Relationships between surface sediment diatom assemblages and
lake trophic status were studied in 50 Canadian Precambrian Shield lakes
in the Muskoka-Haliburton and southern Ontario regions. The purpose of
this study was to develop mathematical regression models to infer lake
trophic status from diatom assemblage data. To achieve this goal,
however, additional investigations dealing with the evaluation of lake
trophic status and the autecological features of key diatom species were
carried out.
Because a unifying index and classification for lake trophic status
was not available, a new multiple index was developed in this study, by
the computation of the physical, chemical and biological data from 85
south Ontario lakes. By using the new trophic parameter, the lake trophic
level (TL) was determined:
TL = 1.37 In[1 +(TP x Chl-a / SD)], where,
TP=total phosphorus, Chl-a=chlorophyll-a and SD=Secchi depth.
The boundaries between 7 lake trophic categories (Ultra-oligotrophic
lakes: 0-0.24; Oligotrophic lakes: 0.241-1.8; Oligomesotrophic lakes: 1.813.0;
Mesotrophic lakes: 3.01-4.20; Mesoeutrophic lakes: 4.21-5.4; Eutrophic
lakes: 5.41-10 and Hyper-eutrophic lakes: above 10) were established.
The new trophic parameter was more convenient for management of water
quality, communication to the public and comparison with other lake
trophic status indices than many of the previously published indices
because the TL index attempts to Increase understanding of the
characteristics of lakes and their comprehensive trophic states. It is more
reasonable and clear for a unifying determination of true trophic states of
lakes.
Diatom specIes autecology analysis was central to this thesis.
However, the autecological relationship of diatom species and lake trophic
status had not previously been well documented. Based on the
investigation of the diatom composition and variety of species abundance
in 30 study lakes, the distribution optima of diatom species were
determined. These determinations were based on a quantitative method
called "weighted average" (Charles 1985). On this basis, the diatom species
were classified into five trophic categories (oligotrophic, oligomesotrophic,
mesotrophic, mesoeutrophic and eutrophic species groups). The resulting
diatom trophic status autecological features were used in the regressIon
analysis between diatom assemblages and lake trophic status.
When the TL trophic level values of the 30 lakes were regressed
against their fi ve corresponding diatom trophic groups, the two
mathematical equations for expressing the assumed linear relationship
between the diatom assemblages composition were determined by
(1) uSIng a single regression technique:
Trophic level of lake (TL) = 2.643 - 7.575 log (Index D)
(r = 0.88 r2 = 0.77 P = 0.0001; n = 30)
Where, Index D = (0% + OM% + M%)/(E% + ME% + M%);
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(2) uSIng a' multiple regressIon technique:
TL=4.285-0.076 0%- 0.055 OM% - 0.026 M% + 0.033 ME% + 0.065 E%
(r=0.89, r2=0.792, P=O.OOOl, n=30)
There was a significant correlation between measured and diatom
inferred trophic levels both by single and multiple regressIon methods (P
< 0.0001, n=20), when both models were applied to another 20 test lakes.
Their correlation coefficients (r2 ) were also statistically significant (r2
>0.68, n=20). As such, the two transfer function models between diatoms
and lake trophic status were validated. The two models obtained as noted
above were developed using one group of lakes and then tested using an
entirely different group of lakes.
This study indicated that diatom assemblages are sensitive to lake
trophic status. As indicators of lake trophic status, diatoms are especially
useful in situations where no local trophic information is available and in
studies of the paleotrophic history of lakes.
Diatom autecological information was used to develop a theory
assessing water quality and lake trophic status