Effects of Environmental Variables on Growth Rates and Physiological Characteristics of Lake Superior Phytoplankton

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Abstract
Phytoplankton taxonomic composition and biovolume, assimilation numbers (PmB); phosphorus kinetics, as well as some physical and chemical variables were measured on 37 occasions during six cruises on Lake Superior during May 1980-October 1981. A larger number of significant differences were detected between thermally stratified and isothermal stations than between inshore and offshore, or among seasons. Phytoplankton from isothermal waters was characterized by lower assimilation numbers and biovolume, showed symptoms of adaptation to a lower light regime, and was less phosphorus deficient than populations from thermally stratified waters. The lower growth rates and the outcome of stepwise multiple regression analyses suggest that phytoplankton growth during isothermal mixing is limited primarily by light.