ИСТИНА

Спектральные характеристики РОВ природной воды: особенности измерения и интерпретация спектров по итогам многолетних исследований The color of natural water and its optical properties are determined by the colored part of dissolved organic matter, CDOM (Chromophoric Dissolved Organic Matter): humic substances, represented by high-molecular aromatic oxycarboxylic acids. Most often, in laboratory studies, CDOM is defined as the сhromophoric fraction of organic matter in natural water passing through filters with a pore size of 0.22 or 0.45 micrometers. However, in remote sensing CDOM is distinguished from other marine components by its optical properties. Due to the presence of humic substances, CDOM of natural origin absorbs well the UV light and emit fluorescence, therefore, optical methods, primarily fluorescence and absorption spectroscopy, are widely used to study the origin and dynamics of CDOM. The absorption spectrum of CDOM usually represents a monotonically decreasing dependence of optical density on wavelength without clearly defined peaks. At 260-270 nm a "shoulder" may appear caused by the absorption of phenolic compounds or protein molecules. A typical fluorescence spectrum of CDOM upon excitation at a wavelength of 270 nm or shorter consists of two broad overlapping bands: a "protein-like" band with an emission maximum in the range of 300-350 nm, caused by the fluorescence of proteins, aromatic amino acids and phenolic compounds, and a much more intense humic-type fluorescence in the blue region. In unfiltered samples, an intense UV emission band arises due to the fluorescence of microorganism cell proteins, but its intensity is significantly reduced upon water filtration. In filtered water "protein-like" fluorescence is usually negligible. However, “protein-like” fluorescence in filtered samples becomes noticeable in layers of water with massive development of microorganisms, such as in the chemocline zone of meromictic reservoirs. Important spectral characteristics of CDOM are the wavelength of the emission maximum and the quantum yield of CDOM fluorescence. The composition and ratio of CDOM components are individual for each water area and for different water layers, therefore "optical markers" are successfully used to identify natural waters, study water mixing processes, and investigate the transformation and degradation of organic matter. The report provides an overview of the spectral and optical characteristics of CDOM, including the dependence of the fluorescence quantum yield and the position of the emission maximum on the excitation wavelength in a wide range of its alteration, from 240 to 500 nm. The know-how of measurement the spectral characteristics and features of their interpretation are described, based on the results of long-term studies from 1995 to 2025. The study of CDOM is of great importance for understanding environmental processes in aquatic systems and developing environmental protection techniques.