EPA-600/3-77-087
August 1977
Ecological Research Series
TROPHIC EQUILIBRIUM OF LAKE WASHINGTON
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
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This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-087
August 1977
TROPHIC EQUILIBRIUM OF LAKE WASHINGTON
by
W. T. Edmondson
Department of Zoology
University of Washington
Seattle, Washington 98195
R 8020 82-03-1
Project Officer
Charles F. Powers
Marine and Freshwater Ecology Branch
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
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DISCLAIMER
This report has been reviewed by the Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
11
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FOREWORD
Effective regulatory and enforcement actions by the Environmental
Protection Agency would be virtually impossible without scientific data on
pollutants and their impact on environmental stability and human health.
Responsibility for building this data base has been assigned to EPA's Office
of Research and Development and its 15 major field installations, one of which
is the Ccrvallis Environmental Research Laboratory (CERL).
The primary mission of the Corvallis Laboratory is research on the
effects of environmental pollutants on terrestrial, freshwater, and marine
ecosystems; the behavior, effects and control of pollutants in lake systems;
and the development of predictive models on the movement of pollutants in the
biosphere.
This report provides important documentation of the effects of reduced
nutrient input in the control of culturally induced eutrophication.
A. F. Bartsch
Director, CERL
111
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ABSTRACT
The purpose of this study was to help establish a description of the
chemical condition of Lake Washington during 1973-1976 after recovery from
diversion of sewage effluent. The condition during this period is compared
with some of the results of extensive earlier studies. The hypothesis was
that the lake would enter into a steady state in equilibrium with the new
conditions in the watershed.
Sewage effluent was diverted progressively from the lake during 1963-
1968, and the chemical conditions changed in close relation to the amount
of sewage entering. The total phosphorus content of the lake decreased rap-
idly to 1971 after which year it varied around a value of about 50,000 kg
(= 17 yg/1) with a slight decreasing trend. The lake has retained about 56%
of the phosphorus that entered during 1971-1975.
Winter means of nitrate and the annual mean total content of Kjeldahl
nitrogen has decreased at a slow rate during the entire period. Phytoplank-
ton as measured by chlorophyll in the epilimnion during summer dropped to a
low value in close proportion to phosphorus during diversion, but has de-
creased faster than phosphorus during 1971-1976.
A large increase in transparency occurred in 1976. A major change is
taking place in the character of the zooplankton of Lake Washington in that
Daphnia became very abundant in 1976. This event is probably not directly
related to recovery from eutrophication, so the lake is entering a new
phase.
This report was submitted in fulfillment of Grant No. R802082 by the
University of Washington under the partial sponsorship of the U.S. Environ-
mental Protection Agency. This report covers the period 1 February, 1973
to 30 November, 1976, and work was completed 10 June, 1977.
iv
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CONTENTS
Foreword ill
Abstract iv
Figures vi
Tables vi
Acknowledgements vii
1. Introduction 1
2. Summa,.; 4
3. Plan of research 5
4. Methods 6
5. Results 9
6. Discussion 13
References 15
Bibliography 17
v
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TABLES
Number Page
1 Transparency, temperature and concentration of selected
substances in surface water of Lake Washington 19
2 Chemical properties of Lake Washington measured at various
depths on selected dates 23
3 Mean values of selected properties of Lake Washington 31
FIGURES
Number
1 Summary of changes in phosphorus, nitrogen and chlorophyll
during the recovery of Lake Washington 32
2 Minimum, mean and maximum Secchi disc transparency during
summer in Lake Washington 34
3 Summary of seasonal changes in Lake Washington 36
VI
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ACKNOWLEDGEMENTS
Most of the data with which the results of this project are compared
were collected with support by a series of grants from the National Science
Foundation which also provided the equipment used. The 1950 data were
collected with support from the State of Washington Research Fund in Biology
and Medicine.
Thanks are due the many people who helped with the large amount of field
and laboratory work on which this report is based, in particular Arni Litt,
David E. Allison, Sally Hartley Abella, Deborah Hairston, Pamela Bissonnette
and Diane Egan. John T. Lehman made some of the calculations of flow, load-
ing and equilibrium.
vii
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SECTION 1
INTRODUCTION
The title of this project derives from the concept that with a given
morphology and climate, the productivity of a lake is largely set by its
nutrient supply. In a stable landscape and climate, the lake will be in
trophic equilibrium with its watershed (Hutchinson and Wollack, 1940). Major
changes in the watershed that affect the amount and character of the nutri-
ents entering the lake will be reflected in the condition of the lake as
expressed by its chemical content, biological productivity, and abundance of
organisms. But, with steady, uniform conditions, as when the lake is sur-
rounded by a climax forest, the lake will have a certain uniformity over a
long span of time. Processes of ecological succession as an initially deep
lake fills in will affect the way the lake distributes its nutrient income
among the various parts of the community; these changes are most pronounced
early and late in the lake's history and smallest in the long middle period.
During this period the lake can be expected to vary around a steady mean from
year to year in response to changes in rainfall, inflow, insolation and other
influential factors. Secular changes in any of these factors can be expected
to be matched by secular changes in the lake. The productivity and abundance
of organisms in a lake will be determined by the combined action of a number
of factors. A significant change in any one of these factors is expected to
affect the productivity in the lake. Lake Washington is one of many lakes
that have been observed to change greatly in response to an increase in
nutrient income in the form of sewage effluent.
Starting in 1941, Lake Washington went through a period of eutrophica-
tion with secondary sewage effluent. The initial effects of increased abun-
dance of algae and decreased transparency coupled with predictions of the
consequences of further enrichment produced considerable concern among resi-
dents of the Lake Washington area. A public vote in 1958 established the
Municipality of Metropolitan Seattle (METRO) which had the responsibility for
improving the sewerage in the region, including the diversion of effluent
from Lake Washington (Chasan, 1971; Edmondson, 1973). The amount of effluent
entering the lake was progressively decreased during the period 1963-1968.
With the first diversion of about one-third of the effluent, the lake stopped
deteriorating, and with further diversion it began to recover, as measured by
increasing transparency and decreasing amount of phytoplankton. By 1972 the
lake appeared to be coming into equilibrium with its new circumstances with
respect to the properties that produce the nuisance conditions associated
with eutrophication (Edmondson, 1972a, b). In any case, the rate of change
was much less than it had been.
A rather detailed limnological study had been made of the lake during
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part of its deterioration and all of its recovery, designed as an experimental
study of lake fertilization (Edmondson, 1972a, 1973). The plan was to measure
at appropriate times and places the chemical and biological properties of the
lake that would be expected to respond to the major changes in nutrient
income. The changes in the condition of the lake were then studied quantita-
tively as a function of the changes in the income of nutrients.
The major support for this study of Lake Washington has come from the
National Science Foundation since 1958, after two initial years of support by
the National Institutes of Health.
By 1972 the experiment could be described as being near completion in
regard to field study (Edmondson 1977a). That is, the lake had reverted to a
condition similar to that observed before eutrophication became publicly evi-
dent in that the concentration of phosphorus was close to that of 1933, and
the transparency was comparable to that observed in 1950. Nevertheless, it
seemed important to continue a study of the lake similar to the one made
during eutrophication and recovery to establish definitely what the basic
condition is. The lake can be expected to vary from year to year with the
normal variation in inflow, nutrients and radiation. Thus, it was necessary
to study the lake long enough to establish the range of variation of the
properties that had been used in the earlier work. The results of such a
study would provide a more secure description of the end-point of the Lake
Washington experiment than would have otherwise been possible, and would also
provide a stronger base against which to measure the response of the lake to
any future changes in its circumstances. For example, a program of sewer
separation is in progress. This will reduce the amount of dilute sewage en-
tering in sewer overflow. Furthermore, while one can expect the lake to
respond to the external conditions mentioned, the magnitude of the changes
could not be predicted as closely as desired. Good advances in evaluation of
phosphorus and water income are being made, but they depend on availability
of appropriate data (Vollenweider and Dillon, 1974; Vollenweider, 1976).
Since this study was beyond the available resources, it seemed appropriate to
request funding from the Environmental Protection Agency to obtain information
about chemical conditions that would permit a comparison of the present
condition of the lake with that during the earlier period when the lake was
still responding strongly to the changes in nutrition. A three-year grant
was secured, extended to cover four summers. Ideally the work should have
been continued long enough to encompass a very wide variation in conditions;
ordinarily a three year period would not be enough. Fortunately, the actual
period of study included a year with minimum inflow of water (1973) and a
year with the largest flood in recorded history (1975-76); however, the range
of annual input of solar radiation was only 44% that experienced during the
past 25 years.
The principal purpose of this report then is to present a description of
chemical conditions in the lake during the period when the work was partly
supported by the Environmental Protection Agency. By itself, such a presen-
tation would not be very useful, since the aim is to compare the different
conditions of the lake and interpret the changes. Therefore, data are pre-
sented for the entire period 1971-1976, and comparison made with three earlier
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years, 1933 and 1950 when the condition of the lake was acceptable, and 1963
when its response to eutrophication was at a maximum (Scheffer and Robinson,
1938; Comita and Anderson, 1959; and Edmondson, 1972a). Because of the bulk,
the entire set of data is not reproduced in this report, but a sampling is
given in Tables 1 and 2. The present report is not an appropriate place to
attempt a full analysis of the changes of the lake during eutrophication and
recovery. Such an analysis is currently under way. Further, data are not
presented on the plankton which has changed in a major way, with the near
disappearance of Oscillatoria and the reappearance of Daphnia after an absence
of at least 23 years (Edmondson, 1977).
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SECTION 2
SUMMARY
During the period 1973-1976, Lake Washington was studied by measuring the
same properties that had been used earlier to evaluate its response to in-
crease and decrease in the amount of sewage effluent reaching the lake. The
lake was considered to have shown most of its reaction to the diversion of
sewage effluent by the beginning of the present study. During the period
covered by this report, concentrations of phosphorus and nitrogen varied, but
very much less than during and immediately after diversion of sewage effluent.
