| Summary: | The physical controls on the distribution of contaminants on the environmentally
sensitive Sturgeon Bank tidal flat of the Fraser River delta is being studied to define the locations
of erosion and deposition, and migration pathways of sediment and associated contaminants.
Sediment erodibility was measured at 10 sites using an insitu benthic annular flume called the
Sea Carousel. At each site, InterOcean S4 current meters were also deployed for one month to
determine current speed and direction, and suspended sediment concentrations were measured
twice weekly for 2 months. Grain size analysis was performed on sediments collected from
these 10 sites and an additional 56 sites. The 56 sites were also analyzed for major and minor
element composition. Sea Carousel data reveal that sediments on the inner bank are not
suspended by the current velocities measured at these stations due to surface cohesion in finegrained
material. Unlike the inner bank, sediments on the outer bank are suspended by waveinduced
currents and in some cases tidal currents, especially in the fine sand-dominated
sediments on the outer southern area of the bank. Eroded sediments from this area appear to be
transported shoreward. Current meter data reveal that currents are variable both spatially and
temporally on the bank. In general, flow is bidirectional with flooding currents on the outer bank
(seaward) having higher average velocities. Currents on the inner bank (shoreward) show no
consistent orientation of peak velocities. Suspended sediment data show an increase in
concentration shoreward and a marked increase as wave height increases. Geochemical results
reveal that surface sediments on Sturgeon Bank show very little contamination in Pb, Cu, Zn,
Ni, Cr and V. The distribution of these elements on Sturgeon Bank is controlled primarily by
sediment texture and physical controls on sediment transport. The coarse-grained nature relatively low clay content of sediments on the bank result in a decreased accumulation of minor
elements. Cobalt concentrations are unusually high in some surface sediments, a result not
explainable in the scope of this study. Results indicate that contaminated sediments known to
have been deposited in the past on Sturgeon Bank due to sewage discharge are not present at the
surface. This probably reflects more recent deposition of less contaminated sediments
transported from the Fraser River distributaries and/or deposition of sediments resuspended from
the outer bank which have been transported shoreward. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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