Estimation of UVB exposure in amphibian aquatic environments.

S.A. Diamond¹, G.T. Ankley¹, and P.C. Trenham². ¹U.S. EPA, 6201 Congdon Blvd., Duluth, MN 55804, ²USGS-Biological Resources Discipline, 5745 Kearny Villa Rd., CA 92123

Estimation of ultraviolet radiation B (UV-B; 280 to 320 nm wavelengths) dose is essential for determining whether UV-B contributes to amphibian population declines and malformations. UV-B dose (the multiple of intensity and duration of exposure) in wetlands is effected by location, time of day and year, atmospheric levels of ozone, aerosol, particulates, and water vapor, elevation of the local horizon, and water-column attenuation. These components of UV-B dose were incorporated into two studies; a risk assessment for UV-B effects in midwestern amphibians, and a landscape-level comparison of amphibian distributions with estimated UV-B doses in selected U.S. National Parks. Among all wetlands (N = 850), mean UV-B dose was 19.3 Whr/m² (range: 3.4 - 32.1 Whr/m²). UV-B doses were reduced an average of 12% by landscape features (range: 0 to 77%), and 22 % by DOC (range: 1 to 87%). Cloud cover, where estimated, reduced UV-B doses by an average of 26% (range: 0 to 79%). Results indicate that UV-B levels found to effect amphibians in controlled experiments were unlikely to be reached in studied wetlands. In the landscape study, there was also little evidence that UV-B has negatively effected amphibian populations within the studied wetlands.