The role of solar UV radiation in the ecology of alpine lakes

Solar ultraviolet radiation (UVR, 290-400 nm) is a crucial environmental fa ctor in alpine lakes because of the natural increase of the UVR flux with e levation and the high water transparency of these ecosystems. The ecologica l importance of UVR, however, has only recently been recognized. This revie w, examines the general features of alpine lakes regarding UVR, summarizes what is known about the role of solar UVR in the ecology of alpine lakes, a nd identifies future research directions. Unlike the pattern observed in mo st lowland lakes, variability of UV attenuation in alpine lakes is poorly e xplained by differences in dissolved organic carbon (DOC) concentrations, a nd depends mainly on optical characteristics (absorption) of the chromophor ic dissolved organic matter (CDOM). Within the water column of lakes with l ow DOC concentrations (0.2-0.4 mg l(-1)), UV attenuation is influenced by p hytoplankton whose development at depth (i.e. the deep chlorophyll maximum) causes important changes in UV attenuation. Alpine aquatic organisms have developed a number of strategies to minimize UV damage. The widespread synt hesis or bioaccumulation of different compounds that directly or indirectly absorb UV energy is one such strategy. Although most benthic and planktoni c primary producers and crustacean zooplankton. are well adapted to high in tensities of solar radiation, heterotrophic protists, bacteria, and viruses seem to be particularly sensitive to UVR. Understanding the overall impact of UVR on alpine lakes would need to consider synergistic and antagonistic processes resulting from the pronounced climatic warming, which have the p otential to modify the UV underwater climate and consequently the stress on aquatic organisms. (C) 2001 Elsevier Science B.V. All rights reserved.