ИСТИНА

The colored/chromophoric dissolved organic matter (СDOM) is present in all types of natural water. Its typical concentration in water is low, however the СDOM is a significant organic carbon reservoir on the Earth, exceeding the organic matter of living organisms. Since the СDOM of natural origin absorbs the UV and short-wave visible light and therefore emits fluorescence, its optical spectra are successfully used in the tasks of monitoring the natural aquatic ecosystems. For the aquatic CDOM in various types of natural aquatic environments (marine, riverine, stratified relic lakes) such spectral characteristics as the wavelength of the emission maximum in fluorescence spectrum, the fluorescence quantum yield, the spectral dependences of optical density and their higher derivatives are very significant. Spectroscopic measurements were performed to analyze water samples from coastal zones of the White Sea, Baltic Sea, several river and lakes, freshwater and saline, located in Karelia to characterize CDOM origin and to reveal its fluorescent components. Fluorescence quantum yield and emission maximum wavelength were described as a function of excitation wavelength within wide spectral range from 230 to 560 nm. The “blue shift” of fluorescence emission was observed for all the CDOM samples with change in excitation wavelength from 270 to 310 nm. The emission maximum suffered the ‘red shift” at excitation wavelengths above 310-340 nm. Fluorescence quantum yield reached maximum at excitation wavelengths about 370 nm and decreased monotonically thereafter. The similarity of spectral characteristics in different freshwater lakes with that observed for coastal and terrestrial CDOM samples revealed that CDOM in coastal zones is composed of a major terrestrial component. Such technique can be successfully used in aquatic ecosystems monitoring. This work was supported by the Russian Foundation for Basic Research (RFBF) under Grant Number 18-016-00078 and by a grant from the “Bazis” Foundation for Development of Theoretical Physics and Mathematics.