Matthew S. Finkenbinder

Copper mining on Isle Royale 6500–5400 years ago identified using sediment geochemistry from McCargoe Cove, Lake Superior

Isle Royale, in Lake Superior, contains evidence of indigenous copper mining; however, the timing and geographical extent of mining activity is poorly known. We analyzed metal, carbon, nitrogen, and organic matter concentrations to document past mining pollution in sediment cores recovered from McCargoe Cove; a long, narrow inlet of Lake Superior on Isle Royale that receives drainage from a watershed that contains numerous ancient copper mines. At McCargoe Cove, concentrations of lead, copper, and potassium increase in the sediments after ad 1860 and between 6500 and 5400 years before ad 1950 (yr BP). Metal pollution increases at McCargoe Cove exceed natural (or background) levels and coincide with radiocarbon dates associated with copper artifacts and existing lead pollution reconstructions from lakes on the Keweenaw Peninsula. Interestingly, a coherent cessation of lead emissions at multiple study sites after ~5400 yr BP coincides with the onset of dry conditions found in regional paleoclimate proxy records. After ~5000 yr BP, lead concentrations on both Isle Royale and the Keweenaw Peninsula remain at background levels until the onset of modern lead pollution ~ad 1860.

Reconstructing Early Industrial Contributions to Legacy Trace Metal Contamination in Southwestern Pennsylvania

Early industrial trace metal loadings are poorly characterized but potentially substantial sources of trace metals to the landscape. The magnitude of legacy contamination in southwestern Pennsylvania, the cradle of North American fossil fuel industrialization, is reconstructed from trace metal concentrations in a sediment core with proxies including major and trace metal chemistry, bulk density, and magnetic susceptibility. Trace metal chemistry in this sediment record reflects 19th and 20th century land use and industry. In particular, early 19th century arsenic loadings to the lake are elevated from pesticides used by early European settlers at a lakeside tannery. Later, sediment barium concentrations rise, likely reflecting the onset of acidic mine drainage from coal operations. Twentieth century zinc, cadmium, and lead concentrations are dominated by emissions from the nearby, infamous Donora Zinc Works yet record both the opening of a nearby coal-fired power plant and amendments to the Clean Air Act. The impact of early industry is substantial and rivals more recent metal fluxes, resulting in a significant potential source of contaminated sediments. Thus, modern assessments of trace metal contamination cannot ignore early industrial inputs, as the potential remobilization of legacy contamination would impact ecosystem and human health.