United States EPA-600/3-81-01 6
Environmental Protection April 1981
Agency
vvEPA Research and
Development
The Dilution/Flushing
Technique in
Lake Restoration
Prepared for
Office of Water Regulations and
Standards
Criteria and Standards Division
Prepared by
Environmental Research Laboratory
Corvallis OR 97330
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EPA-600/3-81-016
April 1981
THE DILUTION/FLUSHING TECHNIQUE IN LAKE RESTORATION
by
E. B. Welch
Department of Civil Engineering
University of Washington
Seattle, Washington 98195
Project Officer
Spencer A. Peterson
Freshwater Division
Corvallis Environmental Research Laboratory
U.S. Environmental Protection Agency
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. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or recom-
mendation for use.
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ABSTRACT
Dilution/flushing has been documented as an effective restoration tech-
nique for Moses and Green Lakes in Washington State. The dilution water added
in both lakes was low in nitrogen and phosphorus content relative to the lake
or normal input water. Consequently, lake nutrient content dropped predict-
ably. Dilution or flushing rates were about ten times normal during the
spring-summer periods in Moses Lake and three times normal on an annual basis
in Green Lake. Improvement in quality (nutrients, algae, and transparency)
was on the order of 50 percent in Moses Lake and even greater in Green Lake.
The facilities for supplying dilution water were largely in place for the
cited lakes; thus, costs for water transport were minimal. Available facil-
ities, and therefore costs, for water transport would usually vary greatly,
however. Achieving maximum benefit from the technique may be more limited by
availability of low nutrient water rather than facilities costs. Quality
improvement may occur from physical effects of washout and instability if only
high nutrient water is available.
m
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CONTENTS
Introduction 1
Theory and Predictions 1
Short Term 2
Long Term 2
Case Studies of Dilution/Flushing 3
Moses Lake 3
Green Lake 9
General Application 10
Summary 11
References 13
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INTRODUCTION
The technique of dilution/flushing can achieve lake quality improvement
by one of at least two processes. On the one hand, the concentration of
limiting nutrient can be reduced, and on the other hand, the water exchange
rate in the lake can be increased. Both changes can result in reductions in
the biomass of plankton algae because loss rates exceed algal growth rate.
The effect of dilution is to primarily reduce the growth rate and of flushing
to increase the loss rate, but when increased inputs of low nutrient water
occur, both effects can result. Other effects of adding dilution water are
also possible, such as increased vertical mixing and a decrease in the concen-
tration of algal excretory products, which can influence the kinds and
abundance of algae.
The technique is most appropriate where large quantities of low nutrient
water are available for transport to the lake needing restoration. The lower
the concentration of limiting nutrient in the dilution water relative to that
in the lake, the greater will be the treatment effectiveness. In some
instances, improvements may be achieved by adding water of even moderate to
high nutrient content; however, results would be less certain than with low
nutrient water.
Dilution has produced striking improvements in the quality of Green Lake
in Seattle (Oglesby, 1969) and in Moses Lake in eastern Washington (Welch and
Patmont, 1979; Welch, 1979; and Welch and Patmont, in press). The technique
has been used intentionally in at least one other situation; Lake Bled in
Yugoslavia was flushed with water from River Radovna (Sketelj and Rejic,
1966). It has been proposed or considered for four other lakes: three in
Washington State and Clear Lake in California (Goldman, 1968). Relatively
high natural rates of dilution/flushing maintaining low phytoplankton concen-
trations is a commonly observed phenomenon (Dillon, 1975; Dickman, 1969; and
Welch, 1969).
The theoretical basis for the dilution/flushing technique will be
discussed followed by a summary of results from Moses Lake and Green Lake.
Finally, some suggestions for application of the technique in general will be
given.
THEORY AND PREDICTIONS
The mechanisms involved in dilution/flushing techniques for the control
of algal biomass in lakes are in many ways analogous to those in continuous
culture systems. By adding low-nutrient dilution water to a culture system,
the inflow concentration of limiting water is reduced, the maximum biomass
concentration possible in the reactor vessel is likewise reduced and, at the
same time, nutrients and algal biomass are more rapidly- washed from the
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reactor vessel since the water exchange rate is increased. Concentration of
limiting nutrient is the critical parameter that determines algal biomass in
lakes as well as continuous culture systems. Therefore, the controlling
factor can be analogous in the two environments.
