DO FRESHWATER MUSSEL SHELLS RECORD ROAD SALT POLLUTION?

Bivalves have the ability to record past environmental information in the isotopic ratios as well as concentrations of elements archived in their shells. This study investigates the freshwater mussel Elliptio complanata as a proxy of road salt pollution in freshwater streams. Due to the large amount of ice and snow that the Northeastern United States receives during the winter, road salt is applied and eventually is carried to streams via surface run-off and groundwater seepage. This salt that infiltrates into the streams is an important environmental concern because it greatly affects the water chemistry of the stream and can have deleterious effects on the flora and fauna that reside in the stream. We sampled Elliptio complanata from four streams in Dutchess County, New York (Casperkill, Sawkill, Crum Elbow, and Fallkill) in May 2008 as well as two specimens that were collected from the Casperkill stream in 1877. Today, the stream that contains the highest amount of road salt pollution is the Casperkill, followed by the Fall Kill, then the more pristine Crum Elbow and Saw Kill (Cunningham et al. 2009, Physical Geography 30:269). Trace element analyses were completed using laser ablation ICP-MS on shell cross sections. We found that average [Na/Ca]_shell is higher in the modern shells from the Casperkill suggesting that [Na/Ca]_shell serves as a proxy for road salt pollution in freshwater ecosystems and that the salt pollution is indeed a modern pollutant in the stream. We expected higher Na/Ca in shell portions representing spring growth. However, high-resolution Na/Ca analyses along the growth axis of the shell did not reveal any clear subannual patterns, which could be the result of the animals not producing shell in winter months and/or reduced shell growth during periods of high sodium concentrations.