USING SPATIAL AND TEMPORAL PATTERNS OF METAL DEPOSITION TO INLAND LAKES TO DIFFERENTIATE SOURCES

Lake sediments have recorded a decrease in loading of many trace metals over the last two decades as a results of environmental regulations. However, accumulation rates of these metals (e.g. lead, copper, cadmium, zinc) still remain above background values, showing the need for continued regulation. An understanding of the dominant sources of a metal to a large regional area, rather than just one lake, would facilitate reducing these dominant sources. Examining multiple lakes across a region may provide insight into some of the dominant sources of metals in the area. The purpose of this study was to determine the relative importance of regional sources (e.g., atmospheric), common local sources (e.g., sewage), and unique local inputs (e.g., local industry).

Sediment cores were collected from 7 lakes in Michigan, analyzed for a suite of metals and dated with 210-Pb. Patterns of lead deposition show a regional trend, and little relationship to population densities, indicating regional atmospheric sources are dominant in this area. Current lead deposition has a weaker regional trend, indicating a shift from regional to unique local courses. Patterns of cadmium deposition are different than those of lead. Inputs of cadmium in the 1930s-40s are strongly related to population densities, but have no regional pattern, indicating the importance of common local sources. Overall, sediment chronologies from multiple lakes can provide information about the relative importance of local and regional sources of metals to a region.