Effects of solar ultraviolet radiation on epilithic metabolism, andnutrient and community composition in a clear-water boreal lake

摘要

Stratospheric ozone depletion, climate change, and acidification will increase the exposure of aquatic eco systems to ultraviolet radiation (UVR; 280-400 nm). The objective of this study was to determine the ecological effects of ambient UVR exposure on epilithon (algal communities attached to rocky substrata) relative to an artificially reduced UVR environment. UVR exposure was altered in the littoral zone of a boreal lake by selectively filtering segments of the solar spectrum with large acrylic sheets. This 130-day study took place at the Experimental Lakes Area, northwestern Ontario, in 1998. Epilithon were monitored for changes in productivity, biomass, pigment, and nutrient and taxonomic composition. The absence of UVR increased epilithic photosynthetic rates 37-46% above epilithon exposed to ambient UVR, increased cellular carbon and nitrogen content, and consequently lowered C:P. UVR effects on algal metabolism were dependent on seasonal trends. Epilithic respiration rates and chlorophyll a concentrations were not significantly different among treatments. A reduction in UV induced taxonomic shifts in epilithon, with diatoms increasingly favoured under low UV conditions. Species richness and diversity were not affected. Overall, the results of this study, considered together with previous research, suggest that the epilithic community is sensitive to changes in the UVR environment of aquatic ecosystems.