[Fluorescence characteristics of dissolved organic matter during algal bloom in Jiaozhou Bay]

Fluorescence excitation-emission matrix spectroscopy (EEMS) was employed to characterize the dissolved organic matter (DOM) in algal bloom seawater of Jiaozhou Bay in February, 2004. The relationships of DOM fluorescence characteristics with phytoplankton multiplication, dissolved organic carbon (DOC), salinity, dissolved oxygen and pH were discussed. In addition, the protein-like and humic-like fluorescence changes fore and aft cross-flow ultrafiltration (CFF) were primarily evaluated. The results show that the intensities of high and low-excitation protein-like fluorescence, which have the same sources, are stronger than that of humic-like during algal bloom. Both correlations between protein-like fluorescence intensities and chlorophyll-a and between humic-like fluorescence intensities and chlorophyll-a are relevant to the phytoplankton multiplication. As a whole, the fluorescence intensities of protein-like and humic-like increases with chlorophyll-a increasing. Furthermore the ratios of new to old DOM increase with phytoplankton biomass increasing. Good positive correlations between protein-like fluorescence intensities and DOC and between the ratios of protein-like to humic-like fluorescence intensities and DOC suggest that the DOC is mainly composed of newly produced matter during algal bloom. Some inorganic factors, such as salinity, dissolved oxygen and pH, have little effects on protein-like and humic-like fluorescence. Fore and aft the CFF experiments, the positions of protein-like and humic-like fluorescence peaks have little alteration, the balance of fluorescence intensity is not so good as organic carbon mass balance as a whole. Fluorescence balance should be used only as a supplementary technique for evaluating contaminations or loss by organic carbon mass balance.