EFFECTS OF ULTRAVIOLET-RADIATION ON PERIPHYTON IN AN ALPINE LAKE

Many alpine lakes have low concentrations of ultraviolet (UV) radiatio n-absorbing dissolved organic matter, yet receive higher UV radiation flux than low-elevation lakes. We tested whether ambient UV radiation affected periphyton development in a small alpine lake in Banff Nation al Park, Canada. After 30 d, total periphytic biomass and chlorophyll accrual on artificial substrates were enhanced similar to 100% (t-test , P < 0.05) by removal of UV radiation (<400 nm). The inhibitory effec t of UV radiation was species-specific, significantly suppressing (Bon ferroni-adjusted t-test, P < 0.05) Achnanthes minutissima Kutzing but not other colonists. Although taxa apparently differed in their sensit ivity to UV radiation, periphyton communities remained dominated by ea rly successional taxa, especially A. minutissima (75% of total biovolu me). In contrast, natural epilithic communities were dominated by cyan obacteria (Anabaena subcylindrica Borge, Calothrix sp.). These finding s suggest that ambient UV radiation at alpine sites can suppress perip hyton development by inhibiting littoral diatom production during the short ice-free season (July-September).