The concentrations of selected heavy metals in water and sediment samples were collected and determined from three sites in each reservoir (Inlet; Site1-S1, Center; Site2-S2 and Outlet; Site3-S3) for three (3) consecutive months (April to June 2018). Physicochemical parameters (DO, temperature, EC, and pH) were measured at the established three sampling sites using portable Multimeter, while turbidometer was used to measure turbidity. The collected water and bottom sediment samples were analyzed by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) for selected heavy metals (Cu, Zn, Mn, Cr, Cd, Hg, Pb, and As). Data analyzed using Analysis of Variance (ANOVA). Physicochemical parameters except for temperature in Aba-Samuel Reservoir varied spatially although the differences in their levels among sampling sites were not significant (p>0.05).
The highest concentrations of all metals measured in water and sediment samples were recorded for Mn in both Dire (0.236±0.014, 1098.90 ± 13.25) and Aba-Samuel (0.504±0.023, 1198.39± 6.85) reservoirs, respectively. Mean concentrations of all metals except Mn in water samples of Dire Reservoir were not significantly different among sampling sites (P>0.05), while the reverse was true for those of Aba-Samuel Reservoir. Some heavy metals in sediment samples of both reservoirs (e.g. Mn, Cr, and Pb) showed significant variations (P<0.05) among sampling sites while Zn showed spatial variations, which were not significant (P>0.05). The mean concentrations of heavy metals in water samples were all below the guideline values set by WHO (2008) and USEPA (2011) with the exception of Mn in both Reservoirs and Cd in Aba-Samuel Reservoir. Concentrations of Zn, Mn, Cr, and Cd in sediment samples are, however, above the respective reference values (ISQG, 2002; USEPA, 2010), while those of Pb and Cu were below the respective reference values (ISQG, 2002; USEPA, 2010) in both reservoirs.
Keywords: Physicochemical parameters, public health, tropical reservoirs, water pollution