THE RIVER BANK: POTENTIAL HEAVY METAL POLLUTION FROM COINS AND IMPACTS TO FRESHWATER MOLLUSCAN COMMUNITIES

Live, dead, and fossil assemblages have been used to document a decline in molluscan biodiversity in the Wakulla River of northern Florida. Among other human impacts, the headspring has historically been used by visitors as a wishing well, resulting in thousands to tens of thousands of coins in and around the spring vent. The practice can be traced back to the 1850s as visitors tossed pennies from glass-bottom boats as part of a guided tour of the spring. We can date coins observed in the headspring back several decades and many show evidence of heavy corrosion, suggesting the metals in these coins have likely entered the ecosystem over time since their deposition. The environmental impacts metals in these coins such as copper, zinc, and nickel, have on freshwater species is an increasing concern for aquatic ecosystems like the Wakulla River. Gastropods are particularly sensitive, with metal toxicity and bioaccumulation causing increased mortality rates. To assess the extent and potential impacts of heavy metals on the Wakulla’s biological communities we sampled live mollusks and associated aquatic vegetation from sites along the upper 11 km of the river, beginning at the headspring. Concentrations of copper, zinc, nickel, and lead were measured from the tissues of a range of gastropod species including Elimia floridensis, Melanoides tuberculata, and Vitta usnea as well as from aquatic vegetation to assess the presence and extent of heavy metal bioaccumulation. Copper and zinc, both metals present in pennies of various ages, were found at elevated levels in tissues of gastropods living near the headspring where these coins are most commonly found. Additional specimens of gastropods and aquatic flora are being currently analyzed for heavy metal concentrations (Cu, Zn, Ni, Pb) in order to see if the general decline in molluscan biodiversity is related to an elevated concentration of heavy metals sourced from coins accumulated in the headspring. Because coin tossing rituals affect many springs in Florida and elsewhere, the results of this study may prove relevant to many river ecosystems.