Deep tropical lakes have a prolonged stratification period, during which changes can occur in the depth of the epilimnion (atelomixis), affecting nutrient and light availability along with phytoplankton composition (Lewis 1973, 1986, Barbosa Padisak 2002). Seasonal temperature reductions and wind turbulence reduce stability of the water column, allowing complete mixing in deep tropical lakes (Lewis 1996). Phytoplanktonic communities reflect changes generated by the stratification and mixing regime. In stratified lakes, the physical and chemical changes associated with mixing act as disturbances, causing community succession (Reynolds 1993) and increasing or decreasing phytoplankton diversity (Reynolds et al. 1993), depending on its intensity and severity (Sommer et al. 1993). Thermal stratification of a lake produces a vertical gradient in the structure of phytoplanktonic communities that allows coexistence of various species in different nutritional and light environments (Reynolds 1984). The objective of this work was to study relationships between phytoplankton diversity and the stratification-mixing regime in a high mountain tropical lake.
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