Estuaries as Sinks for Sediment and Industrial Waste

Many estuaries around the world are being filled by net landward transport of sediment from the continental shelf. One well-known result of this process is the silting up of harbours. Our study of a part of the New England coast shows that strong flood tidal currents move silt and clay in nearbottom suspensions up the Acushnet estuary to its head in New Bedford Harbour, causing siltation. Weaker ebb currents move some of the clay back out into nearby Buzzards Bay. We have combined sedimentological and geochemical methods to try to understand the pattern of accumulation and dispersal of solid waste within the estuary. We try to use the sediment column as a complex historical record of industrial contamination, and to use industrial wastes as tracers for sediment movement. This approach allows us to model the long-term effects of the oceanographic regime on sediment dynamics and environmental contamination. Previous studies (reviewed in the text) showed that the estuarine sediments contained as much as one percent of combined Cu, Cr, and Zn. We have tried to find out how, and at what rate these metals spread within and beyond the harbour away from their industrial point sources. We have also tried to ascertain how organic rich sediment formed by the discharge of sewage has been distributed throughout the area. We concentrated our studies on sedimentary processes, on the distribution of sedimentary organic matter, and on the distributions of the following metals: Ag, Cd, Cr, Cu, Fe, Hg, Mn, Pb, and Zn.