Physicochemical Typologies of South-Central Ontario Lakes

We present basic physicochemical data and principal component analyses (PCA) of both morphometric and chemical variables for 37 Ontario lakes. Multivariately derived composite variables were substituted for more conventional independent variables in several regression models. These composite variables always explained a greater percentage of variance than the standard morphometric variables. A typology derived in part from the PCA was useful in identifying groups of lakes for which the Ragotzkie model predicting maximum depth of the summer thermocline was appropriate and other groups of lakes that appear to be outliers on the basis of insufficient volume. In addition, variables important in defining the typology, particularly [Formula: see text] ratio and lake volume, were shown to be among the most important in a stepwise, multiple linear regression explaining 91% of the variance in nannoplankton to filter-feeding zooplankton ratios in the lakes. This represents a 47% improvement over previously reported results. Total phosphorus still explained more variance in several measures of phytoplankton biomass than did a multivariately derived composite chemical variable, but there were significant explanatory improvements in phosphorus–phytoplankton regressions within lake groups derived from a typology based on a speciated chemical matrix. There appears to be some overlap in biological patterns from morphometrically and chemically defined lake types. We suggest that these may represent ends of a continuum of differing density regulation responses by the biological communities.