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1726368 
Journal Article 
Underwater ultraviolet radiation: Development of spectral models for northern high latitude lakes 
Laurion, I; Vincent, WF; Lean, DRS 
1997 
1 
Photochemistry and Photobiology
ISSN: 0031-8655
EISSN: 1751-1097 
65 
1 
107-114 
WOS:A1997WD16800024 
The penetration of solar ultraviolet radiation (WR) and photosynthetically available radiation (PAR) was measured in a range of subarctic lakes in the forest-tundra zone of northern Quebec. The diffuse attenuation coefficients for PAR (K-dPAR) were highly correlated (r(2) = 0.78) with dissolved organic carbon (DOG) concentration and only weakly correlated with suspended particulate material as measured by chlorophyll a (r(2) = 0.48) or beam transmittance (r(2) = 0.29). Colored dissolved organic matter (CDOM) was also largely responsible for the between-lake differences in spectral attenuation of UVR. The diffuse attenuation coefficient for UVR (K-d) was a nonlinear function of wavelength (lambda) and was accurately described by the model K-d (lambda) = K-d440 exp(-S [lambda-440]). The slope coefficient S was relatively constant among lakes (mean = 0.0151 nm(-1), CV = 7%), whereas K-d440 was a linear function of several CDOM-related variables and best estimated by CDOM fluorescence (r(2) = 0.98). Numerical analysis of spectra for high (subarctic) and low (Arctic) DOC lakes showed that the evaluation of the model parameters K-d440 and S was insensitive to the bandpass characteristics (2-8 nm) of different underwater radiometers. The K-d (lambda) model was then used to develop a nondimensional index of relative spectral composition (RI) to characterize different water masses as a function of dissolved organic matter (DOC and CDOM fluorescence). Below about 4 mg DOC L(-1) there is a sharp nonlinear rise in this index with decreasing DOG. These results show that CDOM controls the spectral composition of underwater WR in northern high-latitude lakes and that the UVR/PAR balance in many of these waters is sensitive to minor changes in CDOM content.