Friday, November 6, 2009: 2:35 PM
Kohlberg (Camino Real Hotel)
Metal concentration data collected from lake sediment cores can provide a historical record of the input of metals to the environment. However, concentration data alone are often insufficient to identify and resolve multiple metal sources. In this investigation we use Zn and Cu isotopes to fingerprint and track the sources of these metals in a sediment core collected from Lake Ballinger, and urban lake in Seattle, Washington, USA. The lower section of the Lake Ballinger core pre-dates settlement in the region, and the middle sections record the impact of atmospheric emissions from the nearby (now closed) Tacoma smelter, while the upper sections of the core record Cu and Zn inputs from other urban sources. Isotopic changes were correlated with the pre-smelter period (d66Zn = +0.40‰; d65Cu = +0.77‰), a period of smelter operation (d66Zn = +0.14 ± 0.06‰; d65Cu = +0.94 ± 0.1‰), and a post-smelting/stable urban land use period (d66Zn = 0.00 ± 0.1‰; d65Cu = +0.82‰). The isotopic data combined with sediment loading calculations suggest that much of the Zn and Cu input into Lake Ballinger occurred during urbanization of the watershed. The isotopes suggest that this metal flux was largely attributable to re-mobilization of soils historically contaminated by the Tacoma smelter. Moreover, the tires samples were analyzed and the unique d66Zn of the post-urbanization Zn input suggests that tire-wear is a likely source.