Hydrochemical Evolution and Seawater Intrusion Processes in Coastal Aquifers of the Niger Delta, Nigeria

Abstract

Groundwater quality deterioration and seawater intrusion have become major environmental concerns in the coastal aquifers of the Niger Delta due to increasing urbanisation, industrial activities, and intensive groundwater abstraction. This study evaluated the hydrochemical evolution and seawater intrusion processes in selected coastal aquifers of the Niger Delta, Nigeria, using physicochemical parameters, major ions, heavy metals, Water Quality Index (WQI), hydrochemical facies, and multivariate statistical techniques. Ten groundwater samples were collected from boreholes and analysed following the American Public Health Association (APHA) standard methods, while the results were compared with the World Health Organization (WHO) drinking water guidelines. Groundwater pH ranged from 6.42 to 7.81, indicating slightly acidic to neutral conditions. Electrical conductivity varied between 284.00 and 2,756.00 \(\mu\)S/cm, whereas total dissolved solids ranged from 176.30 to 1,745.80 mg/L, reflecting progressive salinity towards the coastal environment. Sodium (18.50–462.70 mg/L) and chloride (22.40–785.60 mg/L) were the predominant ions, indicating increasing marine influence within the aquifer system. Elevated concentrations of iron (Fe; 0.08–1.62 mg/L), lead (Pb; 0.001–0.048 mg/L), cadmium (Cd; 0.000–0.009 mg/L), and arsenic (As; 0.001–0.018 mg/L) exceeded the recommended drinking water limits at some sampling locations, suggesting contributions from both geogenic and anthropogenic sources. Hydrochemical facies analysis revealed a transition from calcium–bicarbonate (Ca–HCO3) water in inland areas to sodium–chloride (Na–Cl) water in the coastal communities, indicating hydrochemical evolution controlled by ion exchange, mineral dissolution, and seawater mixing. Water Quality Index values ranged from 38.4 to 112.8, classifying groundwater as excellent (38.4–49.6), good (58.7–95.4), and poor (101.5–112.8). Therefore, groundwater quality showed progressive deterioration towards the coastline due to increasing salinity and trace metal enrichment. The findings highlight the vulnerability of coastal aquifers to seawater intrusion and groundwater quality degradation. Therefore, continuous groundwater quality monitoring, regulated groundwater abstraction, and integrated coastal aquifer management are recommended to minimise seawater intrusion and ensure the long-term sustainability of potable groundwater resources in the Niger Delta.