Seawater intrusion and freshwater–saltwater interface dynamics in central coastal communities of Ghana: a hydrogeochemical perspective
摘要
In southern Ghana, coastal aquifers are a significant water source but are frequently compromised by seawater intrusion, making them unsuitable for drinking and agriculture. This study evaluates seawater intrusion in central coastal communities using integrated hydrogeochemistry and spatial analysis. Sixty-seven groundwater samples from hand-dug wells and boreholes, collected during field measurements, were analysed for major-ion chemistry, nutrients, and metals. The study was analysed using combinations of geochemical plots, hydrochemical indices, and multivariate statistical methods. Total dissolved solids ranged from 120 to 42,431 mg/L (mean 2,158.75 mg/L). 26.47 per cent of the samples exceeded 1,500 mg/L for TDS. Thirty-nine per cent exceeded 200 mg/L for Na+, and 20.59 per cent exceeded 600 mg/L for Cl−. TDS correlated strongly with Cl− (r = 0.95) and Na+ with Cl− (r = 0.93). EC–TDS ratios of 0.5–0.7 and Na+–Cl− dominance on Piper plots indicated marine mixing. Gibbs plots showed rock-water control at moderate salinity and evaporation–mixing at high salinity. Evaporite phases remained undersaturated, supporting mixing and concentration rather than in situ salt dissolution. Positive chloro-alkaline indices signalled reverse ion exchange along saline fringes. Multivariate results separated two regimes. A large carbonate-buffered group represented inland fresh to slightly brackish waters. A smaller Na–Cl-rich group aligned with streams and near-coastal sites, localised saline end members and likely pathways for intrusion. This study recommends that water managers and the government prioritise sentinel-well monitoring in hotspots, seasonal pumping controls, protection of inland recharge zones, and targeted recharge enhancement.