Some of the variations observed could be related to changes in external fac-
tors, particularly silt brought in at times of high flow, but the lake seems
relatively insensitive to the variations that existed during the period of
study. Three properties of the lake did show a systematic trend during the
period of study. The mean summer chlorophyll and annual total phosphorus
values decreased from 1973 through 1976. Secchi disc transparency also showed
a tendency to increase during the period, with a major increase in 1976. Thus
the lake is still changing, but slowly. The reasons for the change will be
found only by additional work.
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SECTION 3
PLAN OF RESEARCH
The general plan was to sample the lake at a standard central station at
intervals of time and depth close enough to define the changes in the condi-
tion with the sensitivity required by the aims of the project as described
above. The chemical sampling, to which this report is devoted, was generally
done at two-week intervals. Every second trip, or once a month, the samples
were analyzed for all the components on the basic list ("complete chemistry").
On the alternate dates, a somewhat simplified scheme of analysis was done
("partial chemistry"). It is desirable to have more frequent measurements of
some properties. Quantitative samples of phytoplankton and zooplankton were
taken every week, and temperature and transparency were almost always mea-
sured on those trips. Additional trips were sometimes made when some special
condition existed. Samples at the central station are adequate for defining
the annual range of conditions and the year to year changes, but on a few
dates, samples were collected at stations widely distributed around the lake
to define the extent of horizontal variation.
The number of depths sampled varied with the stratification of the lake.
When it was unstratified, usually from early December through April or May,
three depths were sampled, surface, mid-depth (30 m) and just over the bottom
(60 m). When it was stratified, usually 12 depths were sampled. Sometimes
additional depths were sampled to permit more exact specification of the gra-
dient of some substance. Examples of the different sampling schemes can be
seen in Table 2, 5 February, 1974 and 16 May, 1974.
On each date of chemical sampling, samples were also collected from the
two major inlets (Cedar River and Sammamish River) and from two minor inlets
(Thornton Creek and Swamp Creek).
2
The area of Lake Washington is 87.615 km , its length 21 km and its maxi-
mum width 5.5 km. The maximum depth is about 62.5 m, the mean 32.9 m, and the
volume 2853.0 million m . Over a 34-year period, the water renewal time,
calculated from a hydrological model, varied between 1.72 and 6.18 years with
a mean of 2.38 years. For more information on the lake and its watershed,
see Edmondson 1977b.
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SECTION 4
METHODS
The properties discussed in this report were selected because they are
direct measures of nutrient input or because they give information about
biological activity.
Phosphorus
Total
Total dissolved
Phosphate phosphorus (inorganic, "reactive")
(filtered and unfiltered)
Nitrogen
Total Kjeldahl N
Dissolved Kjeldahl N
Nitrate
Nitrite
Ammonia
Oxygen
Carbon dioxide
Alkalinity
PH
Seston
Chlorophyll
Transparency
Temperature
In addition, the total study included properties not summarized in this report:
Primary production by C uptake and by oxygen production
Quantitative phytoplankton counts
Quantitative zooplankton counts
Quantitative benthos counts
Periphyton
Sinking material caught by sediment traps (P, N, chlorophyll, dry
weight, diatom counts).
Chemical analysis of water from inlets
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A summary of data on primary production and phosphorus loading has been pre-
pared (Edmondson 1977b) .
Data on insolation measured by a pyrheliometer near Lake Washington were
obtained from the University of Washington Department of Atmospheric Sciences
when available. Otherwise, data from the U. S. Weather Bureau were used.
Measurements of stream flow were supplied by the U. S. Geological Survey,
Tacoma, Washington. Flow data based on a hydrological model were supplied by
METRO. In general, the chemical methods used for this study are based on
standard methods published by Strickland and Parsons (1968), the U. S.
Environmental Protection Agency (1971), and American Public Health Association
(1960). Specific references are given for modifications of different methods.
When filtering was necessary, Millipore HA (0.45 M) filters were used. Most
colorimeteric measurements were made with a Klett industrial model colorimeter
with 5 cm. cell until 1973. Since then, the measurements have been made with
a Brinkman probe colorimeter. Spectrophotometric measurements were made with
a Perkin-Elmer Hitachi recording spectrophotometer .
Phosphorus (Mg/1 of the element P).
Dissolved inorganic phosphate-phosphorus ("reactive") . Ammonium molyb-
date reagent is reduced with stannous chloride (Robinson and Thompson,
1948). Precision is + 5%, limit of detection 1 Mg/1- The analysis is
run on both filtered and unfiltered ("raw") samples with turbidity blank.
The difference, if any, is acid soluble ses tonic P.
Total phosphorus (^g/l). The same reaction as above is carried out on
samples of unfiltered water digested with perchloric acid (Robinson,
1941) . Two ml of 70% perchloric acid are added to a sample. Care is
taken to avoid loss by overheating. The digest is made up to 50 ml and
phosphate determined. The same procedure applied to filtered samples
gives total dissolved phosphorus.
Nitrogen (jzg/1 of the element N) .
Nitrate. Brucine-sulfanilic acid method, (U.S. Environmental Protection
Agency, 1971; Kahn and Brezenski, 1967; Jenkins and Medsker, 1964).
Precision is 5-10%, limit of detection 10 Mg/1.
Nitrite. Sulfanilimide method, (Strickland and Parsons, 1968).
Precision is + 3%, limit of detection 0.2
Ammonia. (Solorzano, 1969). Precision + 5% limit of detection 2 Aig/1.
This method has been in use since May, 1973. Between then and August
1966, ammonia was oxidized and measured as nitrite (Strickland and
Parsons, 1968). Before that, it was measured by Nesslerization.
Organic nitrogen is done by a micro-Kjeldahl method similar to that
described by the American Public Health Association (1960), using
sulfuric acid and hydrogen peroxide. The digested samples are steam-
distilled into 19% hydrochloric acid and the ammonia measured colori-
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metrically with Nessler's Reagent on filtered and unfiltered samples;
the difference is particulate N.
Oxygen (mg/1). Winkler method, unmodified, similar to that described by
American Public Health Association (1960), using a stronger alkaline
iodide reagent (Carpenter, 1965). Precision + 0.2 mg/1.
Carbon dioxide. Titration with 0.1 N sodium bicarbonate to phenolphthalein
endpoint, Precision + 10%. These data have been used in this report,
but CO. can also be calculated from pH and alkalinity with greater
precision for Lake Washington (John T. Lehman, University of Washington
personal communication).
Alkalinity. Titration of 100 ml samples with 0.02 N sulfuric acid to mixed
indicator endpoint (pH 4.5). When pH is above 8.3, the phenolphthalein
endpoint is also recorded. The values in Table 2 are 10 times the
volume of titrant, giving the CaC03 equivalent.
pH. Glass electrode
Seston. (mg/1 dry weight). An appropriate amount of water (100-1000 ml) is
filtered through a prerinsed weighed Millipore HA filter, dried to
constant weight at 80 C. Blank filters are run with distilled water.
Loss on ignition is done with a muffle furnace in porcelain crucibles at
500 C after preignition in air with alcohol.
Chlorophyll a (jig/1 chlorophyll a.). Water is filtered on Millipore HA fil-
ters with vacuum less than 500 mm mercury. Pigments are extracted with
80% acetone for 24 hours in a dark refrigerator. Until 1973 the optical
density of the extract was read with a Klett colorimeter. Since then,
spectrophotometric method described by Strickland and Parsons has been
used with the SCOR/UNESCO equations giving precision of + 0.2 jug/1- The
two methods have been coordinated by reading many samples both ways. The
calculation with Klett measurements was based on a calibration of a
Klett in 1946 by Dr. Harold Haskins of Rutgers University with purified
chlorophyll a. and b_ supplied by Dr. Richard Goodwin of the University of
Connecticut. Preliminary comparison with the spectrophotometric method,
which uses improved knowledge of the specific absorption of chlorophyll,
shows that the original values based on the Klett were low by a factor
of 1.73 (Edmondson 1972a, p. 123 footnote). This correction has been
applied in this report. Unfortunately, some earlier publications gave
uncorrected values.
Temperature. Surface temperature is recorded to nearest 0.1 C with a mercury
thermometer. Temperature at depth is taken with a bathythermograph.,
Transparency (meters). A white 20 cm. Secchi disc is observed under
standardized condition.
Total nutrient content of the lake was calculated by multiplying concentra-
tions by area at depth and by volume of the layers between depths.
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SECTION 5
RESULTS
The figures included in this report have been designed to substitute for
lengthy verbal descriptions of the changes in Lake Washington, and the tables
provide numerical values for a selection of representative dates that indicate
the variations shown during the period of study. The present condition of
the lake can be compared with the recovery stage by examining the means of
certain properties that were sensitive to the changes in nutrient loading.
One needs to be careful in evaluating trends. Minor variations from year to
year produce what may look like new trends at a moment, but in the long run
they turn out to be minor wobbles on the line describing the major trend
(Figure 1).
In 1971, the transparency exceeded that of 1950. In 1972, the values of
phosphorus were almost identical with those of 1933. These events could be
regarded as indicating the recovery of the lake since its condition in 1933
was acceptable (Edmondson, 1972b). Change did not stop at that time. Winter
values of dissolved inorganic phosphate varied widely after 1971, but winter
nitrate showed a generally downward, oscillating trend. The annual mean con-
centration of total phosphorus in the top 10 m decreased during 1971-1976.
The total phosphorus content of the lake decreased proportionally less dur-
ing the same period, its mean value being about 50,000 kg, corresponding to
a concentration of 17 yg/1. Between 1972 and 1976, summer chlorophyll
showed a downward decreasing trend to 54% of its 1972 value. To some extent,
variations above and below the trend lines for these substances are related.
The biggest change during the period of study has been in transparency
(Figure 2). The maximum during the summer of 1976 was 8.2 meters, deeper than
the Secchi disc had ever before been reported at any time of year. Observa-
tions in the preceding few years had suggested that the transparency was
oscillating around a mean of about 3.8 m. Whether 1976 is an aberrant year,
represents a continuing trend, or represents the new condition of the lake
will not be known for some years. This change in transparency is not pro-
portional to the changes in chlorophyll or seston, and must result at least
in part from a change in the character of the plankton.
While the data on plankton are still under analysis, it is known that
there have been substantial changes in recent years (Edmondson, 1977a). Blue
green algae are still present, but the proportions of species and proportions
in relation to other types of algae have changed, especially during 1973-1976.
