UV DAMAGE IN SHALLOW LAKES - THE IMPLICATIONS OF WATER MIXING

The plankton of shallow lakes is expected to experience increasing exp osure to ultraviolet radiation (UVR) within the next decades. In addit ion to stratospheric ozone depletion, decreases in dissolved organic c arbon (DOC), caused by climate warming or acidification, will result i n greater UVR penetration in many lakes. Circulation patterns induced by moderate winds force the plankton of shallow lakes to be cycled thr ough the whole water column. This translates into higher doses and flu ctuating dosage rates. Here, we report the results of a series of 'in situ' UV exposure experiments in which two zooplankton crustaceans (on e capable of photorecovery and the other not) were incubated either at fixed depths or under simulated mixing. Our main goal was to assess t he extent to which the results from static incubations could be extrap olated to vertically moving zooplankton. Static incubations accurately predicted the survival of moving individuals for the species without photorecovery, but failed to do so for the species capable of photorec overy. The fluctuations in dosage rate for high doses tended to increa se the survival of the species with photorecovery. We contend that neg lecting the effects of vertical mixing may result in a biased percepti on of UVR effects in shallow lakes.