o-EPA
United States
Environmental Protection
Agency
Environmental Monitoring
and Support Laboratory
P.O. Box 15027
Las Vegas NV89114
EPA-600/3-79-012
February 1979
Research and Development
Ecological
Research Series
Comparisons of
Models Predicting
Ambient Lake
Phosphorus Concentrations
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environn
Protection Agency, have been grouped into nine series. These nine broad
gories were established to facilitate further development and application <
vironmental technology. Elimination of traditional grouping was consci
planned to foster technology transfer and a maximum interface in related
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
9. Miscellaneous Reports
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 Info1
tion Service, Springfield, Virginia 22161.
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EPA-600/3-79-012
February 1979
COMPARISONS OF MODELS PREDICTING
AMBIENT LAKE PHOSPHORUS CONCENTRATIONS
Stephen C. Hern, Victor W. Lambou
and Llewellyn R. Williams
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
-------
DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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FOREWORD
Protection of the environment requires effective regulatory actions
which are based on sound technical and scientific information. This information
must include the quantitative description and linking of pollutant sources,
transport mechanisms, interactions, and resulting effects on man and his
environment. Because of the complexities involved, assessment of specific
pollutants in the environment requires a total systems approach which tran-
scends the media of air, water, and land. The Environmental Monitoring
and Support Laboratory-Las Vegas contributes to the formation and enhancement
of a sound monitoring data base for exposure assessment through programs
designed to:
develop and optimize systems and strategies for monitoring
pollutants and their impact on the environment
demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of the
Agency's operating programs
This report compares models which classify lakes according to their
trophic state and predict ambient lake phosphorus concentrations. This
report is intended for use by Federal, State and local agencies with responsi-
bility for watershed management as mandated under Sections 305b and 208 of
Public Law 92-500. For further information contact the Water and Land
Quality Branch, Monitoring Operatiojis Division.
Environmental Monitoring and Support Laboratory
Las Vegas
m
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ABSTRACT
The Vollenweider, Dillon, and Larsen/Mercier models for predicting ambient
lake phosphorus concentrations and classifying lakes by trophic state are com-
pared in this report. The Dillon and Larsen/Mercier models gave comparable
results in ranking 39 lakes relative to known ambient phosphorus concentrations.
The Vollenweider model, which does not include a phosphorus retention capacity
component, was unable to achieve the high rank correlations found with the
other models.
Trophic state predictions from the phosphorus loading models are compared
with National Eutrophication Survey lake report designations. Disagreements
of 14, 18, and 25 percent, respectively, were found with the Dillon, Larsen/
Mercier, and Vollenweider concepts.
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INTRODUCTION
The National Eutrophication Survey was initiated in 1972 in response to
an Administration commitment to investigate the nationwide threat of acceler-
ated eutrophication to freshwater lakes and reservoirs. The Survey was
designed to develop, in conjunction with State environmental agencies, infor-
mation on nutrient sources, concentrations, and impact on selected freshwater
lakes as a basis for formulating comprehensive and coordinated national,
regional, and State management practices relating to point source discharge
reduction and nonpoint source pollution abatement in lake watersheds.
The Survey collected physical, chemical, and biological data from 815
lakes and reservoirs throughout the contiguous United States. To date, the
Survey has yielded more than two million data points. In-depth analyses are
being made to advance the rationale and data base for refinement of nutrient
water quality criteria for the Nation's freshwater lakes.
