i ■ ■:.. ■' f ■-: .■- ■- •■■►", ' 



5 • ; Canfield (pers. comm.) pointed out that while diatom indices such as 

 TROPH 1 may be accurate predictors of water-column total P, they 

 are not comprehensive indicators of lakewide trophic state because 

 they ignore the important component of primary production that is 

 in macrophytes, 



Anderson et al. (1990) used the reciprocal averaging (RA) 

 indirect ordination method to study historical changes in lake trophic 

 state in Lough Augher, Northern Ireland resulting from loading and 

 later re-direction of nutrients from point sources. Anderson et al. 

 did not correlate RA axes with water quality indicators to 

 quantitatively assess trophic state changes, but instead plotted RA 

 axes against each other to graphically depict assemblage similarity 

 and ecological change. 



Charles (1985) investigated the relationship between lake-water 

 characteristics and sedimentary diatom assemblages in 38 

 ' Adirondack lakes. Charles used reciprocal averaging to determine 

 which environmental variables influenced the diatom assemblages, 

 and found that total P was a weak correlate with the first RA axis. 

 He concluded that pH proved a more important determinant of 

 diatom assemblage composition in the Adirondack lakes because 

 those lakes spanned a wider range of pH than of trophic state. 



Huttunen and Merilainen (1986) used detrended correspondence 

 analysis, another indirect ordination method, to interpret historical 

 limnological trends in a Finnish lake and were able to demonstrate 

 eutrophication following deforestation and the inception of 

 agriculture, as well as recent lake acidification. 



