Long-term dynamics of spectral water transparency in the surface layer of Lake Teletskoye in summer

Abstract

The article presents the long-term experimental data on spectral water transparency in the surface layer of Lake Teletskoye (21 sampling stations) obtained in summer of 2017‒2022. During the study period, values of the light attenuation index calculated at the natural logarithmic base at four wavelengths (430, 450, 550 and 670 nm) ranged within 0.2‒4.0 m^‒1. The index of light absorption by yellow substance varied from 0.1 to 3.2 m^‒1. Relative transparency measured with the use of a white Secchi disk made up 0.8‒11.7 m at its average of 6.3 m. Over a 6-year study period, the content of chlorophyll-a in the surface layer was 0.1‒4.1 mg/m³ that corresponded to the oligotrophic type of lakes. The concentration of yellow substance in the lake, optically determined through measuring light absorption by yellow substance at a wavelength of λ=450 nm, ranged from 0.9 to 15.0 g/m³. Calculations of the spectral contribution of the main optically active components of lake water to light attenuation in the surface layer of Lake Teletskoye in various sampling sites indicated that yellow substance and suspension had the greatest optical effect on the total attenuation. It is shown that the optic structure of the study reservoir (dynamics of major primary hydro-optical properties) depends on spatial-temporal variability of concentrations of different optically active components influenced by the in-water processes closely related with those occurred in the lake catchment.