Ultraviolet radiation and bio-optics in Crater Lake,Oregon |
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Authors: | B R Hargreaves S F Girdner M W Buktenica R W Collier E Urbach G L Larson |
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Institution: | (1) Department of Earth & Environmental Sciences, Lehigh University, 31 Williams Drive, Bethlehem, PA 18015, USA;(2) Crater Lake National Park, Crater Lake, OR 97604, USA;(3) COAS, Oregon State University, 104 Ocean. Admin. Bldg, Corvallis, OR 97331, USA;(4) Department of Microbiology, Oregon State University, 220 Nash Hall, Corvallis, OR 97331, USA;(5) Present address: eMetagen, L.L.C., 3591 Anderson St., Suite 207, Madison, WI 53704, USA;(6) USGS Forest and Rangeland Ecosystem Science Center, 3200 Jefferson Way, Corvallis, OR 97331, USA |
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Abstract: | Crater Lake, Oregon, is a mid-latitude caldera lake famous for its depth (594 m) and blue color. Recent underwater spectral
measurements of solar radiation (300–800 nm) support earlier observations of unusual transparency and extend these to UV-B
wavelengths. New data suggest that penetration of solar UVR into Crater Lake has a significant ecological impact. Evidence
includes a correlation between water column chlorophyll-a and stratospheric ozone since 1984, the scarcity of organisms in the upper water column, and apparent UV screening pigments
in phytoplankton that vary with depth. The lowest UV-B diffuse attenuation coefficients (K
d,320) were similar to those reported for the clearest natural waters elsewhere, and were lower than estimates for pure water published
in 1981. Optical proxies for UVR attenuation were correlated with chlorophyll-a concentration (0–30 m) during typical dry
summer months from 1984 to 2002. Using all proxies and measurements of UV transparency, decadal and longer cycles were apparent
but no long-term trend since the first optical measurement in 1896. |
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Keywords: | Ultraviolet radiation Plankton Optics UV-B Stratospheric ozone |
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