Constraining the Spatial Distribution of Tritium in Groundwater Across South Africa
Jared van Rooyen, Andrew Watson, László Palcsu, Jodie Miller
Abstract
Abstract Tritium ( 3 H) 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 3 H groundwater activities from 722 sample locations across South Africa to construct a 3 H groundwater distribution surface. Environmental covariables are tested using geostatistical analysis to constrain external controls on 3 H variability, namely: (a) depth to groundwater, (b) distance from the ocean, and (c) summer versus winter rainfall proportion. The inclusion of covariables in the “fit” of residual variograms improved prediction variance significantly yet does not mitigate issues with sample density. The distribution of 3 H in groundwater agrees well to expected controls, with proximal (<100 km) coastal regions, winter rainfall zones, and greater depth to groundwater predicted to have lower 3 H activities. Conversely, inland localities with shallower depth to groundwater and/or summer rainfall are predicted to have elevated 3 H activities. Some 3 H 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 that receive modern groundwater 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 nonrenewable resource for abstraction in South Africa. The application of 3 H distributions in the assessment of hydrological resilience is pertinent to effective groundwater management studies.