There is a significant difference between the effect of "dilution" and
"flushing." Flushing emphasizes what goes out of the lake and can be
described as loss of biomass without consideration of the concentration of
nutrients and their subsequent effect on growth. Dilution, on the other hand,
emphasizes what is left in the lake and implies a reduction in nutrient
concentrations to limit further growth as well as a washout of biomass.
There is an additional factor that greatly influences the lake concentra-
tion and that is sedimentation, which is not considered in continuous
cultures. At very high rates of water exchange, the sedimentation loss can
decrease and result in higher lake concentrations than at moderate exchange
rates where sedimentation loss is greater.
Short Term
The transient reduction in lake concentration of a nutrient by adding
dilution water in rather large quantities can be reasonably predicted in the
short term by a simple continuity equation:
r = c + (C - C ^
t i *• o i;
where C. is the concentration of time t, C. is the concentration in the inflow
t I
water, C is the initial lake concentration, and p is the water exchange or
flushing rate. This equation assumes that the lake is well mixed, that no
other sources of nutrients exist, and that the limiting nutrient "percent lake
water" can be treated as conservative. Since this equation does not include a
sedimentation term, it is really only useful in the short-term as a tracer for
nutrient behavior and with rather large water exchange rates, that is, several
percent per day or more. It allows one to estimate the potential for reducing
lake concentrations with a given source of water and the time necessary for
that reduction.
Long Term
To predict long-term changes in the concentration of limiting nutrient
from adding rather small quantities of low-nutrient dilution water, a term for
sedimentation should be included. That requirement is best approximated_by
Vollenweider's (1969, 1976) equation for steady-state phosphorus content (P):
p = b
Z(p + a)
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where L is the area! loading rate for P, Z is mean depth and p and a are rate
coefficients for flushing and sedimentation, respectively.
Uttormark and Hutchins (1978) have evaluated the use of that and similar
equations for estimating the long-term effect of dilution water addition.
They noted that adding more water with lower nutrient content also increases
nutrient loading, while the resulting increased flushing rate can also
decrease the loss through sedimentation. The processes could be counteracting
in some instances, since "a reduction in the influent concentration tends to
reduce in-lake concentration, but a reduction in phosphorus retention tends to
increase in-lake concentrations." Figure 1 (from Uttormark and Hutchins,
1978) illustrates this phenomenon for a dilution water concentration that is
40 percent of the normal inflow concentration. An increase in combined
flushing rate (p2) obtained by adding low-nutrient water could theoretically
increase the lake nutrient concentration if the original rate (px) was low
enough—0.1 yr-1 or so. If the flushing rate is large initially (> 1.0 yr-1),
a reduction in lake concentration will result, but large quantities of water
will be necessary.
CASE STUDIES OF DILUTION/FLUSHING
Two lakes where dilution is in use can be used as guides to apply the
technique, and both are in the State of Washington. Moses Lake lies in
Eastern Washington, has an area of 2,753 ha and a mean depth of 5.6 m. Dilu-
tion water from the Columbia River has been added to it during the spring-
summer periods of 1977-80 and that practice will continue. Green Lake has an
area of 104 ha and a mean depth of 3.8 m. It has received dilution water from
the city domestic supply beginning in 1965 and continuing to the present. The
suitability of dilution water for the restoration of these lakes is apparent
from the large differences between lake and inflow nutrient concentrations as
a result of adding dilution water. The ratios of lake:inflow concentrations
range from 5 to 10.
Moses Lake
Dilution water from the Columbia River has been added to Parker Horn in
Moses Lake through the U.S. Bureau of Reclamation's East Low Canal and Rocky
Coulee Wasteway (Figure 2). Plans by Brown and Caldwell Engineers call for
the addition of dilution water to Pelican Horn as well as to the upper main
arm (see inset Figure 2) in two remaining project phases. Although a variety
of input patterns was desired for experimental purposes during the spring-
summer periods, those desires have been only partly attained. Three periods
of dilution were provided in 1977 and 1979, but only one in 1978. The total
number of days of dilution ranged from 60 to 138, and the average exchange
rates during April-September for Parker Horn, where the water enters (Figure
2), ranged from 0.07 to 0.13 day-1. The normal summer exchange for that arm
is 0.01 day-1. For the whole lake, the Parker Horn inflow (excluding ground-
water and flow from Rocky Ford Creek into the main arm) represented an
exchange rate of only 0.06 to 1.0 percent per day.
