Inferring fine-grained suspended sediment dynamics through analysis of disaggregated inorganic grain sizes (DIGS)

The goal of this thesis is to infer suspended fine sediment dynamics through analysis of disaggregated inorganic grain sizes (DIGS). Fine sediment is transported through the water column as single grains and flocs. The degree to which a suspension resides as single grains and flocs influences the flux of suspended particles, and hence, associated contaminants and nutrients to the seabed, as well as the optical and acoustical properties of the water. However, suspended fine sediment dynamics are poorly understood. To complicate the matter, flocs are fragile and difficult to sample without disruption. This thesis improves understanding of fine sediment dynamics using a non-invasive approach to infer suspended fine sediment properties. Direct observation of DIGS behaviour was compared to predictions made by a simple parametric model that infers floc properties by considering deposition of particles as single grains and flocs. Results of this thesis suggest that observed DIGS evolution offers insight into fine sediment behaviour within various simulated and in situ marine environments (e.g. settling column, laboratory flume, and the Eel River flood plume) and implicates flocculation as an important mechanism of particle deposition. Results also suggest that the parametric model estimates size-specific effective settling velocities in good agreement with observations, although the environments in which this model is applicable are limited. Findings of this thesis indicate that interpretation of DIGS behaviour within marine environments is limited without direct observations of floc size and floc fraction.