The attenuation of UV radiation in lakes and the role of dissolved organic carbon.

MORRIS, D; MORRIS, D.P.; H.E. ZAGARESE; C.E. WILLIAMSON; E.G HEARDGRAVES.; B. MODENUTTI,; E. BALSEIRO,

LIMNOLOGY AND OCEANOGRAPHY

AMER SOC LIMNOLOGY OCEANOGRAPHY

Año: 1995 vol. 40 p. 1381 - 1391

0024-3590

Diffuse attenuation coefficients (&) for solar UV radiation (UVR) (305, 320, 340, 380 nm, and PAR) weremeasured in the mixed layer of 65 lake sites in Alaska, Colorado, and Pennsylvania and the Bariloche regionof Argentina. Integrated mixed layer samples of lake water were concurrently collected, and a multivariateapproach was used to model Kd with a number of optical and chemical variables.Substantial variation in transparency was observed among lakes. Attenuation depths (zlYO) for UV-Bradiation ranged from several centimeters to > 10 m. In some shallow, low DOC (dissolved organic C) lakestypical of high elevation ecosystems, substantial fluxes of UVR penetrated the entire water column. In deeperlakes with low DOC concentrations, high fluxes of UVR were found in a significant proportion of the mixedlayer. Much of the among-lake variation in & (87-96%) was explained by differences in DOC concentration,which strongly influenced dissolved absorbance. On average, dissolved absorbance accounted for between33% (for PAR) and 68% (for 305 nm) of Kd measured in situ. Throughout the solar UV-A and UV-B range,Kd was best estimated with a univariate power model based solely on DOC concentration. Models are alsopresented that relate absorption coefficients to Kd. These models can be used with archival DOC or colordata to provide approximate estimates of UV transparency of lakes.