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Constraining the Spatial Distribution of Tritium in Groundwater across South Africa
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  • Jared David van Rooyen,
  • Jodie Miller,
  • Andrew Paul Watson,
  • Laszlo Palcsu
Jared David van Rooyen
Stellenbosch University

Corresponding Author:jvanrooyen121@gmail.com

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Jodie Miller
University of Stellenbosch Faculty of Science
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Andrew Paul Watson
Stellenbosch University
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Laszlo Palcsu
Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research
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Tritium (³H) has become synonymous with modern groundwater and is used in a myriad of applications, ranging from sustainability investigations to contaminant transport and groundwater vulnerability. This study uses measured ³H groundwater activities from 722 samples locations across South Africa to construct a ³H groundwater distribution surface. Environmental co-variables are tested using geostatistical analysis to constrain external controls on ³H variability, namely: [1] depth to the water table, [2] distance from the ocean and [3] summer vs winter rainfall proportion. The inclusion of co-variables in the ‘fit’ of residual variograms improved prediction variance significantly, yet does not mitigate issues with sample density. The distribution of ³H in groundwater surface agrees well to expected controls, with proximal (<100km) coastal regions, winter rainfall zones and deeper groundwater tables predicted to have lower ³H activities. Conversely, inland localities with shallower water tables and/or summer rainfall are predicted to have elevated ³H activities. High groundwater ³H anomalies could potentially be attributed to uranium-bearing deposits, as geogenic production of ³H amplifies the activity contributed through recharge. Some ³H high and low anomalies cannot be explained by known phenomena and may simply be regions of variable recharge and/or longer isolated groundwater flow paths. Regions of active recharge are more vulnerable to climate change as well as modern pollution. Less actively recharged groundwater may be more resilient to climate change, yet represents a potentially non-renewable resource for abstraction. The application of ³H distributions in the assessment of hydrological resilience is pertinent to effective groundwater management studies.
Aug 2021Published in Water Resources Research volume 57 issue 8. 10.1029/2020WR028985