
360 ppb
21.4 ppm
13.8 ppm
20.8	ppb
65 ppm
62.9	ppb
0.76 ppb
1.55
EEL RIVER
20 ppb
270 ppb
22.0 ppm
6.4 ppm
4.9 ppb
40 ppm
5 ppb
0.52 ppb
3.44
Particulate
Matter
METHOD
Atomic Absorption
Atomic Absorption
Atomic Absorption
Atomic Absorption
Cadmium Reduction
Flame Emission
Atomic Absorption
Dithiol
Relative Volume to
Obstruct HA Filter
Table ]. A comparison of the water chemistry of Clear Lake and
the Eel River on 6 October 1967. Analyses were
performed in the limnology laboratory of the Institute
of Ecology,,

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Cu Inhibition	Clear Lake-Nov. 2-5,1S'SV
600-
Conlrol
/Control »Co specific chelator
400-
~ I25» natural Cu level (78.6ppb)
+ 1 50 « natural Cu level (944ppb)
100-
~ l?5xnatural Cu lovel (llOOppb)
oJa
60
46
24
36
12
Hours
Figure 3. Inhibition of photosynthesis with copper
additions to Clear Lake phytoplankton.

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dilution experiments discussed in the previous section (II) in explaining
the initial stimulation to photosynthesis below the 50% dilution level.
Additional work is needed over a long period of time to resolve this
interesting consideration, eventually including large _in situ test
vessels of the type described by Goldman, 1962, and Goldman and Carter,
1965.

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Nutnent Regeneration from the Clear Lake Sediment
and _a Recommendation for Altering -the Regime
In evaluating the question of whether or not diversion of Eel River
water through Clear Lake would improve the water quality of Clear Lake,
one of the most important and least documented areas of consideration is
nutrient regeneration from the lake sediments. Clear Lake neither freezes
in the winter nor stratifies permanently in the summer. In this respect
it is very similar to some of the shallow, highly productive lakes of the
Rift Valleys in East Africa. Although light penetration is severely
limited by turbidity the whole system is mixed by the wind so that in-
dividual organisms are constantly returned to the light zone. Actual
measured rates of primary productivity in bottles give values which are
lower than the actual rates since the bottles are not rotated through the
light .zone in the manner that wind constantly returns algae to the illum-
inated surface (Goldman and Wetzel 1963). The lake actually functions
like a giant stabilization (oxidation) pond with only brief periods of
oxygen depletion near the bottom on windless days.
It is clear that in this wind mixed system the biggest obtacle to
reaching a precise prediction about the effect of Eel River diversion
on Clear Lake is the lack of quantitative information about the present and
potential contribution of nutrients from the sediments. Clear Lake, as
a biological system, is more than an isolated body of water. At the very
least it must be viewed as a water-sediment system. Implicit in this view
is the notion that nutrient concentrations in the water and in the sediments
are in equilibrium. Flushing of the Lake with low nutrient water would
upset such an equilibrium condition and increase the rate of regeneration

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of nutrients from the sediments. If low nutrient water were introduced
at a rate that was low relative to the rate at which nutrients were
released from the sediment the rate of decrease in lake waters nutrient
concentrations would also be low. Intuition and experience with other
lakes suggest that the proposed rate of delivery of English Ridge project
water alone without control of nutrient inflows may be small when compared
with the possible capacity of Clear Lake sediment to release nutrients.
As noted above, a relevant characteristic of Clear Lake is that the
water within it circulates continuously. Constant circulation increases
sediment-water contact by agitating the sediment surface; it brings heat
from above to the sediment -surface increasing the rate and extent of
mineralization of dead algae; it carries dissolved nutrients from the
sediment surface into the photic zone where they may be utilized for algal
growth. Unremitting circulation also increases the turbidity of the water.
Constant circulation is not characteristic of all lakes. Many lakes
which are deeper or less exposed to strong winds become thermally strati-
fied during the warmer months. One result of thermal stratification is a
lens of cold stagnant water in contact with the sediments. This lower layer
or hypolimnion isolates the sediments from the upper lighted water where
algal growth occurs. As long as stratification persists the hypolimnion
serves as an effective nutrient trap. Once an algal cell sinks into the
hypolimnion the material of which it is composed is effectively removed
from the productive part of the lake as long as stratification persists.
If Clear Lake were deep enougjh to stratify and based on studies made on
Lake Berryessa (Goldman, unpublished) Clear Lake would be expected to
stratify from late May to mid-September or throughout the period when
algal growth is most intense and recreation use is highest. Thus a

