30 



macrophyte biomass (Canfield et al. 1983a, Canfield et al. 1984). 

 Historic samples indicating low water-column nutrient concentrations 

 may represent times of high macrophyte production, especially if the 

 cyclic changes in water level of Florida's shallow lakes (Deevey 1988) 

 promote a periodic lakeward expansion of macrophyte beds. If the 

 trophic trajectory of lake ecosystems over time is to be fully 

 understood, a more holistic consideration of historical trophic state is 

 required, one that includes the macrophyte component of production. 



Conventional sedimentary indicators of macrophytes are not 

 appropriate for quantitative reconstructions for a variety of reasons: 



1 ) pollen and seed production is species specific quantitatively and 

 is often absent in plants such as Hydrilla that largely undergo 

 vegetative reproduction. Models predicting historical 

 macrophyte standing crop from sedimentary pollen or seeds 

 would have to be calibrated for each individual species; 



2) there are no known photosynthetic pigments that would be 

 preserved in sediments and that are specific to macrophytes; 



3) diagenesis often affects the preservation of macrophyte remains. 



Diatoms are considered as potential macrophyte indicators in 

 this study because diatoms are usually well-preserved in lake 

 sediments and they are ecologically specific. Life-form classifications 

 are available (Lowe 1974) that permit separate consideration of 

 planktonic and periphytic taxa. Sedimentary concentrations and 

 accumulation rates of periphytic taxa might be expected to 

 demonstrate a positive correlation with the amount of submerged 

 macrophyte biomass for 2 reasons. First, a positive relationship 

 exists between periphytic biomass and the increased substrate area 

 afforded by macrophytes with many small or finely-dissected leaves 

 such as Hydrilla (Cattaneo and Kalff 1981). Secondly, evidence also 



