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

Abstract

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.

Freshwater Suspended Particulate Matter – Key Components and Processes in Floc Formation and Dynamics.

“…Simultaneously, the potential of filtered (1.2 µm) river water to flocculate kaolinite suspensions increased (Lee et al, 2017(Lee et al, , 2019. The fine SPM fraction is coined by aluminosilicate and FeOx primary particles with a high specific surface area (Markussen et al, 2016;Poulton and Raiswell, 2005).…”

“…Refractory substances are mostly pedogenic humic substances (HS), predominantly fulvic acids, retrieved from catchment soils by leaching or erosion (Buffle et al, 1998), while labile carbohydrates and proteins, referred to as extracellular polymeric substances (EPS), mainly originate from aquatic microbial production (Droppo et al, 2004;Flemming and Wingender, 2010;Lee et al, 2019;Zimmermann-Timm, 2002) (Figure 1). Consequently, POM content and composition are linked to seasonal variations in primary production and discharge (Figure 2).…”

“…Although certain EPS (e.g. highly charged alginate) could stabilize particles, microbial EPS overall enhance flocculation (Lee et al, 2019;Srivastava et al, 2018;Stone and Droppo, 1994;Wotton, 2011). EPS comprise a diverse mix of substances (mainly polysaccharides, proteins, lipids, DNA), with highly heterogeneous physicochemical properties that allows for various interactions with mineral surfaces and with each other.…”

“…Preferential adsorption of dissolved EPS also yields enrichment within SPM (Aufdenkampe et al, 2001;Cao et al, 2011;Lin et al, 2016;Xinran Liu et al, 2013). With increasing microbial activity in spring or during algal blooms, EPS release induces a shift in DOC composition, with an increase of larger biopolymers (> 20 kDa) (Lee et al, 2019); increased MW of proteinaceous substances, and lower MW of aromatic compounds (Lee et al, 2015) (Lee et al, 2019).…”

Uncertainties associated with in situ high-frequency long-term observations of suspended particulate matter concentration using optical and acoustic sensors

“…JOURNAL PRE-PROOF and sample time. Further differences may also be caused by the presence of coloured dissolved organic matter (CDOM) that affects the optical measurements (Bright et al, 2018) and that may change the size and density of the flocs and thus the inherent properties of the particles (Lee et al, 2019). In order to improve the correlation, the inherent acoustic and optical properties of the particles, and the presence of dissolved OM should be incorporated into the model calibrations.…”