The natural pre-industrial background composition of Lakes Ontario and Erie sediments is compared with the modern contaminated sediment and with the shoreline bluff materials. Quartz, carbonates, feldspars, and clay minerals are the dominant minerals in the bluff samples. The carbonate-carbon content of the bluff samples is generally high, averaging 2.4% of the sample weight. Calcite and dolomite are the predominant forms of carbonate in bluffs. However, the carbonate-carbon of the pre-industrial sediment is low, averaging around 0.6%. The depletion of carbonates in the offshore sediments is due to their solution during transport and deposition. Ca follows the same trend as carbonates in all the samples. Mg is also depleted in the lake sediments, reflecting a decrease in dolomite from the bluffs to the sediments.Feldspars, which are a dominant mineral in the bluff samples, are only present in small amounts in the offshore sediments. Na is also depleted in the sediments. It is not certain if the decrease in Na from the bluffs to the sediments is due to weathering or sorting of feldspars during transport and deposition.Organic-C, N, Mn, P, Hg, Pb, Zn, Cu, Cd, Be, and V are all highly enriched in the modern sediments relative to the bluffs and the pre-industrial sediments. With the exception of Mn, the enrichments of these elements is due to anthropogenic inputs.

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