EVALUATING CHANGES IN ANTHROPOGENIC ACCUMULATION RATES AND SOURCES OF TRACE METALS

Lake sediments record the history of trace metals inputs, and may also provide insight into the sources and pathways of these metals through the environment. Sediment cores were collected from seventeen lakes throughout the state of Michigan to determine changes in anthropogenic accumulation rates of cadmium, copper, lead and zinc over time and space. Results from the 1970s and 1990s were compared to watershed characteristics (e.g., land cover, population density) that represented potential sources and pathways of these metals.

Anthropogenic accumulation rates of cadmium, lead and zinc have decreased in the majority of lakes since the 1970s and have shifted from regional sources (e.g., atmospheric deposition) in the 1970s to watershed scale sources in the 1990s. Copper accumulation rates have decreased only slightly or increased over time in most lakes. In the 1990s the best predictor of anthropogenic accumulation rates for all four metals was percentage urban land cover within the watershed. These data show loadings of these metals can be quantitatively related to watershed characteristics, and that change in these relationships over time represent shifting sources of these metals.