The Hydrochemical Characteristics and Evolution of Groundwater in Semiarid Yola Area, Northeast, Nigeria

Gabriel I. Obiefuna；Donatus M. Orazulike

Chemical indicators ； dissolution ； hydrgeochemical studies ； Nigeria ； Yola area

Research Journal of Environmental and Earth Sciences

3卷4期（2011 / 06 / 05）

400 - 416

英文

The aim of the study is to characterize groundwater in semiarid Yola area of northeastern Nigeria employing chemical indicators. The dissolution of halite, gypsum, dolomite and calcite determines Na^+, Mg^(2+), Ca^(2+), Cl^-, SO_4^(2-) and HCO_3^- chemistry while other processes such as evaporation and ion exchange also influence the water composition. Surface water and groundwater chemistry data enabled geographical zones and chemical types to be differentiated. Groundwater in the study area is slightly acidic to neutral in nature. Chemistry of groundwater suggests that alkaline earths (Ca+Mg) significantly exceed the alkalis (Na+K) and weak acids (HCO_3+CO_3) exceed the strong acids (Cl+SO_4), suggesting the dominance of CO_3 weathering followed by silicate weathering. Hydrogeochemical studies disclosed that Na^+-HCO_3^- and Na^+-Cl^- are the dominant ion types for the shallow groundwater (＜25 m), Mg^(2+)-Cl^-, Mg^(2+)-HCO_3^- and Na^+-Cl^- for the deep groundwater (＞25 m) and Na^+-Cl^- for the surface water bodies. A high positive correlation (r^2=0.87) between Na+ and Cl^- suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Chemical fertilizers and anthropogenic activities are contributing to sulphate, nitrate and chloride concentrations measured in some surface water and groundwater samples in the study area as evidenced by the relatively high sulphate, nitrate and chloride concentrations. Most of the groundwater samples are suitable for domestic purposes.