Investigation of the Hydrological Quality of Ethiope River Watershed, Southern Nigeria

The surface and groundwater resources of the Ethiope river watershed have been investigated for its hydrological and quality characteristics. The results indicate that Ethiope River is perennial and fed by groundwater seepages, precipitation and surface run-off from adjacent areas. The lowest discharge rate of the river is recorded in June and increases steadily reaching its peak in October. The physico-chemical parameters of both water sources include, pH (5.28-7.06), turbidity (1.16 – 8.12 NTU), conductivity (65.00- 127.0 μs/cm), dissolved oxygen (4.40-7.60 mg/l) and total hardness (25.50 – 45.0 mg/l). Others include, Na+ (3.91 – 27.05 mg/l), K+ (3.91 – 8.73 mg/l), Ca2+ (3.21 – 9.60 mg/l), Mg2+ (1.46- 5.84 mg/l), HCO3- (31.50-80.00 mg/l), Cl- (17.55 –35.10 mg/l), SO42- (0.25-0.58 mg/l), NO32- (0.19-0.55 mg/l) and PO42- (0.20-19.00 mg/l). This physico-chemical quality is generally compatible with WHO guideline for domestic use. Nevertheless, the water samples consist of high microbial population including total coliform bacteria counts (39.00 – 1100 MPN/100ml) and Escherichia coli (21.00 – 305.00 MPN/100ml), which render both surface and groundwater unfit for domestic use without disinfection. An assessment of surface water-groundwater homogeneity using the parametric student’s t and F tests on selected constituents (chloride, nitrate, sulphate, phosphate, sodium, potassium, calcium and magnesium), indicate non-significance in the variation within the tested parameters except for nitrate. This suggests some groundwater-surface water intermixing or communication, and the activity of denitrifying bacteria in surface water. A groundwater pollution vulnerability assessment using DRASTIC model indicates moderately high pollution risk level for the aquifer system