Relationship between Phytoplankton and Environmental Variables from Bien Ho and Lak Lakes in Central Highland of Vietnam

Being the primary producers of the food chain, phytoplankton including micro algae and cyanobacteria play a key role in freshwater ecosystems. This study aimed to investigate the seasonal variation of phytoplankton in relation to the environmental parameters such as temperature, pH, electric conductivity, transparency, turbidity, dissolved oxygen, biochemical oxygen demand, nutrients, trace metals in two natural lakes, Bien Ho and Lak lakes, from central highland of Vietnam. The cluster analysis revealed that the similarity of aquatic environmental parameters of Bien Ho Lake was clearly separated among the seasons and that of Lak Lake was overlap between the dry season and trans-season period. The results showed that the physical conditions and trace metal concentrations in surface water of the two lakes were comparable and favored the phytoplankton growth. Nutrients including nitrogen and phosphorus concentrations in Lak Lake were higher and advantageous for the development of phytoplankton whereas nitrogen concentration in Bien Ho seemed to limit the algal growth.From the monitoring, 98 and 312 species of phytoplankton in Bien Ho and Lak Lakes, respectively, which belong to green algae, Diatoms, golden algae, euglenoids, dinoflagellates and cyanobacteria. Phytoplankton densities were from 1 577 000 – 10 312 000 individuals/L in surface water from Bien Ho Lake and from 62 400 – 14 580 000 individuals/L in Lak Lake. The Canonical Correspondence Analysis showed that Bien Ho and Lak Lakes had similar characters of group distribution in each sampling time on the ordination plane. In Lak Lake, the parameters of pH, turbidity, chemical oxygen demand, iron, electric conductivity, and aluminum had a close correlation with the algal distribution. The transparencyrevealed the clearest correlation with the phytoplankton distribution in Bien Ho.