Redox control on trace element geochemistry and provenance of groundwater in fractured basement of Blantyre, Malawi

Abstract

pH effect on species variations was tested using PHREEQC modeled main species. Two redox states of groundwater were identified using USGS redox scheme. d18O varied between -5.89‰ and -3.32‰ while d2H ranged between -36.98‰ and -20.42‰. d2H/d18O ratios revealed the groundwater was of meteoric origin. d-Excess suggested minimal impact of secondary evaporative processes on isotopic signature. Assessment of redox state, pH, environmental isotope ratios (d18O, d2H) coupled with PHREEQC speciation modeling investigations were conducted to understand trace element geochemical controls in basement complex aquifer in Blantyre, Malawi. Groundwater in the area is typical Ca-Mg-Na-HCO3 type suggesting more of carbonate weathering and significance of carbon dioxide with dissolution of evaporites, silicate weathering and cation exchange being part of the processes contributing to groundwater mineralization. The significance of pH and redox status of groundwater was observed. The groundwater...