Heavy-metal enrichment in surficial sediments in the Oder River discharge area: source or sink for heavy metals?

The Oder river drains a highly polluted industrial area and enters the Baltic Sea through a system of shallow lagoons. Surficial sediments in the discharge area of the Oder are highly enriched in heavy metals compared to their preindustrial background levels. Pore-water studies in short sediment cores reveal anoxic environments over the entire sediment column, except for a suboxic layer in the uppermost 5 to 20 mm of the sediment where Mn- and Fe-oxyhydroxides are reduced by organic matter. Heavy metals (such as Cu, Zn and Pb) are mobilized within the suboxic zones in the inner lagoon (represented by the Oder Lagoon) and in the open Baltic (represented by the Arkona Basin). The Achterwasser, located between the Oder Lagoon and the Arkona Basin, is directly affected by sea-level fluctuations in the Baltic. Pore-water studies indicate that, in contrast to the situation in the Oder Lagoon and Arkona Basin, surficial sediments of the Achterwasser represent a sink for heavy metals. This is associated with the high rate of Fe-sulphide formation occurring there, at least seasonally during saltwater inflow. (C) 1998 Elsevier Science Ltd. All rights reserved.