Filamentous blue greens (Oscillatoria, Pseudanabaena, Lyngbya) are very scarce
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during the summer. The ones that are present form chunky, tight colonies
(Coelosphaerium, Anabaena flos aquae). Since the Secchi disc is very sensi-
tive to the number of light-scattering particles rather than their volume, a
given volume of algae collected together in large colonies will affect the
transparency less than the same amount of material dispersed in many fine
filaments and small cells. With the reduction in total amount of algae,
diatoms have become relatively more prominent than blue greens, and the pro-
portions of species have changed. After many years of relative stability,
the zooplankton has changed importantly in that Daphnia reappeared in 1972,
increased by the year, and became prominent in 1976 after an absence of more
than 23 years (Edmondson 1977a).
The differences among the annual means of chemical properties are not
clearly related in an obvious way to changes in some of the factors that are
known to affect lakes. In the period 1971-1974, total phosphorus loading
varied between 0.43 and 1.00 g/m (Edmondson 1977). The high year was 1972
when floods and landslides in the Cedar River watershed caused delivery of a
great deal of silt to the lake; dissolved phosphate was low during that time.
Since probably most of the mineral phosphorus was not available biologically
dissolved phosphorus is probably a more meaningful component for calculating
loading. The low was 1973, a year of very low water flow (Table 3). Inso-
lation varied more during the period of study than it had during the previous
period of recovery (1963-1973). It was maximum in 1975, minimum in 1973, and
intermediate in the other years (Table 3).
Examination of annual mean values gives only a partial understanding of
the changes in the lake. To some extent, the annual change or the rate of
change of a property may be more revealing than the absolute values. Thus, a
study of the seasonal changes provides the context for the means (Figure 3).
Thermal stratification is important in the seasonal events in a lake.
Lake Washington is monomictic, circulating freely all winter except during
unusual calm spells when it may develop slight transitory stratification.
Stable stratification usually begins to develop late in April or in May and
establishes an epilimnion about 10 m thick and a metalimnion another 10 m.
The surface water begins to cool late in August or early in September, the
epilimnion progressively thickens, and the lake achieves homothermality late
in November or during December. The minimum winter temperature observed
during the period of study was 6.4 C and the maximum summer surface tempera-
ture was 22.9°C (Table 1).
Transparency has shown great variations (Figure 3C). The depth to which
a Secchi disc can be seen is strongly affected by the amount of light scat-
tered back by suspended particles. Thus, transparency will be reduced by
input of silt or by increase of phytoplankton. The maximum inflow through
the tributaries takes place in winter, with low flow usually occurring May-
September; high concentrations of phosphorus tend to accompany high flow
(Figure 3 G,H). Thus, during summer the opportunity for input of large
volumes of silty water is at a minimum, and changes in transparency will be
dominated by changes in phytoplankton (Figure 8 of Edmondson, 1972a).
Despite the increased inflow during winter, the lake usually becomes much
10
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clearer as the phytoplankton declines during fall, and maximum transparency
usually occurs sometime in the period December-March. Two exceptional events
in recent years have reduced the winter transparency. In February, 1972,
heavy local rains and high flow of the Cedar River coupled with landslides
along the Cedar River and near the north end of the lake brought much silty
water into the lake and the transparency was less than in the two bracketing
years. Again in December 1975 and January, 1976, high flow brought in much
silty water through the Cedar River, and the transparency was reduced to
little more than half what it had been the winter before. As mentioned
above, the following summer, the transparency broke all records, reaching 8.2
m on 4 August, 1976. The maximum, 10.2 m occurred in December.
The seasonal changes of phytoplankton as reflected by the chlorophyll
content of surface water show the common pattern of a rapid increase from a
winter low to a maximum in April or May, and a subsequent decrease in summer
(Figure 3D). In 1973, there was a slight indication of a resurgence in fall,
and a much more pronounced fall bloom in 1974. The year 1963 had maximum
chlorophyll development, reaching its peak in June, and maintaining high
concentrations all summer and fall.
Of all the nutrients, phosphorus is given particular attention since it
has been shown to be especially important in controlling the abundance of
phytoplankton in several lakes including Lake Washington (Edmondson, 1972a).
In general, inorganic phosphate is at a maximum during the first three or
four months each year, decreasing in the surface water rapidly during April
and May as the phytoplankton increases (Figure 3A). As shown earlier, a
strong correlation exists between the concentration of phosphate in the
winter and the amount of phytoplankton developed and maintained the next
summer as measured by chlorophyll and particulate phosphorus (Edmondson,
1972a). Total phosphorus varies somewhat during the year, but tends to be
more uniform than phosphate. While in most years it tends to decrease during
stratification, it does not decrease nearly as much as phosphate because it
is held by the plankton.
In the years of heavy eutrophication, phosphorus was in excess relative
to use by phytoplankton, and substantial concentrations of phosphate were
left in the surface water at the end of the spring, but in 1933 and in recent
years, phosphate approached closely to zero (Table 1).
Phosphorus remains in the hypolimnion during the summer at about the
same concentration it had at the beginning of stratification, generally with
some tendency to increase (Table 2 and Edmondson 1972a, 1977a).
The phosphate concentration was distinctly lower during the first three
months of 1972 than it was during the preceding winter or any of the fol-
lowing winters. This minimum came after the flood that brought silt into the
lake. It seems likely that the settling clay absorbed part of the phosphate
and carried it to the bottom. The phosphate in the early months of 1976,
also following a flood and period of silty inflow, was less than in the
preceding two years, but higher than in 1972.
11
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The pattern of annual changes of nitrogen are similar to those of phos-
phorus (Figure 3B). Nitrate is at a maximum during winter and decreases
during the growth of the spring phytoplankton. Total Kjeldahl nitrogen varies
irregularly within a rather narrow range. Ammonia and nitrite are always very
small compared to nitrate (Table 2). The ratio of nitrogen to phosphorus has
changed greatly over the years (Edmondson 1972a). In its unpolluted state,
Lake Washington had an excess of nitrate in the sense that during the growth
of the plankton in spring, phosphate came close to zero values while nitrate
still maintained significant concentrations. During the years of heavy
eutrophication, significant concentrations of phosphate were left when nitrate
was nearing zero. This was attributed to the fact sewage has a large excess
of phosphorus relative to the proportion in natural waters and in organisms.
This characteristic was accentuated by the use of detergents based on phos-
phorus. Thus, during eutrophication, the lake developed a very unnatural N:P
ratio, and during recovery it reverted to a condition in which phosphorus is
limiting.
Oxygen is well known to be a sensitive indicator of changes in productive
conditions in stratified lakes. Each summer, the oxygen concentration in the
hypolimnion progressively decreases, but in recent years the concentration in
most of the water remained above 5 or 6 mg/1 at the end of summer (Table 2).
In contrast, during the years of eutrophication, values less than 4.0 were
common in much of the hypolimnion at the end of summer (Edmondson 1963, 1972a).
Changes in rate of development of the hypolimnetic oxygen debt were used
as strong indicators of approaching deterioration in the early studies of the
eutrophication of Lake Washington but its usefulness was lessened by qualita-
tive changes in the phytoplankton (Edmondson, 1966).
During the summer, carbon dioxide increases in the hypolimnion, in strong
inverse correlation with oxygen (Table 2).
12
-------
SECTION 6
DISCUSSION
The aim of this study was to help establish a description of the condi-
tion of Lake Washington after the diversion of secondary sewage effluent
which took place over a five year period. In 1963 about 28% of the effluent
was diverted, about half had been diverted by 1965, and the project was com-
pleted early in 1968, although most of the effluent had been diverted early
in 1967. The lake responded sensitively to each stage of diversion and rap-
idly returned to a condition comparable in some ways with the condition be-
fore eutrophication had become a problem. The rapidity of response probably
results from several features. Although the mean residence time of water is
2.38 years, it was only 2.08 years during 1968-1971. The lake has steep sides
in most parts and there is relatively little littoral development with dense
growths of rooted plants. Less than 8% of the bottom area is less than 5 m
deep. Even at the height of eutrophication, large volumes of hypolimnion
did not become anoxic for long periods.
Using the total phosphorus content of the entire lake as a criterion of
the effect of diversion of effluent, we can identify a period of recovery
after diversion, 1968-1970, and a post-recovery period during which the phos-
phorus content varied above and below a mean value of about 50,000 kg with
only a slight decreasing trend during the period (Figure 1). Since the vol-
ume of the lake is 2853.0 million m , the corresponding concentration is
about 17 yg/1.
The interpretation of these data on phosphorus is somewhat subjective,
being influenced by the selection of the beginning of the post-recovery per-
iod. The year 1971 is a reasonable choice since it was in that year that a
major prediction about the rate of recovery of the lake was confirmed (Ed-
mondson, 1972b). A linear regression fitted to the individual measurements
on which the means of Figure 1C are based for 1971-1976 has a slope of
minus 2700 kg/year, significantly different from zero at the 0.03 level by
the _t test. In view of the magnitude of the year to year differences in
phosphorus and hydraulic loading and the small number of years involved, a
horizontal line may be a satisfactory description of the data (Figure 1C).
These figures suggest that Lake Washington has come into or is about to
come into equilibrium with the present conditions in the watershed in terms
of its phosphorus content. The assumption behind this statement is that
conditions in the watershed that affect phosphorus are not changing in a
secular manner.
Considerable attention has been given to the budgetary relations of
phosphorus in terms of input, sedimentation and output, and a variety of
13
-------
models or computational schemes elaborated (Piontelli and Tonolli, 1964; Vol-
lenweider 1969, 1976). On the basis of the mean annual inflow of water and
input of phosphorus for the period 1971-1975, the equilibrium value for the
total phosphorus content of the lake can be calculated using one of the sim-
pler methods (Piontelli and Tonolli, 1964; Vollenweider, 1969). Phosphorus
input was 52,600 kg and water was 1352 million m^ per year. (These figures
may become subject to slight revision on the basis of improved knowledge of
hydrological conditions, probably about 10% upward.) Since the area of the
lake is 87.615 km , the mean areal loading during the period was 0.67 g/m
year. With retention values of 50%, 60% and 70%, the equilibrium values for
total phosphorus would be 57,500, 46,000 and 34,500 kg respectively (Fig.
