88 



TROPH 1 diatom index (Whitmore 1989) to predict log-transformed 

 water-column total P. Figure 9 shows a plot of log-transformed 

 water-column total P versus the TROPHl diatom index for 51 Florida 

 lakes. The four nitrogen-limited lakes shown demonstrated 

 anomalously low diatom index values for their total P values, and 

 were removed from the regression data set. The resulting predictive 

 model was: 



logio(total P) = -1.795 + 0.973(logio(TROPH 1)) 3.9 



r2 = 0.807, p < 0.001, n = 47. 



Assessing Confoundedness in the Water-Column Total P Predictive 



Model 

 The significant negative correlation coefficient that was observed 

 between log-transformed total P and percent-area coverage (Table 

 11) confirmed the inverse relationship previously observed (Canfield 

 et al. 1984) between macrophyte presence and water-column 

 nutrient concentrations. The correlation coefficient between the log- 

 transformed TROPH 1 diatom index and percent-area coverage, 

 however, was not significant (Table 11). The model for predicting 

 water-column total P from the TROPH 1 diatom index is not 

 confounded by the macrophyte variable percent-area coverage. 



