^^' 



74 



3.1 shows a negative coefficient for PRIN3, however, which is 

 contrary to the expectation that periphytic taxa would demonstrate 

 greater representation in lakes with greater floating-leaved biomass. 



Partial correlation coefficients showed that the 3rd principal 

 component was significantly correlated with floating-leaved biomass 

 (r = -0.618, p = 0.003, n = 22) when the effect of pH was held 

 constant. Despite the non-significant correlation between pH and 

 floating-leaved biomass (Table 3), partial correlations showed that 

 pH was significantly correlated with the 3rd principal component (r = 

 0.521, p = 0.016, n = 29) when floating-leaved biomass was held 

 constant. This implies that the model predicting floating-leaved 

 biomass is confounded by the effect of pH, and should only be 

 applied historically when it can be demonstrated that significant 

 changes in pH have not occurred. 



When the principal components analysis based on the 

 sedimentary concentration of diatom groups was repeated partialling 

 out the effects of TSl(AVG) and pH, the first principal component 

 explained 16.0% of the variance in the diatom assemblages and was 

 positively correlated with floating-leaved biomass (r = 0.460, p = 

 Uj\ 0.031, n = 22) and with TSI(AVG). This correlation with floating- 

 leaved biomass was less robust than in the previous correlation with 

 , unpartialled effects. None of the remaining principal components in 



the partialled analysis had significant correlations with macrophyte 

 variables. 



The principal components procedure was repeated using log- 

 transformed sedimentary diatom concentrations. The first principal 

 component accounted for 30.4% of the variance in the diatom 