3C). The observed total retention during 1971-1975 was 56.1% of the phos-
phorus that entered the lake, corresponding closely to the observed mean of
about 50,000 kg.
Nitrogen has continued to decrease during the entire so-called post-
recovery period, so the lake cannot be said to have achieved full trophic
equilibrium. This may be a result of the biogeochemical versatility of
nitrogen in contrast to phosphorus. At least three differences are involved.
Nitrate is more mobile than phosphate, and more easily displaced from the
soil when land is developed. The nitrate concentration of the Cedar River
increased after 1957 (Edmondson 1972a). The diversion of sewage would have
affected nitrogen less than phosphorus because the N:P ratio of secondary
sewage effluent is very much lower than in tributary waters (Edmondson 1969).
Finally, Lake Washington contained significant amounts of nitrogen-fixing
blue green algae. Thus there is no reason to have expected the nitrogen con-
tent of the lake to have changed in the same way as that of phosphorus.
Chlorophyll has continued to decrease during the post-recovery period,
but phytoplankton is strongly affected by zooplankton, and zooplankton has
been changing since 1972 for reasons probably unrelated to diversion of
sewage (Edmondson, 1977a). Lake Washington is entering a new phase, and more
time must pass and work be done before we can understand the changes that are
happening now.
14
-------
REFERENCES
American Public Health Association. 1960. Standard Methods for the Examin-
ation of Water and Wastewater. (llth edition, earlier editions were used in
the 1950's).
Carpenter, J. H. 1965. The Chesapeake Bay Institute Technique for the Wink-
ler Dissolved Oxygen Method. Limnol. Oceanog. 10:141-143.
Chasan, D. J. 1971. The Seattle Area Wouldn't Allow Death of Its Lake.
Smithsonian 2:6-13.
Comita, G. W., and G. C. Anderson. 1959. The Seasonal Development of a
Population of Diaptomus ashlandi Marsh, and Related Phytoplankton Cycles in
Lake Washington. Limnol. Oceanogr. 4:37-52.
Edmondson, W. T. 1963. Pacific Coast and Great Basin, p. 371-392 In D. G.
Frey (ed.) Limnology in North America. University of Wisconsin Press, Madi-
son, Wisconsin.
Edmondson, W. T. 1969. Eutrophication in North America, pp. 124-149 in
Eutrophication: Causes, Consequences, Correctives. National Academy of
Sciences Publication No. 1700.
Edmondson, W. T. 1972a. Nutrients and Phytoplankton in Lake Washington.
pp. 172-193 In Nutrients and Eutrophication, G. Likens (ed.). American
Society of Limnology and Oceanography, Special Symposia No. 1.
Edmondson, W. T. 1972b. The Present Condition of Lake Washington. Verh.
Internat. Verein. Limnol. 18:284-291.
Edmondson, W. T. 1973. Lake Washington, pp. 281-298 in Environmental
Quality and Water Development. C. R. Goldman, James McEvoy III and Peter
J. Richerson, eds. Freeman. (Originally published as a report to the
National Water Commission.)
Edmondson, W. T. 1977a. The Recovery of Lake Washington from Eutrophica-
tion. pp. 102-109 in Recovery and Restoration of Damaged Ecosystems, ed.
J. Cairns, Jr., R. L. Dickson and E. E. Herricks. University Press of
Virginia.
Edmondson, W. T. 1977b. Lake Washington in: North American Project—A
Study of U.S. Water Bodies: a Report for the Organization for Economic
Cooperation and Development. Published by Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency (in press).
15
-------
Hutchinson, G. E., and A. Wollack, 1940. Studies on Connecticut Lake Sedi-
ments. II. Chemical Analyses of a Core from Linsley Pond, North Branford.
Am. Jour. Sci. 238:493-517.
Jenkins, D., and L. L. Medsker. 1964. Brucine Method for Determination of
Nitrate in Ocean, Estuarine and Fresh Waters. Anal. Chem. 36:610:612.
Kahn, L. , and F. T. Brezenski. 1967. Determination of Nitrate in Estuarine
Waters. Envir. Sci. and Technol. 1:488-491
Piontelli, R., and V. Tonolli. 1964. II Tempo A± Residenza Acque Lacustri
in Relazione ai Fenomeni di Arricchimento in Soztanze Immesse, con Parti-
colare Riguardo al Lago Maggiore. Mem. 1st. Ital Idrobiol. 17:247-266.
Robinson, R. J. 1938. The Data of Lake Washington. Typewritten, University
of Washington Library. For summary, see Scheffer and Robinson (1938).
Robinson, R. J. 1941. Perchloric Acid Oxidation of Organic Phosphorus in
Lake Waters. Anal. Chem. 13:465-466.
Robinson, R. J. , and T. G. Thompson. 1948. The Determination of Phosphates
in Sea Water. J. Mar. Res. 7:33-41.
Scheffer, V. B., and R. J. Robinson. 1939. A Limnological Study of Lake
Washington. Ecol. Mongr. 9:95-143.
Solorzano, L. 1969. Determination of Ammonia in Natural Waters by the
Phenolhypochlorite Method. Limnol. Oceanog. 14:799-801.
Strickland, J. D. H., and T. R. Parsons. 1968. A Practical Handbook of
Seawater Analysis. Bull. 167 Fish. Res. Bd. Canada, (second edition).
U.S. Environmental Protection Agency. 1971. Methods for Chemical Analysis
of Water and Wastes.
Vollenweider, R. A. 1969. MSglichkeiten und Grenzen Elementarer Modelle
der Stoffbilanz von Seen. Arch. Hydrobiol. 66:1-36.
Vollenweider, R. A. 1976. Advances in Defining Critical Loading Levels for
Phosphorus in Lake Eutrophication. Mem. 1st. Ital. Idrobiol. 33:53-83.
Vollenweider, R. A., and P. Dillon. 1974. The Application of the Phosphorus
Loading Concept to Eutrophication Research. NRCC Report No. 13690, 42 pp.
16
-------
BIBLIOGRAPHY
Carlson, R. E. 1977. A Trophic State Index for Lakes. Limnol. Oceanog.
22:361-369.
Chapra, S. C., and S. T. Tarapchak. 1976. A Chlorophyll a_ Model and Its
Relationship to Phosphorus Loading Plots for Lakes. Water Resources
Research. 12:1260-1264.
Chen, C. W., and G. T. Orlob. 1975. Ecologic Simulation for Aquatic En-
vironment, pp. 476-588., in B. C. Patten ed. Systems Analysis and
Simulation in Ecology. Vol. III.
Davis, M. B. 1973. Pollen Evidence of Changing Land Use Around the Shores
of Lake Washington. Northwest Science. 47:133-148.
Dillon, P. J., and F. H. Rigler. 1974. The Phosphorus-Chlorophyll Rela-
tionship in Lakes. Limnol. Oceanog. 19:767-773.
Edmondson, W. T., G. C. Anderson and D. R. Peterson. 1956. Artificial
Eutrophication of Lake Washington. Limnol. Oceanog. 1:47-53.
Edmondson, W. T. 1961. Changes in Lake Washington Following an Increase
in the Nutrient Income. Verh. Internat. Verein. Limnol. 14:167-175.
Edmondson, W. T. 1966. Changes in the Oxygen Deficit of Lake Washington.
Verh. Internat. Limnol. Verein. 16:153-158.
Edmondson, W. T. 1968. Water Quality Management and Lake Eutrophication:
The Lake Washington Case. pp. 139-178 in Water Resources Management
and Public Policy. T. H. Campbell and R. 0. Sylvester (eds.) Univer-
sity of Washington Press.
Edmondson, W. T. 1969b. Cultural Eutrophication with Special Reference to
Lake Washington. Mitt. Internat. Verein. Limnol. 17:19-32.
Edmondson, W. T. 1970. Phosphorus, Nitrogen and Algae in Lake Washington
after Diversion of Sewage. Science 196:960-691.
Edmondson, W. T. 1974a. Review of The Environmental Phosphorus Handbook.
Limnol. Oceanog. 19:369-375.
Edmondson, W. T. 1974b. The Sedimentary Record of the Eutrophication of
Lake Washington. Proc. Nat. Acad. Sci. 71:5093-5095.
17
-------
Kemmerer, H. , J. F. Bovard and W. R. Boorman. 1924. Northwestern Lakes of
the United States: Biological and Chemical Studies with Reference to
Possibilities in Production of Fish. Bull. U. S. Bureau Fish. 39:51-140.
Oglesby, R. T. , W. R. Schaffner and E. L. Mills. 1975. Nitrogen, Phosphorus
and Eutrophication in the Finger Lakes. Tech Rep. No. 94, Cornell Univ.
Water Resources and Marine Sciences Center.
Shapiro, J., W. T. Edmondson and D. E. Allison. 1971. Changes in Chemical
Composition of Sediments of Lake Washington, 1958-1970. Limnol. Oceanog.
16:437-452.
Snodgrass, W. J. and C. R. O'Melia. 1975. Predictive Model for Phosphorus
in Lakes. Environ. Sci. Technol. 9:937-944.
Thut, R. 1969. A Study of the Profundal Bottom Fauna of Lake Washington.
Ecol. Mongr. 39:79-100.
Wydowski, R. S. 1972. Annotated Bibliography on the Ecology of the Lake
Washington Drainage. Coniferous Forest Biome Bull. No. 1, Seattle.
Fisheries Research Institute, University of Washington, Seattle.
18
-------
TABLE 1. TRANSPARENCY, TEMPERATURE AND CONCENTRATION OF SELECTED SUBSTANCES
IN SURFACE WATER OF LAKE WASHINGTON
A. Total P
B. Phosphate-P (unfiltered)
C. Total Kjeldahl N
D. Nitrate-N
E. Seston, dry weight
F. Chlorophyll a
G. Transparency, m (Secchi disc)
H. Surface temperature
Note: Chlorophyll, phosphorus and nitrogen as vg/1, seston as mgm/1,
transparency in meters, temperature, degrees Celsius. Blanks mean
no determination. Zeros mean the concentration was below the level
of detection. Transparency and temperature were measured on 171
trips when no chemical samples were taken.
