Evaluation of water quality using hydrochemistry, stable isotopes, and water quality indices in the Lower Volta River Basin of Ghana

Abstract

The Lower Volta River Basin of Ghana is an important international and local tourism destination. Communities in the basin depend on shallow aquifer systems, the Volta River, and nearby streams as their sources of water for domestic purposes, cattle watering, and irrigation. Due to increasing human activities and limited information on water quality in the area, a holistic assessment of the quality of the water resources in the basin was conducted using hydrochemistry, δ2H and δ18O, principal components analysis, and selected indices. EC ranged from 141 to 19,370 μS/cm and 60.9–986 μS/cm for shallow groundwater and surface water respectively. NO3− levels above 45–1049.9 mg/l were observed in 45% of analyzed wells. Na–Cl- and HCO3–Ca-dominant facies are identified. Silicate weathering, evaporite dissolution, cation exchange, and salinity are the hydrochemical processes influencing the shallow groundwater in the area. δ2H–δ18O‰ plot showed meteoric shallow groundwater recharge. Ion ratios, EC, and Cl− versus δ18O‰ relationships suggest dissolution and seawater intrusion as causes of groundwater salinity. Hydrochemistry, principal components analyses, and NO3− versus δ18O showed evidence of anthropogenic pollution on water in the basin. All analyzed surface water and 79% of well samples were within suitable range for irrigation. Based on the CCMEWQI model criteria, 85% of the surface water were in good-to-excellent categories while majority of the shallow groundwater were in fair, marginal, and poor categories. The combined approach provided vital information on water quality in the basin. Strategic control measures were proposed.