Phytoplankton-volume-based productivity in the North American Great Lakes and the St. Lawrence River

Summary

Surface samples from the North American Great Lakes and the St. Lawrence River are compared with respect to photosynthetic rate per liter of water (P), phytoplankton biovolume (B), the P/B ratio, and SIMPSON'S Diversity Index. Major component species of phytoplankton are also presented. Lakes Superior, Michigan and Huron exhibited relatively low values of P and B, with Superior being the lowest. But a dramatic peak was observed in the western basin of Lake Erie. The central and eastern basins of Lake Erie and Lake Ontario exhibited lower values than the western basin, but distinctly higher than the three upper lakes. The St. Lawrence River exhibited high photosynthetic rates, but relatively low phytoplankton biovolumes; consequently, the P/B ratio there was higher than that observed in any of the lakes.

The three upper lakes (Superior, Michigan and Huron) were dominated by diatom species (Asterionella formosa, Tabellaria fenestrata, Fragilaria crotonensis), but Erie and Huron exhibited different diatom dominants (Coscinodiscus rothii, Melosira sp., Fragilaria capucina) and contained dominant biovolumes of greens (Pediastrum, Cosmarium) and blue-greens.