Seasonal Variations of Groundwater Chemistry in the Basement and Sedimentary Rocks of Ibadan and Lagos Areas, Southwestern Nigeria

Anthony Temidayo Bolarinwa

doi:10.5539/esr.v7n1p55

Abstract

Hydrochemical investigation of forty boreholes drilled on the basement and sedimentary rocks in Ibadan and Lagos metropolis southwestern Nigeria respectively were carried out in order to determine the portability of the groundwater in both areas and to highlight differences in their chemical characters and variations with seasons. Data obtained indicated that the groundwater in Ibadan area is mainly the Na + Ca – HCO3type, while that of Lagos is Na + Ca – C1 + SO4 type. The groundwater chemistry reflects weathering of sodic plagioclase feldspars in the basement rocks as well as arkosic sandstone in the sedimentary terrain. The higher chloride (ca. 124.2 mg/L) content of the Lagos water is probably due to salt-water intrusion along the coastal area. Elevated Na+ (58.5-1021.2), Fe2+ (0.3-2.8) and Mn2+ (0.04-2.34) mg/L concentrations, particularly during the dry season, adversely affect the portability of the water from both localities. Apart from making the water unsuitable for irrigation, high Na+ content is considered harmful to persons suffering from cardiac, renal and circulatory diseases. The Fe2+and Mn2+ contents could also create staining problem. It is therefore desirable to remove these elements from the borehole water prior to consumption.

Highlights

1.1 Background and ObjectiveHarnessing groundwater for developmental purposes require adequate knowledge of the geologic and chemical properties of the aquifers
Total dissolved solids (TDS) are relatively higher in the sedimentary water compared to the basement water
Geological studies show that the Na2+ and Ca2+ in the basement water may be sourced from the weathering of plagioclase feldspars present in the bedrock, while salt-water intrusion may be implicated in the sedimentary area

Summary

Introduction

1.1 Background and ObjectiveHarnessing groundwater for developmental purposes require adequate knowledge of the geologic and chemical properties of the aquifers. Despite the immense benefits of increased irrigation for food production most especially during the dry season (Kemp & Hafi 2001), there are reported cases of excess intake of inorganic compound from drinking water in Africa and most especially nitrate in agricultural areas with heavy use of fertilizers (UNESCO, 1997-1998). Aesthetic problems such as bad odour, taste or staining caused by iron, hydrogen sulphide and manganese may adversely affect optimum utilization of groundwater

Results

Discussion

Conclusion