The purpose of this study was to develop predictive models for 

 inferring historic macrophyte biomass using diatoms, and to 

 incorporate those models into a scheme that permits a more 

 complete assessment of former lake trophic state than do models 

 based solely on water-column nutrient concentrations. 



Subfossil diatom assemblages were analyzed from the surface 

 sediments of 29 Florida lakes covering a range of macrophyte 

 abundance. Trophic-state, pH, and specific conductance formed an 

 environmental gradient that was the principal influence on diatom 

 communities in the limnologically diverse set of lakes. The 

 planktonic proportion of the diatom community was positively 

 correlated with trophic state, whereas the periphytic proportion was 

 negatively correlated with trophic state. Sedimentary diatom 

 concentrations, however, showed that both of these life-form 

 communities had a positive response to increase in water-column 

 nutrients. 



Multivariate models are presented that permit estimates of 

 1 former macrophyte biomass from fossil diatom assemblages. The kg 

 of P contained in once-living macrophyte biomass can be estimated 

 using a mean percent P value for macrophyte taxa. This mass of P 

 divided by lake volume yields a concentration that can be added to 

 limnetic P inferences obtained from diatom predictive models to 

 estimate the potential total P content of the water column (WCP) 

 Trophic state index values calculated with historic WCP will reflect 

 both former macrophyte and phytoplankton aspects of trophic state. 



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