94 



A positive response of periphyton biomass to higher water- 

 column nutrients has been demonstrated in previous experimental 

 studies and lake surveys (Stockner and Armstrong 1971, Ennis 1975, 

 Shortreed et al. 1984). Sand-Jensen and Sondergaard (1981) came to 

 the unusual conclusion that epiphyton biomass increased more than 

 phytoplankton biomass in response to increased nutrient loading. 

 Other studies, which appear less conclusive, have shown that 

 periphytic biomass may be unaffected or even decline with 

 increasing water-column P concentrations. Cattaneo (1987) 

 concluded that periphytic biomass showed a low and variable 

 response to water-column total P in his survey of 10 Canadian lakes, 

 but admitted that wave intensity may have altered periphytic 

 biomass on the surface of the large stones in shallow water where he 

 obtained his samples. Hansson (1988) found a weak, negative 

 correlation between log-transformed periphytic algal biomass, as 

 assessed from colonization rates on nylon net, and log-transformed 

 total P in 20 Swedish lakes. 



Hansson speculated that in lakes of higher trophic state, plankton 

 may limit periphyton populations to some extent by shading. 

 Hansson noted, however, that cold temperatures in the subalpine 

 lakes of his survey may have affected colonization rates and led to 

 some underestimates of periphyton standing crop. 



One study of periphyton and plankton communities in a Florida 

 lake demonstrated a strong negative relationship between the 

 biomass of these groups over a 5-month period (Hodgson et al. 

 1986). This negative correlation, however, reflected seasonal 

 variation in community dominance within a single, closed system. 



