IMPINGEMENT OF ORGANIC-RICH, CONTAMINATED SEDIMENTS ON MANATEE POCKET, FLORIDA

Fine-grained, organic-rich sediments are adversely impacting portions of the coastal zone in Florida. One extreme example is found in Manatee Pocket, on the southeastern coast of Florida, where sediments with >4% organic carbon have an average thickness of about 1 m and a total volume of 340,000 m3. These deposits formed as soil and organic matter were carried into Manatee Pocket and trapped during the past 100 years of regional development. Vertical profiles for Cd, Cu, Hg, Pb, and Zn show that contamination, at 5-10 times above natural levels, is restricted to the top 15-30% of the organic-rich layers of sediment. Thus, despite a long history of sedimentation problems, incoming sediments have been burdened with contaminants only since the 1950s.