38 



conductivity bridge. pH was measured with an Orion 601 A pH 

 meter. 



Statistical Analyses 



Data for diatom, macrophyte and water chemisty variables were 

 stored as Statistical Analysis System (SAS Inst., Inc. 1985) data sets 

 using the University of Florida's Northeast Regional Data Center. I 

 plotted the percent-area coverage, percent-volume infestation, and 

 submerged, emergent and floating-leaved biomass for macrophytes 

 against the percentage, concentration and accumulation rates of 

 diatom species to identify taxa responding to macrophyte presence. 

 Pearson product-moment correlation coefficients were obtained 

 between percent loss on ignition, organic-matter accumulation rates 

 and macrophyte variables using the SAS CORR procedure (SAS Inst., 

 Inc. 1985). I also obtained correlation coefficients between 

 macrophyte variables and the percentages, concentrations and 

 accumulation rates of planktonic and periphytic diatoms. Correlation 

 coefficients were calculated between the macrophyte variables and 

 log-transformed concentrations and accumulation rates of diatoms. 

 In order to determine whether morphometric and chemical variables 

 have covariable effects on diatom-macrophyte relationships, I 

 obtained correlation coefficients between macrophyte, morphometric 

 and water chemistry variables. 



For purposes of multivariate statistical analyses, it was essential 

 to reduce the number of diatom species from the 223 diatom taxa 

 observed. I examined plots of diatom percentages versus percent- 

 area coverage and percent-volume infestation, and selected forty- 

 seven taxonomic groups, several of which were the sum of taxa in 



