Fluctuations of phytoplankton biomass and its composition in a subarctic lake during summer

• Published in: Canadian Journal of Botany
• Main Authors: Sheath, Robert G., Munawar, Mohiuddin, Hellebust, Johan A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1975
• Subjects: Plant Science; Subarctic
• Online Access: http://dx.doi.org/10.1139/b75-247; http://www.nrcresearchpress.com/doi/pdf/10.1139/b75-247

Phytoplankton biomass was determined for a shallow subarctic lake from June to August, 1973, with one peak being observed at the beginning of July (300 mg m −3 ). Phytoplankton then declined until the end of August when a relatively high value of 240 mg m −3 was observed. The Chlorophyta and Diatomeae were the dominant taxa during periods of high biomass, whereas other algal groups had relative increases only during the minima. The early summer population was almost entirely composed of diatoms, followed by a mixed population of diatoms and cryptomonads, and then by the Chlorophyta, which dominated during midsummer. Subsequently, there were successive increases of chrysomonads, dinoflagellates, and then diatoms. Fluctuations of major species were examined in relation to changes in biomass of the algal groups. Net plankton species were dominant throughout most of the summer but nanoplankters were abundant for short periods in mid-June and July. Based on a few comparisons done in July, it was found that the species composition of phytoplankton was not similar to that of the benthic algae since only 15% of the species were common to both habitats and these species contributed to 21% of the phytoplankton biomass estimated.