Ecology of algae in a subarctic stream

Abstract

Changes in the density of planktonic, epilithic, and epiphytic algae in a subarctic stream (Baker Creek) were estimated from collections made at least every 2 weeks between June 1975 and November 1976. Simultaneous determinations of 17 nutrients. pH, temperature, discharge, and the gut contents of 29 herbivorous animals were made. Multiple regression analysis indicated that temperature had the greatest overall effect on changes in the density of the plankton (Ankistrodesmus falcatus, Scenedesmus quadricauda, Nostoc pruniforme, and Chlamydomonas lapponica) and epilithon (Nostoc pruniforme) during the growing season. It was followed in significance by either NO₃-N, hardness, or discharge. NO₃-N was always primarily responsible for initiating changes in the epiphyton (Achnanthes minutissima, A. linearis, and Cocconeis placentula). Temperature did, however, assume secondary importance followed by SiO₂. Other environmental factors usually had little effect on all three communities.