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MOSES LAKE, WASHINGTON
LAKE OUTLETS
FROM
EAST
LOW
CANAL
ROCKY
COULEE
WASTE WAY
MOSES LK.
STATE PARK
4 MILES
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The suitability of Columbia River water for dilution can be seen in Table
1. Because the P and N concentrations in Crab Creek are so high, relatively
large quantities of Columbia River water (25 pg I-1) are needed to signifi-
cantly lower the composite inflow concentration which is necessary to lower
the lake concentration. This results in larger exchange rates than would
otherwise be necessary without the Crab Creek inflow. Unfortunately, however,
the diversion of Crab Creek is economically infeasible.
TABLE 1. INFLOW CONCENTRATIONS TO PARKER HORN DURING MAY-SEPTEMBER, 1977 AND
1978 (ug I-1)
Total P Total N P04-P N03-N
Inflow Without Dilution
East Low Canal Dilution Water
148
25
1,331
308
90
8
1,096
19
As a short term phenomenon, the addition of dilution water to Moses Lake,
Washington predictably and rapidly replaced lake water as judged by specific
conductance measurements (Figure 3). Values for percent lake water were
calculated assuming that 100 percent was represented by the conductance of
Crab Creek and 0 percent by the conductance of Columbia River water. Percent
lake water reached values of 20 in Parker Horn (where the water enters), much
less than in other parts of the lake. This was expected because the average
dilution rate during the April to June dilution period described here was 15%
day-1 for Parker Horn, which is a small (8 percent) portion of the lake
volume. The dilution rate decreased, of course, as more lake volume was
included. As the dilution water input declined in June, the percent lake
water quickly rose to between 50 and 60 percent. Part of that increase was no
doubt caused by wind pushing lake water into Parker Horn.
Because Moses Lake is rather dissected and most of the lake's volume
(63%) appeared out of a direct path of the inflow, dilution water was expected
to have little effect other than in Parker Horn and the lower lake, which
together represent 29 percent of lake volume. However, the lake water
residual decreased similarly in the whole lake as well as the lower lake.
Lake water residuals reached levels between 50 and 60 percent in late May and
early June and then began the more gradual return to normal as dilution input
declined. In fact, there was little difference between actual and predicted
removal of lake water in the whole and lower lake (Figure 3).
Improvement of lake quality in 1977-79, compared to 1969-70, was near or
in excess of 50 percent for P and N as well as chlorophyll a for not only
Parker Horn, but also most of the lake (Table 2). Visibility was also
substantially improved. Of course, improvement was better in Parker Horn
where the fraction of dilution water was greater, but most of the lake
responded almost as well. As noted earlier, the dilution water was distrib-
uted throughout the lake, largely due to the wind and probably the large
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T 40
'o
O)
nT 2°
r^
1 1
^T DILUTION WATER
1 — 1
100 r
80
LU
LU
h-
z
LU
O
tr
LU
Q.
60
40
20
0
8« !
O
O
o
APR
MAY
JUN
Figure 3. Residual percent lake water in Parker Horn (Station 7, open
circles), the lower lake (Station 9, closed circles), and the whole
lake (triangles) compared to that predicted (based on an average
inflow) for the whole lake and Parker Horn in response to dilution
water addition in 1978. Parker Horn, the lower lake, and the whole
lake represent 8, 21, and 100 percent of the lake volume. Dotted
lines represent predicted values.
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TABLE 2. AVERAGE APRIL-SEPTEMBER DILUTION RATES AND MAY-SEPTEMBER CHLOROPHYLL
a, TOTAL PHOSPHORUS, AND SECCHI VISIBILITY FOR TWO PORTIONS OF MOSES
LAKE DURING THE SPRING-SUMMER PERIODS OF 1977-79 COMPARED TO THE
CONTROL YEARS 1969-70. PERCENT IMPROVEMENT IN (0-100%)
Years
Dilution Rate,
% Day-1
Total P,
ug I-1
Chi a,
|jg I-1
Secchi ,
m
1969-70
1977-79
No Dilution
10.0
PARKER HORN
8 Percent of Lake Volume
158
71 (54%)
58 Percent of Lake Volume
71
26 (63%)
0.6
1.3 (54%)
1969-70
1977-79
No Dilution
10.0
158
71 (54%)
71
26 (63%)
0.6
1.3 (54%)
volumes introduced (Welch and Patmont, in press). Part of the improvement in
areas away from Parker Horn is considered to be due to the natural depletion
of usable fractions of nutrients with time.
