Effects of ultraviolet radiation on periphyton in an alpine lake

Many alpine lakes have low concentrations of ultraviolet (UV) radiation-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 National 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 effect of UV radiation was species-specific, significantly suppressing (Bonferroni-adjusted t-test, P < 0.05) Achnanthes minutissima Kutzing but not other colonists. Although taxa apparently differed in their sensitivity to UV radiation, periphyton communities remained dominated by early successional taxa, especially A. minutissima (75% of total biovolume). In contrast, natural epilithic communities were dominated by cyanobacteria (Anabaena subcylindrica Borge, Calothrix sp.). These findings suggest that ambient UV radiation at alpine sites can suppress periphyton development by inhibiting littoral diatom production during the short ice-free season (July-September).