Groundwater stable isotope maps for Germany: recommendations and perspectives working with heterogeneous data

Gaillard A, Neuner A, Landgraf J, Koeniger P, Braune S, Kringel R, Walker B, Schmidt A, Barth J, van Geldern R (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Book Volume: 38

Article Number: 77

Journal Issue: 1

DOI: 10.1186/s12302-026-01361-4

Abstract

Background: Stable water isotopes δ18O and δ2H in the water molecule are ideal tracers of the hydrological cycle to understand mixing processes between different aquifers, groundwater-surface water interactions or groundwater recharge. To date, no centralized access to standardized groundwater isotope data is available in Europe. This study addresses this gap in Germany by assembling existing historical data, completing the spatial coverage with new samplings and presenting the gained data in the form of spatially interpolated maps, so-called isoscapes. Results: Collected data from more than 8 000 groundwater sampling stations cover the entire German territory and span the last 50 years. We successfully implemented co-kriging interpolation algorithms taking into account elevation and temperature. This produced several isoscapes for 15 years periods to accurately represent typical young groundwater residence times. Here we present two representative δ18O isoscapes for the periods 1965-1980 and 2015-present. These examples allow assessments of this commonly used interpolation method. The emerging trends correspond to similar observations in precipitation. Despite the large discrepancies in data quality and density, the absolute error of the isoscapes remained under 3.1 ‰ for δ18O. Major limitations are the extrapolation to regions with no primary data as well as boundaries between data-rich and data-scarce areas. Conclusions: With this work, we provide the basis for further comprehensive large-scale isotope research, as well as reliable background values for local investigations in Germany. We also formulate recommendations to work with heterogeneous and scarce data, to ensure the plausibility of isotope values and to identify unknown deep groundwater samples using additional information such as tritium activities. These strategies could be applied to develop similar initiatives in other European countries and across national borders.

Authors with CRIS profile

Involved external institutions

Bundesanstalt für Gewässerkunde (BfG) / Federal Institute of Hydrology Germany (DE) Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) Germany (DE)

How to cite

APA:

Gaillard, A., Neuner, A., Landgraf, J., Koeniger, P., Braune, S., Kringel, R.,... van Geldern, R. (2026). Groundwater stable isotope maps for Germany: recommendations and perspectives working with heterogeneous data. Environmental Sciences Europe, 38(1). https://doi.org/10.1186/s12302-026-01361-4

MLA:

Gaillard, Aixala, et al. "Groundwater stable isotope maps for Germany: recommendations and perspectives working with heterogeneous data." Environmental Sciences Europe 38.1 (2026).

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