Water Quality Aspects of River Okpoka in Relation to Watershed Activities

The quality of River Okpoka in south-south Nigeria was investigated by a field survey during the dry season. Water and sediment samples were collected from three sites (capturing the activities in an Abattoir, a market and residential community) along the River course. Three fish species (Tilapia sparrmanii, Mugilcephalus and Clariasgariepinus) were also collected for heavy metal analysis. Samples were analysed for microbiological and physicochemical parameters using standard methods. Heavy metals (Ni, Fe, Pb, Hg, Zn, Cr and Cd) in water, sediment and fish samples were carried out using Atomic Absorption Spectrophotometer (AAS). Descriptive statistics and Pearson correlation were used to analyze data at P Cd>Fe>Pb>Zn>Cr>Hg. Heavy metal values from sediment recorded low concentrations, with Fe (60.60–73.40mg/kg), Zn (2.58–5.93mg/kg) and Cr (3.00–9.50mg/kg) recording significant values in relative order of Fe>Cr>Zn>Pb>Ni>Cd>Hg. Cr (2.50–5.00mg/kg) and Ni (1.40–6.60mg/kg) in fish species were at elevated levels, with relative order of abundance in the order Cr>Fe>Ni>Zn>Cd>Pb>Hg. Significant correlations at p<0.01 were recorded for Conductivity with TDS (+1.00**), and pH A Fe and Pb (–0.946**), Cr and Cd (–0.870*), Zn and Cd (–0.869), Ni and Cd (+0.867*). Water quality index value of 22 indicated that River Okpoka is almost always threatened or impaired; conditions usually depart from natural or desirable levels. The heavy metal species and some physical and chemical parameters in the River Okpoka were to a large extent above the WHO limits; and thereby pose a health risk to rural communities who rely heavily on the river primarily as their source of domestic water. The study revealed a need for continuous pollution monitoring and management program of surface water in River state and Nigeria as a whole.