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COMPARISONS OF MODELS PREDICTING
AMBIENT LAKE PHOSPHORUS CONCENTRATIONS
The phosphorus loading-mean depth relationship formulated by Vollenweider
(1968) has been widely accepted and used to indicate the degree of eutrophy of
lakes and evaluate the level of phosphorus loading to lakes. Dillon (1975)
pointed out that there has been too little thought and criticism given to the
limitations of the model by people using it. Subsequently, modifications
of the basic mass balance equation have been derived to predict mean ambient
lake phosphorus concentrations at equilibrium. Dillon (1975) utilizes phos-
phorus areal loading (L), the retention coefficient for phosphorus (R), the
hydraulic flushing rate (P), and mean depth (Z), in a plot of the form
L (1-R)
P
versus Z, to estimate trophic state. Vollenweider (1975) revised his original
formula to include Tw, hydraulic residence time, so that areal phosphorus
loading (L) is plotted against mean depth (Z) divided by Tw. Larsen and
Mercier (1976) provide an alternative (to the prior loading concepts) which
avoids the criticism of Edmondson (1970) that the effect of an increasing
phosphorus load upon a lake depends, in part, upon whether that increase re-
sults from increases in influent flows, concentrations, or both. The Larsen/
Mercier formula plots mean tributary phosphorus concentration against
phosphorus retention coefficient, called R experimental, computed in the same
way as Dillon's R, i.e.,
i Total phosphorus leaving
K ~ ' Total phosphorus entering
It is interesting to note that in applying the above-mentioned formula,
each of the authors has selected to use levels of 10 and 20 micrograms per
liter (pg/l)of ambient lake phosphorus to divide lakes into three standard
trophic classifications—oligotrophic, mesotrophic, and eutrophic.
To compare the three models, we selected 39 lakes sampled during 1973
by the National Eutrophication Survey (U.S. Environmental Protection Agency,
1975) which represented the entire range of water transparency as measured
by Secchi disk. Table 1 demonstrates the variety of lakes selected.
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TABLE 1. THE NUMERICAL AVERAGE AND RANGE OF MEAN CHEMICAL, PHYSICAL AND
BIOLOGICAL CHARACTERISTICS OF 39 LAKES, SELECTED FROM THOSE
SAMPLED DURING 1973 BY THE NATIONAL EUTROPHICATION SURVEY
PARAMETERMEANRANGE
Surface Area (km2)
Drainage Area (km2)
Mean Depth (m)
Maximum Depth (m)
Volume (m3 x 106)
Hydraulic Retention Time (Days)
Secchi Disk (cm)
Total Phosphorus (yg/liter)
Chlorophyll a (yg/liter)
40.75
3502.6
7.5
21.6
379.28
251
177.8
147
53.9
0.23
4.3
0.9
1.5
0.45
1
15.2
5
1.4
263.05
38850.0
21.0
57.8
2608.00
2446
563.9
1120
456.6
The data used in this report are from the various individual National
Eutrophication Survey (NES) lake reports for the lakes listed in Table 2,
e.g., Report on Lake Lulu (EPA, 1976). Similarly, NES lake reports provide
data for Lake Mead (EPA, 1977a) and Flaming Gorge Reservoir (EPA, 1977b),
included as examples of the application of the formulas.
Solution analyses based on 20 ug/1 were employed to place the three
formulas on an equivalent basis by dividing the appropriate theoretical minimum
eutrophic "loading" rate for a given lake (i.e., that which would produce an
ambient lake concentration of 20 yg/1) into the actual "loading" rate
determined for that lake. Hereafter, this ratio will be referred to as the
"trophic ratio". Trophic ratios which exceed or equal 1.0 represent eutrophic
loadings, whereas trophic ratios extending from 0.5 to less than 1.0 represent
mesotrophic loadings and trophic ratios below 0.5 represent oligotrophic
loadings, regardless of the formula employed.
Table 2 lists the 39 lakes used in this study, ranked in descending
order by total phosphorus concentration, and gives the mean total phosphorus
concentration and mean Secchi disk value for each lake. In addition, the
trophic states given in the individual NES lake reports are listed along with
the trophic ratios calculated for the Larsen/Mercier, Dillon, and Vollenweider
models and the trophic states predicted by the ratios. The trophic states
indicated in the NES reports were based largely upon lake mean total
phosphorus, chlorophyll a_, Secchi depth, hypolimnetic dissolved oxygen values
and phytoplankton data (Allurn et al., 1977).
