Vertical distribution of phytoplankton in a clear water lake of Colombian Amazon (Lake Boa, Middle Caquetá)

Vertical distribution of phytoplankton is highly influenced by physical and chemical factors, but the knowledge about these aspects remain unknown in Colombian Amazon lakes. In this work, the relations between the physico-chemical variables and the vertical distribution of phytoplankton community of a clear water lake (Lake Boa) are analyzed. Samples were taken at every 30 cm from surface to bottom in the center of the lake at different times of the hydrological cycle. Phytoplankton transformed from a diluted community dominated by cyanobacteria in high waters to one with elevated abundance of coccal chlorophytes in low waters. In the low water phase, the vertical distribution of Cryptomonas spp., Peridinium cf. umbonatum and Chlamydomonas spp. had significant statistical associations with the redox potential (RP), reactive phosphorus (PO₄), and hydrogen sulfide (H₂S) (p ≤ 0.05). During the flood stage the conditions were more varied and significant associations were detected between the vertical arrangement of Botryococcus braunii, Oscillatoria splendida, Dinobryon serturlaria, Euglena acus, and Trachelomonas volvocina with conductivity, dissolved oxygen (DO), pH, temperature, dissolved organic carbon (DOC), PO₄, RP, and ammonia (NH₄). The vertical structure of the Lake Boa’s phytoplankton responds to annual changes produced by the flood pulse, and to the vertical environmental variations, which are stronger during the high water phase.