Depth variations in the chemistry of Oguta Lake in Southeastern Nigeria

Monthly changes in the depth profiles of some chemical characteristics were studied for Oguta Lake, the largest natural lake in the southeastern region of Nigeria. The investigations were conducted from May, 1982, to April, 1983. Hydrogen ion concentration, salinity and alkalinity did not show significant variations with depth. Nitrate-nitrogen showed no definite pattern but in February, October and November, distinct metalimnetic nitrate maxima occurred. Silica was approximately homogeneously distributed with slight negative heterograde curves in February and October. Total phosphorus levels were relatively lower in the bottom water but the most distinct discontinuity occurred in November when a metalimnetic maximum co-occurred with a nitrate-nitrogen maximum. Dissolved oxygen concentration showed a consistent clinograde profile typical of thermally stratified eutrophic waters (WETZEL, 1975). Biochemical oxygen demand values followed the dissolved oxygen pattern very closely.