Sedimentological advances concerning the flocculation and zooplankton pelletization of suspended sediment in Howe Sound, British Columbia : a fjord receiving glacial meltwater
Creators: name: Syvitski, James P. M.
Publisher: name: University of British Columbia
Year: 2010

description: The study of suspended sediment provides insights into the transport and accumulation of sediment in depositional basins. Past investigations have suffered, however, from a lack of methodology that can deal with the low concentrations of suspended sediment. The theory and method of three techniques to be used in the analysis of suspended sediment have been outlined. 1) VSA, provides a rapid, accurate and precise method of determining grain size distributions of low weight samples. The method is based on the solution to a set of equations that discretely define the increasing volume of a homogeneous sediment sample settling in an enclosed volume of water. The results are in terms of sedimentation diameters, a hydrodynamically sensitive property. 2) The Ag filter mount provides a fast technique for a low sample weight random oriented mount to be used in quantitative XRD analysis. The method has excellent precision and does not fractionate the mineral component due to their settling velocity. 3) Suspended sediment collectors have been used to measure the downward flux of sediment in the fjord environment. The traps have also provided a means to calculate the natural settling velocity of flocculated or otherwise enhanced particle settlement. Laboratory and field studies have dealt with the interaction of zooplankton with suspended sediment. Marine zooplankton ingest suspended sediment at a rate dependent on sediment concentration and mineralogy. Ingested mineral particles undergo chemical and mineral transformations which are functions of mineralogy, cation exchange capacity and residence time in the digestive tract. Zooplankton fecal pellets have a much larger settling velocity than their component particles. This increased settling rate allows clay to be deposited where the hydrodynamic nature of the environment would only allow coarse silt to fine sand deposition. Glacial flour (feldspar, quartz, trioctahedral mica, chlorite, amphibole, tourmaline, and vermiculite) enters the surface-layer of the Howe Sound fjord as a sediment plume which moves quickly down inlet while slowly mixing with the marine water. Although flocculation occurs in the lower brackish water of the surface-layer, mixing and diffusion are the dominant means for sediment to enter the lower-marine-water. Once in the lower-marine-water, zooplankton pelletization and biologic agglomeration of inorganic floccules takes place. These processes that enhance the individual particle settlement, generate a fast response time between the surface-layer and the lower-marine-layer in terms of sedimentation of particulate matter. Settling velocities of particles less than 1 μm have been enhanced over 1400 times. Size distributions of sediment deposited on the sea-bed are a function of variable multimodal and/or non log-normal size distributions from sub-laminae falling through the water column. The increase in deviation away from log-normality down inlet, for size distributions of both suspended and deposited sediment, is an artifact of the size analytical method.