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Anthropogenic tritium as a continental-scale tracer in river-derived recharge

Nature Water (2026)Cite this article

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Abstract

Groundwater, enhanced through managed aquifer recharge (MAR), plays a central role in mitigating current and future water stress. Here we evaluate anthropogenic and natural water isotopes as tracers of groundwater flow dynamics within alluvial MAR systems. High-resolution sampling (daily/weekly) of stable isotopes (δ18O and δ2H) and tritium (3H), influenced by nuclear power plant effluents, is used to trace and quantify the movement of infiltrated river water through an alluvial aquifer along the Rhine River in Switzerland. Time-series deconvolution is applied to quantify the tracer-based travel time distribution and to predict travel times throughout the entire MAR scheme. The results demonstrate the suitability of 3H as a quasi-conservative travel time tracer in systems where the infiltrating river water is marked by nuclear power plant discharges—a situation prevalent along the banks of many large river basins globally. Deuterium excess proved equally effective as a bulk travel time tracer, reflecting distinct seasonal meltwater signals expected in major European rivers. These findings quantify MAR recovery rates and wellhead protection zones, supporting sustainable groundwater management under natural and anthropogenic pressures.

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Fig. 1: NPPs and MAR in major river basins.
Fig. 2: The Hardwald MAR site near Basel, Switzerland.
Fig. 3: Time series of measured isotopic values of infiltrate and abstracted water.
Fig. 4: Transfer functions derived for d-excess and 3H using non-parametric deconvolution.
Fig. 5: Travel time distributions derived from observed tracer levels across the Hardwald MAR scheme.

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Data availability

Records of tritium in rivers, and the exact locations of the stations considered in this Article, can be accessed through the International Atomic Energy Agency (IAEA) Global Network of Isotopes in Rivers (GNIR) database at https://nucleus.iaea.org/wiser. The measured isotope time series presented in this publication can be accessed via CUAHSI’s online collaboration platform, HydroShare, at http://www.hydroshare.org/resource/e3b0781994ed447cad10364e9c880652.

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Acknowledgements

We thank Hardwasser AG and IWB for their support during the experimental stage of this study. We thank K. Solomon for the fruitful discussions within the framework of the IAEA CRP F33029. We acknowledge T. Wagner for his assistance with the tritium measurements. This work was supported by the Swiss National Science Foundation’s (SNSF) and the Japan Society for the Promotion of Science’s (JSPS) Strategic Japanese-Swiss Science and Technology Programme (SJSSTP) grant 214048 as well as the SNSF BRIDGE project 218621.

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Authors and Affiliations

  1. Water Resources and Drinking Water, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland

    Jared van Rooyen, Matthias S. Brennwald, Rolf Kipfer & Oliver S. Schilling

  2. Hydrogeology, Department of Environmental Sciences, University of Basel, Basel, Switzerland

    Jared van Rooyen, Annette Affolter Kast & Oliver S. Schilling

  3. Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland

    Torsten Vennemann

  4. Climate and Environmental Physics and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland

    Roland Purtschert

  5. Applied and Environmental Geology, Hydrogeology, Department of Environmental Sciences, University of Basel, Basel, Switzerland

    Annette Affolter Kast

  6. Institute of Biogeochemistry and Pollutant Dynamics and Institute of Geochemistry and Petrology, Swiss Federal Institute of Technology Zurich (ETHZ), Zurich, Switzerland

    Rolf Kipfer

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  1. Jared van Rooyen
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Contributions

J.v.R., R.K. and O.S.S. conceived and designed research; T.V. and R.P. performed sample analysis, J.v.R., T.V., R.P., M.S.B., A.A.K. and O.S.S. analysed/modelled data and performed research; J.v.R., O.S.S., M.S.B. and R.K. analysed and discussed results; J.v.R. and O.S.S. prepared all figures; J.v.R. and O.S.S. wrote the paper with important contributions from all authors.

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Correspondence to Jared van Rooyen.

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van Rooyen, J., Vennemann, T., Purtschert, R. et al. Anthropogenic tritium as a continental-scale tracer in river-derived recharge. Nat Water (2026). https://doi.org/10.1038/s44221-026-00616-x

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