The vertical and horizontal distribution of selected trace metals in the Baltic Sea off Poland

Concentrations of dissolved and particulate heavy metals (Fe, Co, Ni, Cd, C u, Pb, Mn, Zn) were measured in the Baltic Proper off Poland in September 1 996. Water samples were collected along two offshore horizontal transects f rom the mouths of the rivers Vistula and Odra and two vertical profiles in the Gdansk and Bornholm Deeps. Particulate/dissolved metal concentrations i n the following ranges were measured (mg kg(-1)/mu g l(-1)): Cd-0(.)89-89(. )1/0(.)003-0(.)022, Pb-10(.)2-114/0(.)004-0(.)0088, Cu-20(.)2-214/0(.)14-0( .)80, Ni-27-71/0(.)59-1(.)63, Mn-53-7590/0-971, Zn-124-3460/0(.)30-1(.)62, Co-not analysed/0(.)003-0(.)235, Fe (%)-0(.)14-3(.)29/0-190, Al (%)-0(.)11- 3(.)92/not analysed. Horizontal concentration gradients were found in the Gulf of Gdansk, which were attributed to the inflow of metals with the Vistula runoff. The lack o f gradients in the Pomeranian Bay was explained by the Odra runoff having t o pass through the Szczecin Lagoon, which acts as a trap for the suspended and dissolved loads carried by the river. The steep vertical gradients of b oth dissolved and particulate metals were put down to bioaccumulation at th e surface, the presence of accumulated colloids above the halocline and red ox phenomena in the suboxic zone below the halocline. These last involve di ffusion of Fe(II) and Mn(II) from anoxic sediments, their oxidation to Fe(I II) and Mn(IV) and possible formation of poorly soluble sulphides. (C) 2000 Academic Press.