34 



V = cm3 of sediment in initial sample 



D = g dry weight of sediment cm"3 of initial sample. 



Life-form autecological information for the majority of diatom 

 taxa was obtained from the literature (Lowe 1974, Patrick and 

 Reimer 1966-1975, Hustedt 1930). The concentrations of periphytic 

 valves (PERICONC) and euplanktonic valves (PLNKCONC) were 

 calculated by multiplying the concentration of diatoms in the 

 samples by the proportion of periphyton and euplankton in each 

 sample. Tychoplanktonic diatoms normally show a periphytic life- 

 form, though are often suspended with the plankton (Lowe 1974). 

 Tychoplanktonic taxa were arbitrarily assumed to be 1/3 

 euplanktonic for these calculations. 



Bulk-sediment accumulation rates were measured for each 

 sediment sample using the Binford and Brenner (1986) dilution 

 tracer method based on 2l0p5 assay. 210pb assay for 8 lakes from 

 Survey Set 1 was performed by a modification of the Eakins and 

 Morrison (1978) method that involved estimating 210pb recovery of 

 samples from the proportion of recovery onto copper planchettes of a 

 208po spike. Atmospherically derived (unsupported) ^lOp^ activity 

 was calculated as the difference between total residual 2l0pb activity 

 in the samples and an average supported 2l0pb activity (0.80 pCi g"^) 

 that was estimated from sediment cores of nine other Florida lakes 

 (Binford and Brenner 1986). 



Sediment samples for 21 Opt, assay of Survey Set 2 lakes were 

 dried, ground with mortar and pestle and weighed. These samples 

 were sealed in polypropylene tubes for greater than 3 weeks to 

 permit ingrowth of 226Ra daughter products. Radionuclide activity 



