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\begin{document}

\title{Constraining the Spatial Distribution of Tritium in Groundwater across
South Africa}



\author[1]{Jared David van Rooyen}%
\author[2]{Jodie Miller}%
\author[1]{Andrew Paul Watson}%
\author[3]{Laszlo Palcsu}%
\affil[1]{Stellenbosch University}%
\affil[2]{University of Stellenbosch Faculty of Science}%
\affil[3]{Isotope Climatology and Environmental Research Centre, Institute for Nuclear Research}%


\vspace{-1em}



  
  \date{June 13, 2024}


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\begin{abstract}
Tritium (\selectlanguage{ngerman}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
(\textless{}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.%
\end{abstract}\selectlanguage{ngerman}%



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