Spectral composition of light in the chemocline of stratified water bodies at different stages of isolation from the White Sea
E.D. Krasnova1, V.I. Lobyshev1, E.A. Labunskaya1, D.A. Voronov2, Yu.G. Sokolovskaya1, A.A. Zhiltsova1, S.V. Patsaeva1
1Lomonosov Moscow State University, Moscow, Russia
2Institute for Information Transmission Problems of the Russian Academy of Sciences, Moscow, Russia
Keywords: humic substance, chromophoric dissolved organic matter, meromictic water body, light transmittance spectra, phototrophic microorganism, photosynthetic pigment, spectral ecological niche, colored water layer
Abstract
In coastal water bodies formed by separation from the White Sea during the post-glacial uplift of the coast, in the chemocline (the gradient zone between the aerobic and hydrogen sulfide zones), a colored layer of water with a development of phototrophic microorganisms is often observed. The solar light transmission spectra measured at different horizons under water in three stratified water bodies in the coastal marine area using a submersible fiber optic probe are compared with the absorption spectra of light by water from the same horizons. In the layers with massive development of anoxygenic phototrophs, the concentrations of bacteriochlorophylls were determined from the absorption spectra. According to the data obtained, the ranges of the transmitted solar spectrum in the water column (“color ecological niches”) are largely determined by humic substances dissolved in water. Their concentration increases as the water body is isolated from the sea, due to which the photic zone narrows with depth, the chemocline becomes closer to the surface, and a shift towards longer wavelengths appears in the spectrum of light entering the chemocline. In the marine bay, the 520- 600 nm part of the spectrum reaches the chemocline, in the marine stratified lagoon, wavelengths of 510-6700 nm predominate, in reservoirs with a fresh surface layer of water, the solar spectrum is shifted to the red region (520-7200 nm). It is shown that "color ecological niches" in various water bodies are occupied by organisms whose light-collecting antennas are adapted to absorb light quanta of the corresponding spectral range.
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