Assessment of impact of climatic change on groundwater quality around Igbokoda Coastal area, southwestern Nigeria

Hydrochemical assessment of 39 groundwater samples within Igbokoda coastal zone are presented and discussed in terms of impact of coastal saltwater on the quality and subsequent hydrochemical evolution. The pH range from 6.8 to 9.8, temperature from 28.3 to 33.5oC, EC from 67 to 2440µS/cm and TH from 66.36 to 369.22mg/L. Hydrochemical results showed higher concentrations of Na+ (3.56 – 624.14mg/L) compared to Ca2+ (19.21 – 104.32mg/L), K+ (1.49 – 62.94mg/L) compared to Mg2+ (3.36 – 75.01mg/L) and Cl- (72.0 – 2592.00mg/L) compared to HCO3- (15.25 – 152.50mg/L). This hydrochemical profile reflects a Na-Cl dominated water type suggesting impact of salt water on the groundwater system. Nonetheless, with the exception of higher Cl- values, the major ions concentrations are within recommended WHO standard for drinking water while the concentrations of Fe (0.01-13.4mg/L) and Mn (0.00-1.00mg/L) above the WHO guideline values in about 88% and 35% of the samples respectively call for concern. Estimated major ionic ratios such as Mg/Ca (0.13 – 3.09), Cl/HCO3 (1.18 – 25.50) signify brackish water in most of the locations due to impact of saltwater mixing. This is clearly reflected in the water characterization that revealed largely Na-(K)-Cl-SO4 water type as brackish water and minor occurrence of Ca-(Mg)-HCO3 water type as freshwater sources