Leibniz-Institut für Ostseeforschung, Warnemünde
(IOW) (Baltic Sea Research Institute, Warnemünde)
Bundesamtes für Seeschifffahrt und Hydrographie, Hamburg, Rostock
(Federal Maritime and Hydrographic Agency of Germany, Hamburg, Rostock)
In general the 2004 results of heavy metal concentrations in the Baltic Sea revealed no pronounced changes compared to previous years. Regional and temporal limited variations of trace metal concentrations, which have been observed periodically in the western Baltic, have been attributed to the changing enrichment of suspended matter in the water column.
Changes induced by the main saltwater inflow event in February 2003 were observed in the vertical trace metal distribution in the Bornholm- and Gotland Basin with nearly homogeneous concentrations for Cddiss, Cudiss and Zndiss in surface- and deep waters. For the contents of CdSPM, CuSPM and ZnSPM a slight increase was observed with depth, a possible hint for the beginning of a new stagnation period. Still stagnant conditions with anoxia and very low trace metal conditions were noticed below 100 m in the Landsort Deep. Long term trends were only slightly influenced by the saltwater inflow event in the central Baltic Sea.
The question has been discussed, if long-term trace metal trends in surface- and deep waters of the Gotland Basin (Central Baltic) are a result of enhanced / reduced input to the Baltic Sea or if they are related to a "feedback mechanism” including the stabilisation of the anoxic deep water regime and the irreversible trace metal export by diffusive exchange across the oxic-anoxic interface. Estimations of the diffusive and particulate internal trace metal fluxes and export rates showed under consideration of the data from the pollution load compilation (latest revision) (HELCOM 2004), that about 50 % of the Cd-input; 53 % of the Pb-input; 63 % of the Zn-input and 60 % of the Cu-input into the Baltic Sea, are eliminated by internal biogeochemical processes at the oxic-anoxic interface.
Heavy metal concentrations in sediments of the western Baltic Sea (BLMP-stations) still not show a significant temporal trend (1998 to 2004). Inter annual variability at the stations is partly much higher than the local (small scale) variability of the trace metals. The local "hot spot” Lübeck Bay was capped by uncontaminated sediments. A normalisation of the situation at this site is to be expected for the next future. The cause of the enriched Hg-concentrations in sediments of the station in the western Arkona Basin is still unclear. Special investigations at a sediment core from this station in 2005 should contribute to the solution of this problem.
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