Thirty-two samples were collected from eight typical areas in Lake Taihu. Three-dimensional excitation-emission matrix fluorescence spectra (EEMs) and a parallel factor analysis (PARAFAC) were applied to investigate the fluorescence properties, the sources, and environmental significance of particulate organic matter (POM) from the overlying water in Lake Taihu in summer. Differences in fluorescence characteristics between POM and DOM (dissolved organic matter), and that in POM between the grass lake and the algal lake were further examined. There are five kinds of fluorophores in Lake Taihu:tyrosine-like fluorophores (C1 and C2), humic-like fluorophores (C3 and C4), and tryptophan-like fluorophores (C5), among which significant correlations were found between C1 and C2, C3 and C4, and C5 and two humic-like fluorophores (C4, C3). By comparing with the fluorescence characteristics of DOM from earlier studies, it is found that there are differences in compositions, sources, and correlations with water quality between POM and DOM in Lake Taihu in summer. In summer, the contribution of endogenous inputs to POM is greater than that of exogenous inputs in Lake Taihu because the ranges in the fluorescence indices, FI, BIX, and HIX, are 1.78-2.35, 0.3-2.7, and 0.8-1.1, respectively. Significant correlations have been found between humic-like fluorescent components and TN, TP, Chla, COD, POC, and SS, suggesting that fluorescence analysis can be used as an important method for a semi-quantitative analysis of nutrients. The protein-like components of the algal lake mainly consist of tryptophan and tyrosine, while that of the grass lake mainly contain tyrosine and a few tryptophan. It is worth noting that, the grass lake contains more tyrosine relative to the algal lake (t test, P < 0.01). Significant positive correlations between the protein-like and the humic-like fluorescence are found in the algal lake, while it is not significant in the grass lake. Significant positive correlations are found between the fluorescent components (protein-like and humic-like) and chlorophyll-a in the algal lake, while the correlation was only found between humic-like components and chlorophyll-a in the grass lake.
Keywords: eutrophication; fluorescent characteristics; parallel factor analysis (PARAFAC); particulate organic matter (POM); three-dimensional excitation-emission matrix fluorescence spectra (EEMs).