Using Sr-Nd-Pb isotope systems to trace sources of sediment and trace metals to the Weser River system (Germany) and assessment of input to the North Sea

Abstract

In order to trace the sources of sediment materials and trace metals in the Weser River system (Germany), and the riverine input to the North Sea, Sr, Nd and Pb isotopes, together with multi-elemental compositions, were measured for sediments collected over the entire Weser River Basin, from headwaters to the estuary. Mass fractions of metals, including Ag, Cd, and Pb, and of one metalloid, Sb, higher than their crustal abundance, were observed within the entire Weser Basin. Isotope-amount ratio n(87Sr)/n(86Sr) and εNd ranged from 0.71182 ± 0.00005 to 0.72880 ± 0.00009 and −11.3 ± 0.3 to −21.0 ± 0.3, respectively. n(206Pb)/n(204Pb), n(207Pb)/n(204Pb), and n(208Pb)/n(204Pb) ranged from 18.226 ± 0.008 to 18.703 ± 0.012, 15.613 ± 0.007 to 15.653 ± 0.012 and 38.14 ± 0.02 to 38.84 ± 0.02, respectively. Sr and Nd isotope compositions reflected primarily a mixture of natural materials derived from the Weser Basin. Pb isotope signatures indicated strong anthropogenic influences in the middle-lower Weser region. Pb isotopic compositions in the sediments from the Aller (tributary of the Weser) and its tributary suggested influence from historical Pb-Zn ore mining in the Harz Mountains that might contribute to the observed elevated mass fractions of Ag, Cd, Sb and Pb in that region. K-means cluster and principal component analysis of the Sr, Nd, and Pb isotope data yielded results consistent with their isotope systematics, supporting statistical analysis as an unsupervised tool in isotope fingerprinting studies. Sr, Nd, and Pb isotopic signatures in the sediments of the Weser were distinctively different from those of another major river discharging into the North Sea, the Elbe. This suggested that this Sr, Nd, and Pb isotope dataset can be used to distinguish riverine input of sediment materials and metals between the two rivers, thereby assessing their individual contribution to materials transported into the North Sea.