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hypoliniiion in Clear Lake would be expected to have a beneficial effect
on the quality of the surface water during the summer. It would act as
a sink Into which nutrients would drain throughout the growing season
with a concomitant increase in water clarity.
During the winter months stratification would disappear and all of
the lakes dissolved nutrients would again be uniformly distributed
throughout the water mass. However, natural light intensities are low
during the winter and there is much less algal growth potential regardless
of the nutrient concentration. In short, stratifying Clear Lake would
certainly'reduce its primary productivity and probably lower the intensity
of algal blooms.
How to stratify Clear Lake in the most economical manner would require
an intensive analysis of existing data and collection of at least a years
supplementary information on air and water temperature and eensity, and
wind velocity. With the availability of colder Eel River water it might
well be possible to inject a cold hypolimnion beneath the warmer Clear
Lake water thus producing a strong temperature and density gradient with-
out the necessity of greatly deepening the basin. If disposal sites were
available the Army Engineers could probably be encouraged to undertake
dredging the main shallow basin of the lake. The high nutrient sediment
would be valuable as fill or top soil and its removal from the lake basin
would eliminate the last half century of high nutrient accumulation as
well as Increasing the depth for thermal stratification of the lake's
water.

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Conclusions
In general this writer is in agreement with the recommendations of the
FWPCA report of March 1968. The lower nutrient water, if introduced into the
lake in sufficient volume would reduce the present concentration of algal
nutrients, particularly nitrogen, and probably begin to flush out some of the
nutrients stored in the lake's sediments.
Because of the possibility of stratifying Clear Lake as suggested in
Section IV, multi-level outlets will be essential in the.reservoirs tapped.
Proper manipulation of the Clear Lake thermal regime may have numerous bene-
ficial side effects such as nutrient trapping in a hypolimnion during summer
with a greater contribution to the sediments. There is even the possibility
of destroying the ideal habitat now provided by the lake for Clear Lake gnat
(Chaoborus astictopus).
The serious lack of information on regeneration of nutrients from the
lake sediment should be rectified by research. Without this information
our ability to predict with a high degree of certainty the influence of Eel
River water on the algal production is admittedly reduced.
With the projected population increase on the Clear Lake watershed drastic
pollution control measures .must be established if the lake is to be maintained
even at its present, less than satisfactory, condition.' Further, if water
quality is to be improved in the lake for recreational benefits by diversion
of Eel River water, concommitant steps must be taken to reduce the nutrient
input. Unless this is done the steady increase in pollution which, unabated,
will follow the population rise on the watershed, will tend to diminsh any
benefits of Eel River diversion as well aS degrading the quality of the water
leaving Clear Lake. A complete sewage and irrigation run-off bipass system
would seem the best solution.

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References Cited
Antia, N.J., C.D. McAllister, T.R. Parsons, K. Stephens, and J.D.H. Strickland.
1963. Further measurements of primary production using a large-volume
plastic sphere. Limnol. and Oceanogr. 8(2) : 166—183.'
Cowgill, U.M. and G.E. Hutchinson. 1964. Cultural eutrophication in Lago
di Monterosi during Roman antiquity. Verh. Inder. Verein Limnol. 15:644-5.
Goldman, D.R. 1960. Primary productivity and limiting factors in three lakes
of the Alaska Peninsula* Ecol. Monogr. 30:207-230.
Goldman, C.R. 1963. The measurement of primary productivity and limiting
factors in freshwater with carbon-14. Pages 103-113. In M.S. Doty, [ed.],
Proceedings of the Conference on Primary Productivity Measurement, Marine
and Freshwater, U.S. Atomic Energy Commission, TID-7633.
Goldman, C.R. and R.G. Wetzel. 1963. A study of the primary productivity of
Clear Lake, Lake County, California. Ecology 44(2) .*283-294.
Goldman, C.R. and R.C. Carter. 1965. An investigation by rapid carbon-14
bioassay of factors affecting the cultural eutrophication of Lake Tahoe,
California-Nevada. Journal Water Pollution Control Federation.
37:1044-1059.
Ryther, J.H. and D.W. Menzel. 1965. Comparison of the ^C-technique with
direct measurement of photosynthetic carbon fixation. Limnol. and
Oceanogr. 10(3):490-492.

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