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Physical controls on the distribution of contaminants on Sturgeon Bank, Fraser River Delta, British Columbia

University of British Columbia

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.

Thesis/Dissertation

application/pdf

2009-02-03

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http://hdl.handle.net/2429/4144

Oceanography

University of British Columbia

UBCV

DSpace