Seasonal Dynamics of Organic Matter Composition and Its Effects on Suspended Sediment Flocculation in River Water

Organic matter (OM) and suspended sediment are abundant, and interact with each other, in rivers and lakes. OM is usually adsorbed by suspended sediment and causes either particle stabilization or flocculation. In this study, the OM composition and suspended sediment flocculation potential of river water were regularly measured throughout the year 2016. The OM composition of the river water samples was measured with a liquid chromatography‐organic carbon detection system and fluorescence excitation‐emission matrix spectroscopy, and the flocculation potential was measured in a standard jar test experiment. Results from the OM analyses and flocculation potential tests, in association with a multivariate data analysis, demonstrated that the OM composition and flocculation potential of the river water were dynamic under different meteorological, hydrological, ecological, and anthropogenic conditions and closely correlated with each other. Dry seasons with low rainfall and water discharge induced a lacustrine condition and led to the OM composition being more aquagenic and flocculation‐favorable. The most favorable condition for the enhancement of flocculation was during algae bloom and associated with the production of biopolymers from algae. In contrast, rainy seasons were advantageous for stabilization of suspended sediment because of excessive transport of terrigenous humic substances from catchment areas into the river. Such terrigenous humic substances enhanced stabilization by creating enhanced electrostatic repulsion via adsorption onto the sediment surface. Findings from this research provide a better insight into the highly complex behaviors of and interactions between OM and suspended sediment in natural water environments. Key Points Weather, hydrological, biochemistry, and anthropogenic conditions control organic‐sediment interactions and dynamics in river water Dry weather condition enhances production of aquagenic organic matter and flocculation‐deposition of particulate matter in river water High rainfalls facilitate transportation of terrigenous humic substances and stabilization‐resuspension of particulate matter