Using Environmental Tracers to Characterize Groundwater Flow Mechanisms in the Fractured Crystalline and Karst Aquifers in Upper Crocodile River Basin, Johannesburg, South Africa

Abstract

Environmental isotope tracers were applied in the Upper Crocodile River Basin, Johannesburg, South Africa, to understand the groundwater recharge conditions, flow mechanisms and interactions between surface and subsurface water. Stable isotope analysis indicated that recharge into the fractured quartzite aquifer occurs through direct mechanisms. The high variability in the stable isotope signature of temporal samples from Albert Farm spring indicated the importance of multiple samples for groundwater characterization, and that using a single sample may be yielding biased conclusions. The observed inverse relationship between spring discharge and isotope signature indicated the traces of rainfall amount effect during recharge, thereby suggesting piston groundwater flow. It is deduced that a measured discharge value can be used in this relationship to calculate the isotopic signature, which resembles effective rainfall. In the shallow alluvial deposits that overlie the granitic bed-rock, piezometer levels and stable isotopes revealed an interaction between Montgomery stream and interflow, which regulates streamflow throughout the year. This suggests that caution should be taken where hydrograph separation is applied for baseflow estimates, because the stream flow that overlies such geology may include significant interflow. The hydrochemistry evolution was observed in a stream fed by karst springs. As pH rises due to CO2 degassing, CaCO3 precipitates, thereby forming travertine moulds. The values of saturation indices that were greater than zero in all samples indicated supersaturation by calcite and dolomite and hence precipitation. Through 14C analysis, groundwater flow rate in the karst aquifer was estimated as 11 km/year, suggesting deep circulation in karst structures.

Assessment of Water Quality Changes Using Physical Parameter and Stable Isotope in Ciliwung River

“…The pH level is a significant factor in assessing the appropriateness of water for different purposes [43]. Hydrochemical fluctuations were visualized by creating plots of pH concerning electrical conductivity (EC) and oxidation-reduction potential (ORP) [51]. The upstream area exhibits a lower oxidation-reduction potential (ORP).…”

Hydrochemical and Stable Isotope Analyses Show Limited Interactions Between Groundwater and Lake Water in the Lake Bosomtwi Impact Crater, Ghana.

“…The investigation of environmental isotopes of natural waters has proven in recent studies to be a relevant tool in the management and assessment of water resources. This enables deductions with regard to the recharge mechanism, identification of recharge and discharge areas, (Gopinath et al, 2021;Leketa and Abiye, 2021), aquifer interconnectivity and groundwater turnover time (IAEA, 1983;Chen et al, 2006;Doveri and Mussi, 2014) and to identify interactions between groundwater and surface water (Ojiambo et al, 2001;Zhang et al, 2016, Zhu et al, 2019Leketa and Abiye, 2021).…”

“…These isotopes have equally been valuable in tracking the groundwater flow paths, evaluate residence time and aquifer discharge, identifying paleo waters, --investigating water-rock interactions (Abid et al, 2010;Pu et al 2020;Zhang et al, 2020;Zhou et al, 2021;Carreira et al, 2021). For instance, Leketa and Abiye (2021) used stable isotopes of δ 18 O and δD to show that recharge into the fractured quartzite aquifer of the Upper Crocodile River Basin occurs through direct mechanisms. Likewise, stable isotopes were used by Dogramaci et al (2012), to evaluate the groundwater recharge in dry and semi-arid areas where high-intensity rain is supposed to control recharge.…”