A modeling assessment of contaminant fate in the Bay of Quinte, Lake Ontario: Part 1. Metals

Abstract

A mass balance model of contaminant fate-transport was used to assess the fate of four metals: As, Cd, Cu and Zn, in the Bay of Quinte for hydrologic conditions and loadings in 2000. Results were compared with previous model results of 1988. The model was based on the QWASI (Quantitative Water Air Sediment Interaction) approach and the fugacity/aquivalence concept. The Bay was divided into five geographic segments based on hydrodynamics and chemical loadings. The model identified tributaries and Lake Ontario as the major sources of metal loadings to the Upper and Lower Bays, respectively. Metal concentrations in water decreased by 40–75% in the tributaries between May 1988 and 2000, which resulted in decreased metal concentrations that were, in 2000, all below the Provincial Water Quality Objectives. Measured sediment concentrations exceeded the Lowest Effect Levels (LEL) for all metals at many sites in the Upper and Lower Bays. Using 2000 metal loadings from tributaries and Lake Ontario, the model predicted that sediment concentrations will meet or come within 20% of LELs for all metals in segment 1, As in segments 2 and 3, and Zn in segment 3 within 40 years. Although the model predicted that sediment concentrations would decline to the LEL for all segments within 26 (Zn) to 54 (Cu) years, evidence suggests that benthos are now not impaired by ambient sediment concentrations (excluding “hot spots”). Reducing sediment concentrations faster is expected to be very difficult because their loadings originate from diffuse sources in the watersheds of tributaries and Lake Ontario.