Algal communities associated with different alpine stream types

Abstract

We investigated major physical-chemical characteristics and benthic algae of different alpine lotic systems comprising streams and lake outlets of rhithral and kryal origin over an annual cycle. We also evaluated the structure of the algal communities and its relation to environmental characteristics for the different stream types. Algal communities were generally dominated by diatoms, Cyanophyta, and Hydrurus foetidus (Chrysophyceae). Community structure was similar among alpine streams and lake outlets, but more algal taxa occurred in lake outlets (rhithral and kryal) than in kryal streams. Although algae were identified mainly to genera, distinct patterns in community structure were evident. A major environmental determinant of the algal community among stream types was the presence of a glacier and resulting seasonal differences in flow, temperature, and turbidity. An upstream lake was a secondary determinant in buffering seasonal fluctuations in environmental conditions thus leading to greater stability. Algal communities, consequently, were more diverse and less seasonally variable at lake outlets. The diatom genera Amphora, Denticula, Fragilaria, Gomphonema, Nitzschia, and Synedra and the blue-green algae Oscillatoria and Phormidium were characteristic of lake outlets, whereas Chamaesiphon (blue-green) and Hydrurus foetidus were indicative of kryal sites.