Preliminary Study to Find Occurrence and Dynamics of Toxic Cyanobacteria in Nuwara wewa and Nachchaduwa wewa, Two Man-made Reservoirs in Sri Lanka

Abstract

Bloom of cyanobacteria in water bodies causes devastating problems to the ecosystem and humans when they depend on these waters for drinking purpose. Microcystin and nodularin, produced by some cyanobacteria, are toxic for human and many other aquatic organisms. Nuwara wewa and Nachchaduwa wewa are two important reservoirs supplying water for drinking purpose in addition to agricultural use. Therefore, preliminary study was conducted to evaluate these reservoirs for the presence of toxic cyanobacteria and their dynamics is of importance to take proper measures to control cyanobacterial growth and to ensure supply of quality water for human drinking purpose. Water samples were collected for 12 months from both reservoirs and physic-chemicals parameters of water were also recorded. Correlations between the physico-chemical parameters of water and the cyanobacterial density were established. Toxic cyanobacteria were isolated and identified using conventional and molecular methods. 16S rRNA gene and mcy-A gene were targeted for molecular identification using PCR. Cyanobacterial density had strong positive correlations with some physico-chemical parameters such as pH, temperature and dissolved oxygen in both reservoirs. These parameters can be used as good indicators to evaluate the condition these reservoirs with respect to cyanobacterial bloom. Some cyanobacterial isolates recovered from both reservoirs harboured mcy-A gene, showing the potential of microcystin production.