Date
1973
Jan 2
18
30
Feb 13
Mar 8
20
Apr 3
17
May 8
22
Jun 6
19
Jul 3
17
Aug 1
14
29
Sep 11
25
Oct 10
23
Nov 6
20
Dec 4
11
A
19.7
-
18.4
-
20.3
-
19.9
-
14.5
-
14.8
-
12.6
-
14.0
-
9.7
-
20.0
—
8.6
_
20.0
—
19.3
B
10.9
10.5
11.1
13.6
9.3
10.0
2.2
2.0
1.2
4.2
1.2
2.4
0
0
1.1
0
0
1.1
2.0
0.6
0.8
1.7
8.2
12.7
16.4
C
214
204
250
230
301
235
301
308
402
264
231
169
D
315
301
333
321
316
329
262
250
213
113
89
49
25
35
6
20
19
38
50
30
46
118
202
251
261
E
1.1
1.2
1.4
3.0
1.7
2.4
3.5
2.2
2.6
1.6
1.2
0.6
F
1.7
1.2
1.0
1.2
1.0
1.0
4.4
6.6
2.3
4.5
3.2
3.6
2.9
2.4
3.8
2.4
1.2
2.4
1.6
2.8
1.2
1.5
0.6
1.3
G
5.0
4.6
6.2
6.0
5.9
4.0
3.6
6.5
3.5
4.0
3.0
3.0
3.5
3.2
3.4
3.6
3.4
3.6
4.5
5.0
5.0
5.5
5.5
6.0
H
8.4
8.1
7.8
8.6
9.0
7.4
10.2
8.7
10.8
14.7
16.5
15.6
18.1
21.7
21.3
20.3
18.8
19.0
17.3
15.3
14.0
11.5
9.7
9.0
8.6
(continued)
19
-------
TABLE 1 (continued)
Date
1974
Jan 8
22
Feb 5
21
Mar 5
21
Apr 4
18
May 2
16
29
Jun 13
27
Jul 10
24
Aug 8
22
29
Sep 4
17
Oct 2
15
29
Nov 12
25
Dec 5
10
23
1975
Jan 7
21
Feb 4
18
Mar 4
19
27
Apr 1
8
15
29
May 14
23
27
Jun 6
10
18
24
A
20.0
—
26.9
—
32.0
_
25.2
15.9
-
20.7
7.6
_
10.0
-
6.3
-
11.4
_
3.2
_
9.7
_
10.0
-
15.2
_
17.2
21.2
21.2
_
22.1
22.6
16.2
13.6
11.3
14.7
12.8
9.4
10.0
8.6
9.4
B
19.2
19.3
20.7
19.7
20.4
17.1
11.6
5.9
6.1
0
0.2
0
0.3
1.5
0.9
0.5
0
1.0
0
0
1.6
0
0.5
3.4
8.0
9.5
14.4
16.9
15.4
15.5
13.3
14.8
10.6
10.0
4.1
0.6
1.6
1.8
0
0
1.3
0.5
0
C
194
168
217
273
218
170
265
298
233
238
214
294
227
224
188
186
228
341
258
256
D
355
360
350
390
353
321
278
274
307
220
180
110
99
50
33
26
32
36
27
24
31
54
73
108
168
209
267
277
314
317
304
333
324
201
177
149
103
101
66
55
50
37
E
1.4
1.7
1.7
2.4
2.1
3.0
2.8
2.1
2.6
2.4
2.0
1.8
1.3
1.4
1.6
1.2
2.2
4.5
2.6
2.6
F
1.3
1.3
1.3
1.4
2.0
4.3
7.2
7.0
10.0
5.0
5.5
5.3
5.1
4.2
2.1
3.1
2.3
4.2
4.8
5.8
5.3
5.8
5.4
4.3
4.5
3.5
2.4
1.9
2.2
2.1
4.0
3.9
6.8
13.0
12.9
16.9
15.4
10.3
6.7
1.4
5.8
2.7
6.2
G
6.0
4.5
4.5
5.0
5.0
5.3
5.0
4.5
5.5
4.0
4.0
3.0
3.5
3.3
2.7
4.2
4.5
4.7
5.5
5.5
4.8
4.4
4.7
5.5
5.4
5.7
5.7
6.2
6.2
7.5
7.3
6.4
6.0
4.4
3.3
4.0
2.8
3.4
3.3
3.4
2.9
4.4
4.0
( f*r\v\ t- '
H
7.2
6.6
6.5
6.4
7.1
7.6
9.4
9.3
10.2
13.8
18.2
15.6
16.7
19.8
21.9
20.5
22.3
20.9
19.8
18.1
16.4
14.7
12.6
11.1
10.1
9.8
9.4
8*\
.3
8.2
8.0
7.5
7.2
7.4
7.4
7.8
9.1
9.7
9.9
13.2
12.7
14.1
16.4
16.4
16.8
16.2
I r\fte*r\ ^
20
-------
TABLE 1 (continued)
(1975 cont.
Jul 2
8
9
15
22
Aug 5
12
19
Sep 3
16
24
30
Oct 14
22
29
Nov 4
11
18
25
Dec 9
17
23
30
1976
Jan 6
20
28
Feb 3
17
Mar 2
9
16
30
Apr 8
14
21
28
May 6
11
19
Jun 1
15
23
) A
10.2
11.5
12.7
13.6
13.3
12.0
5.1
7.4
-
-
11.2
11.9
12.4
12.8
12.6
12.1
14.8
21.9
22.2
22.5
11.1
17.5
19.5
19.5
20.6
16.1
23.4
20.8
18.2
16.6
14.6
15.3
11.4
11.5
8.8
12.4
11.4
10.6
19.4
11.5
B
0.8
1.1
0
0.7
0.9
0.4
0.2
0.7
0.2
1.4
0.5
0.8
1.0
1.4
2.0
5.2
7.8
10.8
11.6
14.2
14.1
12.3
12.8
14.4
12.3
14.2
13.3
11.1
7.6
6.4
4.5
1.1
1.9
1.0
2.4
1.1
1.0
1.2
0
1.4
C
239
319
247
291
231
221
202
198
250
197
196
276
228
243
D
23
16
19
23
32
11
36
24
25
19
21
33
37
68
104
151
182
217
254
282
277
276
319
321
311
308
295
296
272
257
275
216
213
201
196
177
184
138
130
100
74
E
2.0
2.0
1.8
1.7
1.1
1.6
1.3
1.3
1.4
3.0
2.8
2.3
1.9
3.1
3.2
2.9
3.4
4.2
2.0
2.2
2.3
0.7
F
4.7
2.2
4.2
3.3
3.5
4.4
4.1
2.1
0
1.0
5.6
6.2
4.7
3.3
4.2
0.7
2.9
2.6
3.6
2.3
2.4
2.4
2.8
3.3
4.2
6.9
6.9
6.8
7.6
7.6
6.8
6.9
6.4
3.9
4.6
G
4.1
4.8
5.6
4.4
3.8
3.8
3.4
4.0
4.1
4.0
4.0
4.0
5.6
6.5
6.0
6.0
6.2
6.5
6.8
5.3
2.5
3.3
4.2
4.6
4.5
4.9
5.2
5.0
5.5
4.2
4.4
4.6
5.4
4.9
4.2
4.2
4.1
4.3
H
16.4
20.5
21.7
20.4
21.0
20.4
20.7
19.4
17.8
18.0
18.3
17.5
15.2
14.2
12.6
12.9
10.8
10.0
9.5
8.8
8.0
7.6
7.2
7.2
7.0
6.7
6.4
6.5
7.0
8.3
8.1
8.8
9.3
10.7
12.7
11.0
12.7
12.2
15.5
15.6
(continued)
21
-------
TABLE 1 (continued)
(1976 cont.
Jul 1
8
15
21
27
Aug 4
10
18
24
Sep 2
7
15
21
30
Oct 6
13
20
27
Nov 2
10
17
23
30
Dec 9
15
21
28
) A
9.7
10.0
14.5
11.1
9.4
14.2
10.3
9.7
7.8
10.0
7.8
9.7
7.1
8.1
6.7
4.8
7.8
6.8
6.9
7.9
9.6
10.3
11.9
11.3
14.5
14.3
B
0.5
0.5
0.3
0.5
0.6
0
0.5
0
0
0.3
1.8
0
0
0.5
1.0
0
1.0
0.5
1.6
2.9
5.3
7
10.3
10.0
C D
258 134
53
52
231 32
32
27
213 31
23
8
246 73
44
55
54
197 55
54
83
89
207 108
110
162
186
195 207
103
266
E
1.1
1.8
1.8
2.1
2.8
2.1
1.7
0.8
1.1
0.8
0.9
0.7
0.7
0.8
F
4.0
2.3
4.3
5.1
2.7
3.2
2.3
3.1
1.9
3.0
2.3
2.5
2.7
1.5
2.8
2.7
3.9
3.4
2.9
3.4
2.4
1.8
2.6
1.8
1.4
G
6.0
6.3*
5.5
4.8
5.0
5.4
5.7
4.6
5.1
5.4
5.5
6.5
8.2
8.4
9.2
9.2
8.9
9.8
9.2
9.2
9.8
9.8
9.0
9.5
10.2
9.4
H
17.9
19.2
19.4
19.9
20.5
20.1
19.6
18.9
20.4
18.8
18.3
18.5
17.2
16.9
15.6
14.5
13.8
13.3
12.6
12.0
10.8
10.0
9.8
9.5
9.0
* 8.2 on 13 July
22
-------
TABLE 2. CHEMICAL PROPERTIES OF LAKE WASHINGTON MEASURED AT VARIOUS DEPTHS ON SELECTED DATES
A. Chlorophyll a_ I.
B. Total phosphorus J.
C. Dissolved phosphorus K.
D. Phosphate-phosphorus (unfiltered) L.
E. Phosphate-phosphorus (filtered) M.
F. Total Kjeldahl nitrogen N.
G. Dissolved Kjeldahl nitrogen 0.
H. Nitrate nitrogen P.
Nitrite nitrogen
Ammonium nitrogen
Oxygen
Carbon dioxide
Alkalinity
Seston
pH
Total alkalinity
Note: Chlorophyll, phosphorus and nitrogen as yg/1, other concentrations as mg/1. Data are from two
stations, the usual main station at Madison Park (MP) and a station north of the Evergreen Point
Bridge (NEPB), occupied when strong winds are blowing from the south. Surface temperature is
given in degrees Celsius and Secchi disc transparency in meters.
