PHYTOPLANKTON IN QUEBEC LAKES - VARIATION WITH LAKE MORPHOMETRY, AND WITH NATURAL AND ANTHROPOGENIC ACIDIFICATION

Phytoplankton of 54 Quebec lakes were studied. The phytoplankton groups data matrix was submitted to a flexible linkage cluster analysis. The resulted 6 clusters of lakes are distributed along the NE-SW geographic axis and are related to an ascending density gradient in total phytoplankton, chlorophytes, cyanophytes, and microflagellates. Factor analysis produced 5 derived environmental factors (hardness-alkalinity, lake depth and transparency, dystrophy, lake size and salinity-sulphates loading), which explain 73% of the total variance of the abiotic data matrix. Alkalinity-acidity gradient is the most important factor related to phytoplankton groups and species distribution. Most of the cyanophyte taxa and some chlorophytes are positively related to the hardness-alkalinity and the sulphates loading factors. The abundances of pyrrophytes increases in alkaline lakes subjected to great sulphates loading. Lake morphometry and trophy also influence the phytoplankton distribution. Deep and clear lakes in E Quebec are dominated by chrysophycean species. Few species are related to the dystrophy factor. -from Authors