Trace metal budget, transport, modification and sink in the transition area between the oder and peene rivers and the southern pomeranian bight

Concentrations of Cd, Pb, Cu, Zn, Co, Ni, Fe, Mn and Hg in the dissolved phase, in particles and in surface sediments (< 63 μm) were analysed during four transects, between January and October 1995 in the Pomeranian Bight. Additional samples were also taken once in the inner coastal Oder Lagoons in August 1996. Modification processes influenced by seasonal variations were observed for the redox relevant manganese. Highest Mn(diss) and Mn(SPM) values were determined in summer, when the decomposition of organic material resulted in a change of conditions, from oxic to anoxic, in surface sediments of the Oder Lagoon. A lateral wind induced transport of dissolved manganese through the river outlets resulted in higher Mn(diss) and Mn(SPM) contents in the southern Pomeranian Bight. The distribution of Cd(diss) was linked to phytoplankton growth. A mean Cd(diss) removal from the water column of 50% was calculated during summer 1995. In addition, the cadmium inflow with river discharge waters into the Pomeranian Bight was lower in June 1995, because most of the Cd(diss) had been eliminated during phytoplankton growth in the highly productive waters of the Oder Lagoon. Gradients between the Oder Lagoon and the river mouth of the Peenestrom showed, that only a very small net percentage of river transported trace metals entered the Pomeranian Bight in August 1996. Most of the Pb (90.4%), Cd (90.6%), Cu (79.7%), Zn (94.9%), Co (83.4%), Ni (68.3%) and Fe (93.6%) was retained in the inner coastal lagoons. In this connection the percentage of metals in the particulate phase is of greatest significance. In August 1996, approx. Fe (80%), Mn (70%), Cd, Pb, Zn (45%), Co (40%), Cu, Ni (35%) are associated with particles in the inner coastal lagoons, while at the stations in the Pomeranian Bight this proportion decreased drastically, due to factor 50 lower particle contents. Maximum anthropogenic enrichment factors (EF) of 15–30 (Cd), 10–17 (Pb) and 5–10 (Zn) were found in the surface sediment fraction < 63 μm in the western part of the Pomeranian Bight.