Abstract

Temporal trends in sediment metal concentrations near a large wastewater outfall in southern California were evaluated with respect to changes in effluent metal concentrations and mass‐emission rates (MERs). During 1985 to 1992, metal concentrations and MERs in the County Sanitation Districts of Orange County effluent decreased by approximately 30% to 90%. Relatively smaller but statistically significant changes in metal concentrations in sediments adjacent to the outfall also occurred during this period. At nearfield sites, significant decreases in sediment concentrations were apparent for a subset of the metals that were more highly enriched in the effluent relative to background sediment concentrations. Changes in effluent concentrations of Cd, Cu, Cr, Ni, and Zn explained 48% to 62% of the variance in the corresponding metal concentrations in sediments immediately adjacent to the outfall. Appreciable but relatively smaller decreases in sediment metal concentrations occurred at other shelf locations. Correlations between effluent and sediment metal concentrations generally were weaker at greater distance from the outfall.

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