Presentation of means for the May-September period obscures the high
quality conditions, such as visibility reaching a maximum of 3 m in June in
most of the lake as well as poor quality such as maximum chlorophyll a
reaching peaks near 50 ug I-1 in late July-August after water input had been
curtailed for 2-4 weeks. Unless water was continually added, blooms would
return as the fraction of dilution water left in the lake declined. This
"boom and bust" situation promoted by large inputs followed by no input at all
has prompted the proposing of continual input at low rates throughout the
summer, employing similar total amounts of water. The large quantities added
over a short period of time, that exchanged water in Parker Horn at the rate
of about 20 percent per day and in most of the lake at 2-3 percent per day,
are probably unnecessary considering the general response of the phyto-
plankton, particularly the blue-greens, to dilution water addition.
The exact cause(s) for the improvement of Moses Lake quality from the
addition of Columbia River water is not entirely clear. Several possibilities
exist, and these have been discussed elsewhere (Welch and Patmont, in press;
and Welch, in press). Of the nutrients and particulate fractions that could
account for the decreased biomass, total N appears most important. Soluble N,
rather than P, has always been the nutrient that most frequently limits growth
rate in Moses Lake. Although soluble N was not appreciably reduced by
dilution, total N was and appeared to set the limit on average chlorophyll a
and probably biomass as well. One lake N was decreased below about 600 ug
I-1, chlorophyll a likewise decreased (Welch, in press).
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Other factors contributed to the biomass decrease as well. The physical
loss of algal cells by washout no doubt affected biomass in Parker Horn where
high rates of exchange (20-25% day-1) existed. However, instability of the
water column, as indicated by decreased vertical temperature gradient, prob-
ably contributed to the crash and/or prevention of blue-green blooms there as
well as elsewhere in the lake (Welch, in press). Because the flotation capa-
bility of blue-greens provides them with advantages over greens and diatoms
when mixing is poor, decreased stability may hinder the dominance of blue-
greens.
There are yet other factors resulting from dilution that may have
contributed to reduced biomass of algae and reduce contribution by blue-
greens. Some of those considered are: iron limitation of the N fixation
process in blue-greens, a reduction in free C02 favoring greens and diatoms,
and the dilution of excretory productions of blue-greens decreasing their
inhibition of diatoms and greens (Patmont, 1980; Welch and Patmont, in press;
and Welch, in press).
Although the specific cause(s) for the improvement is unclear, attaining
a lake water residual of 50 percent or less provided desirable results in
Moses Lake. Dilution of lake water to fractions between 40 and 65% was
attained during mid-summer in various areas of Moses Lake during 1978 (Figure
2), along with mean chlorophyll a values of about 14 |jg I-1, when the exchange
rate in Parker Horn was 0.07 day-1. Therefore, a conservative estimate of an
adequate dilution rate for Parker Horn would be around 0.05 day-1 or a flow of
dilution water of about 6 m3 sec-1. That would represent a 3:1 dilution of
Crab Creek, which flows at about 1.52 m3 day-1 in summer. Such a flow would
represent about 87 x 106 m3 of dilution water for the entire summer. In 1978,
about 112 x 106 m3 of dilution water entered the lake, but over a two-month
period. Thus, slightly less total water volume spread evenly over the whole
summer should provide for ^ 50 percent lake water remaining by mid-summer
throughout Parker Horn and the lower lake.
Although not specifically tested, it seems that a continuous low-rate
input would be preferable to a high rate input for a relatively short period,
followed by complete cessation of input. This "low-inflow" procedure will not
reduce the lake water fraction as quickly as the large spring output "boom and
bust" approach, but it may, nonetheless, more effectively restrict the large
blooms of blue-greens during mid and late summer.
Green Lake
The dilution of Green Lake beginning in 1962 represents another case for
the benefits of this technique of restoring lakes. Sylvester and Anderson
(1964) proposed the manipulations, and Oglesby (1969) reported the water
quality changes. The technique applied to Green Lake was one of long-term
dilution at a relatively low rate. The average combined water exchange rate
was increased from an estimated 0.83 yr-1 to 2.3 yr-1 as a result of adding
low-nutrient water from the Seattle domestic supply. The addition of dilution
water over 13 years of data during 1965-1978 produced a flushing rate for the
dilution water only that ranged from 0.88 yr-1 to 2.4 yr-1.
