Protein-like and humic fluorescence of CDOM in meromictic lakes of the White sea

Abstract

Chromophoric dissolved organic matter (CDOM) is a complex mixture of humic substances, proteins, amino acids, and their degradation products, playing a key role in the global carbon cycle. Optical methods such as absorption and fluorescence spectroscopy are highly sensitive tools for monitoring CDOM composition and transformation. Meromictic lakes at different stages of separation from the sea serve as unique natural objects for such studies.
This study investigates the spectral luminescent properties of CDOM in natural water samples from two meromictic lakes of the White Sea: Lake Trekhzvetnoe, a completely isolated waterbody, and Biofilter Bay, which is in the initial stage of separation from the sea. Samples were collected at various depths, covering the aerobic and anaerobic zones as well as the chemocline. The study included sample filtration, measurement of absorption and fluorescence spectra, correction for the internal filter effect, calculation of the fluorescence quantum yield (FQY) and determination of the blue shift of the long-wavelength emission maximum.
The fluorescence spectra revealed protein-like and humic-like emission bands typical of natural waters. In Lake Trekhzvetnoe the ratio of the band intensities was the same at all depth horizons, whereas in Biofilter Bay it varied significantly with depth. The blue shift in Biofilter Bay was greater than in Lake Trekhzvetnoe, and the FQY dependence on the excitation wavelength differed between the two reservoirs, indicating difference in CDOM composition.
The results demonstrate that the fluorescence band ratios reflect CDOM composition, and this is further supported by FQY and blue shift measurements.

Speaker

Afanaseva Anna Andreevna
Department of Physics, Moscow State University, Moscow, Russia
Russia

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