TRACERS FOR FINE SEDIMENT TRANSPORT IN HUMBER BAY, LAKE-ONTARIO

In a qualitative approach to the difficult problem of determining long-term transport behavior of fine sediments, we investigated the use of both "natural" physical and chemical attributes of bottom sediments as well as an atificial sediment as tracers of medium- and long-term transport patterns. The locality studied was Humber Bay, Lake Ontario. Among the approaches tested for cases where the source of the contaminant is not known, grain-size parameters, primarily median size and percentage coarse fraction, showed weak patterns attributable to long-term net transport. Cluster analysis of chemical data from the Ontario Ministry of the Environment sediment survey of 1979 resulted in distribution patterns which suggested transport from sources such as the sewage treatment plant (STP) outfall and Western Gap opening to Toronto Harbour. Tracer tests on two suspected contaminant point-sources: the Humber River and the Humber STP, used spatial distributions of an artificial cesium-containing tracer, anthropogenic trace metals, and the sewage-related organic compounds: coprostanol and alpha-tocopheryl acetate. Interpretable sediment transport patterns related to the Humber River were obtained for the cesium tracer, as well as for cobalt apparently originating upstream in the Humber River watershed. These indicated a transport that tended to follow the western shore of the bay. Likewise, well-defined transport patterns were identified for the discharges from the Humber STP outfall. In this case the patterns were more complex and showed significant transport northward as well as toward the south and southwest.