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Variability in the amount and composition of DOC: Implications for UV-B attenuation and observed patterns of amphibian decline.
Brooks, Paul1,2, Tonnessen, Kathy3, Diamond, Steve 4, Czarnowski, Ken5, Ronca, Carlie5, 1 2 3 4 5
ABSTRACT- Climate induced, interannual variability in the amount of photoreactive DOC in surface water forms a significant control on potential UV exposure to amphibians. Two years of monitoring UV extinction and DOC composition in Rocky Mountain National Park demonstrates that variability in this hydrophobic fraction is much more important than the total DOC pool in controlling UV attenuation in amphibian habitats. Because the photoreactive component of DOC originates primarily in soil, biogeochemical controls (e.g. temperature, moisture, vegetation, soil type) on its production, and hydrologic controls on transport are the 2 primary factors affecting the amount of hydrophobic DOC transported to surface water and consequently UV-B extinction/ exposure. Both the amount of DOC produced in the soils surrounding these water bodies and the strength of the hydrologic connection transporting this DOC in these environments are positively related to winter and spring precipitation. Interannual variability in precipitation resulted in the amount of photoreactive DOC ranging from 0.5 to 1.4 mg/L at a site in 1999, while values at the same site ranged from 2.0 to 3.5 mg/L in 2000, even though total DOC amounts were similar during the two years. This difference in the amount of hydrophobic DOC represented a doubling of the 90% UV-B extinction depth (~15 cm in 2000, but > 30 cm in 1999). Implications of these findings for observed patterns of amphibian decline will be discussed.
KEY WORDS: dissolved organic carbon, amphibians, uv-b, climate