Geochemical considerations on trace element distributions in suspended matter and sediments at the river-sea interface, Adige River mouth, northern Adriatic sea

The particulate matter at the Adige River mouth has been investigated in order to determine the natural geochemical processes in the estuarine environment, and the anthropogenic influence on the biogeochemical cycling of heavy metals. The determination of suspended matter and sediment physico-chemical characteristics (grain size, mineralogy, organic matter content, specific surface area), and of concentrations of major and trace elements in the Adige River mouth in different hydrological conditions, has shown that this mouth acts as a trap for most heavy metals. Heavy metals were found to be preferentially bonded to the particulates, and in the estuarine mixing zone scavenging of most dissolved metals occurs, due to salinity and pH gradients, and to the formation of new particulate organic matter. The surface characteristics of suspended particulate matter [fine grain size, abundance of clay minerals, large specific surface area (SSA), organic and inorganic coatings] favour the adsorption of heavy metals. The sedimentation pattern (rapid deposition due to flocculation of fine particles, and to low environmental energy and estuarine circulation) causes accumulation of particulate matter, enriched in heavy metals, in the prodelta zone. Moderate anthropogenic influence on Cu, Pb, Cd, and Cr concentrations has been recognised in the Adige River. The environmental fate of these elements is determined by the same natural processes, and therefore accumulation in front of the river mouth occurs. The elevated partitioning in the organic phase of the anthropogenically influenced elements, could favour their mobility in different environmental conditions. © 1989.