EXCHANGE DYNAMICS OF A SHALLOW CONTAMINATED WETLAND

Flux pathways are investigated for a wetland system comprised of a riv er flowing through two shallow forebays and then entering the main bas in of a lake. The hydrodynamic exchanges between these three component s influence the fate and transport of heavy metals in the system. Duri ng non-storm summer flows the river plume, comprised of river water an d entrained forebay water, was cooler than the lake surface water and so plunged as it entered the main basin and inserted near the seasonal thermocline. Because the river plume plunged, only a fraction of its metals flux was available to the epilimnion. A return now into the for ebay was always observed immediately above the river inflow, ensuring a predominantly two-layer exchange system. However during days of nega tive heat flux (surface heating), an additional exchange mechanism exi sted when the surface waters from the forebay formed a buoyant plume, flowing out into the main basin. This heated outflow produced a signif icant, but short-lived, arsenic nux from the forebay into the surface waters of the lake.