THE EFFECTS OF ORGANIC MATTER ON INLAND LAKE TRACE METAL PROFILES

The accumulation of organic matter in lake sediment serves as an important control of the retention of inorganic contaminants, particularly those with an affinity for organic compounds such as Hg, As, Pb, and Cd. Thus, changes in the organic matter fraction of lake sediment can affect the interpretation system recovery from anthropogenic disturbance especially with regards to a reference condition. For this study, it was hypothesized that changes in organic matter content would be positively correlated to changes in trace metal concentrations. To test this hypothesis, sediment cores were collected from 30 inland lakes ranging in size and geochemical composition from across the State of Michigan. Percent carbon and percent nitrogen data were compared to elemental analysis by ICP-MS from sediment collected at the deepest point of each lake. Results show positive relationships between percent nitrogen/carbon and select elements in oligotrophic to mesotrophic lake systems possibly indicating that organic matter is the most significant pathway of scavenging trace metals to sediment in these systems. However, results from most eutrophic lakes appear to show elevated organic material relative to the trace metals studied. These results have implications that sorption mechanisms to organic material during burial, not increased loadings, may elicit the observed results of some elements in lake sediment core analysis. This serves to alter the interpretations of lake system recovery particularly with regard to reference conditions.