[Fluorescence Characteristics and Environmental Significance of Organic Matter in the Northern Part of Lake Taihu in Spring and Winter].

Organic matter (OM), rich in carbon, nitrogen, phosphorus and other biogenic elements, has numerous geochemical and ecological functions in all kinds of water bodies, and is highly valued in ecological studies of both marine and inland environments. The formation, transformation, and fate of OM, and its accompanying nutrient regeneration process are key links in the biogeochemical cycling of nutrients in aquatic ecosystems. Furthermore OM, as a provider of nutrients, also plays a very significant role during the outbreak of algal blooms in inland lakes. Two extensive sampling campaigns were conducted at the same site (n=17) in Lake Taihu in February and May of 2015, and 34 (17×2) samples were collected. Excitation-emission matrix (EEM) fluorescence was combined with parallel factor analysis (PARAFAC) to characterize the spatial-temporal variations in the components and sources of particulate (POM) and dissolved (DOM) organic matter. Moreover, the correlations between fluorescence intensity and Chla were studied. Significant differences between the fluorescence peaks, fluorescence positions, and fluorescence intensities of POM and DOM indicated that the components of POM were more complex than those of DOM. Fluorescence intensities and fluorescence indices indicated that POM and DOM possessed endogenous characteristics and that estuaries possessed obvious exogenous characteristics. Five types of fluorophores were present in POM (C1p-C5p) and DOM (C1d-C5d):tyrosine-like fluorophores (C1 and C2), humic-like fluorophores (C3 and C4), and tryptophan-like fluorophores (C5). The fluorescent components of POM and DOM differed significantly. C3p was the dominant fluorophore in POM during spring and winter, and fluorescence intensities of C1p-C5p were higher in the Meiliang Bay and the central part of thelake than in other areas. C2d, C1d, and C5d were the dominant fluorophores in DOM during spring and winter, and fluorescence intensities of C1d-C5d were higher in the Zhushan Bay than in other areas. In spring, positive correlations were observed between C1d and C2d (P<0.01), C3d and C4d (P<0.01), C1p and C4p (P<0.05), and C2p and C5p (P<0.01). Remarkably, C3p and C3d (P<0.01) and C3p and C4d (P<0.05) were positively correlated, suggesting that these two forms of OM were correlated. Similarly, highly significant, positive correlations were observed between C1d and C2d (P<0.01), C3d and C4d (P<0.01), C1p and C2p (P<0.01), and C1d and C2p (P<0.01) during winter. Furthermore, Chla and C5d were significantly and positively correlated (P<0.01). However, both Chla/C2d and Chla/C3p were negatively correlated in spring. Furthermore, Chla and C4d were negatively correlated in winter.