The clay mineral composition, the concentrations of carbonates, the proportions of carbon and oxygen isotopes in carbonates and organic matter as well as the concentrations of different elements have been used to determine the origin of several grain size fractions of the sediment and the suspended matter from the Elbe estuary.
The clay mineral composition, especially the smectite-kaolinite proportion, demonstrated that solid material ≤µ* from the North Sea is transported up the river, about 50 km beyond the average position of the salt wedge. As far as the fraction 2-20µ is concerned, the upward transport of North Sea material was proved by the calcite concentration, the Ca:Sr proportion in total particulates and the isotopic composition of the carbonates, demonstrating a transport of at least 40 km beyond the marine water limit. The transport behavior of the grain size fraction 20-63µ could be determined by the Hf concentration. In this case, the distance of the transport beyond the salt wedge was around 30 km. The isotopic composition of the carbonates confirmed the landward transport of this fraction. The organic matter in the coarser fractions was partly derived from debris of marsh vegetation. Due to the contribution of sources within the estuary, information obtained from this tracer pertained to the origin of the organic matter only.
The results demonstrate the mixing between marine and fluvial sediments and transport of marine sediments past the salt wedge. This physical process occurs with chemical processes responsible for the observed decrease of pollutants concentrations in solid matter along the estuary. Additionally, the different amounts of the upstream transport distances of the investigated grain size fractions support the hypothesis of settling and scour lag induced particulate transport.