Characterization and stability of sedimentary colloids in different ecology regions in Taihu Lake

Colloidal particles, heterogeneous mixture with various organic components and continuous molecular weight (MW) distribution, is omnipresent in lake sediments and substantially influence the retention, transportation, and fate of contaminants in lake ecosystem. We sampled and extracted sedimentary colloids from different ecology regions in Taihu Lake, Jiangsu, East China, in June 2020, and they were further separated into four different particle size ranges by tangent ultrafiltration, and the properties of colloids were studied in various methods, including zeta potential analysis, transmission electron micrograph images (TEM), Fourier transformation infrared (FTIR), and 3D fluorescence. Results show that the surface of the colloids is covered with organic macromolecular substances, such as humus-like substances and protein-like substances. There were significant differences in molecular weight and fraction content of colloids in the sediments from macrophyte-dominant (MD) area and algae-dominant (AD) area in the lake. Colloids from MD area are mainly composed of humic acid, protein, and fulvic acid; the content of fulvic acid is lower than that of humic acid and protein. The humic acid exists mainly in small molecular weight (10–100 kDa), protein exists in mainly large molecular weight colloids (0.45–1 µm). Colloids from AD area are mainly composed of humic acid, and mainly distributed in the molecular weight (10 kDa–0.45 µm). The presence of humic acid inhibits effectively the agglomeration of the colloids. Especially, the stability of colloids is closely related to the molecular weight, with low molecular weight from MD area show higher stability. The existence of humic acid in colloids increases the electrostatic repulsion between colloidal particles, which can effectively inhibit the agglomeration of colloids, thus enhancing the stability of colloids. Furthermore, both monovalent and divalent electrolytes enhance colloidal aggregation, and the low-molecular-weight (LMW) colloid fraction exhibits higher stability efficiency than the high-molecular-weight (HMW) colloidal.