16 



To summarize, traditional methods of macrophyte community 

 reconstruction tend to over-represent, under-represent or miss 

 entire portions of the macrophyte community. No single method has 

 been developed that will provide reasonably accurate quantitative 

 estimates of historical macrophyte standing crop. 



Diatom Methods in Paleolimnology 

 Some Quantitative Diatom Methods Used in pH Reconstructions 



Most quantitative work using diatoms to reconstruct past 

 limnological conditions has been concerned with lake acidification 

 due to anthropogenically induced acid precipitation. The large 

 number of lake acidification studies recently funded (Davis 1987) 

 indicates that lake acidification has occupied an important place on 

 the agenda of national and international environmental concerns. 

 The high costs of implementing more rigid air pollution standards 

 necessitated statistical rigor to determine if atmospheric loadings of 

 sulfur and N oxides were having significant fallout effects on aquatic 

 ecosystems. As a consequence, lake acidification studies received 

 priority funding and were numerous. Davis (1987) reviewed many 

 such studies that used diatoms to infer historical pH trends. 



The earliest quantitative index relating diatom assemblages to 

 pH of lakewater was the a index described by Nygaard (1956), a 

 ratio of acidic to alkaline diatoms in a sample based on the pH 

 autecological classifications (Hustedt 1937-38) of the individual taxa. 

 Renberg and Hellberg (1982) developed the somewhat more 

 sophisticated index B that was also a ratio of the percentage of 

 diatoms in pH autecological categories. These authors regressed log- 



