Figure 31.  Profiles of zinc and copper concentrations near the Bonnet Carré Spillway

a.  Plot of Cu and Zn concentrations for the southwest sector of Lake Pontchartrain, adjacent to the Bonnet Carré Spillway. Data of Flowers  (1987) as discussed in Flowers and Isphording (1990), Demcheck and others (1996), and other sources.

b.  Location of station data for above samples.

c.  Depths for samples along transect A-A’.

see appendix B for more source information

The profiles demonstrate:

• a strong linkage between Zn and Cu concentrations
• lower metal concentrations closer to shore
• reasonable agreement in the concentrations among samples analyzed by different laboratories

The lower concentrations near shore and the strong correlation between Cu and Zn concentrations can be interpreted in large part as a result of the variable dilution of a fine (clayey) sediment fraction with metal-poor sand. In the absence of local contributions of contaminants, this fraction appears to have relatively consistent metal levels over large areas.

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