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- The sources of chemical constituents of groundwater and its associated hydrogeochemical processes in the part of Mhlathuze catchment was identified. Groundwater of the area is classified into soft to very hard and the nature is identified as acidic to alkaline. The overall electrical conductivity is < 3000 μS/cm except in three wells. The predominant water type is NaCl (69% of samples) and CaMgCl facies. Gibbs plots, mCa/Mg ratio, mNa/Cl ratio, Ca + Mg vs HCO3+SO4 plot, Na + K vs HCO3 plot, Ca/Na vs HCO3/Na, Chloroalkaline indices (CAI 1, CAI 2) and Ca + Mg–HCO3–SO4 vs Na + K–Cl plots confirm the impact of silicate, carbonate mineral weathering and ion exchange reaction in this aquifer. However, few wells are influenced by the evaporation process. Groundwater is highly undersaturated with sulphate, chloride minerals and saturated with carbonate minerals. CA revealed that Cl and SO4 are derived from anthropogenic sources and a significant positive correlation between HCO3 and Cl reveals that wastewater recharge has most likely simulated the mineral weathering in the vadose zone, which could have further enhanced HCO3 and Cl in the aquifer. PCA resulted in three factors. Factor 1 defines the influence of geogenic and anthropogenic processes while Factors 2 and 3 imply the mineral weathering and nitrification processes. Hierarchical cluster analysis defines that evaporation, anthropogenic input, silicate and carbonate weathering and nitrification process are the sources of chemical constituents of groundwater in this aquifer.
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- Impact of irrigation return flow induced mineral weathering and ion exchange reactions in the groundwater was studied in Limpopo region, South Africa. Based on EC (>500) and HCO3 (>150mg/l), groundwater samples are classified into two groups due to its heterogeneous nature. Water types in group 1 and 2 wells are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3, respectively. Gibbs plots, bivariate plots and ionic ratios (Mg/Na vs Ca/Na; HCO3/Na vs Ca/Na; mCa + Mg vs mHCO3; mNa + K vs mHCO3; Ca + Mg-HCO3-SO4 vs Na + K-Cl; mCa + Mg/HCO3 vs Cl; Ca + Mg/SO4 +HCO3 >1; Na/Cl ratio; Cl + SO4 vs HCO3), chloro alkaline indices (CAI, CA2) and Pearson correlation analysis imply that groundwater chemistry is influenced by mineral weathering (carbonate > silicate minerals), reverse ion exchange and irrigation return flow. In group 1 wells, Cl + SO4 and HCO3 have strong positive correlation and both increases together, suggesting induced mineral weathering caused by nitrification and wastewater infiltration from the surface. Group 2 wells are generally deep with low groundwater level fluctuation and high concentration of major ions. Overall, water chemistry in the group 1 wells is highly affected by the contamination sources than group 2 wells.
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