Hydrochemistry, hydrogen and oxygen isotopes, and radon in waters of the greater Timbavati catchment, South Africa

Abstract

A baseline study was conducted to gain a better understanding of the relationship between groundwater, geology, and geography of the Greater Timbavati Area, to advance the knowledge of hydrostratigraphical settings affected by various socioeconomic and environmental factors. Samples were collected from both surface water and groundwater and were taken in both nature reserves and rural communities for comparison. An Aquaread AP-5000 probe was used to measure basic water chemistry parameters as well as nitrates, ammonium, and ammonia in the field. Samples were also taken and analysed for radon using a Durridge RAD7. Rainwater samples were also collected from two sites for hydrogen and oxygen isotope analysis using a Los Gatos Research (LGR) Liquid Water Isotope Analyzer. There are noticeable differences between the surface water and groundwater chemistry and isotopic signatures. Groundwater samples have a mean TDS of 1217 mg/l and pH of 7.5 while surface water samples have a mean TDS of 332 mg/l and pH of 8.3. A close correlation between land use and nitrate concentrations is observed with higher values being found in groundwater in the more developed areas, over 500 mg/l, suggesting human and agricultural contamination. Unfortunately, there also appears to be no relationship between radon concentration and the underlying geology with mean values in groundwater ranging from 188 Bq/m3 to 51400 Bq/m3 .