Spearman rank correlation coefficients (rs) were calculated for each
trophic ratio against measured mean ambient phosphorus concentrations with
the following results: Larsen/Mercier (0.94), Dillion (0.92), and Vollen-
weider (0.82). The Larsen/Mercier model provided the best estimation of the
relative rank of the lakes based on ambient phosphorus concentrations. It
was followed closely by the Dillon model. Both of these models take into
consideration the phosphorus retention capacity of lakes. These models are
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TABLE 2. COMPARISON OF LAKE AMBIENT PHOSPHORUS PREDICTION MODELS AND TROPHIC CLASSIFICATIONS WITH
ACTUAL AMBIENT LAKE CONDITIONS. THE 39 LAKES COMPARED ARE RANKED IN DESCENDING ORDER
BY MEAN SUMMER AMBIENT PHOSPHORUS CONCENTRATION
RANK
1
2
3
4
5
6
7
8
9
10
11
LAKE NAME
(STATE)
Lake Lulu
(Fla.)
Slocum Lake
(111.)
Lake Hancock
(Fla.)
Alligator Lake
(Fla.)
Fox Lake
(111.)
Highland (Silver) Lake
(111.)
Horseshoe Lake
(111.)
Kill en Pond
(Del.)
Lake Loramie
(Ohio)
Crab Orchard Lake
(111.)
Duhernal Lake
(N.J.)
MEAN
AMBIENT
TOTAL-P
(yq/D
1120
882
608
429
322
258
256
216
204
184
179
MEAN
AMBIENT
SECCHI
DEPTH
(cm)
23
20
30
58
i
23
20
25
66
15
58
61
NES
TROPHIC
STATE*
E
E
E
E
E
E
E
E
E
E
E
LARSEN/KERCIER
TROPHIC TROPHIC
RATIO STATE*
259
61
79
38
10
14
11
5
18
7
3
.90 -
.77 -
.90 -
.92 -
.81 -
.61 -
.81 -
.58 -
.57 -
.40 -
.17 -
E
E
E
E
E
E
E
E
E
E
E
DILLON
VOLLENWEIDER
TROPHIC TROPHIC
RATIO STATE*
A
74.00 -
A
A
3.40 -
15.38 -
12.00 -
5.67 -
18.67 -
7.33 -
3.33 -
E
E
E
E
E
E
E
E
TROPHIC
RATIO
75.62
29.42
A
A
12.66
5.43
1.96
9.25
5.02
7.42
18.92
TROPHIC
STATE*
- E
- E
- E
- E
_ £
- E
- E
- E
- E
* E = eutrophic, M = mesotrophic, 0
trophic ratio.
oligotrophic and A = insufficient data to make estimate of
(Continued)
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en
TABLE 2. COMPARISON OF LAKE AMBIENT PHOSPHORUS PREDICTION MODELS AND TROPHIC CLASSIFICATIONS WITH
ACTUAL AMBIENT LAKE CONDITIONS. THE 39 LAKES COMPARED ARE RANKED IN DESCENDING ORDER
BY MEAN SUMMER AMBIENT PHOSPHORUS CONCENTRATION (Continued)
RANK
12
13
14
15
16
17
18
19
20
21
22
LAKE NAME
(STATE)
Lake Charleston
(111.)
Lake Apopka
(Fla.)
Marsh Lake
(Ind.)
Saluda Lake
(S.C.)
Arkabutla Reservoir
(Miss.)
Barren River Reservoir
(Ky.)
Lake Chesdin
(Va.)
Lay Lake
(Ala.)
Cherokee Lake
(Tenn.)
Hickory Lake
(N.C.)
Walter F. George
Reservoir (Ga.)
MEAN
AMBIENT
TOTAL-P
(pq/1)
164
161
115
73
58
49
40
39
37
34
30
MEAN
AMBIENT
SECCHI
DEPTH
(cm)
23
29
127
68
i
64
123
120
'104
141
114
110
NES
TROPHIC
STATE*
E
E
E
M
E
E
E
E
E
E
E
LARSEN/MERCIER
TROPHIC TROPHII
RATIO STATE*
8
19
5
1
11
3
2
4
2
2
3
.57 -
.17 -
.80 -
.84 -
.28 -
.35 -
.20 -
.84 -
.28 -
.04 -
.12 -
E
E
E
E
E
E
E
E
E
E
E
DILLON
: TROPHIC
RATIO
7.50 -
22.00 -
5.92 -
1.88 -
11.39 -
2.32 -
2.21 -
4.20 -
2.43 -
1.74 -
3.25 -
VOLLENWEIDER
TROPHIC TROPHIC
STATE* RATIO
E
E
E
E
E
E
E
E
E
E
E
15.91
3.94
4.54
5.07
2.58
2.10
2.24
5.72
3.61
3.13
3.44
TROPHIC
STATE*
- E
- E
- E
- E
- E
- E
- E
- E
- E
- E
- E
* E = eutrophic, M = mesotrophic, 0 = oligotrophic and A = insufficient data to make estimate of
trophic ratio.
