Comparative transparency, depth of mixing, and stability of stratification in lakes of Cameroon, West Africa’

Morphometry, oxygen concentration, temperature, and transparency were studied in 39 natural lakes in Cameroon, West Africa. Thermal profiles from 3 1 of the lakes and data from published studies were used to calculate stability of thermal stratification and evaluate morphological cor-relates of mixing depth. Twenty-six lakes showed some degree of stratification and 17 had distinct thermoclines and well-developed, anoxic hypolimnia. Total stability of the water column ranged from 0 to 5,784 J m-2. The high values were similar to or greater than those of other tropical and temperate lakes. Lake depth seems to exert a stronger influence on stability than does lake area, but depth or stability measures alone provide little information about heat distribution or mixing regime. A strong positive relationship between water transparency and thermocline depth in both tropical and temperate lakes suggests that reductions in buoyant resistance to vertical mixing, caused by deeper penetration of solar radiation, are important in establishing mixing depths in various lakes. Comparisons of persistent thermocline depth in tropical vs. temperate lakes, re-gardless of size, indicate that mixing depths in tropical lakes are often greater than those in their temperate counterparts. This difference is caused in part by the narrow ranges of temperature and smaller absolute density gradients in these tropical lakes, against which the mixed layer is deepened. Knowledge concerning the formation and maintainence of the upper mixed layer in oceans and lakes has expanded greatly in recent years (Phillips 1977; Imberger 1985). Entrainment of deeper, denser water into the base of the epilimnion is the primary mechanism of mixed-layer thickening. The turbulent kinetic energy required has been shown to come from stirring processes such as wind mixing or penetrative convectio