Evaluation of Shelf, Harbor and Disposed Dredged Sediments as Potential Sources of Deposited Muds on South Florida Reefs

In 1995, three quarters of a million cubic yards of material was dredged from Fort Pierce Harbor (Florida) and disposed in the Fort Pierce, Florida Ocean Dredged Material Disposal Site (ODMDS). By 1996, reports of thick mud deposits (muck) discovered on shelf hard-bottom resources raised concerns of potential adverse impacts of offshore dredged material disposal. Sediment samples were collected from hard-bottom muck deposits, the Fort Pierce ODMDS, harbor, and shelf off of St. Lucie County, Florida. Fifteen trace elements and three naturally occurring radioelements were analyzed in the silt and clay (fine) particle size fraction. Numerical classification (clustering) analysis and multidimensional scaling (ordination) of the trace element and radiometric data failed to show any strong degree of similarity between hard-bottom muck and fine sediments collected from the ODMDS or harbor locations. Hard-bottom muck tended to form unique clusters and groupings in ordination space. These data show that hard-bottom muck was unique in elemental composition and their dissimilarity to sediments taken from the dredged material disposal site and the harbor locations suggest that the muck was comprised mainly of non-dredged sediments of indeterminate origin.