21 



and determined that changes in diatom species composition support 

 the eutrophication inferences of sedimentary biogenic silica. 

 Schelske (1988) demonstrated that recent declines in sedimentary 

 biogenic silica are consistent with historic water concentration data 

 that showed a decline in dissolved silica in Lake Michigan. 



Whitmore (in press) studied the relationship in Florida lakes 

 between sedimentary diatom concentrations and accumulation rates 

 and lake trophic state as indicated by a TSI based on water-column 

 Chi a. Both periphyton and planktonic diatom concentrations were 

 positively correlated with water-column Chi a. Because diatom 

 accumulation rates were determined by three order of magnitude 

 differences in sedimentary diatom concentrations rather than by the 

 small range in bulk sediment accumulation rates, sedimentary 

 diatom concentrations were shown to be more expedient predictors 

 of Chi a than diatom accumulation rates. Sedimentary concentrations 

 were found to be unreliable predictors of trophic state when factors 

 such as silica limitation or blue-green bacterial inhibition limit 

 phytoplankton production, or when post-depositional changes affect 

 preservation of diatom valves. 



Bailey and Davis (1978) used a multiple regression of diatom 

 taxa to predict water-column total P in a set of 19 lakes in Maine. 

 The best model explained 96% of the variance of total P in these 

 lakes, but contained only a few species of Fragilaria as independent 

 variables. Such models based on a limited number of taxa may 

 prove unreliable when applied to lakes outside of their calibration 

 data sets because of the large number of environmental factors that 

 can influence the distribution and abundance of species (Patrick 



