Erosional Sorting of Fine Marine Sediments

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The transport of fine sediment in intertidal waters affects the health and sustainable uses of the coastal zone in Canada. The response of the shoreline to sea level rise, navigability of coastal waters and exposure of humans and other organisms to sediment-bound contaminants all depend on fine sediment transport. To complicate matters, all of these effects are tied to the sortability of fine marine sediment, which is not well understood. The goal of this research is to improve understanding of the factors that affect the erosional sortability of fine marine sediment and ultimately to incorporate this understanding into models of fine sediment transport. Conceptually, erosional sortability simply describes how easy or difficult it is to separate particles of different sizes from one another during erosion of sediment from the seabed. "Fine sediment" is the term applied to sediments with mean particle diameters less than 63 micrometres. For decades, sedimentologists treated fine sediment particles as non-sortable, a hypothesis that led to poor predictions of fine sediment size distributions and concentrations in the seabed and in suspension. It also led to crude models for the mobility of particle-attached substances. Recent studies have shown, however, that fine sediments are sortable, but that the sortability depends on the interaction of biotic and abiotic factors. This research will focus on five factors that are likely to dominate the sortability of fine marine sediments: sediment texture, sediment water content, abundance of sediment-attached (epipelic) diatoms, abundance of bacteria, and concentration and properties of sediment exopolymeric substances (EPS). These factors will be examined with a combination of field studies, laboratory experiments, and modeling.