Hydrochemistry of Lakes in Opi Agu, Enugu State, Southeastern Nigeria

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Author(s) D. C. Ozoko
Pages 304-311
Volume 4
Issue 6
Date June, 2015
Keywords Lakes; Total Phosphorous; Eutrophication; Groundwater-Surface Interactions; Leaching.
Abstract

A total of nine lakes and three rivers situated in Opi Agu of southeastern Nigeria was studied. The study area is underlain by (from the oldest), Nkporo Shales, Mamu and Ajali Formations. Two of the lakes were formed in the lower stretches of Ajali Formation while six of them were formed within the Mamu Formation. Only one lake was formed within the Nkporo Formation. The lakes originated as a result of fluvial processes and tectonism associated with the formation of the Nsukka – Okigwe Cuesta. The nine lakes were examined for their hydrogeologic settings,, limnology and hydrochemistry. Three types were identified on the basis of their groundwater – surface interaction and these were seepage, groundwater – drainage and drainage lakes. Limnological evaluation showed that two lakes and two rivers are trending towards eutrophication. Chemical analyses of the lake waters revealed that they have very low solute concentrations possibly due to small residence time of the precipitation in the lakes and their pH ranges from 5.6 to 6.8. Sodium (Na+) and potassium (K+) make up over 90% of the cations while chloride and bicarbonate dominate the anion levels. Hydrochemically the lake waters are of the Na+ - Cl- type. Some of the lakes have excess concentrations of total phosphorous and nitrate-nitrogen. Three trophic classes were identified on the basis of total phosphorous concentration. The excess nitrate – nitrogen levels are due to leaching from adjacent farmlands. The overall Na+ - Cl- composition of the lake waters are due to soil leaching, mixing and evaporation effects.

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