Proceedings - Teaching and Learning Centre - Simon Fraser ...

Fraser River Action Plan 3rd Research Workshop
1. To contrast the geochemistry of trace metals Cd, Pb, Hg and Zn at three sites along the mudflats of the
Fraser River estuary; and,
2. Relate these differences in trace metal geochemistry to metal availability in Macoma balthica.
1. Sediment Geochemistry
• sediment matrix plays an important role in the bioavailability of metals;
• the key geochemical components in terms of metal binding are organic matter and oxides of Fe and Mn;
and,
• it is the sediment matrix, as well as the partitioning of a metal among these geochemical components,
that will influence metal availability.
2. Porewater
• used to obtain profiles of total dissolved Fe and Mn in the interstitial water at different depths; and,
• profiles reveal contribution of diagenesis to concentrations of particulate Mn and Fe at the sediment
water interface (i.e., whether the sediments are a sink or source of these elements).
3. Tissue Chemistry
Why use Macoma balthica?
• it lives and feeds in the upper portion of the deposit sediments;
• tissue levels tend to reflect levels of metals in the sediment; and,
• it forms an important link in the estuarine food web and ingestion by higher trophic levels could lead to
transfer of metals to higher trophic levels.
Methods
• levels of metals in Macoma balthica were measured in the tissue and shell; and,
• by correlating tissue levels with sediment levels, it will give us indication of the source of the
bioavailable fraction of metals, as well as which sites pose a greater risk of metal bioaccumulation.
Objective One
To contrast the geochemistry of trace metals Cd, Pb, Hg and Zn at three sites along the mudflats of the Fraser
River estuary. Will be addressed by:
Sediment geochemistry
• grain size, % LOI, concentrations of Fe and Mn oxides and concentrations of the above mentioned
metals in the different sediment fraction.
Porewater
• will reveal profiles of dissolved Fe and Mn at depth in the sediment; and,
• help determine whether the sediments are a source or a sink of Mn and Fe oxides.
Objective Two
Relate these differences in trace metal geochemistry to metal availability in Macoma balthica and, potentially,
other benthic dwelling organisms. Will be addressed by:
Field Component
• benthic samples have been collected from each site;
• Macoma balthica only found at Sturgeon Bank and part of Roberts Bank;
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