Rooyen et al. (2026) Anthropogenic tritium as a continental-scale tracer in river-derived recharge

Identification

• Journal: Nature Water
• Year: 2026
• Date: 2026-03-23
• Authors: Jared van Rooyen, Torsten Vennemann, Roland Purtschert, Annette Affolter Kast, Matthias S. Brennwald, Rolf Kipfer, Oliver S. Schilling
• DOI: 10.1038/s44221-026-00616-x

Research Groups

• Water Resources and Drinking Water, Eawag, Swiss Federal Institute of Aquatic Science and Technology (Dübendorf, Switzerland)
• Hydrogeology, Department of Environmental Sciences, University of Basel (Basel, Switzerland)
• Institute of Earth Surface Dynamics, University of Lausanne (Lausanne, Switzerland)
• Climate and Environmental Physics and Oeschger Center for Climate Change Research, University of Bern (Bern, Switzerland)
• Institute of Biogeochemistry and Pollutant Dynamics and Institute of Geochemistry and Petrology, Swiss Federal Institute of Technology Zurich (ETHZ) (Zurich, Switzerland)

Short Summary

This study evaluates anthropogenic tritium (³H) and natural stable isotopes (δ¹⁸O, δ²H, deuterium excess) as tracers to quantify groundwater flow dynamics and travel times in an alluvial Managed Aquifer Recharge (MAR) system along the Rhine River in Switzerland, demonstrating their effectiveness for sustainable groundwater management.

Objective

• To evaluate anthropogenic and natural water isotopes (δ¹⁸O, δ²H, ³H) as tracers of groundwater flow dynamics within alluvial Managed Aquifer Recharge (MAR) systems.
• To quantify the movement of infiltrated river water through an alluvial aquifer and predict travel times throughout the entire MAR scheme.

Study Configuration

• Spatial Scale: An alluvial aquifer along the Rhine River in Switzerland, specifically the Hardwald MAR site near Basel. The findings are discussed in the context of continental-scale applicability for large river basins globally.
• Temporal Scale: High-resolution sampling (daily/weekly) of stable isotopes and tritium was conducted over a period sufficient for time-series deconvolution to quantify tracer-based travel time distributions.

Methodology and Data

• Models used: Time-series deconvolution (specifically, non-parametric deconvolution) was applied to quantify tracer-based travel time distributions and predict travel times.
• Data sources:
  • High-resolution (daily/weekly) in-situ sampling of stable isotopes (δ¹⁸O and δ²H) and tritium (³H) from infiltrated river water and abstracted groundwater.
  • Tritium concentrations were influenced by nuclear power plant effluents.
  • Records of tritium in rivers and station locations from the International Atomic Energy Agency (IAEA) Global Network of Isotopes in Rivers (GNIR) database (https://nucleus.iaea.org/wiser).
  • Measured isotope time series accessed via CUAHSI’s online collaboration platform, HydroShare (http://www.hydroshare.org/resource/e3b0781994ed447cad10364e9c880652).

Main Results

• Tritium (³H), influenced by nuclear power plant discharges, proved suitable as a quasi-conservative travel time tracer in alluvial MAR systems, a situation common in many large river basins globally.
• Deuterium excess was equally effective as a bulk travel time tracer, accurately reflecting distinct seasonal meltwater signals characteristic of major European rivers.
• The study successfully quantified MAR recovery rates and delineated wellhead protection zones using these isotopic tracers.
• Tracer-based travel time distributions were derived and used to predict travel times across the entire MAR scheme.

Contributions

• Demonstrates the novel application and suitability of anthropogenic tritium, originating from nuclear power plant effluents, as a quasi-conservative, continental-scale tracer for quantifying groundwater flow dynamics and travel times in MAR systems.
• Provides a robust methodology using high-resolution isotopic sampling and time-series deconvolution to quantify MAR recovery rates and define wellhead protection zones, directly supporting sustainable groundwater management.
• Highlights the complementary role of natural deuterium excess as an effective bulk travel time tracer, reflecting seasonal hydrological signals in river-derived recharge.

Funding

• 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.
• SNSF BRIDGE project 218621.
• International Atomic Energy Agency (IAEA) CRP F33029 (for discussions).

Citation

@article{Rooyen2026Anthropogenic,
  author = {Rooyen, Jared van and Vennemann, Torsten and Purtschert, Roland and Kast, Annette Affolter and Brennwald, Matthias S. and Kipfer, Rolf and Schilling, Oliver S.},
  title = {Anthropogenic tritium as a continental-scale tracer in river-derived recharge},
  journal = {Nature Water},
  year = {2026},
  doi = {10.1038/s44221-026-00616-x},
  url = {https://doi.org/10.1038/s44221-026-00616-x}
}