A New Water-Based 87Sr/86Sr Isoscape Map of Central and NE Germany, with Special Emphasis on Mountainous Regions

In this study, we present a new ⁸⁷Sr/⁸⁶Sr isoscape map of Central and NE Germany. This area is characterized by an alternation of sedimentary basins and mountainous regions with a very variable lithology. Since lithology and rock age have a major impact on the isotopic composition of biologically available strontium, Central and NE Germany should reveal highly variable ⁸⁷Sr/⁸⁶Sr ratios. From lithological characteristics, particularly high ratios are expected in the mountainous regions of the Erzgebirge/Fichtelgebirge and the Harz Mountains. In contrast to these predictions, published ⁸⁷Sr/⁸⁶Sr isoscape maps of Central and NE Germany record rather uniform and low ⁸⁷Sr/⁸⁶Sr ratios. From this observation, we suspected that existing isoscape maps might be computed from an insufficient database, with mountainous regions being underrepresented. Our goal was to gather ⁸⁷Sr/⁸⁶Sr baselines for each major lithology of Central and NE Germany and to produce an accurate isoscape map of Central and NE Germany. In the first step, we evaluated the suitability of stream water and groundwater as a proxy for biologically available strontium. In a selected watershed, we present mixing relationships and a stream network model. We show that groundwater is prone to very local geologic and anthropogenic influences and should thus be avoided. Instead, we focussed our further sampling on stream water. Altogether, we used 119 new measurements of groundwater and stream water and a set of 23 auxiliary variables as a database for our new isoscape map of Central and NE Germany. Due to a sampling strategy that focussed on covering each major lithology, our measurements and the final isoscape map show a clear contrast between sedimentary basins and mountainous regions. For regions that have been sufficiently sampled, a direct comparison of the isoscape map with published and new data shows good agreement. Although Central and NE Germany were part of published isoscape maps, our new map is the first that predicts ⁸⁷Sr/⁸⁶Sr ratios in mountainous regions with high accuracy.