N5
30 January, 1973
NEPB
Temp. 7.8°
Trans. 4.6 m
Depth
0
30
59
8 March,
Depth
0
30
60
A
1.7
1.6
1.7
1973
A
1.0
0.8
0.8
B
18.
20.
21.
B
20.
19.
23.
4
6
6
3
5
0
C
13.1
11.9
13.1
MP
C
10.9
12.8
14.4
D
11.1
10.7
11.1
D
9.3
12.7
16.0
E
10.
10.
11.
Temp.
E
9.
12.
14.
0
0
1
9.
3
7
0
F
204
229
208
0°
F
250
228
222
G
191
148
166
Trans
G
163
172
202
H
333
326
314
. 6.0
H
316
329
345
I
0.7
0.7
0.6
m
I
0.0
0.0
0.0
J K L M N 0
0.0 10.97 2.24 30.2 1.20 7.35
0.0 10.99 2.08 30.1 1.48 7.35
0.0 10.85 2.20 30.2 1.44 7.30
J K L M N 0
0.0 11.83 1.40 30.7 1.36 7.80
0.0 11.22 2.32 30.4 0.96 7.45
0.0 10.51 2.48 30.4 0.96 7.30
(continued)
-------
TABLE 2 (continued)
3 April, 1973 MP Temp
Depth
0
5
15
30
60
6 June,
Depth
0
5
10
15
20
30
40
50
59
A B C D
4.4 19.9 6.7 2.2
6.2 19.9 6.4 2.8
4.3 20.2 8.9 7.8
2.4 18.9 12.0 8.9
1.5 20.8 15.4 13.3
1973 NEPB Temp
A B C D
3.2 14.8 4.6 1.2
2.4 12.2 3.0 1.2
4.3 13.5 3.7 1.9
1.4 11.6 4.0 2.5
1.2 11.3 6.2 5.0
0.7 16.7 13.8 12.2
0.6 16.7 13.8 13.3
0.4 23.1 16.7 16.7
0.5 23.1 16.7 16.7
25 September, 1973 NEPB Temp
Depth
0
5
10
12
15
18
20
25
30
40
50
55
59
A B C D
1.6 20.0 11.1 2.0
1.6 - - 1.7
2.0 15.6 - 1.5
2.0 13.3 4.7 1.2
1.2 13.3 4.0 1.0
0.6 8.0 4.7 2.2
0.0 15.6 9.3 6.1
0.0 17.8 12.2 8.5
0.6 25.0 20.7 15.0
0.0 25.0 22.9 16.9
0.0 32.1 27.9 21.9
0.0 32.1 27.1 23.3
0.4 40.0 30.0 26.1
. 10.20
E
2.2
2.2
4.4
8.3
12.2
. 16.5°
E
1.2
0.6
1.2
1.9
3.8
12.2
12.8
15.6
14.6
. 17.3°
E
0.2
0.0
0.5
1.7
0.2
0.7
4.1
7.6
13.3
15.3
18.3
18.3
21.7
Trans . 4 .
F
230
270
217
322
322
G
162
254
175
171
166
Trans. 4.
F
235
225
190
181
171
148
119
181
181
G
157
114
114
105
119
138
90
105
105
Trans . 3 .
F
264
217
231
302
207
231
192
122
159
186
202
186
192
G
138
132
138
154
154
149
127
149
122
176
202
132
192
0 m
H
262
287
329
343
364
0 m
H
89
96
155
277
319
366
378
394
394
6 m
H
50
55
50
57
110
330
353
377
385
406
416
431
436
I
0.6
0.6
0.8
1.8
0.0
I
2.2
1.9
1.2
0.8
0.1
0.3
0.3
0.6
0.6
I
0.5
0.5
0.5
0.5
0.0
0.6
0.5
9.5
0.7
0.2
0.6
0.6
0.1
J
0.0
0.0
0.0
0.0
0.0
J
2.1
0.1
6.2
9.0
0.2
1.0
0.0
2.4
2.4
J
3.0
4.5
4.8
3.3
5.0
1.3
2.0
1.3
2.3
1.5
0.5
1.8
15.0
K
12.92
12.56
11.81
11.32
10.50
K
10.99
10.99
10.32
9.80
9.76
9.52
9.38
8.93
8.22
K
9.84
9.66
9.54
9.50
7.88
8.00
6.05
7.18
6.77
7.20
6.85
6.09
4.20
L
0.20
0.68
1.12
0.60
2.00
L
0.0
0.0
0.20
2.20
2.60
2.96
3.60
4.24
4.60
L
0.60
0.80
0.80
1.00
4.20
7.60
7.80
-
7.00
7.00
7.80
8.80
10.20
M
30.9
31.3
21.3
30.5
30.3
M
28.5
28.1
32.5
31.2
30.9
30.6
30.6
30.4
30.5
M
33.3
33.5
33.4
33.2
32.0
30.3
30.0
30.0
29.8
20.5
29.4
29.5
29.5
N
3.04
3.60
2.44
1.28
1.08
N
2.40
2.48
2.32
0.96
0.72
0.60
0.60
0.64
0.76
N
1.55
1.86
1.81
1.65
1.17
0.56
0.64
0.44
0.52
0.70
0.52
0.64
0.80
0
8.00
7.95
7.65
7.50
7.30
0 P
8.20 32.9
8.45 33.1
8.00
7.50
7.40
7.30
7.30
7.20
7.20
0
8.02
8.20
8.11
8.12
7.30
7.07
7.01
7.04
7.04
7.07
7.00
6.96
6.82
(continued)
-------
TABLE 2 (continued)
Oi
20 November, 1973 NEPB Temp. 9.7°
Depth
0
5
10
20
30
40
50
55
59
ABODE
1.5 20.0 11.4 8.2 7.1
21.8 6.9 7.4 6.8
1.5 25.4 10.0 7.9 6.8
21.8 10.0 8.2 7.6
41.8 29.1 29.7 24.3
49.0 30.9 35.6 27.0
0.6 50.9 36.4 37.6 28.9
50.9 38.2 35.9 30.6
5 February, 1974 MP Temp. 6.6°
Depth
0
5
30
60
16 May,
Depth
0
5
10
20
25
30
40
50
60
A B C D E
1.3 26.9 20.6 20.7 18.9
1.2 29.6 20.2 20.0 18.9
1.0 27.1 19.0 21.4 17.9
1974 MP Temp. 10.2°
A B C D E
10.0 0.0 0.0
9.9 0.8 0.0
7.6 1.1 0.0
7.1 1.4 1.4
6.8 1.7 2.3
2.6 7.6 6.8
1.3 14.1 13.0
0.7 20.7 18.0
0.8 19.7 19.1
Trans . 5 .
F
231
220
242
220
236
187
181
214
G
171
165
128
160
144
155
Trans . 4 .
F
168
141
G
162
200
114
Trans . n .
