19 



Scottish lochs and their recovery following abatement of atmospheric 

 sulfate emissions in the United Kingdom. 



Diatom Methods for Reconstructing Trophic State 



Historical trophic state studies generally have not received the 

 degree of quantitative treatment that studies of lake acidification 

 have. Diatom/trophic reconstructions have often relied heavily on 

 autecological information of specific taxa for qualitative 

 interpretation of diatom percentage diagrams from lake sediment 

 cores. Brugam (1978), for instance, documented the eutrophication 

 of Linsley Pond in Connecticut and Bradbury (1975) used diatoms to 

 interpret the history and eutrophication of Minnesota lakes. 

 Battarbee (1978) observed the influence of land use and sewage 

 effluent on the eutrophication of Lough Neagh, Northern Ireland. 

 Mkansson (1982) presented an excellent ecological analysis of the 

 diatom flora from HdvgSrdssjon in Sweden and documented 

 eutrophication after 1900 due to agricultural activity. Qualitative 

 >v, studies have provided understanding of gross trends in the trophic 

 trajectory of lakes because of climatic patterns and anthropogenic 

 influence, but they have lacked ability to discern subtle trophic 

 differences, assess rates of change or demonstrate statistical 

 significance. 



Ratios have been proposed that quantitatively describe lake 

 productivity using the percentages of diatom species separated at 

 high taxonomic levels. Nygaard's (1949) C/P index was a ratio of the 

 number of valves in the diatom orders Centrales and Pennales. High 

 C/P values were thought to indicate eutrophic conditions because of 



