Major ions and trace elements partitioning in unsaturated zone profile of the Densu river basin, Ghana and the implications for groundwater

Abstract

Soil solution samples were extracted from a vertical unsaturated zone profile and groundwater samples were obtained from the Densu river basin, Ghana. Major ions and trace metals in the soil solution, groundwater samples and solid soil (Ca2+, Na+, Mg2+, K+, NO3-, SO42-, Cl-, HCO32-, PO43-, Fe, Mn, V, Cu, Zn, Cr) were analyzed along with other hydrochemical parameters. Impact of the unsaturated zone soil solution chemistry on the groundwater and metal mobility and potential of leaching into the groundwater system have been evaluated. The groundwater were characterized by slightly alkaline pH (6.22 to 6.67), EC (98.8 to 382.0 µS/cm), TDS (49.7 to 192.4) and total alkalinity (43.63 to 149.14 mg/L). Calcium was the dominant cation, with major amounts of sulphate, chloride, nitrate and carbonate species present. Na/K cations dominated the leached soil-solution with SO42-and Cl- anions. Soil−liquid partitioning coefficients (Kd) for the metals Fe, Cu, Mn, Cr, V and Zn evaluated after experimental determinations showed wide variability within the profile. The relationships between the calculated values were explored relative to variations in soil solution pH, soil organic carbon (SOC), and concentrations of total soil metal. The results of the empirical linear regressions showed Kd values were best predicted with total soil metal contents (with R2 values of 0.04 to 0.69). Key words: Unsaturated zone, groundwater, major ions, trace elements, partitioning coefficient