Photochemical degradation characteristics of alga-sourced dissolved organic matter in Chaohu Lake, China

Abstract

Abstract Abundant algae-sourced dissolved organic matter (A-DOM) is produced during algal blooms in eutrophic lakes. Natural-light-driven photodegradation plays an important role in A-DOM function and its migration in aqueous systems. The photodegradation performance of A-DOM extracted from Chaohu Lake was tested and characterized under UV-A, UV-C irradiation, and dark condition, and the photochemical degradation characteristics and molecular weight changes of A-DOM during degradation were analyzed. A-DOM mainly includes four EEM-PARAFAC components, namely, C1 (protein-like tryptophan), C2 (protein-like tyrosine), C3 (long-wave humus), and C4 (short-wave humus). After irradiation for 168 h under UV-C, the protein-like components C1 and C2 had the highest fluorescence intensity reduction of 95.4% and 100%, respectively. The fluorescence intensities of fulvic-like components, namely C3 and C4, increased. The absorption coefficients (A355) of A-DOM were decreased by 84.46%, 70.83%, and 52.98% with UV-A, UV-C irradiation, and dark condition, respectively. The degradation reaction of C1 and C2 fitted with the first-order kinetic equation with a half-life of 21.59–83.51 h. The SUVA254 value decreased under UV irradiation and increased under dark condition, which is in accordance with the change of molecular weight results. The A-DOM photochemical reaction was driven by UV light irradiation, and the humification rate and molecular weight decreased.