Quantitative importance of Cyanobacteria populations in a hypertrophic shallow lake in the subequatorial African region (Yaounde Municipal Lake, Cameroon)

摘要

Cyanobacteria species composition, abundance and spatio-temporal variations were recorded weekly in the Yaounde municipal lake (3degrees 52', 11degrees 32', Cameroon, Central Africa), during an annual cycle, in relation to physico-chemical parameters of the water. Qualitatively, Cyanobacteria were represented in this biotope by 6 species: Planktothrix mougeotii, Oscillatoria putrida, Microcystis aeruginosa, M. wesenbergii, Merimopedia punctata and Aphanocapsa elachista. These species represented about 6% of phytoplankton taxa recorded in this lake. Quantitatively, this algae group developed almost exclusively during the dry seasons. Their maximum biomass, representing 44% and 38% of the total phytoplankton biomass, was recorded at the end of December and at the end of August, respectively. The vertical distribution of Cyanobacteria in this water body followed a unique pattern; the main part of the biomass was concentrated in the uppermost metre layer of the water column, and dominated by P. mougeotii. Temperature constituted the main factor controlling cyanobacterial efflorescence in this lake, this factor being associated with the relative constant weather conditions prevailing during dry seasons. The pH fluctuations in the lake appear to be the consequence of Cyanobacteria bloom formation. [References: 59]