Chronology of anthropogenic heavy-metal fluxes and Pb isotope ratios derived from radiometrically dated lake sediments in Northern Germany

Anthropogenic inventories and fluxes of Pb, Zn, Cu, and Sn into the sediments of two lakes, a drinking water reservoir (Neumuhler See) and an urban lake (Ziegelsee), both in or near Schwerin, Germany, were investigated. A simple freeze-coring technique was used for reproducible sampling of undisturbed surface sediments. Sediment chronology was established for Ziegelsee by gamma spectrometry of the nuclides Cs-134, Cs-137, Am-241, Pb-214, Bi-214 and Pb-210; bioturbation in Neumuhler See prevents this. Anthropogenic heavy-metal loads were determined using Co as tracer for the geogenic portion. Anthropogenic heavy-metal inventories of Ziegelsee exceed those of Neumuhler See by factors of 3.0, 6.0, 5.6, and 6.8 for the heavy metals Pb, Cu, Zn, and Sn, respectively. The anthropogenic Pb flux into Ziegelsee increased from 1870 to 1965 and decreased below the 1870 level by 1990. Isotope ratios of anthropogenic Pb change with time and indicate different sources (lignite, gasoline). The anthropogenic Cu, Zn, and Sn fluxes into Ziegelsee with respect to time are comparable to that of Pb, but between 1960 and 1980 pronounced local peaks appear and this was not determined in the Pb flux.