UV-climate interactions in alpine lakes from the molecular to the ecosystem level.
Williamson, Craig*,1, Saros, Jasmine2, Lockwood, Ryan1, Dee, Gaby1, 1 Lehigh University, Bethlehem, PA, USA2 University of Wisconsin, LaCrosse, LaCrosse, WI, USA
ABSTRACT- Ice-out dates in many alpine lakes occur close to summer solstice when daily incident UV radiation peaks. Low temperatures during these periods of high UV exposure are likely to reduce the effectiveness of enzyme-driven molecular repair processes such as photoenzymatic repair (PER). Photoprotective compounds such as melanin or carotenoids are thus likely to be a more effective UV defense than PER during these periods. We tested this hypothesis in two dominant crustacean zooplankton from shallow rock pools in the Beartooth Mountains of Montana. Zooplankton were exposed to UV radiation in the presence and absence of photorepair radiation that stimulated PER. The copepod Hesperodiaptomus shoshone depended heavily on photoprotection but had little PER as predicted by the enzyme kinetics hypothesis. In contrast, the cladoceran Daphnia middendorffiana did not survive at even the lowest levels of UV in the absence of PER. UV and temperature profiles in the deeper alpine lakes studied indicate that the 1% attenuation depths (of surface 320 nm UV) extend down to or below the mixed layer depth in the low DOC systems. Cladocerans and nauplii but not more mature calanoids were generally distributed deeper in these lower DOC, higher UV lakes. In addition to UV, greater food availability in the deep chlorophyll maximum may contribute to these deeper distribution patterns in high UV alpine lakes. Anthropogenic impacts including climate induced changes in DOC inputs and surface deposition of fixed nitrogen are likely to alter UV-temperature-nutrient relationships of plankton in these already UV sensitive alpine lakes.
Key words: climate change, alpine lakes, ultraviolet radiation, zooplankton
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