HEAVY METAL GEOCHEMISTRY OF OGUTA LAKE, SOUTH-EASTERN, NIGERIA

The prevalence of natural events like erosion and flooding; and other anthropogenic activities such as oil spills, urbanization, industrial operations and sand mining activities within the Oguta Lake could constitute heavy metals pollution in the lake. In order to evaluate the heavy metal geochemistry of the Oguta Lake, seventy-two (72) samples of water and sediment were collected and analyzed over the periods of dry and rainy seasons. Concentrations of As, Cd, Cr, Fe, Ni, Hg, Pb and Zn were determined using Atomic Absorption Spectrometry AAS. The mean concentrations of water samples (mg/l) were 0.006±0.002, 0.001±0.001, 0.023±0.003, 0.213±0.025, 0.004±0.002, 0.008±0.002, 0.010±0.003, and 1.971, ±0.043 respectively for the rainy season. Result of water analysis during the dry season were 0.007±0.001, 0.002±0.001,0.029±0.010, 0.218±0.031, 0.007±0.001, 0.010±0.002, 0.012±0.002, and 1.981±0.036, respectively. The mean concentration of heavy metal in bottom sediment (mg/kg dry weight) for the rainy season were 1.953±0.143, 0.096±0.007, 20.28±0.804, 3426.4±374.5, 2.693±0.609, 0.141±0.008, 26.33±0.977 and 41.36±1.405, respectively. While the results obtained during the dry season were 1.978±0.120, 0.097±0.008, 20.36±0.881, 3484.8±326.02, 2.793±0.589, 0.146±0.004, 26.61±0.872 and 41.89±1.414, respectively. Apart from Pb, the values of the other heavy metals were in conformity with the WHO and USEPA regulations. Seasonal and spatial variations were observed in the concentration levels of heavy metals. Heavy metal pollution index of 40.71% and 39.08% for the dry and rainy season, respectively, suggest that the Oguta Lake water can be classified as Good. Except for lead Pb, the other analyzed heavy metals showed no sign of enrichment in sediment. The Pearson correlation of multivariate analysis of variance (MANOVA) were used to analyze the inter-relationship between heavy metals in water and bottom sediment for the dry and rainy seasons. Traceability analysis of PCA shows that the origins of heavy metals of component 1, which includes As, Cd and Pb are from a mixture of natural (materials of parent rock) and anthropogenic sources.