BEHAVIOR OF HEAVY METALS IN MARINE AND LACUSTRINE SEDIMENT CORES, SOUTH PUGET SOUND, WASHINGTON
Cores (62-98 cm in length) were collected with gravity or piston corers, sub-sampled at 1 cm intervals, subjected to 20% HNO3 leach, and analyzed for Pb, Cu, Mn, and Fe (by AAS) and organic content (by LOI). Cores from American Lake, located upwind from the smelter, show elevated levels of metals within the top ~45 cm. The extent of this enrichment is described with an enrichment factor (EF = [metal]max/[metal]background). For Pb at American Lake, EF = 30 with Pbmax = 810 ppm. In both lakes studied, Cu and Pb co-vary closely with each other and with Fe (and to a lesser extent, Mn) implying an important role for Fe-Mn coatings in sequestering the metals.
In contrast cores from Quartermaster Harbor, a marine site downwind from the smelter show similar up-section increases in Cu, Pb but with lower EF (14) and Pbmax (483 ppm). In addition, there is no apparent correlation between the behavior of Fe or Mn and heavy metal levels in this core. We attribute the higher near-surface metal concentrations and greater EF at the upwind site to remobilization and upward transport of metals in the lacustrine system. Factors that may facilitate remobilization in lacustrine settings compared to marine settings include more reducing conditions within the sediment column and lower pH.