Holomixis and stratification patterns of a Northern Nigeria Lake
This study investigated the holomixis and stratification patterns of Lake Tiga, Nigeria’s second largest artificial lake, from March 2009 to March 2011. Samples were collected at the dam site of the lake every six weeks, from the surface (0 m) down to the bottom (20-30 m), at 5 m depth interval using a 2-liter Van Dorn water sampler. Water temperature, pH and dissolved oxygen (DO) were determined for these various depths at each sampling period. Near uniform values were observed for water temperature, pH and dissolved oxygen (DO) between December and January, and this was followed by a thermal stratification between February and June. pH stratification was observed in most periods of the year, though it was also most pronounced between February and June. Dissolved oxygen stratification also showed some similarity to thermal stratification, but not so clear-cut as thermal stratification. Lake Tiga is a warm, monomictic lake which experiences overturn between December and January, and thermal stratification between February and June. Upwelling of deposited nutrients in the epilimnion and photic zone during holomixis, followed by high incident solar radiation in stratification months could greatly enhance the productivity of the lake in the latter period.
Key Words: Epilimnion, hypolimnion, Lake Tiga, overturn, stratification