Abstract
Increased nutrients have led cyanobacteria to become dominant in many ponds, lakes and reservoirs in many countries of the world. The occurrence and abundance of cyanobacterial population were monitored in a lake (known as Ishakha Lake) at Bangladesh Agricultural University campus, Mymensingh, Bangladesh. The hydrographic parameters such as water temperature, pH, chlorophyll a and nutrients (NO3-N and PO4-P) were recorded to find out their relationship with the cyanobacterial bloom formation. During the study period five species of cyanobacteria namely, Microcystis aeruginosa Kutz., M. wesenbergii Kom., M. botrys Teli., M. viridis (A. Br.) Lemm. and Anabaena circinalis Rabenh., were identified and among them M. aeruginosa was the dominant species during the bloom period. At the peak period of bloom, the highest cell density of M. aeruginosa was 1550 x 10(3) cells ml(-1) which comprised 97.45 % among the blue-green algae and 96.84 % to the total phytoplankton. The initiation and persistence of natural bloom of cyanobacteria, especially Microcystis spp. was found to be controlled by relatively high temperature (> 25.00 A degrees C) and nutrients, especially high NO3-N (3.80 mg l(-1)) concentration. Temperature and NO3-N showed positive correlation with cyanobacterial cells abundance which were r = 0.62 and r = 0.92. Therefore, it could be said that temperature and NO3-N made a favorable circumstance to form cyanobacterial bloom in as Ishakha Lake. The Enzyme-linked Immunosorbent Assay revealed that the concentration of MCs 37,460.00 pg ml(-1) at the peak period of bloom.