Dark recovery of photodegraded dissolved organic matter as a source of a protein-like fluorophore in natural waters

摘要： Excitation-emission matrix (EEM) fluorescence spectroscopy is being widely used to characterize dissolved organic matter in aquatic environments. The main types of fluorophores in natural waters, defined by this technique, are humic-like and the protein-like ones. The latter is generally thought to be of biological origin. In this study, we show that the emergence of the protein-like fluorophore may be the result of DOM phototransformation. Samples of natural waters were irradiated using ultraviolet radiation in the solar wavelength range. Their EMM spectra were recorded before and directly after irradiation, and after 72 h long dark storage. Fluorescence of the photodegraded water samples partially recovered during the storage. The highest increase in fluorescence was observed in the spectral range ascribed to the protein-like fluorophore. It suggests that microbial production is not the only source of this component of DOM.