The use of stable isotopes to identify surface water–groundwater interaction in the Kruger National Park, South Africa

Abstract

The role of groundwater, in general, is often overlooked in freshwater ecosystem management policies and in the management of South Africa’s flagship conservation area, the Kruger National Park (KNP). To address this gap, a generalised conceptual model of surface water–ground water (sw–gw) interactions in the southern and central regions of the KNP was developed. To do this, stable isotope ratios (d¹⁸O and d²H) of groundwater, rainfall and surface water were used to determine the extent to which the base flow of perennial, seasonal and ephemeral streams on different geologies (granite vs. basalt) is driven by rainfall or groundwater. These results show that the δ¹⁸O and δ²H ratios of perennial rivers are similar to that of groundwater, while seasonal and ephemeral rivers on basalts have values closer to rainfall. On granite substrates, however, the isotope ratios of the seasonal and ephemeral rivers have values closer to groundwater than rainfall. The larger seasonal Mbyamiti River had similar isotope ratios to that of groundwater, and the highly ephemeral Nwaswitsontso had episodic interaction with groundwater (i.e. isotopic ratios overlap occasionally). These results show that decisions necessary for the sustainable management of groundwater resources are better informed when the natural interaction, movement, and exchange between groundwater and rivers are understood. This has particular relevance for large conservation areas in southern Africa that are expected to experience more variable climates in the future with both increases in drought and rainfall intensities.