PARENT SESSION
Oral Session #36: Conservation of aquatic systems: Ecology and ecotoxicology. Presiding: R. Lathrop.
Tuesday, August 7, 2001. 1:00 PM to 5:15 PM. Hall of Ideas H.
Seasonal changes in exposure of pool-breeding amphibians to UVR in sub-alpine ponds.
PALEN*, WENDY1, SCHINDLER, DANIEL1, ADAMS, MICHAEL2, 1 2
ABSTRACT- Amphibians exhibit species specific physiological susceptibility to ultraviolet radiation. UVR affects multiple life history stages and can cause direct mortality, increased pathogenic infection, and changes in behavior. Populations in sub-alpine areas with low vegetative cover and increased surface irradiance may be at especially high risk. However, exposure of amphibians to UVR is a function of ambient flux of UVR, optical properties of the environment, and behavioral adaptations of individuals. In aquatic systems, dissolved organic matter (DOM) directly reduces the intensity of UVR in the water column by absorbing high-energy wavelengths of radiation. In sub-alpine ponds of Olympic National Park (WA), we find that 98% of observed variation in UVR exposure at 10cm water depth is explained by water color, or DOM concentration, emphasizing the ecological importance of DOM in determining UVR exposure for aquatic organisms. Additionally, we demonstrate that DOM concentrations are dynamic through the ice-free season, a result driven by the relative hydrologic inputs of snow-melt and rainfall. We found that the highest seasonal UVR exposure (lowest concentrations of DOM) occurs just after ice-out, a period which coincides with amphibian egg deposition and incubation. Here we present field results of amphibian egg deposition and survivorship rates in ponds across a gradient of DOM concentrations. We suggest that examining biological sensitivity to UVR without consideration for the optical properties of the water itself produces results with limited relevance for natural ecosystems.
KEY WORDS: ultraviolet radiation, amphibian, dissolved organic matter, Olympic National Park