Spectral characteristics of organic matter from algae and its complexation with copper: a case study of Ulva prolifera.

The changes in dissolved organic matter (DOM) during algal decay play a crucial role in the biochemical processes in nearshore ecosystems. The decay processes of Ulva prolifera under dark and light conditions were simulated in laboratory to investigate the characteristics of the DOM released during its settlement. The spectral characteristics of Ulva prolifera-DOM were analyzed using ultraviolet-visible spectra (UV-Vis) and fluorescence excitation-emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC), and the copper complexation characteristics were evaluated by anodic stripping voltammetry (ASV). It was found that the DOM derived from Ulva prolifera decay contained labile substances and was sensitive to light, which had significant metal complexation abilities. In dark, relatively high molecular weight DOM was released and then transformed into humic-like substances with a high degree of humification and aromaticity. DOM with stronger copper complexation ability and more copper complexing sites gradually became the dominant. EEMs-PARAFAC showed the DOM was composed of humic-like components C1, C3, tryptophan-like component C2, fulvic acid-like component C4, and tyrosine-like component C6 in the dark degradation, while under light, the DOM was composed of C1, C2, C3, C6 and fulvic acid-like component C5. Lower levels of DOM were released under light. Fulvic acid was the main component with a relatively low degree of humification. The copper complexation capacity (CuCC) and conditional stability constants (log K) increased first and then declined rapidly, with the data significantly lower than those of the degradation in dark at the end of the experiment.