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

MORRIS, DP; ZAGARESE, HE; WILLIAMSON, C; BALSEIRO, EG; HARGREAVES, BR; MOELLER, R; QUEIMALIÑOS, CP

LIMNOLOGY AND OCEANOGRAPHY

The American Society of Limnology and OceanographyWaco (USA)

Lugar: Waco (EEUU); Año: 1995 vol. 40 p. 1381 - 1391

0024-3590

Diffuse attenuation coefficients (Kd) for solar UV radiation (UVR) (305, 320, 340, 380 nm, and PAR) were measured in the mixed layer of 65 lakes in Alaska, Colorado, Pennsylvania and the Bariloche region of Argentina. Integrated mixed layer samples of lake water were concurrently collected, and a multivariate approach was used to model Kd with a number of optical and chemical variables. Substantial variation in transparency was observed among lakes. Attenuation depths (z1%) for UV-B radiation ranged from several centimetres to > 10 m. In some shallow, low DOC (dissolved organic C) lakes typical of high elevation ecosystems, substantial fluxes of UVR were found in a significant proportion of the mixed layer. Much of the among-variation in Kd (87-96%) was explained by differences in DOC concentration, which strongly influenced dissolved absorbance. On average, dissolved absorbance accounted for between 33% (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 also presented that relate absorption coefficients to Kd. These models can be used with archival DOC or color data to provide approximate estimates of UV transparency of lakes.