Sediment lipid biomarkers as recorders of the contamination and cultural eutrophication of Lake Erie, 1909-2003

Lake Erie is a large lake that has a well documented history of changes in organic matter (OM) production. We have evaluated the hydrocarbon (HC), fatty acid (FA) and fatty alcohol (OL) contents of a century-long sediment core from the lake as recorders of the changes in biogeochemical processes that accompanied its eutrophication. Although variations in the concentrations of the three groups of biomarkers are closely linked to changes in primary productivity within the lake, their molecular distributions reflect different aspects of the biogeochemical processes affecting OM preservation and accumulation. Even numbered n-alkenes from C16-C22 constitute an important fraction of the HC composition. Even numbered dominance is observed in the n-alkanes < C22, and an odd dominance occurs in higher homologs. The source of this unusual HC distribution is uncertain, but may be microorganism populations sustained by anthropogenic oil contaminants. Changes in the relative inputs from terrigenous and aquatic sources are reflected in variations in the distributions of the OLs, whereas the FAs only reflect aquatic input and a dominance of aquatic organisms. Post-burial diagenetic alteration of OM is especially evident from decreases in the unsaturated and branched FAs with depth.