F
G
5 m
H
202
200
196
200
409
440
437
447
5 m
H
350
342
336
0 u
H
220
228
288
283
316
349
379
397
426
I
1.0
0.5
0.5
0.6
0.1
0.5
0.1
0.2
I
0.5
0.5
1.0
I
2.3
2.1
2.9
3.0
3.7
8.6
8.6
0.7
0.6
J
9.1
3.4
1.7
0.0
1.1
0.0
8.2
2.0
J
0.0
0.0
0.0
J
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.9
1.0
K
9.38
9.25
9.15
9.11
4.87
4.19
3.89
3.89
K
11.54
11.44
11.50
K
12.08
12.12
11.78
11.70
11.67
11.37
11.00
10.29
10.22
L
3.00
3.12
3.40
3.40
8.00
10.44
10.96
10.64
L
2.00
2.00
1.96
1.96
L
M
31.1
31.3
31.1
31.2
31.2
29.7
29.5
29.5
29.4
M
30.0
30.1
29.1
M
N
7
7
7
7
7
6
6
6
6
N
1.67 7
7
1.55 7
2.29 7
N
0
.21
.57
.32
.31
.30
.92
.91
.88
.72
0
.22
.13
.08
.29
0
(continued)
-------
TABLE 2 (continued)
27 June
Depth
0
5
10
15
20
25
30
40
50
55
60
, 1974
A
5.3
5.8
4.2
1.6
0.6
0.4
0.4
0.5
0.5
0.4
0.4
17 September,
Depth
0
5
10
12.5
15
17.5
20
25
30
40
50
55
60
A
4.2
4.4
4.7
1.3
0.2
0.3
0.1
0.1
0.2
0.3
0.3
NEPB
B C
7.6 1.2
12.3 3.6
13.9 13.2
10.4 3.7
9.7 4.8
13.8 9.4
9.3 6.8
19.6 13.8
31.3 18.1
33.5 18.4
26.8 32.2
1974 MP
B C
11.4 3.7
10.3 3.9
15.7 3.9
9.1 3.0
10.0 7.6
17.3 3.9
21.4 15.9
16.5 19.2
37.1 31.4
54.8 39.5
47.1 39.5
Temp
D
0.3
0.6
1.8
3.3
3.9
9.7
7.0
14.1
22.1
20.3
21.4
Temp
D
0.5
1.0
1.0
1.4
5.7
11.6
15.8
18.9
24.6
30.0
36.1
. 15.6°
E
0.6
0.9
0.9
1.2
3.0
9.1
6.7
14.9
19.7
19.4
21.0
. 19.8°
E
1.0
1.0
1.0
1.4
5.2
11.6
15.3
18.9
24.2
28.3
29.6
Trans . 3
F
265
270
270
226
184
167
151
151
209
222
172
G
167
167
209
184
145
194
156
184
167
226
184
Trans . 4
F
238
238
244
182
177
197
203
197
167
182
249
G
187
167
156
172
167
157
116
167
172
157
228
.5 m
H
99
101
99
213
281
332
315
351
371
366
374
.3 m
H
27
26
21
204
330
364
345
398
410
451
459
I
4.2
4.5
4.8
3.2
1.2
0.5
0.6
0.5
0.5
1.0
1.1
I
0.2
0.0
0.2
0.3
0.3
0.2
0.2
0.3
0.3
0.7
0.5
J
31.0
23.0
31.0
35.0
9.0
1.0
4.0
9.0
2.0
3.0
7.0
J
5.0
0.0
2.0
3.0
6.0
2.0
0.0
1.0
8.0
7.0
8.0
K
10.33
10.27
10.07
9.79
9.81
9.81
9.77
9.63
9.05
8.89
8.83
K
9.55
9.22
7.38
7.16
5.70
6.71
7.06
8.07
9.26
8.70
6.86
5.91
4.37
L ,
0.0
0.0
0.84
2.20
3.16
3.84
3.84
4.40
6.48
7.64
6.00
L
0..0
0.0
0.36
5.56
5.52
4.28
4.92
5.64
6.96
9.40
9.60
M
27.5
27.6
28.1
29.7
29.7
29.4
29.5
29.5
20.5
29.6
20.6
M
29.9
30.3
30.7
29.6
29.5
29.0
29.5
20.5
29.5
29.4
29.7
N 0
2.82 8.58
2.66 8.58
2.84 8.12
1.40 7.49
1.09 7.48
0.97 7.38
0.67 7.37
0.89 7.36
0.65 7.15
1.09 7.12
1.01 7.20
N 0
2.37 8.54
2.27 8.67
2.22 8.21
1.34 7.29
0.63 7.21
0.75 7.21
0.67 7.21
0.51 7.20
0.55 7.09
1.03 6.98
1.50 6.92
P
29.5
29.5
29.6
P
31.9
31.9
31.3
(continued)
-------
TABLE 2 (continued)
to
12 November, 1974 MP Temp
Depth
0
5
10
12.5
15
17.5
20
25
30
40
50
55
60
A B C D
5.8 9.7 2.4 0.5
5.9 9.4 5.8 0.2
5.6 12.9 0.0 0.5
6.1 5.8 1.5 0.7
1.2 12.9 7.0 5.1
0.4 27.1 22.5 18.3
0.6 23.3 15.5 14.5
0.2 30.4 31.2 23.5
0.1 40.4 38.7 30.9
0.1 54.2 42.1 37.4
0.4 52.1 37.9 36.0
4 February, 1975 MP Temp
Depth
0
5
30
60
20 April
Depth
0
5
20
30
35
40
60
A B C D
1.9 17.2 14.8 15.4
1.9 22.3 17.8 16.8
2.0 23.1 19.5 17.8
,1975 MP Temp
A B C D
16.9 13.6 5.6 1.6
18.1 17.9 4.1 4.2
18.1 15.2 2.6 3.2
13.5 3.2 4.4 4.2
10.1 17.6 6.2
8.2 20.0 10.0 10.0
5.1 21.5 14.5 17.2
. 12.6°
E
0.7
0.2
1.2
1.4
5.1
18.5
14.5
22.9
29.4
32.0
32.3
. 8.0°
E
16.1
17.1
17.6
.9.9°
E
2.4
3.2
3.2
4.2
6.3
10.0
17.2
Trans . 4 .
F
294
253
235
226
187
176
170
243
147
217
193
G
159
334
153
125
147
164
170
187
159
170
198
Trans . 6 .
F
188
202
179
G
156
167
172
Trans. 4.
F
341
358
276
289
380
216
289
G
194
189
174
206
207
229
165
7 m
H
73
63
59
89
350
387
381
894
408
436
442
2 m
H
314
303
306
0 m
H
149
157
166
200
247
274
300
I
0.8
0.5
0.5
0.5
0.5
0.0
0.0
0.2
0.8
0.6
0.8
I
0.2
0.3
0.3
I
1.9
1.6
1.6
1.7
2.7
4.1
6.3
J
0.0
1.0
2.0
1.0
3.0
0.0
0.0
0.0
1.0
2.0
5.0
J
3.0
3.0
4.0
J
2.0
3.0
5.0
8.0
14.0
6.0
6.0
K
0.58
9.56
9.50
9.60
9.50
9.54
6.48
6.78
6.54
6.60
4.96
3.64
3.14
K
10.64
10.56
10.56
K
13.62
13.32
12.75
12.30
11.90
11.58
10.68
L
1.60
1.72
1.52
1.80
6.24
6.40
6.60
6.64
5.88
10.80
10.40
L
2.8
3.0
2.8
3.0
L
0.0
0.0
0.0
0.2
0.8
1.92
2.40
M
31.5
32.0
31.7
31.6
29.5
29.6
30.0
29.9
30.4
30.5
30.5
M
30.3
30.3
30.5
30.7
M
23.6
25.0
26.0
31.0
31.0
30.5
30.5
N
1.76
1.92
1.78
1.67
0.96
0.56
0.60
0.56
0.76
1.04
1.36
N
1.6
1.6
1.8
N
4.5
4.6
4.2
3.6
2.9
2.2
1.6
0
7.65
7.74
7.70
7.72
7.13
7.05
7.10
7.05
7.00
6.92
6.88
0
7.50
7.53
7.52
7.50
0 P
9.00 31.0
9.28 31.2
9.08 31.0
7.75
7.74
7.45
7.45
(continued
-------
TABLE 2 (continued)
to
CO
24 June
Depth
0
5
10
15
20
25
30
40
50
55
60
, 1975 MP
A
6.2
6.0
5.6
1.7
1.6
1.4
1.4
1.0
0.9
0.9
0.8
14 October,
Depth
0
5
10
15
20
25
30
40
50
55
60
A
1.0
3.6
4.0
3.7
2.6
1.2
0.8
0.7
0.6
0.9
0.4
B C
9.4 0.0
11.2 11.5
10.3 2.1
7.6 0.7
5.9 1.4
0.3 3.4
9.0 2.8
11.2 11.2
14.7 9.6
14.4 10.6
18.8 13.2
1975 NEPB
B C
11.9 5.2
11.0 5.0
13.0 0.0
13.0 4.0
11.0 7.0
17.0 14.0
18.0 14.0
21.0 16.0
21.0 18.0
25.0 18.0
31.0 15.0
Temp
D
0.0
0.0
0.0
0.0
0.5
2.6
4.7
6.3
7.4
10.6
12.7
Temp
D
0.8
1.0
0.5
1.0
4.0
10.7
12.7
16.0
18.0
21.3
25.3
. 16.2°
E
0.0
0.0
0.0
0.0
0.5
3.2
3.7
5.8
7.4
8.9
11.7
. 15.2°
E
1.0
1.0
1.0
1.0
4.0
10.0
12.0
14.7
16.0
18.7
13.3
Trans . 4 .
F
256
247
199
180
170
161
194
207
194
207
G
175
161
147
142
85
175
194
142
170
52
189
Trans . 5 .
F
291
271
238
267
308
197
172
172
157
153
279
G
182
182
192
197
172
197
182
197
192
213
201
0 m
H
37
41
40
178
273
276
298
219
324
332
349
6 m
H
33
25
15
23
233
296
295
216
320
340
357
I
4.1
4.1
4.2
4.2
0.8
0.8
0.8
0.7
1.2
0.8
0.6
I
0.3
0.2
0.5
0.3
0.5
0.2
0.2
0.2
0.2
0.0
0.8
J
8.0
10.0
13.0
7.0
8.0
5.0
4.0
5.0
7.0
5.0
21.0
J
31.0
30.0
31.0
29.0
8.0
6.0
5.0
6.0
7.0
3.0
24.0
K L
10.28 0.00
10.28 0.00
10.06 0.00
9.88 3.40
9.74 3.52
9.60 3.64
9.78 3.80
9.70 4.20
9.27 4.80
8.55 4.00
7.38 7.08
K L
9.19 3.60
9.11 3.92
9.11 3.76
8.88 6.00
6.20 8.80
6.06 10.60
6.40 7.40
6.89 9.04
6.59 8.80
5.41 11.60
3.93 12.80
M
29.8
30.4
31.2
31.5
31.0
30.8
30.9
30.1
30.7
32.0
31.4
M
32.4
32.0
32.6
32.3
20.7
30.0
31.4
29.5
29.5
30.0
30.2
N
2.61
2.19
1.86
1.17
0.25
0.81
0.97
0.69
0.93
0.89
1.33
N
1.12
1.03
1.09
1.12
0.76
0.64
0.68
0.56
0.56
0.84
1.44
0
8.19
8.31
8.25
7.29
7.08
7.01
7.01
6.99
6.95
6.79
6.82
0
7.48
7.58
7.50
7.49
6.86
6.90
6.88
6.82
6.82
6.74
6.69
P
32.0
32.0
32.0
(continued)
-------
TABLE 2 (continued)
S3
9 December, 1975 NEPB
Depth
0
5
10
20
30
45
50
55
60
ABC
2.9 22.0 17.0
2.7 28.0 18.0
2.5 23.0 17.0
2.6 24.0 18.0
2.4 19.0 18.0
0.9 26.0 18.0
2.0 37.0 20.0
1.9 34.0 17.0
6 January, 1976 NEPB
Depth
0
5
30
60
30 March
Depth
0
5
10
15
20
30
60
ABC
2.4 19.5 13.5
2.8 21.0 15.0
3.0 20.5 14.0
, 1976 MP
ABC
7.6 16.6 6.7
11.7 21.2 4.1
11.3 18.6 7.6
9.9
10.3 15.8 3.3
10.8 13.8 4.6
11.9 17.2 2.8
Temp
D
11.6
10.5
10.5
10.0
10.0
11.9
20.5
25.0
Temp
D
12.8
13.6
13.8
Temp
D
4.5
3.8
3.8
5.7
4.8
5.2
. 8.8°
E
11.1
9.6
9.6
9.6
9.1
10.0
9.6
8.7
. 7.6°
E
11.7
11.9
11.9
. 8.3°
E
3.1
3.3
3.8
5.2
4.8
4.3
Trans. 5
F
202
209
178
174
174
178
200
204
G
161
148
174
148
148
153
170
120
Trans. 3
F
250
202
216
G
182
187
169
Trans . 5
F
276
249
257
232
236
270
G
172
141
179
179
184
179
.3 m
H
254
264
261
264
259
270
374
288
.3 m
H
219
311
317
.0 m
H
275
259
251
264
263
267
I
0.0
0.0
0.0
0.0
0.0
0.0
0.7
0.0
I
0.3
0.3
0.3
I
0.3
0.2
0.2
0.3
0.2
0.3
J
8.8
8.0
6.0
6.0
5.0
9.0
17.0
7.0
J
6.0
4.0
3.0
J
9.0
9.0
3.0
12.0
4.0
7.0
K
10.18
9.88
9.98
9.98
9.94
9.70
9.77
10.14
K
10.71
10.81
10.62
K
12.65
12.55
12.14
12.14
11.94
L
L
4.88
4.00
4.60
5.04
L
2.40
2.15
1.80
2.40
2.20
3.84
M
30.7
30.7
30.5
30.0
30.7
30.5
30.3
28.2
27.0
M
30.0
29.6
30.1
29.8
M
29.3
29.5
29.4
29.3
29.3
29.6
N
1.36
1.23
1.36
1.48
1.80
3.44
13.60
27.40
N
2.77
2.88
2.93
N
3.40
3.76
3.68
3.60
3.52
4.08
0
7.11
7.21
7.21
7.21
7.20
7.20
7.21
7.07
7.05
0
7.20
7.12
7.13
7.11
0
7.91
7.98
7.90
7.74
7.68
7.65
(continued)