(Continued)
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TABLE 2. COMPARISON OF LAKE AMBIENT PHOSPHORUS PREDICTION MODELS AND TROPHIC CLASSIFICATIONS WITH
ACTUAL AMBIENT LAKE CONDITIONS. THE 39 LAKES COMPARED ARE RANKED IN DESCENDING ORDER
BY MEAN SUMMER AMBIENT PHOSPHORUS CONCENTRATION (Continued)
RANK
23
24
25
26
27
28
29
30
31
32
LAKE MAKE
(STATE)
Moultrie Lake
(S.C.)
Lake Hopatcong
(N.J.)
Tims Ford Reservoir
(Tenn.)
Lake Minnehaha
(Fla.)
Murray Lake
(S.C.)
Chatuge Lake
(Ga.)
Liberty Reservoir
(Md.)
Wanaque Reservoir
(N.J.)
Maxinkuckee Lake
(Ind.)
Dale Hollow Reservoir
(Ky.)
MEAN
AMBIENT
TOTAL -P
(pg/l)
25
25
25
22
20
17
15
14
14
13
MEAN
AMBIENT
SECCHI
DEPTH
(cm)
134
231
240
140
218
310
381
467
221
318
NES
TROPHIC
STATE*
E
E
E
E
E
M
M
M
M
M
LARSEN/MERCIER
TROPHIC TROPHIC
RATIO STATE*
1
1
2
2
1
1
0
1
1
0
.51
.32
.22
.11
.56
.06
.71
.31
.20
.49
- E
- E
- E
- E
- E
- E
- M
- E
- E
- 0
DILLON
TROPHIC
RATIO
1.55
1.00
2.70
A
1.56
1.10
0.76
0.96
1.33
0.47
TROPHIC
STATE*
- E
- E
- E
- E
- E
- M
- M
- E
- 0
VOLLENWEIDER
TROPHIC
RATIO
1.70
0.34
1.11
A
1.49
0.56
1.80
0.48
0.75
0.49
TROPHIC
STATE*
- E
- 0
- E
- E
- M
- E
- 0
- M
- 0
* E = eutrophic, M = mesotrophic, 0 - oligotrophic and A = insufficient data to make estimate of
trophic ratio.
(Continued)
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TABLE 2. COMPARISON OF LAKE AMBIENT PHOSPHORUS PREDICTION MODELS AND TROPHIC CLASSIFICATIONS WITH
ACTUAL AMBIENT LAKE CONDITIONS. THE 39 LAKES COMPARED ARE RANKED IN DESCENDING ORDER
BY MEAN SUMMER AMBIENT PHOSPHORUS CONCENTRATION (Continued)
RANK
33
34
35
36
37
38
39
LAKE NAME
(STATE) _
Lake Wallenpaupack
(Penn.)
Martin Lake
(Ala.)
John W. Flannagan
Reservoir (Va.)
Deep Creek Lake
(Md.)
Summersville
(W.Va.)
Harveys Lake
(Pen-n.)
Tygart Reservoir
(W.Va.)
MEAN
AMBIENT
TOTAL-P
(iiq/1)
13
13
11
11
10
9
5
MEAN
AMBIENT
SECCHI
DEPTH
(cm)
434
230
366
366
1
549
564
320
NES
TROPHIC
STATE*
M
M
M
M
M
M
M
LARSEN/MERCIER
TROPHIC TROPHIC
RATIO STATE*
1.10 -
1.04 -
0.66 -
0.39 -
0.83 -
0.55 -
0.95 -
E
E
M
0
M
M
M
DILLON
TROPHIC
RATIO
1.12 -
0.96 -
0.69 -
0.38 -
0.83 -
0.59 -
0.94 -
VOLLENWEIOER
TROPHIC
STATE*
E
M
M
0
M
M
M
TROPHIC
RATIO
0.50 -
1.35 -
1.92 -
0.34 -
1.28 -
0.54 -
2,02 -
TROPHIC
STATE*
M
E
E
0
E
M
E
* E = eutrophic, M = mesotrophic, 0 = oligotrophic and A = insufficient data to make estimate of
trophic ratio.
