EVALUATING THE FRESHWATER MUSSEL ELLIPTIO COMPLANATA AS A PROXY FOR ROAD SALT POLLUTION IN NORTHEASTERN US STREAMS

Bivalve shells record environmental information in the form of isotope and trace element concentrations and allow important insights into past environmental conditions. Most previous work has focused on marine bivalves, however with the increasing need to monitor pollution, freshwater mussels must be evaluated as environmental proxies. In this study the freshwater mussel Elliptio complanata is analyzed as a proxy of road salt pollution. Road salt is applied to the icy roads of the Northern US in the winter time, and surface run-off and groundwater seepage transport it into nearby streams. It is important to monitor this contamination as it significantly affects water chemistry in the stream and may have important consequences for freshwater ecosystems. We sampled E. complanata specimens from four streams in Dutchess County, NY (Casperkill, Sawkill, Crum Elbow, and Fallkill) in May, 2008 and received two specimens collected from the Casperkill at Vassar College in 1877. Out of the four streams, the Casperkill has the highest amount of road salt pollution. Trace element concentrations were analyzed in annual samples taken from the outer nacreous. Na appears to be transported through the mantle epithelium by a different mechanism than Sr, Mg, Ba, and Mn. [Mn/Ca]_shell in E. complanata has a significant growth rate dependence and may display seasonal growth cycles. Finally, [Na/Ca]_shell values are generally elevated in Casperkill shells suggesting that [Na/Ca]_shell may serve as a proxy for road salt contamination in freshwater streams. Oxygen isotope analysis in the future is needed to confirm seasonal cycles of [Na/Ca]_shell and may provide a quantitative relationship between water and shell [Na/Ca].