The Elbe River was long considered as one of the most anthropogenically impacted rivers in Europe. Its estuary is characterized by strong tidal effects, continuous dredging and dumping of sediments and intense ship traffic between the North Sea and the Port of Hamburg. These activities make the estuary a highly dynamic study area of interest to numerous parties. The aim of this study was to elucidate if a combined multi-element fingerprinting and isotopic tracer approach represents a suitable tool to investigate transport and mixing processes of inorganic contaminants within a complex and highly dynamic estuarine environment.
Therefore, a total of 37 surface sediment samples (<63 µm grain size fraction) of the Elbe River Estuary were characterized in a comprehensive survey by determining the mass fractions of 48 elements and the isotopic signatures of stable Sr, Nd and Pb. By the combination of multi-element and isotopic data, statistical data analysis resolved four discrete clusters of sampling locations in the estuary: One cluster upstream of the city of Hamburg, two clusters within the mixing zone between Hamburg and the mouth of the Elbe Estuary and one cluster in the mouth of the estuary. Our results indicate that river sediments entering the estuary carry significantly higher loads of heavy metals (e.g. Cu, Zn, Sb, Cd and Pb), which are rapidly “diluted” by lower elemental mass fractions in marine sediments on a remarkably small regional scale (investigated river transect: 144 km). The cluster within the mouth of the estuary is mainly characterized by extreme isotopic variations of n(208Pb)/n(204Pb) ranging from 38.67 ± 0.15 to 73.86 ± 0.29, beside high mass fractions of U, Th and some rare-earth elements. Determined Pb isotope ratios are among the highest reported values for terrestrial materials. These extreme variations are unique as they occur on a small spatial scale and cannot be explained by the underlying geology of the Elbe Estuary solely. Hence, it can be assumed that this material is not exclusively original to the area but was transported into the Elbe Estuary either by tidal dynamics or human activities.
In summary, this study indicates the general potential of combined element fingerprinting and isotope tracer approaches to elucidate processes in complex river systems. Moreover does it represent an initial characterization of the catchment area of the Elbe River as basis for future studies on river and harbor management.
