A RECENT HISTORY OF METAL ACCUMULATION IN THE SEDIMENTS OF THE THAMESESTUARY, UNITED-KINGDOM

Sediment cores were collected from the Tilbury Tidal Basin in the Tham es Estuary to determine the depositional history of metals in the estu ary. Profiles of metals in sediments deposited in the lower Thames Est uary show a 30-50% decrease in concentration for Ag, Cd, Cu, Ph, and Z n, and a 70% decrease for Hg in recent decades. Historic depth soundin gs data showed the decreases in metal concentrations occurred between 1944 and 1966. The decline in sediment metal concentrations has been a ttributed to reduced inputs to the estuary, following updating of the major sewage treatment works in 1959 and 1963. This is indicated by th e through-core distribution of Mn which implies that prior to 1960 the sediments were deposited in anoxic conditions, which subsequently imp roved. An increase in Mn concentrations observed in one of the cores h as been attributed to increases in the dissolved oxygen of the estuari ne waters resulting from the increased efficiency of the sewage treatm ent works.