REGULATION OF THE DOMINANCE OF PLANKTONIC DIATOMS AND CYANOBACTERIA IN 4 EUTROPHIC HARDWATER LAKES BY NUTRIENTS, WATER COLUMN STABILITY, AND TEMPERATURE

Temporal dynamics of planktonic diatoms and cyanobacteria in four eutr ophic hardwater lakes in central Alberta, Canada, were investigated fr om May to October for up to 4 years. Biomass of individual species of the two phytoplankton groups was related to seven environmental variab les with canonical correspondence analysis. Temporal dynamics of the t wo groups differed among lakes in a given year, suggesting that region al weather patterns did not cause these variations. In a given lake, d iatom biomass varied up to 15-fold whereas cyanobacterial biomass rema ined relatively stable over the years. Diatoms were dominant at low wa ter column stability (Brunt Vasala: frequency, N-2 < 5 x 10(-4) s(-2)) and temperature (<15 degrees C). In contrast, except for some species (e.g., Aphanizomenon flos-aquae), cyanobacteria generally preferred h igher water temperature and N-2 than diatoms. Total phosphorus concent rations were more closely related to total phytoplankton biomass than to diatom or cyanobacterial biomass. These results suggested that the dominance of cyanobacteria or diatoms in these phytoplankton communiti es was related to water temperature and mixing patterns, whereas the t otal phytoplankton biomass was related to total phosphorus concentrati ons.