Abstract:
Theoptical properties of chromophoric dissolved organic matter (CDOM) of the natural water of the stratified lake Kislo-Sladkoe in the late winter and summer-autumn seasons of 2024 are investigated. The absorption spectra, fluorescence emission spectra, synchronous spectra and fluorescence kinetics were measured. The fluorescence spectra show the presence of “protein-like” and humic fluorescence bands. The highest intensity of protein-like fluorescence was observed for samples with high microbial activity: subglacial and bottom water in winter and in summer-for a layer of 2.4–2.5m with massive development of cryptophytic algae. The dependence of the fluorescence quantum yield (FQY) on the excitation wavelength is calculated, and it is shown that the nature of the dependence, as well as the absolute value of the FQY, are consistent with the data obtained earlier for other White Sea meromictic reservoirs. The dependences of the FQY on the sampling horizon are constructed, and the difference between these dependences in the winter and summer seasons is shown. Synchronous fluorescence spectra are presented, and it is shown that at a wavelength difference of excitation and registration of 14 nm, a band of fluorophores with a small Stokes shift is observed (a “protein-like band” is the glow of aromatic amino acids, phenolic compounds and hydroquinones). Synchronous fluorescence spectra with a greater wavelength difference of 90 nm show the excitation of the humic fluorescence band. The lifetime and amplitude ratios of the short and long-lived components of the fluorescence of the CDOM are calculated from the kinetics of fluorescence attenuation. The fluorescence lifetime sturned out to be very similar for different sampling horizons in the summer season, despite the difference in hydrochemical characteristics, which allows us to conclude that the humic fluorescence band of the CDOM is of the same nature in different water layers of this reservoir.
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