Spectral properties of dissolved organic matter and their dependence on depth in artificially and naturally separated meromictic reservoirs

The spectral properties of the dissolved organic matter of the natural water of two parts of the reservoir artificially separated from the White Sea – the Kanda Bay: the sea reach and the meromictic Fedoseevsky reach. For comparison, data were analyzed for natural meromictic reservoirs – lakes Spruce, Tricolor, Lagoon on the Green Cape. Absorption spectra, fluorescence spectra and the dependence of the fluorescence quantum yield on the excitation wavelength in the range of the excitation wavelength of 250–500 nm were obtained for water samples from different horizons. The dependences of the wavelength of the emission maximum on the excitation wavelength are constructed and the value of the “blue shift” is calculated – the displacement of the maximum of the emission band in the short-wave direction. It is shown that the fluorescence intensity of dissolved organic matter in the Fedoseevsky Ples is higher than in the marine one, while the dependence of the fluorescence quantum yield on the excitation wavelength in both parts of the Kanda Lip is qualitatively similar, but differs in absolute values. In natural meromictic reservoirs, this dependence has a similar character, also differing in the absolute value of the fluorescence quantum yield, which indicates a different ratio of aromatic and aliphatic organic compounds. Thus, differences in the spectral and optical properties of the dissolved organic matter of two parts of an artificially separated reservoir and natural reservoirs isolated from the White Sea were revealed. The spectral and optical characteristics of the water column of sea bays, naturally or artificially separated from the main marine basin, can serve as an objective indicator of the trophic (ecological) state of the reservoir.