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

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                                 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.

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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

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                              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
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 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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