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A striking improvement in the chlorophyll a, P, and Secchi visibility
depth resulted from the dilution. Only one pre-dilution measurement existed
and post-dilution three years of monitoring was not begun until 1965 in spite
of dilution starting in 1962. Based on these limited data, summer water
clarity increased nearly four-fold and chlorophyll a decreased over 90%.
Total P declined to about 20 ug I-1 from a summer mean of 65 ug I-1. A marked
decrease in the fraction of blue-green algae was seen, particularly in the
spring and early summer.
The percent decrease in P concentration is about what would be expected,
using Vollenweider's equation for steady-state P and a = VP (Uttormark and
Hutchins, 1978). The expected P concentration in Green Lake prior to dilution
and based on external loading should have been about 80 ug I-1, but in fact,
the P content was about 65 ug I-1. Following dilution, the steady-state
concentration should have been about 35 ug I-1, but it actually declined much
lower, to about 20 ug I-1 by 1967. The concentration decrease (45 ug I-1) is
the same, however, for actual and expected. The reductions in P and chloro-
phyll a in Green Lake occurred over several years, and were closely related.
This is in contrast to the rapid, more short-term response in Moses Lake
resulting in marked improvements in blue-green algae and chlorophyll a content
that begin to wane when dilution is curtailed.
The Moses Lake and Green Lake cases illustrate the difference between
short-term and long-term dilution schemes. Both have attained greater than
expected results in lake quality.
GENERAL APPLICATION
Dilution is frequently used synonomously with flushing as a restoration
technique. In fact, the effect of dilution includes both a reduction in the
concentration of nutrients and a washout of algal cells, while flushing may
only cause the latter. For dilution, or a reduction in nutrient concentration
to occur, the inflow water must be lower in concentration than that of the
lake. Effectiveness will, of course, increase as the difference between
inflow and lake concentrations becomes greater. For washout of algal cells to
be an effective control on algal blooms, the water exchange rate must be a
sizable fraction of or preferably approach the algal growth rate.
The ideal dilution scheme would be one to attain a long-term reduction of
the limiting nutrient content through low-rate input of low-nutrient water.
Where there is an existing high nutrient input, it should be diverted if
possible in order for the low dilution rate to be most effective. This scheme
would provide for reduction in biomass primarily through nutrient limitation.
If diversion is not possible, one is faced with high-rate inputs over the
short-term in order to sufficiently reduce the inflow nutrient concentration.
If only moderate to high-nutrient water is available, a short-term dilution
may work well because the loss rate of cells is sufficiently great relative to
the growth rate and washout becomes significant. Also, the blue-green blooms
may be discouraged by decreased water column stability.
10
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Costs will be highly variable depending upon the presence of facilities
to deliver the water and the availability of water. If the lake is in an
urban setting and domestic water is available, then improvement may be
possible for less than $100,000 for construction and first year maintenance
and operation. If near a free-flowing river and diversion of a portion of the
flow through the lake during the summer is feasible, then the costs involve
that of facilities, pumps and pipes, operations, and prevention of side
effects (entraining fish).
The advantages for using dilution water are primarily: (1) relatively
low cost if water is available; (2) immediate and proven effectiveness; and
(3) may be successful even if only moderate-to-high-nutrient water is avail-
able through physical limitations to large algal concentrations. The
principal limitation for use is, of course, that the availability of low
nutrient dilution water, the effect of which has been demonstrated, is
probably poor in most areas.
SUMMARY
Two examples of the use of dilution water for lake restoration are in the
State of Washington—Green Lake in Seattle and Moses Lake in the eastern part
of the state. Green Lake received nutrients from urban runoff and subsurface
inflow. Domestic water, low in P, was added by the City of Seattle beginning
in 1962. The amount added raised the water exchange rate to an annual average
of 2.4 yr-1 from 0.83 yr-1. After five years of treatment, the summer Secchi
visibility had changed from 1 to 4 m, chlorophyll a from about 45 to 3 ug I-1,
and total P from about 54 to 20 |jg I-1. The treatment has continued to the
present.
