Sediment geochemistry reveals the Anthropocene history of metals in the Great Lakes

• Published in: Earth and Space Science Open Archive ESSOAr
• Main Authors: Aliff, Meagan, Reavie, Euan, Post, Sara, Zanko, Lawrence
• Format: Paper
• Language: English
• Published: Washington American Geophysical Union 04.12.2019
• Subjects: Agricultural pollution; Agriculture; Air pollution; Algae; Analytical chemistry; Anthropocene; Anthropogenic factors; Antimony; Cadmium; Calcium carbonate; Carbonates; Cluster analysis; Contaminants; Contamination; Copper; Cores; Correlation analysis; Environmental changes; Fossil fuels; Fuel combustion; Functional groups; Gasoline; Geochemistry; Lake sediments; Lakes; Lead; Manganese; Metals; Nuclear electric power generation; Nuclear energy; Nuclear fuels; Pollutants; Pollution; Pollution effects; Rare earth elements; Road salt; Subgroups; Tin; Trends; Zinc
• DOI: 10.1002/essoar.10501243.1

Geochemical analyses applied to lake sedimentary records can reveal the history of pollution by metals and the effects of remedial efforts. Lakes provide ideal environments for geochemical studies because they have steady deposition of fine grained material suitable for fixation of pollutants. The Laurentian Great Lakes are the most studied system in this field and they have well-preserved chronological profiles. To date this important system has been considered in parts, hampering basin-wide conclusions regarding metal contamination. Therefore, we synthesized all relevant literature to create a central understanding of geochemical research to date in the Great Lakes. We also filled spatial and temporal gaps in a comprehensive geochemical analysis of 11 sediment cores collected from all five Great Lakes. Hierarchical cluster analysis of all Great Lakes samples divided the metal analytes into five functional groups: (1) carbonate elements; (2) metals and oxides with diverse natural sources, including a subgroup of analytes known to be anthropogenically enriched (Cd, Pb, Sn, Zn, and Sb); (3) common crustal elements; (4) metals related to coal and nuclear power generation; and (5) all of the rare earth elements. Two contamination indices (Igeo and EF) applied to sedimentary metals indicated that Na, Co, Mn, Cd, Pb, Ta, and Cu were the most enriched metal pollutants in this system, at some point during the Anthropocene. Land uses correlated with the metal analytes, such as increases in contaminant metals with the rise in catchment population and increases in carbonate elements (e.g. Ca) with agriculture. Certain contamination trends were observed basin-wide, such as for the atmospheric pollutant Pb, which followed a rise associated with fossil fuel combustion and a decline following the ban of leaded gasoline. Other trends were lake-specific such as recent high concentrations of Na in Lake Superior due to road salt applications and a late-20th century peak in Ca associated with algal whiting events in Lake Ontario. The Great Lakes are sensitive to environmental changes such as pollution by metals and it clear that, while there has been remedial success, results from the uppermost intervals of cores indicate ongoing problems.