IsoGW: groundwater isoscapes for Germany

Landuse and climate change alter hydrological processes and affect drinking water resources. Practical tools for understanding and quantifying these processes becomes increasingly important, for example to sustainably manage groundwater reservoirs. Analyses of the water isotopes deuterium (δ²H), oxygen (δ¹⁸O), and tritium (³H) provide useful tools, which can be applied to determine groundwater ages, assess bank filtration quantities, identify mixings of groundwater aquifers or long-term climate-induced changes. The objective of the IsoGW-project (2023-2026) is to create nation-wide interpolated isotope maps (i.e., isoscapes) of δ²H, δ¹⁸O and of ³H concentrations in German groundwaters. Aiming to provide public access to the data, an online map service and portal are set to present both the interpolated and interpreted maps as well as harmonised isotope data across the 16 German states in all relevant hydrologic compartments (groundwater, precipitation and surface waters). This work, based on an exceptional density of data points, provides new opportunities for a systematic and large-scale assessment of interactions between different compartments of the water cycle such as surface water-groundwater interactions and groundwater renewal. By establishing such a service for the first time, Germany is following its European partners, which have already published some preliminary work on the matter.

Existing data has been collected from German state offices, literature, companies and is being completed by new sampling campaigns within the project until a satisfying spacial point distribution and density is reached. Additionally, several interpolation algorithms for δ²H and δ¹⁸O, as well as different methods accounting for the ³H half-life of 12.3 years, are compared. Here, we present the latest updates regarding data research, sampling and  analyses, interpolation algorithms, as well as database and web tool development. Overall, we are confident that this database and online portal will enable large-scale assessments of the water cycle and provide an important basis also for local studies. This work will be accompanied by a practice guide that will allow researchers and practitioners to use the data and tools for all these assessments.