-------
TABLE 2 (continued)
1 June,
Depth
0
5
10
15
20
25
30
40
50
55
60
1976
A B
10.6
12.5
9.1
12.7
11.1
7.6
8.8
7.9
10.5
12.7
14.1
MP
C
5.4
3.3
5.4
3.0
3.6
2.6
5.4
6.7
7.6
8.8
9.7
Temp. 13.8° Trans. 11.5 m
D
0.0
0.0
0.0
0.0
0.0
0.0
0.7
2.3
4.0
5.3
5.7
E
0.0
0.0
0.0
0.0
0.0
0.0
0.3
1.7
3.3
4.7
5.3
F
243
223
256
252
289
235
177
165
173
173
177
G
158
256
185
169
169
190
173
160
152
148
219
H
130
121
130
128
129
185
247
262
265
287
295
I
5.9
6.0
6.0
6.0
6.0
2.0
0.3
0.3
0.3
0.2
0.6
J
7.0
8.0
10.0
8.0
7.0
14.0
4.0
5.0
9.0
5.0
9.0
K
10.99
10.91
10.99
10.89
10.89
10.35
10.29
10.39
10.23
10.19
9.88
L
1.60
1.80
1.80
1.76
1.48
3.68
3.48
3.80
4.20
4.20
5.60
M
30.0
30.4
30.1
30.5
30.1
29.6
29.6
29.5
29.5
30.0
N
2.29
2.05
2.21
2.21
2.21
1.25
0.93
0.93
0.85
1.01
1.09
0
7.87
7.98
7.99
7.90
7.83
7.48
7.31
7.30
7.20
7.21
7.14
u>
o
-------
TABLE 3. MEAN VALUES OF SELECTED PROPERTIES OF LAKE WASHINGTON
A. Total phosphorus, annual mean, whole lake
B. Total phosphorus, annual mean, top 10 m.
C. Phosphate-P, January-March mean, top 10 m.
D. Nitrate-N, January-March mean, top 10 m.
E. Chlorophyll a^ July-August mean, top 10 m.
F. Solar radiation, annual total, thousands cal./cm 'year
G. Total inflow in streams, millions m-vyear
Radiation data from University of Washington Department of Atmospheric
Sciences and U.S. Weather Bureau. Flow data from U.S. Geological
Survey, Tacoma, Washington and Municipality of Metropolitan Seattle.
Data for 1933 from Robinson (1938), for 1950 from Comita and Anderson
(1959). Flow data subject to slight revision. Concentrations, yg/1.
Year
1933
1950
1963
1971
1972
1973
1974
1975
1976
A
18.0
-
70.3
17.6
16.1
18.8
19.4
15.8
14.4
B
16.0
-
65.7
18.4
16.0
16.8
14.8
14.5
13.4
C
7.8
14.3
55.3
14.6
8.8
11.3
18.9
15.3
10.1
D
120
-
425
375
310
255
350
305
295
E
-
2.7
34.8
6.1
7.2
4.7
4.3
3.9
4.0
F
-
99.1
109.5
95.3
101.4
96.5
98.7
110.6
112.1
G
-
1682
964
1540
1514
898
1329
1480
-
31
-------
B
tons/lake
1000-
100%-
50 -
50-
PHOSPHATE
CHLOROPHYLL
10-
5—
3 -
TOTAL PHOSPHORUS
CHLOROPHYLL
(•wage diversion
start finish
100-
50-
30-
o|933
KJELDAHL
NITROGEN
TOTAL PHOSPHORUS
1933
f
— 0.5
— 0.6
0.7
1963
1970
1975
1962 1965
1970
1975
1962 1965
1970
1975
Figure 1. Summary of changes in phosphorus, nitrogen and chlorophyll during the recovery of Lake Washington
A. Mean values for the top 10 meters, related to the absolute values in 1963, shown in parentheses as 100%
Total phosphorus for whole year (65.7 yg/1).
Dissolved inorganic phosphate phosphorus, January-March (55.3 yg/1).
Nitrate nitrogen, January-March (425 yg/1).
Chlorophyll, July-August (34.8 yg/1).
The symbols at the left show values for 1933 (Scheffer and Robinson, 1939). Note that the winter values
are for a slightly different time from those published earlier (Edmondson, 1970). Sewage diversion
started in February, 1963 and ended in February, 1968, but most sewage had been diverted by March, 1967.
Winter phosphate phosphorus can exceed the annual mean for total phosphorus when the latter decreases
considerably during the summer as in 1974 (see Fig. 2). This is an updated modification of a graph used
previously to report on the progress of the recovery of Lake Washington (Edmondson, 1970, 1976b).
B. Total phosphorus and chlorophyll as in A, on a logarithmic scale. Lines fitted by eye.
For details of sewage diversions, see C.
C. Annual means of total content of lake of Kjeldahl nitrogen and total phosphorus on a logarithmic scale
The equilibrium values are shown for three different retention fractions (f) at right (see text).
-------
o-
I -
2-
3-
4-
w
£ 5-
0>
6-
7-
8-
9-
- i
o> o>
I I I II
o>
o>
o>
SECCHI TRANSPARENCY
t
JULY-AUGUST
MEAN AND RANGE
I
It
100%-
50 -
start
SEWAGE
DIVERSION
.finish
Figure 2. Minimum, mean and maximum Secchi disc transparency during summer in
Lake Washington. Dots are single observations; the one for 1913 is
from Kemmerer et al. (1924). This is an updated version of a graph
published earlier (Edmondson, 1973).
33
-------
Figure 3. Summary of seasonal changes in Lake Washington. The condition in
the post-recovery period 1971-1975 is compared with that in two years before
eutrophication was a problem (1933 and 1950), one year at the height of eu-
trophication (1963), and 1976.
A. Total phosphorus (dots) and phosphate-phosphorus (x).
B. Total Kjeldahl nitrogen (dots) and nitrate-nitrogen (x) .
C. Secchi disc transparency, mean, maximum and minimum.
D. Chlorophyll _a.
E. Surface temperature.
F. Solar radiation.
G. Flow of Cedar River.
H. Phosphorus in Cedar River (symbols as in A.)
The values are monthly means, based on all observations made during the month.
For N, P and chlorophyll, this was usually about 4 per month in recent years,
less frequently in earlier years. Temperature and transparency were measur-
ed more frequently. Radiation and water flow are based on daily measurements.
Phosphorus in the Cedar River was measured every two weeks.
Concentrations as yg/1. Transparency, meters. Temperature, degrees Celsius.
Radiation, cal/cm^'day (data from University of Washington Department of At-
mospheric Sciences and U.S. Weather Bureau). Flow nrYmin. (data from U.S.
Geological Survey, Tacoma, Washington).
Note. Total nitrogen means for 1963 varied between 160 and 690 pg/1, and
most points would be off scale on this graph. Data for 1933 from Robinson
(1938), for 1950 from Comita and Anderson (1958).
34
-------
-EPA project-
100
1933 1950 1963 1971 1972 1973 1974 1975 1976
H 20-
35
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-087
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Trophic Equilibrium of Lake Washington
5. REPORT DATE
August 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
W. T. Edmondson
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Zoology
University of Washington
Seattle, Washington 98195
10. PROGRAM ELEMENT NO.
1BA6Q8
11. CONTRACT/GRANT NO.
R 8020 82-03-1
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory-Corvallis
U.S. Environmental Protection Agency
200 S.W. 35th Street
Corvallis, OR 97330
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/02
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Sewage effluent was diverted progressively from Lake Washington during 1963-1968,
and the chemical conditions changed In close relation to the amount of sewage
entering. The total phosphorus content of the lake decreased rapidly to 1971
after which year It varied around a value of about 50,000 kg (= 17 yg/1) with a
slight decreasing trend. The lake has retained about 56% of the phosphorus that
entered during 1971-1975.
Winter means of nitrate and the annual mean total content of Kjeldahl nitrogen
has decreased at a slow rate during the entire period. Phytoplankton as measured
by chlorophyll In the epilimnion during summer dropped to a low value in close
proportion to phosphorus during diversion, but has decreased faster than phosphorus
during 1971-1976.
A large increase in transparency occurred in 1976. A major change is taking
place in the character of the zooplankton of Lake Washington in that Daphnia
became very abundant in 1976. This event Is probably not directly related to
recovery from eutrophication, so the lake is entering a new phase.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. cos AT I Field/Group
Limnology, Lakes, Plankton blooms,
Phosphorus
eutrophlcat ion
lake restoration
08 H
18. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
44
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE 36
t, U. S. GOVERNMENT PRINTING OFFICE: 1977-798-505/198 REGION 10
------- |