Hydrogeochemical processes in a shallow coastal plain sand aquifer and tidal river systems (Calabar, Southeastern Nigeria): tracking wastewater and seawater pollution in ground and river waters

The coastal part of Nigeria where the study area is located depends on river and groundwater for domestic, agricultural and industrial use. An understanding of the chemical origin of the groundwater provides insight into the interaction of water with the environment and contributes to a better resource management. Data from systematic field sampling and analysis were integrated using descriptive statistics; correlation matrices, bivariant plots, geochemical modelling and a mixing model have been used to gain insight into the hydrogeochemical processes of water in the area. The dominant processes controlling groundwater chemistry are silicate weathering, cation exchange and human activity (waste disposal). The prevalent water type is Na–HCO₃, which make up 67% of all the water samples (53% of river water and 78% of groundwater); Na–HCO₃–Cl make up 19% of all the samples (comprising 20% of river water and 21% of groundwater) and 14% classified as Na–Cl (27% river water; 1% of groundwater). Deterioration in water quality has resulted from tidal flushing for river water and human activity (waste disposal) for groundwater. Presently, the estimated amount of freshwater decreases southwards towards the coast for both river and groundwater. In contrast, the amount of brackish water and wastewater increases southwards for the river water and groundwater, respectively. These findings are important since they contribute to identification of suitable areas for developing water resources that could yield relatively better quality of water and they may lead to strategies that ameliorate groundwater quality.