Biodegradation of Dissolved Organic Matter (DOM) Released from Phytoplankton in Lake Biwa

The biodegradation study of algal dissolved organic matter (DOM) released from Microcystis aeruginosa, Staurastrum dorsidentiferum and Cryptomonas ovata was carried out. The algal DOM released from Microcystis aeruginosa and Staurastrum dorsidentiferum is relatively stable, while a part of the algal DOM released from Cryptomonas ovata may be easily decomposed. Before biodegradation, two fulvic-like fluorescence peaks (A and B) and a protein-like fluorescence peak (C) and another peak with Ex/Em values of 320 – 330/390 nm (peak D) were observed in the algal DOM released from three kinds of phytoplankton. The fulvic-like fluorophores may be refractory regardless of the kinds of phytoplankton, while protein-like fluorophores released from Microcystis aeruginosa and Staurastrum dorsidentiferum may be relatively refractory and those from Cryptomonas ovata may be unstable. Peak D in the surface water of Lake Biwa may be attributed to low-molecular-weight substances produced during cultivation and/or biodegradation of several kinds of phytoplankton. The ratios of the fluorescence intensities (RFI/DOC) of peak A to peak B in algal DOM (< 1.0) were lower than those in soil Dando FA (1.8). On the other hand, no relationships between peak A and peak C were observed for three kinds of phytoplankton.