Systematic Study of CDOM in the Volga River Basin Using EEM-PARAFAC
Drozdova, A. N., Molkov, A. A., Kapustin, I. A., Ermoshkin, A. V., Leshchev, G. V., Krylov, I. N., Labutin, T. A.
Continuing a series on the bio-optical characteristics of the Volga River and the development of regional bio-optical models, this study addresses dissolved organic matter (DOM), its component composition, spectral absorption, and the lack of satellite retrieval algorithms. Using excitation–emission matrix fluorescence spectroscopy, the fluorescent DOM fraction of the surface layer was examined along more than 1500 km from the Gorky Reservoir to the Volgograd Reservoir, between May and September 2022–2024. Parallel factor analysis validated four fluorescent components whose proportions were largely stable while their intensities varied widely, fluorescence in the Gorky Reservoir and the Kama River differed more than 2.5-fold, with the highest FDOM in the Gorky Reservoir, decreasing downstream after the Oka and Kama inflows. The work shows that neither conventional lidar plus in-situ DOM probing nor DOM absorption at 440 nm captures all fluorescent components, so their efficiency depends on the correlation between fluorophore groups.