Problems in conducting in-situ experiments to evaluate the influence of UV-B radiation on amphibian eggs and larvae

Amphibian embryos and tadpoles may be sensitive to UV-B radiation in shallow pond water, and methods are needed to conduct W-B exposures in the field. We exposed embryos and tadpoles of a variety of southern Ontario species in small flow-through containers in lake and pond conditions to W-B radiation. The containers were supported on anchored racks, were submerged just below the water surface, and were exposed to solar radiation, solar radiation with W-B blocked by Mylar-D, and solar radiation augmented with artificial UV-B produced by UV-B lamps. We found that the containers could not protect the embryos and tadpoles from even minor wave action in the lake site; these containers will work only in very protected sites. Initially, containers exposed to solar radiation and to augmented UV-B radiation had lids of cellulose acetate. Pond and lab tests subsequently established that, if the cellulose acetate came in contact with the water, toxicity to tadpoles was very high even in darkness. Therefore we raised the containers on their racks so that their lids were no longer submerged. Because UV-B radiation attenuates very rapidly in water with high DOC concentrations, it is difficult to significantly increase UV-B levels in pond water below a few cm. In situ experiments such as these demonstrate that interactive and often uncontrollable environmental variables can mitigate or enhance the effects of UV-B radiation.