Seasonal changes in the spectral composition of downwelling irradiance in lake kinneret israel
Dubinsky, Z.; Berman, T.
Limnology and Oceanography 24(4): 652-663
A submersible scanning radiometer was used to measure seasonal variations in the intensity and spectral characteristics of downwelling irradiance in Lake Kinneret, Israel. Extinction coefficients for photosynthetically active radiation (350-750 nm) varied from 0.2-3.3 ln units .cntdot. m-1, the euphotic zone (1% of light energy at surface) ranged from 1.7-11 m. Specific extinction coefficients of chlorophyll, kc (ln units .cntdot. mg-1 .cntdot. m-2), and water kw (ln units .cntdot. m-1) were dependent on the wavelength at which they were measured (at 650 nm, kc = 0.011, kw = 0.693; for 350-750 nm, kc = 0.007, kw = 0.489). High concentrations of chlorophyll and other cell pigments during the annual Peridinium bloom strongly attenuated light penetrance and caused a spectral shift toward the red to give elevated quantum to joule (Q:W) ratios (2.96 .times. 1018).