Investigation of Ojirami reservoir, Akoko-Edo, Southsouth, Nigeria: the physical and chemical hydrology

Abstract

Ojirami Reservoir was constructed between 1971 and 1974 for the purpose of supplying potable water to Edo North senatorial zone, Nigeria. The reservoir is aging, with evidence of siltation but relatively free of any anthropogenic activities. A study was carried out between January 2009 and December 2010 to monitor the monthly and seasonal variations in the limnological variables. Water samples were collected monthly from six stations (A, B, C, D, E and F) and analyzed following standard methods. Water temperature, depth and varied from 24.0-33.0 ^oC, and 0.62-5.2 m. Turbidity varied from 0-150 NTU, total dissolved and suspended solids - 25.00 – 82.00 ppm and 0–105mg/l respectively, pH - 5.7–8.6, conductivity - 50–150 μS/cm, alkalinity - 6.0-67.0 mg/l and chloride - 4.0–28 mg/l. , and total hardness, dissolved oxygen, biochemical oxygen demand and free CO₂ varied between 22.0 – 98.0 mg/l, 2.3–6.8 mg/l, 0.1–3.7 mg/l and 8.0-75 mg/l; Phosphate, sodium, potassium and iron were between 1.0–23.4 mg/l, 4.6–10.1mg/l, 2.7–8.7 mg/l and 0.8–13.46 mg/l respectively. Mean values at the study stations were statistically not significant (P>0.05) except depth (P<0.01). The Duncan multiple range test revealed that mean depth was highest at station C. However wet and dry season comparison showed significant difference (P<0.05) in turbidity, total dissolved solids, and total suspended solids; and highly significant difference (P<0.01) in conductivity, alkalinity, iron and phosphate, with higher wet season mean values in all except depth and alkalinity that recorded higher dry season means. Some of the measured physical and chemical parameters were within the acceptable or permissible limits of Standards Organization of Nigeria (SON) and World Health Organization (WHO) guidelines for drinking water. However, total suspended solids, dissolved oxygen, biochemical oxygen demand, phosphate and iron were far above recommended standards

Keywords: Akoko-Edo, physico-chemical conditions, seasonality, regulatory standards