The effects of nitrogen/phosphorus ratios on the prediction of chlorophyll in phosphorus-limited lakes in central Ontario

71 Pages·1991·20.6 MB·English

by  Dillon, P. J.|Reid, R. A.|Molot, Lewis A.|Ontario Ministry of the Environment. Dorset Research Centre.|York University. Faculty of Environmental Studies.|Ontario Ministry of the Environment. Water Resources Branch. Limnology Section.

THE EFFECTS OF
NITROGEN/PHOSPHORUS RATIOS
ON THE PREDICTION OF
CHLOROPHYLL IN PHOSPHORUS-LIMITED
LAKES IN CENTRAL ONTARIO
JANUARY. 1991
Environment
Environnement
Ontario
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THE EFFECTS OF NITROGEN/PHOSPHORUS RATIOS ON THE
PREDICTION OF CHLOROPHYLL IN PHOSPHORUS—LIMITED LAKES
IN CENTRAL ONTARXO
Report prepared by:
P. 7. Dillon and R. A. Reid, Dorset Research Centre
with Lewis A. Molot, York University
Report prepared for:
Lianology Section
Water Resources Branch
Ontario Ministry of the Environment
JANUARY 1991
Cette publication technique
n'est disponible qu'en anglais
Copyright: Queen's Printer for Ontario, 1991
This publication may be reproduced for non—commercial purposes
with appropriate attribution
PIBS 1407
log 90—2345—053
ThE EFFECTS OF NITROGEN/PHOSPHORUS RA'IIOS ON ThE
nE
DICTION OF CHLOROPHYLL IN PHOSPHORUS-LIMITED LAKE S
IN 'CENTRAL ONTARIO
P1 Dillon
Ontario Ministry Øf the Environment
Dorset Research Centre
P.O. Box 39
Dorset, Ontario
POA lEO
Lewis A. Molot
Faculty of Environmental Studies
York University
4700 Keele Street
loronto,
M3J 1P3
and
R,A. Reid
O'ntario Ministry of the Environment
Dorset Research Centre
P.O. Box 39
Dorset, 'Ontario
FOA lEO
PREFACE
Relationships between chlorophyll and total phosphorus (1?) were examined on
phosphorus-limited oligotrophic and mesotrophic lakes in central Ontario. Linear
regression analysis indicated mostly random associations between chlorophyll and total P,
,.a
suggestIng a steady state. Chlorophyll A/total regression models have an inherent
inability to predict annual variations for the period 1976 to 1987.
ABSTRACT
I
The response of mean animal ice-free chlorophyll in 15 stratified, P-limited
oligotrophic and mesotrophic lakes in central Ontario to changes in mean epilimnetic total
phosphorus (IT) within a lake was highly! years during the period 1976 to
1987. The 11± ear regression coefficient of: determination, R2, using: all annual means was
only 0.36 (n = 172 a:nd' within-lake regressions revealed mostly random
associations between chiorcphyli and TP, suggesting fluctuations about steady state
levels, Nevertheless, by using the long-term average of animal means for each a
bivariate linear regression model was developed relating the long-term, average response
of chlorophyll to the long-term, average TV concentratlon in these lakes (R2 = 0.78).
Annual variation could not be explained by changes in TN/i?. R2 slightly from
078 to 082 with TN/i? as a second independent variable using long-term averages but
remained at 0.78 with 1/IT as a second variable, Reanalysis of published data excluding
lakes which were not P-limited showed that TN/i? is of little or no her efit as an
independent variable. A minimum of 6 consecutive years of sampling was required to
avoid poor !(defined as R2 < 0,6) for this set of lakes. Therefore,
chlorophyll .a/TP regression models should be vlewed as steady state models with an
inherent inability to predict annual variation. I
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RÉSUMÉ
Durant la pSiode aiThnt de 1976 a 1987, la rÔaction de la moyenne annuelie de
chiorophylle non cornbi'née la glace, aux changements moyens du phosphore total
.a,
(TP) de la surface aqueuse d'un la.c Ôtait trÔs variable dans 15 lacs stratifies, oligotrophes
limitÔs en P et mésotrophes du centre de l'Ontario. En tenant conipte de toutes les
moyennes anxuelles, le coefficient de dÔtermination de la regression linéaire, R2, était de
seulernent 0.36 (n = 172 iacs-annêes) et les regressions a i'intêrieur meme du lac ont
des associations des plus alÔatoires entre le chiorophyfle et le TP, suggérant ainsi
des fluctuations relatives aux niveaux d'etat constant. Néanm:oins, en utilisant la moyenne
a. long terme des moyennes annuelles pour chaque lac, un modéle de regression linéaire
deux variables a ete d6veloppé d'établir un rapport entre la reaction moyenne a
a.
long terme du chlorophylle et la concentration moyenne a long du TP de ces lacs
(R2 = 0.78). La variation annuelle ne pouvait pas être exphquée par les char gements du
Th/TR Le R2 a legerernent augmenté de 0.78 a 0.82 avec ie TN/TP en tant que
variable independante en les moyerrnes a. long terme mais West
maintenu a. 0.78 avec 1/TP en tant que deuxiême variable. Une analyse subsAquente des
donnees excluant les lacs qui n'Ôtaient pas limites en P a indiqué que le
est peu ou pas utile en- tant que variable independante. Un minimum de 6 années
d'échantillonnage requis pour éviter des ajustements anormaux (dCfinis
cone
étant R2 < 0.6) pour cet ensemble de lacs. Par consequent, les modêles de
regression chlorophylle WTP doivent donc étre vus comme des modéles d'etat constant,
possédant une habilité ithérente pour prédire la variation annueHe.
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TABLE OF CONTEN'IS
Page
Preface
i
Abstract ii
Introduction
1
Methods
3
Results
4
Discussion 7
Acknowledgements
13
References
14
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Lit
of 'Tables
!Tabie R2 range for linear regression of ice-free chlorophyll versus
iT
epiimentic using running averages of annual means for! the
period 1976-1987. 18
Table 2. R2 for linear regression of chlorophyll .a versus epilimnetic TP,
TN/i?
versus !TP and 1/TP, and versus 1 and '(by weight) using
untransformed and logarithmically transformed data.! Annual means
for each of the 15 lakes were av!eraged! for the two periods 1976-79
and 1976-87. ss summer stratificatiom if - ice-free. 19
Table 3. range for linear regression- of ice-free chlorophyll versus
epilinmetic TP using running averages of annual means for the
period 1976-1!! 987. 20
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List of Figures
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Figure 1(a). Ice-free chlorophyll .a versus epilinmetic T for 15 P-limited lakes
in central Ontario for the 12 year period 1976-1987. Average of I
annual means. The regression equation is Chl11 = 0.332 TP ±
0.57 1 (n = 15, R2 = 0.78, slope SE: = 0.049 and the intercept
SE = 0.358). 21
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Figure 1(b). Ice-free chlorophyll ia versus epilimnetic TP for 15 P-limited lakes
in central Ontario for the 12 period Annual
means (n = 172 lake-years, R2 = 0.36).! 22
Figure 2(a) Annual ice-free chlorophyll .a versus epihrnnetic TP for Harp
Lake 1976 - 1987. 23
Figure 2(b). Annual ice-free chlorophyll .a versus :epiiimn!etic TP for Crosson
Lake, 1976 - 1987. 24
Figure 3(a). responses of annual ice-free chlorophyll in Harp and
Crosson Lakes from 1976 to 1987. 25
Figure 3(b) Temporal responses of annual ice-free epilmuetic TP in Harp
and Crosson Lakes from 1976 to 1987. 26
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