Seasonal variation in phytoplankton taxa and size structure in Lake Cromwell (Laurentian Shield) Quebec (1983-1985)

Seasonal variation in phytoplankton families and 9 size classes were studied over a year in a small, mesotrophic, brown-water lake of the Laurentian Shield (Quebec). Chrysophyceae and Prymnesiophyceae dominated the phytoplankton community, particularly flagellated species. Diatoms and Chlorophyceae were only important at certain seasons and Cryptophyceae, dinoflagellates and euglenophytes showed irregular distributions over the seasons. The predominant size groups were comprised of species ranging from 2-16 µm of greatest axial linear dimension (GALD). Small phytoplankters (2-8 µm) were predominant in winter and early spring while larger algar (8-16 µm) became important in summer. Water temperature was controlling the seasonal development of phytoplankton community in the Laurentian Shield lakes.