UV damage in shallow lakes: The implications of water mixing

Abstract

The plankton of shallow lakes is expected to experience increasing exposure to ultraviolet radiation (UVR) within the next decades. In addition to stratospheric ozone depletion, decreases in dissolved organic carbon (DOC), caused by climate warming or acidification, will result in greater UVR penetration in many lakes. Circulation patterns induced by moderate winds force the plankton of shallow lakes to be cycled through the whole water column. This translates into higher doses and fluctuating dosage rates. Here, we report the results of a series of 'in situ' UV exposure experiments in which two zooplankton crustaceans (one capable of photorecovery and the other not) were incubated either at fixed depths or under simulated mixing. Our main goal was to assess the extent to which the results from static incubations could be extrapolated 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 photorecovery. The fluctuations in dosage rate for high doses tended to increase the survival of the species with photorecovery. We contend that neglecting the effects of vertical mixing may result in a biased perception of UVR effects in shallow lakes.