Excitation-Dependent Fluorescence Quantum Yield for Freshwater Chromophoric Dissolved Organic Matter from Northern Russian Lakes

Svetlana Patsaeva,Daria Khundzhua,Olga E Trubetskaya,Oleg A Trubetskoj

doi:10.1155/2018/3168320

Abstract

Advanced fluorescence analysis within the wide range of excitation wavelengths from 230 to 510 nm accompanied with chromatography was used to study natural chromophoric dissolved organic matter (CDOM) from three freshwater Karelian lakes. The influence of excitation wavelength (λex) on fluorescence quantum yield and emission maximum position was determined. The CDOM fluorescence quantum yield has reached a minimum at λex∼270–280 nm and a maximum at λex∼340–360 nm. It was monotonously decreasing after 370 nm towards longer excitation wavelengths. Analytical reversed-phase high-performance liquid chromatography with multiwavelength fluorescence detector characterized distribution of fluorophores between hydrophilic/hydrophobic CDOM parts. This technique revealed “hidden” protein-like fluorophores for some CDOM fractions, in spite of the absence of protein-like fluorescence in the initial CDOM samples. The humic-like fluorescence was documented for all hydrophilic and hydrophobic CDOM chromatographic peaks, and its intensity was decreasing along with peaks’ hydrophobicity. On contrary, the protein-like fluorescence was found only in the hydrophobic peaks, and its intensity was increasing along with peaks’ hydrophobicity. This work provides new data on the CDOM optical properties consistent with the formation of supramolecular assemblies controlled by association of low-molecular size components. In addition, these data are very useful for understanding the CDOM function in the environment.

Highlights

Chromophoric dissolved organic matter (CDOM) naturally occurring in all aquatic environments is colored and contains materials of different molecular sizes (MSs). ese chemically complex compounds of irregular structure exert physical-chemical properties of water, affect sorption capacity, and control transport of pollutants in different environments. e CDOM absorbs light in the UV and shortwave visible ranges and governs the optical properties for both freshwater and marine aquatic ecosystems directly influencing the spectral quality of the underwater light field
3.2. e Fluorescence Spectra and the Humic-Like Fluorescence Emission Maximum as a Function of the Excitation Wavelength. e emission spectra of the CDOM from three Karelian lakes excited at wavelengths from 230 to 510 nm are presented in Figure 2 after subtraction of the blank emission at each excitation wavelength
In our previous study [21], we have found that the highest content of hydrophilic fraction was in the CDOM from the Onego lake

Summary

Introduction

Chromophoric dissolved organic matter (CDOM) naturally occurring in all aquatic environments is colored and contains materials of different molecular sizes (MSs). ese chemically complex compounds of irregular structure exert physical-chemical properties of water, affect sorption capacity, and control transport of pollutants in different environments. e CDOM absorbs light in the UV and shortwave visible ranges and governs the optical properties for both freshwater and marine aquatic ecosystems directly influencing the spectral quality of the underwater light field. Chromophoric dissolved organic matter (CDOM) naturally occurring in all aquatic environments is colored and contains materials of different molecular sizes (MSs). Fluorescence measurements provide essential information about the chemical structure of aquatic CDOM and require small sample amounts. It can be applied in the remote sensing using lidar systems for CDOM fluorescence detection from aboard the ship or aircraft. As it is currently accepted, the fluorescence of aquatic CDOM consists of two main bands, the so-called protein-like and humic-like fluorescence coming from two main groups of fluorophores [2, 3].

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Conclusion