36 



combustion in a muffle furnace for 1 hr at 550 °C. Percent loss on 

 ignition was then calculated as: 



% L.O.I. = 100 X (1- (sample weight before combustion/sample 

 weight after combustion)). 



Organic matter accumulation rates (ORGACCUM) were calculated with 



the following equation: 



ORGACCUM = SEDACCUM x (% L.O.I./lOO) 



where ORGACCUM = g dry organic matter cm'2 yr-l. 



Quantifying Macrophyte Presence 

 Researchers from the Department of Fisheries and Aquaculture 

 at the University of Florida obtained quantitative macrophyte data 

 for the survey lakes in field work conducted between 1982 and 

 1988. The percentage of the lake area covered by macrophytes 

 (percent-area coverage) was obtained for 23 lakes by planimetry on 

 morphometric maps. The area covered by submergent vegetation as 

 estimated from recording fathometer transects (Canfield and Duarte 

 1988) was added to the area covered by emergent and floating- 

 leaved vegetation. The percentage of the lake volume filled with 

 macrophytes (percent-volume infestation) was also estimated 

 morphometrically for 30 lakes using the percent areal coverage of 

 submerged macrophytes and the height of submerged vegetation as 

 indicated by fathometry (Maceina and Shireman 1980). 

 Morphometric data including lake surface area, shoreline length, 

 shoreline development and mean depth were available for 24 of the 

 survey lakes. 



