37 



The average wet-weight biomass per unit area of submerged, 

 emergent and floating-leaved macrophytes was determined from 

 0.25 m2 quadrats randomly sampled from 10 transects through the 

 littoral zones of 23 lakes. Above-ground biomass in each quadrat 

 was collected by divers, spun to remove excess water and weighed to 

 the nearest 0.1 kg (Canfield and Duarte 1988). 



Water Chemistry Data 



Median water chemistry values for the lakes in Survey Set 1 

 were obtained from the Florida Lakes Data Base of the Water 

 Resources Research Center at the University of Florida. Water 

 quality variables selected from this data set included median values 

 for total P, total N, Chi a, Secchi depth, specific conductance and pH. 



Mean water chemistry values were obtained by the Department 

 of Fisheries and Aquaculture for each lake in Survey Set 2 by 

 averaging data from 3 mid-lake stations (M. Hoyer, pers. comm.). 

 Total P analyses were performed following persulfate digestion 

 (Murphy and Riley 1962, Menzel and Corwin 1965), and total N was 

 measured using a modified Kjeldahl technique (Nelson and Sommers 

 1975). Water samples were filtered through a Gelman type A-E glass 

 fiber filter and Chi a was measured using the Yentsch and Menzel 

 (1963) method and Parson and Strickland (1963) equations. Secchi 

 depth was measured with a 20-cm black and white Secchi disk. 

 Trophic state index (TSI) values (Huber et al. 1982) were calculated 

 using the mean or median values of total P, total N, Chi a and Secchi 

 depth for each lake in Survey Sets 1 and 2. Specific conductance was 

 measured with a Yellow Springs Instrument Company model 31 



