Fluorescence characterization of fractionated dissolved organic matter in the five tributaries of Poyang Lake, China

Highlights: • Fluorescence properties of fractionated COM were identified by PARAFAC or/and SOM. • Three humic-like components and a protein-like component were modeled by PARAFAC. • Fluorescence components are primarily present in • PARAFAC-SOM was the best method to assess the fluorescence properties. • Fluorescence properties can be used as proxy indicators of COM size and source. Characterization of natural colloids is the key to understand pollutant fate and transport in the environment. The present study investigates the relationship between size and fluorescence properties of colloidal organic matter (COM) from five tributaries of Poyang Lake. Colloids were size-fractionated using cross-flow ultrafiltration and their fluorescence properties were measured by three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM). Parallel factor analysis (PARAFAC) and/or Self-organizing map (SOM) were applied to assess fluorescence properties as proxy indicators for the different size of colloids. PARAFAC analysis identified four fluorescence components including three humic-like components (C1-C3) and a protein-like component (C4). These four fluorescence components, and in particular the protein-like component, are primarily present in <1 kDa phase. For the colloidal fractions (1–10 kDa, 10–100 kDa, and 100 kDa–0.7 μm), the majority of fluorophores are associated with the smallest size fraction. SOM analysis demonstrated that relatively high fluorescence intensity and aromaticity occur primarily in <1 kDa phase, followed by 1–10 kDa colloids. Coupling PARAFAC and SOM facilitate the visualization and interpretation of the relationship between colloidal size and fluorescence properties with fewer input variables, shorter running time, higher reliability, and nondestructive results. Fluorescence indices analysis reveals that the smallest colloidal fraction (1–10 kDa) was dominated by higher humified and less autochthonous COM.