Partitioning of trace metals in suspended matter from the elbe estuary fractioned by a sedimentation method

Abstract

The particulate matter in water samples from the freshwater region of the Elbe estuary was fractioned by its setting characteristics. The sedimenting and the permanently suspended fractions of the particulate matter were analyzed separately for trace metals (cd, Pb, Cu, Cr, Co, Ni) and organic composition. The two fractions differed significantly in organic and metal content and 13C in organic matter. Permanently suspended particles rich in riverine biogenic material contained amounts of trace metals enhanced by a factor of about three in comparison to the sedimented fraction. Also, 80% of the total particulate trace metals was transported downstream by this fraction. Along the profile of the Elbe from km 630 to km 670 a decrease in suspended particulate trace metals occurred in both fractions, which amounted to a reduction of approximately 50% between March and June. The largest decrease was detected just below Hamburg harbour and was explained by mixing of highly polluted riverine SPM with less polluted sedimenting SPM from downstream regions. The specific loading of the particulates with trace metals was linked to the particulate organic matter content which was in part degraded during the transport downstream. The adsorption characteristics of the organic matter remained quite constant both over the freshwater profile and at different times of the year and accumulation [C/Metal (g·mg −1)] varied mostly between 0.5 and 1 for Cu, Pb, Cr and Ni and 15 to 30 for Cd. The results indicate that even small changes in the perticulate matter composition might produce great differences in the total particulate tarce-metal content.