Date: Wed, 28 Mar 2001 10:23:01 -0500
From: Gerald Lloyd Mackie
To: "S.M. Mandaville"
Subject: Re: Thanks and some questions
> RE: [B] Question#1 : On page AIV-9 (Appendix IV) titled, "Summary of morphometric, physical, chemical and biological criteria for assessing trophic status of lakes", I would like to know your reference for the classification based on Chlorophyll a (<2,
2-5 and >5 ug/l). I will appreciate same since there is so much contradictory info in published literature. To date I have been using the Final Report of the 20-yr research of the OECD lead by Environment Canada (Vollenwedier and Kerekes, 1982).
A: I derived my values from Dillons (et al) Lake capacity paper, using his model to fill in the intermediate values for the table he provides. For the criteria, I used Carlson's TSI models. I gave the values rather than have students/readers infer from th
e Probability Distribution diagrams with fixed boundaries because it is easier to use for those interested in estimating trophic status of their lake/river. The criteria also fit with the PWQO for Ontario, especially since the models are based mostly on O
ntario lakes. But, you are wise to use the Probability Distribution diagrams because they are based on more than Ontario Lakes.
> The OECD figures are quite different, especially at the meso to eutro transition. The 5 ug/l is low compared to the OECD tables. OECD itself has a few models, basically the Fixed Boundary which takes into account peak Ch-a in addition to other parameter
s, the Management Model (which is used for prediction purposes and incorporates the class mid-points) and the Probability Distribution Diagrams for mean yearly TP, mean yearly Ch-a, peak yearly Ch-a and mean yearly SD. I had been advised during the early
1990s by both Dr. Vollenweider of Burlington and Dr. Kerekes of Halifax to put more faith in the Probability Distribution Diagrams because of the probability aspects inherent in the classification of lakes!! It seems those diagrams were derived from the c
onsensus of numerous leading scientists from Europe and North America.
>
> RE: [C] Question# 2: In the same Appendix, what is the reference w.r.t the Total Nitrogen classification system? FURTHER, am I right in assuming that it only applies to lakes which are nitrogen limited??
A: No, in fact the criteria are based on P-limited lakes. The criteria are derived from PWQO again and reflect N:P ratios greater than 16 which are typical of P-limited lakes. Our rivers in southern Ontario have N:P ratios <10, typically 6-12, and many
have blue-green algae that are charcateristic of N-limited waters.
Hope this clears things up.
Gerry