MEPS 173:197-213 (1998)  -  doi:10.3354/meps173197

ABSTRACT: Surficial sediment and biota samples were collected from 26 locations in the intertidal region of the Fraser River estuary (British Columbia, Canada). Sediment samples were collected in May and July of 1995. Benthic samples of Macoma balthica, a deposit feeding bivalve, were collected from each site in July. Sediments were characterized by a simultaneous extraction procedure that characterized the sediment matrix into oxides of manganese and iron (easily reducible Mn, ER Mn, and reducible Fe, RED Fe) and organic matter and separated the trace metals, cadmium, copper, lead, nickel and zinc among these 3 'biologically relevant' sediment components, i.e. metals associated with ER Mn, RED Fe and organic matter. Total mercury was also determined in each sediment sample. Bivalve samples were separated into shell and tissue and analysed for the same metals. An R² MAX procedure was applied to determine if the concentration of trace metals in the shell and tissue of M. balthica was related to sediment geochemistry using sediment geochemistry and bivalve metal concentrations as the independent variable and dependent variable respectively. The partitioning of trace metals was dependent on the location-specific geochemistry (i.e. amounts of ER Mn, RED Fe and organic matter recovered at each location). This in turn led to differences in metal uptake by M. balthica that were related to sediment geochemistry. The relationships with tissues were highly significant (p <= 0.001), except for mercury (p <= 0.05). Sediment geochemistry accounted for 31% of the variability for cadmium, 39% for zinc, 51% for copper and 54% for lead. Relationships were not as strong for shells; sediment geochemistry explained 12% of the variation for mercury, 15% for zinc, 21% for nickel and 43% for copper. Overall, metal levels in the tissue and shell of M. balthica were best related to the concentration of metal associated with the ER Mn component of sediment. The sediment geochemical matrix as defined by ER Mn, RED Fe and organic matter and the partitioning of trace metals among the 3 fractions was highly site-specific. This in turn led to site-specific patterns in metal bioavailability to M. balthica. The spatial heterogeneity that occurs within an estuary, on the scale of metres, must be considered when assessing the impact of metals on such regions.

KEY WORDS: Sediment geochemistry · Metal bioavailability · Macoma balthica