Moses Lake has received low-nutrient dilution water from the Columbia
River via an irrigation canal during the spring-summer periods of 1977-79.
The average total P concentration for the whole lake during spring-summer had
been normally about 150 ug I-1 and chlorophyll a 45 ug I-1 before dilution.
Although the dilution water addition quickly reduced the P to about 50 ug I-1,
a much greater improvement was seen in chlorophyll a to less than 10 ug I-1.
Average post-dilution spring-summer values for P and chlorophyll a were 86 and
21 ug I-1. Secchi visibility improved from 0.9 to 1.5 m. Dilution addition
reduced the biomass of algae as well as the blue-green fraction in Moses Lake
by presumably a combination of reducing total N, decreasing the water column
stability, limitation by iron, and reducing the free C02 content, which are
discussed elsewhere (Patmont, 1980; Welch and Patmont, in press; Welch, in
press).
Dilution/flushing can be considered as an effective technique for
restoring lakes, especially if a supply of low nutrient water exists. The
costs involved are the facilities to deliver the water and maintenance and
operation. In the case of the two lakes mentioned here, the facilities were
largely in existence. While the irrigation water had a cost, the Bureau of
Reclamation was able to deliver the water to users via the lake. For Green
Lake, a domestic supply was used, and with the facilities, the dilution water
has been added since 1962 with little operation cost. Thus, the costs for
11
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this technique may not limit its use as much as the availability of low-
nutrient water. Even if a supply of such water is not readily available, high
nutrient water may provide improvements.
12
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REFERENCES
Dickman, M. 1969. Some effects of lake renewal on phytoplankton productivity
and species composition. Limnol. and Oceanogr. 14:660-666.
Dillon, P. J. 1975. The phosphorus budget of Cameron Lake, Ontario: the
importance of flushing rate relative to the degree of eutrophy of a lake.
Limnol. and Oceanogr. 29:28-39.
Goldman, C. R. 1968. Limnological aspects of Clear Lake, California with
special reference to the proposed diversion of Eel River water through
the lake, report to Fed. Water Poll. Cont. Admin.
Oglesby, R. T. 1969. Effects of controlled nutrient dilution on the eutro-
phication of a lake. In Eutrophication: causes, consequences, and
correctives, National Academy of Science, Washington, D.C., p. 483-493.
Patmont, C. R. 1980. Phytoplankton and nutrient responses to dilutiion in
Moses Lake. M.S. Thesis, Univ. of Washington, 100 pp.
Sketelj, M. and M. Rejic. 1966. Pollutional phases of Lake Bled. Ln
Advances in Water Pollution Research. Proc. 2nd Intl. Conf. Water Poll.
Res., Pergamon Press Ltd., London, England 1:345-362.
Sylvester, R. 0. and G. C. Anderson. 1964. A lake's response to its environ-
ment. ASCE, SED 90:1-22.
Uttormark, P. D. and M. L. Hutchins. 1978. Input-output models as decision
criteria for lake restoration. Wise. W.R.C. Tech. Rept. 78-03, 61 pp.
Vollenweider, R. A. 1976. Advances in defining critical loading levels for
phosphorus in lake eutrophication. Mem. 1st. Ital. Idrobio. 33:53-83.
Vollenweider, R. A. 1969. Possibilities and limits of elementary models
concerning the budget of substances in lakes. Arch. Hydrobiology
66:1-36.
Welch, E. B. 1969. Factors controlling the phytoplankton blooms and
resulting dissolved oxygen in Duwamish River estuary, Washington. U.S.
Geological Survey Supply Paper 1873-A, 62 pp.
Welch, E. B. and C. R. Patmont. 1979. Dilution effects in Moses Lake. EPA
Ecological Research Series, p. 187-212.
Welch, E. B. 1979. Lake restoration by dilution. In Lake Restoration,
Proceedings of a National Conference, U.S. EPA, EPA-400/5-79-001, pp.
133-139.
Welch, E. B. and C. R. Patmont. 1981. Lake restoration by dilution; Moses
Lake, Washington. Water Research, in press.
Welch, E. B. 1980. Effectiveness of the dilution technique in Moses Lake,
Washington. Proceedings, Internet. Symposium for Inland Waters and Lake
Rest., September 1980, Portland, Maine.
13 « US GOVERNMENT PRINTING OFFICE 1961 -757-064/0317
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