Distribution and abundance of periphyton and phytoplankton species in two subarctic Canadian rivers

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Abstract
Periphytic and planktonic algal populations were sampled over a yearly cycle in the Ogilvie and Swift rivers located in the northern and southern Yukon, respectively. Diatoms and green algae dominated periphytic assemblages during spring, summer, and fall, whereas the bulk of the overwintering cells was diatoms. The 96 species of periphytic diatoms were dominated by Achnanthes minutissima Kütz., an unidentified species of Achnanthes, Cocconeis placentula Ehr., Diatoma hiemale var. mesodon (Ehr.) Grun., Diatoma tenue var. elongatum Lyngb., Anomoeoneis vitrea (Grun.) Ross, and Fragilaria crotonensis Kitton. Most diatoms encountered are also generally abundant in more temperate locations. Periphytic green algae were dominated by Mougeotia sp., Oedogonium sp., Ulothrix sp., and Stigeoclonium sp. In high flow regions of the Ogilvie River the red alga Lemanea fucina Bory was extremely abundant. Phytoplankton was sparse and generally represented by the same species as found in periphytic habitats. Results indicate that the phytoplankton cells were probably derived from sloughed periphytic cells. Achnanthes minutissima, Diatoma tenue var. elongatum, Fragilaria construens var. binodis (Ehr.) Grun., Fragilaria vaucheriae (Kütz.) Peters, and Synedra ulna (Nitz.) Ehr. were the most abundant species in the plankton.