Correlations between environmental factors and toxic and non-toxic Microcystis dynamics during bloom in Daechung Reservoir, Korea

Abstract

While it has been known that toxic and non-toxic Microcystis coexist in lakes and their relative proportions vary depending on environmental factors, the main driving force for such variations is still unclear. Therefore, this study attempted to verify the environmental factors related to the dynamics of the abundance of toxic and non-toxic Microcystis in the Daechung Reservoir, Korea. Water samples were collected at weekly intervals from June to October, 2006. Microcystis was a dominant cyanobacterial genus during this period. The proportion of toxic Microcystis genotypes was quantified using a real-time PCR with 2 primer sets for the cpcBA-IGS and mcyJ genes to determine the total Microcystis and potentially toxic genotypes, respectively. Cell densities of toxic and non-toxic Microcystis were strongly related, implying that their growth may be governed by the same environmental factors. Although non-toxic Microcystis was generally dominant over potentially toxic genotypes, the toxic proportion briefly predominated during the Microcystis bloom. While the phosphorus concentration was the fundamental regulating factor for cyanobacterial proliferation, the proportion changes of potentially toxic Microcystis genotypes were more closely related with the water temperature (P< 0.01), suggesting that eutrophication together with global warming could lead to more frequent toxic blooms.