On the Variability of Floc Characteristics in a Shallow Estuary

Abstract

The properties of aggregated marine sediment, or flocs, exert an influence on numerous estuarine processes (Dyer, 1989). For example, suspended sediment settling fluxes are a strong function of both particle size and composition (Manning & Bass, 2006), and predicting these fluxes is critical as sea level rise drives unprecedented morphological changes along coastlines and within estuaries worldwide (Prandle & Lane, 2015). Additionally, the transport of contaminants that readily adhere to sediment aggregates is largely determined by the transport properties of the aggregates themselves (Lick, 2008;Mehta et al., 2014), necessitating a comprehensive understanding of how flocs move and evolve in wavy, turbulent flows. Rates of photosynthesis and the potential for algal blooms, too, are controlled by the vertical distribution of particles throughout the water column (Cloern, 1996), which itself depends on the interplay between hydrodynamic forcing and particle characteristics.Numerical models often simulate the transport of flocs by separating them into discrete size classes (James et al., 2010;Soulsby et al., 2013;Verney et al., 2009). Each size class is then treated as an Eulerian concentration field with a superimposed settling velocity, 𝐴𝐴 𝐴𝐴𝑠𝑠 , assumed to follow Stokes Law (Stokes, 1851), 𝑤𝑤𝑠𝑠 =

The Flocculation State of Mud in the Lowermost Freshwater Reaches of the Mississippi River: Spatial Distribution of Sizes, Seasonal Changes, and Their Impact on Vertical Concentration Profiles

“…Similar correlations between water temperature and floc size and strength have been made by Droppo et al (1998) and Egan et al (2022), both of whom suggest that increasing temperature leads to an increase in the productivity of the particle-attached bacteria and associated enhancement of EPS. Therefore, while tightly controlled data linking floc size to increased bacterial production brought on by temperature changes is not available in our study or the studies of Droppo et al (1998) and Egan et al (2022), all three point to the utility of temperature as a proxy for EPS production and hence floc aggregation efficiency and strength. For example, calibration of the equilibrium floc size model (see Appendix A for details), which yields d fe = d fe (C, G), of Winterwerp (1998) can be made for summer and winter along the Mississippi at the different stations by increasing the ratio of the aggregation to breakup efficiency terms, 𝐴𝐴 𝐴𝐴 ′ 𝐴𝐴 ∕𝐴𝐴 ′ 𝐵𝐵 , by a factor of 5 (Figure 8).…”

“…(1998) and Egan et al. (2022), all three point to the utility of temperature as a proxy for EPS production and hence floc aggregation efficiency and strength. For example, calibration of the equilibrium floc size model (see Appendix A for details), which yields d fe = d fe ( C , G ), of Winterwerp (1998) can be made for summer and winter along the Mississippi at the different stations by increasing the ratio of the aggregation to breakup efficiency terms, $${k}_{A}^{\prime }/{k}_{B}^{\prime }$$, by a factor of 5 (Figure 8).…”

“…(1998) and Egan et al. (2022), both of whom suggest that increasing temperature leads to an increase in the productivity of the particle‐attached bacteria and associated enhancement of EPS. Therefore, while tightly controlled data linking floc size to increased bacterial production brought on by temperature changes is not available in our study or the studies of Droppo et al.…”

The flocculation state of mud in the lowermost freshwater reaches of the Mississippi River: spatial distribution of sizes, seasonal changes, and their impact on vertical concentration profiles

“…of particle-attached bacterial secreting EPS and enhancing the capture potential and strength of the mud aggregates. Similar correlations between water temperature and floc size and strength have been made byDroppo et al (1998) andEgan et al (2022), both of whom suggest that increasing temperature leads to an increase in the productivity of the particleattached bacteria and associated enhancement of EPS. Therefore, while tightly controlled data linking floc size to increased bacterial production brought on by temperature changes is not available in our study or the studies ofDroppo et al (1998) andEgan et al (2022), all three point to the utility of temperature as a proxy for EPS production and hence floc aggregation efficiency and strength.…”

“…Similar correlations between water temperature and floc size and strength have been made byDroppo et al (1998) andEgan et al (2022), both of whom suggest that increasing temperature leads to an increase in the productivity of the particleattached bacteria and associated enhancement of EPS. Therefore, while tightly controlled data linking floc size to increased bacterial production brought on by temperature changes is not available in our study or the studies ofDroppo et al (1998) andEgan et al (2022), all three point to the utility of temperature as a proxy for EPS production and hence floc aggregation efficiency and strength. For example, calibration of the equilibrium floc size model (see appendix for details), which yields d f e = d f e (C, G), ofWinterwerp (1998) can be made for summer and winter along the Mississippi at the different stations by increasing the ratio of the aggregation to breakup efficiency terms, k A /k B , by a factor of 5 (Figure7).…”