A MULTIVARIATE ASSESSMENT OF METAL DISTRIBUTION IN INTER-TIDAL SEDIMENTS OF THE BLACKWATER ESTUARY, UK

The Backwater Estuary, Essex, UK is the primary site for the investiga tion of Managed Retreat: a coastal management technique aimed at the r estoration of salt marshes, The success of Managed Retreat trials will be judged by the development of healthy salt marsh communities. Accre tion of sediments is a key part of this development, The metal content of accreting sediments may be significant in salt marsh development a nd has environmental importance, Therefore, information on estuarine s ediment geochemistry in the Blackwater Estuary will be valuable in int erpretation of the geochemical development of Managed Retreat sites. T he spatial distribution of 15 metals in the sediments of the estuary h as been assessed by the use of the multivaraite statistical techniques cluster analysis; multidimensional scaling; principal component analy sis; and canonical variate discriminant analysis, The assessment indic ated a general landward to seaward decrease in heavy metal concentrati ons in the estuary, This was the effect of elevated concentrations of heavy metals, particularly Pb, Zn, Cd and Cu, at the head of the estua ry resulting from specific discharges associated with the congregation of anthropogenic activity in this zone. In comparison, sediments in t he lower estuary, where Managed Retreat schemes have been instigated, were less contaminated. However, heavy metal concentrations were eleva ted in the Bower estuary at a site of enhanced deposition, which was p roximal to a localized source of metals, This has implications for con centrations of metals incorporated into sediments at Managed Retreat s ites in the lower estuary where accretion is being actively promoted. a depletion of calcium was observed in salt marshes as compared to mud flats throughout the estuary, (C) 1997 Elsevier Science Ltd.