A RATE-CONSTANT MODEL OF CHEMICAL-DYNAMICS IN A LAKE ECOSYSTEM - PCBS IN LAKE-ONTARIO

A comprehensive mass balance model of the fate of a contaminant in a lake is described which may be used to gain an appreciation of the relative importance of various fate processes and for estimating the lake's time response to loading reductions. Three compartments are treated; the atmosphere, a single well-mired water column, and a well-mixed surficial sediment layer. Sources of contaminant include land-based discharges and atmospheric deposition. Processes of chemical degradation in the water column and sediment, outflow, sediment-water exchange, and sediment burial are quantified. A simple aquatic food chain model is also included. To facilitate interpretation the process rates are expressed as rate constants. The model can be applied in steady-state or unsteady-state forms, the latter solution being obtained from either numerical or analytical solutions to the differential equations. The effects of various remedial measures on short- and long-term concentrations throughout the lake ecosystem can be assessed. Emphasis is placed on developing a complete and uniform quantification of all processes, thus providing a decision support tool to improve management and remediation of aquatic systems by linking loadings to concentration. The approach is applied in a purely illustrative manner to PCBs in Lake Ontario.