-------
very similar, as area! phosphorus loading (L) divided by mean depth (Z)
approximates mean tributary concentration. The major difference between the
models is the flushing rate (P) employed by Dillon.
The Vollenweider model, which does not contain a phosphorus retention
capacity element, produced the poorest estimate of the ambient phosphorus
concentration.
Comparison of the NES trophic state assignment to the various phosphorus
model predictions revealed a 14, 18, and 25 percent disagreement, respectively,
for the Dillon, Larsen/Mercier, and Vollenweider concepts. The Dillon and
Larsen/Mercier models predicted the same trophic state in 33 of 35 lakes. The
only exceptions were in Martin Lake and Wanaque Reservoir where the trophic
ratios, although very close, lay on opposite sides of the somewhat arbitrary
borderline. Nine of the 35 Vollenweider trophic state predictions differed
from the Dillon model predictions, while 8 differed from the Larsen/Mercier
model estimates. Generally, the Dillon and Larsen/Mercier models not only
predicted the same trophic state but their respective trophic ratios were
mathematically quite consistent. By comparison, the Vollenweider model
provided less consistent trophic state results and greater variation in trophic
ratios.
Wanaque Reservoir was classified as eutrophic, mesotrophic, and oligo-
trophic by the three concepts. However, the Dillon and Larsen/Mercier trophic
ratios were actually very close (0.96 and 1.13, respectively).
Even though all of the models produced relatively high Spearman rank
correlation coefficients, these models must be used with caution as the com-
parisons given in Table 3 illustrate. For the two western reservoirs, the
Vollenweider model predicted a much higher eutrophic loading rate than the
other models. Both of these reservoirs have high phosphorus retention capacities
(associated with high suspended sediment deposition)--Lake Mead (0.93), and
Flaming Gorge Reservoir (0.82). These examples reinforce the concept that
the Dillon and the Larsen/Mercier models give comparable results. However,
the Larsen/Mercier model requires less information [(P) flushing rate and (Z)
mean depth are not required] and produced the highest Spearman rank correlation
coefficient (rs). Also, the Dillon model required mean depth information
which is neither uniformly available nor necessarily accurate, without an
extensive bathymetric survey. The mean depth of the lake is the only independ-
ent variable which sets the level of the theoretical eutrophic "loading" rate
in the Dillon model. In the Larsen/Mercier model the independent variable
which controls the theoretical eutrophic loading rate is the phosphorus
retention capacity.
8
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TABLE 3. COMPARISON OF THREE MODELS TO PREDICT MEAN AMBIENT LAKE PHOSPHORUS CONCENTRATIONS
AT EQUILIBRIUM IN TWO RESERVOIRS
CALCULATED
MODEL
VALUE
TROPHIC
STATE LEVELS
EUTROPHIC OLIGOTROPHIC
TROPHIC
RATIO
PREDICTED
TROPHIC
STATE
Lake Mead, Nev./Ariz.
Vollenweider
Larsen/Mercier
Dillon
Flaming Gorge, Wyo
Vollenweider
Larsen/Mercier
Dillon
6.23 g/m2/yr
372 yg/1
1 .47 g/m2
./Utah
1.35 g/m2/yr
93.5 yg/1
0.41 g/m2
0.78 g/m2/yr
298.5 yg/1
1.18 g/m2
0.76 g/m2/yr
152.6 yg/1
0.68 g/m2
0.39
149.
