TRACE-METALS IN SEDIMENTS OF A MEDITERRANEAN ESTUARY AFFECTED BY HUMAN ACTIVITIES (ACHELOOS RIVER ESTUARY, GREECE)

Trace metals were studied in the sediments of the ecologically, econom ically and scientifically important estuary of the Acheloos river, in western Greece. Human activities (dams, agriculture, traffic, etc.) in fluence the estuarine system of Acheloos and in combination with the h ydrological, mineralogical and morphological characteristics of the es tuary affect the chemical behaviour and the distribution patterns of t race metals in its sediments. The large scale disturbance of the syste m is imminent in the near future as it is planned to divert similar to 50% of the river water. A study of the distribution patterns of trace metals revealed that in the estuary there are zones with different me tal levels. The concentrations of most metals (Al, Fe, Cu, Ni, Zn) are elevated in three of these zones (upstream, sill, seawards). A differ ent behaviour was observed for Mn due to its association with carbonat es that were observed in significant concentrations throughout the est uarine zone. A sequential extraction procedure, applied to the sedimen ts, indicated low percentages of easily exchangeable metals, increased mobility of Cu and Zn and increased association of Ni, Cr and Fe with the aluminosilicate lattice. Although the river is not considered to be heavily polluted, some metals have shown an enrichment in the surfa ce sediments as a result of general anthropogenic activities not deriv ed from point sources.