The Historical Record of Metal Enrichment in Two Florida Estuaries

Historical profiles of metal accumulation have been generated for the lower St. Johns River and Hillsborough Bay, Florida, in cores representing approximately 50 yr of sediment and metal accumulation. These profiles demonstrate that Cd, Pb, and Zn are enriched in these Florida estuarine sediments. Pb enrichment has decreased since the mid 1970s because of reduced use of leaded gasoline. In the St. Johns River, most metals exhibit a trend of increasing enrichment with time. Cd enrichment significantly decreased between 1970 and 1975 as a result of reduced discharges into the river and control of aquatic vegetation. In Hillsborough Bay, enrichment factors for most metals are relatively high and show little change downcore. Cr, Cu, and Ni border on enrichment and Pb, Cd, and Zn are enriched. The results of this study are consistent with other studies of surficial-sediment metal concentration in other Florida estuaries.