0.59
0.38
76.9
0.34
g/m2/yr
5 yg/1
g/m2
g/m2/yr
yg/1
g/m2
7.98
1.29
1.24
1.77
0.60
0.60
Eutrophic
Eu trophic
Eutrophic
Eutrophic
Meso trophic
Mesotrophic
-------
LITERATURE CITED
Allum, M.O., R.E. Glessner, and J.H. Gakstatter. 1977. An evaluation of the
National Eutrophication Survey data. Working Paper No. 900. Assessment and
Criteria Development Division, Corvallis Environmental Research Laboratory,
Corvallis, Oregon. 75 p.
Dillon, P.O. 1975. The phosphorus budget of Cameron Lake, Ontario: The
importance of flushing rate to the degree of eutrophy of lakes. Limnoll_.
Oceanogr. 20:28-39.
Edmondson, W.T. 1970. Book review (Water management research). Limnol.
Oceanogr. 15:169-170.
Larsen, D.P. and H.T. Mercier. 1976. Phosphorus retention capacity of
lakes. J_. Fish. Res. Board Can. 33:1742-1750.
U.S. Environmental Protection Agency. 1975. National Eutrophication Survey
Methods 1973 - 1976. Working Paper No. 175. Environmental Monitoring and
Support Laboratory, Las Vegas, Nevada, and Corvallis Environmental Research
Laboratory, Corvallis, Oregon. 91 p.
U.S. Environmental Protection Agency. 1976. Report on Lake Lulu, Florida.
Working Paper No. 263. Environmental Monitoring and Support Laboratory, Las
Vegas, Nevada, and Corvallis Environmental Research Laboratory, Corvallis,
Oregon. 30 p.
U.S. Environmental Protection Agency. 1977a. Report on Lake Mead, Nevada
and Arizona. Working Paper No. 808. Environmental Monitoring and Support
Laboratory. Las Vegas, Nevada, and Corvallis Environmental Research
Laboratory, Corvallis, Oregon. 91 p.
U.S. Environmental Protection Agency. 1977b. Report on Flaming Gorge
Reservoir, Utah and Wyoming. Working Paper No. 885. Environmental Monitoring
and Support Laboratory. Las Vegas, Nevada, and Corvallis Environmental Research
Laboratory, Corvallis, Oregon. 67 p.
Vollenweider, R.A. 1968. Scientific fundamentals of the eutrophication of
lakes and flowing waters, with particular reference to nitrogen and phosphorus
as factors in eutrophication. Organ. Econ. Coop. Dev., Paris. Tech. Rep.
DAS/CSI/68.27.-159 p.
Vollenweider, R.A. 1975. Input - output models with special reference to
phosphorus loading concept in limnology. Schweiz. Z. Hydro!. 37:53-83.
10
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-600/3-79-012
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
COMPARISONS OF MODELS PREDICTING AMBIENT LAKE
PHOSPHORUS CONCENTRATIONS
REPORT DATE
February 1979
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
S.C. Hern, V.W. Lambou, L.R. Williams
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, NV 89114
10. PROGRAM ELEMENT NO.
1BA608
11. CONTRACT/GRANT NO.
2. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency-Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV 89114
13. TYPE OF REPORT AND PERIOD COVERED
03-07-73 to 11-14-73
14. SPONSORING AGENCY CODE
EPA/600/07
5. SUPPLEMENTARY NOTES
Previously released in limited distribution as No. 704 in the Working Paper Series
for the National Eutrophication Survey
6. ABSTRACT
The Vollenweider, Dillon, and Larsen/Mercier models for predicting ambient
lake phosphorus concentrations and classifying lakes by trophic state are com-
pared in this report. The Dillon and Larsen/Mercier models gave comparable
results in ranking 39 lakes relative to known ambient phosphorus concentrations.
The Vollenweider model, which does not include a phosphorus retention capacity
component, was unable to achieve the high rank correlations found with the
other models.
Trophic state predictions from the phosphorus loading models are compared
with National Eutrophication Survey lake report designations. Disagreements
of 14, 18, and 25 percent, respectively, were found with the Dillon, Larsen/
Mercier, and Vollenweider concepts.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Rates
Water Quality
Mathematical Models
Trophic State
Phosphorus Loading
07C
18. DISTRIBUTION STATEMENl
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
16
20 SECURITY CLASS (Thispage)
22. PRIC
UNCLASSIFIED
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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