Constraining the Spatial Distribution of Tritium in Groundwater Across South Africa

Water Resources Research
Volume 57: e2020WR028985

Abstract. 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 sample locations across South Africa to construct a 3H groundwater distribution surface. Environmental covariables are tested using geostatistical analysis to constrain external controls on 3H 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 3H 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 3H activities. Conversely, inland localities with shallower depth to groundwater and/or summer rainfall are predicted to have elevated 3H activities. 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 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 3H distributions in the assessment of hydrological resilience is pertinent to effective groundwater management studies.

Read more: https://doi.org/10.1029/2020WR028985