[Biodegradation of Algae-derived Organic Matter (I-DOM) from Lake Taihu]

A large amount of intracellular dissolved organic matter (I-DOM) is released during the senescent phase of phytoplankton cultures. This research investigated the bio-incubation of I-DOM of cyanobacteria in Lake Taihu under various temperatures (20, 25, and 30℃) and I-DOM initial concentrations (5, 10, and 20 mg·L^-1) with the aid of ultraviolet-visible spectroscopy (UV-Vis) and three-dimensional fluorescence matrix-parallel factor (EEM-PARAFAC). I-DOM was effectively degraded during the incubation. After 14 days, the DOC removal ratio was 50% ~74%. A tryptophan-like component (C1), a ubiquitous humic-like component (C2), and two microbially-derived humic-like components (C3 and C4) contributed 80.0%, 16.0%, 3.7%, and 0.3% to the initial I-DOM, respectively. During the bio-degradation, these components are not only consumed but also produced. C1 decreased during the incubation, while C3 and C4 increased at the beginning of biodegradation and then decreased. The change trend of C2 was complicated, i.e., it decreased firstly and then increased, but decreased again after 7 days. The changes in the optical indices of S_r, E₂:E₃ and HIX revealed that the molecular weight of DOM increased, and the aromaticity was enhanced during degradation. The reaction temperature and the initial concentration of I-DOM did not change the trend of the PARAFAC components. The temperature of 25℃ was the most suitable for I-DOM bio-degradation. Additionally, the degradation of I-DOM was enhanced with the increase in the initial concentration of I-DOM. Combined with our study on the photodegradation of I-DOM, the possible fate of I-DOM in Lake Taihu was proposed. The tryptophan-like compound could be effectively degraded, while the humic-like components could not be degraded completely. These humic-like components would potentially settle through adsorption or coprecipitation with metal substances. These results are helpful to understand the fate of I-DOM released by a cyanobacteria bloom in Lake Taihu.