Seung-Hyun Joung

Annual variation of Microcystis genotypes and their potential toxicity in water and sediment from a eutrophic reservoir

The relative genetic diversity of microcystin-producing Microcystis in the water and sediment of the Daechung Reservoir, Korea, was investigated over an entire year, including the cyanobacterial bloom season. The cells of potentially toxic Microcystis strains containing mcyJ genotypes and cells containing the genus-specific cpcBA gene were quantified by a real-time PCR. The ratio of cells with mcyJ genotypes to the total Microcystis population in the water body was the highest (68.3%) in August when the cyanobacterial bloom reached its peak and the microcystin concentration in the water began to increase. A denaturing gradient gel electrophoresis profile analysis of the mcyJ genotypes performed to monitor any changes in the toxic Microcystis population showed the appearance of new genotypes and the disappearance of existing genotypes in the reservoir water collected during the summer months, when compared with the profile for the samples collected in spring and autumn. However, very little change was observed over the course of the year as regards the population diversity of the sediment samples.

Selective Control of Cyanobacteria in Eutrophic Pond by a Combined Device of Ultrasonication and Water Pumps

A combined device consisting of an ultrasonic apparatus and water pumps was operated in a eutrophic pond to study its effect on the control of cyanobacteria as compared with those of a non-treated, neighboring pond. The combined apparatus seemed to be enough to spread the sonicated water to the whole surface of a 9,000 m3 pond. Although the high rainfall in 2003 resulted in an overall dominance of diatoms, cyanobacterial growth was significantly inhibited by the apparatus in the treated pond. In addition, the chlorophyll-a concentration and total algae in the treated pond were 61 and 53%, respectively, of the levels in the control pond. The reduced algal growth (7% of the control) by the combined apparatus was mainly due to the inhibition on the growth of cyanobacteria. The cyanobacterial proportion in the treated pond, however, increased significantly for several days, when the apparatus was stopped. Meanwhile, the proportion of green algae increased in the treated pond. The successful selective control of cyanobacteria using the combined apparatus suggests that ultrasonication can be a practical method to control bloom and toxin production in eutrophic waters.

Dynamic variation of toxic and non-toxic Microcystis proportion in the eutrophic Daechung Reservoir in Korea.

This study was conducted to determine the environmental factors affecting the level of potentially toxic Microcystis. The long-term tendencies of temperature, precipitation, and water quality factors were analyzed to determine the environmental characteristics of the Daechung Reservoir in Korea, and water samples were directly collected to analyze the dynamics of toxic and non-toxic Microcystis at weekly intervals from May to October 2012. Microcystis was the dominant genus during the study period, and it was composed of potentially toxic and non-toxic Microcystis. The fraction of potentially toxic Microcystis ranged from 6.0% to 61.1%. The amount of toxic Microcystis was highly related to the intracellular microcystin concentration (r = 0.760, P < 0.01). Therefore, the fraction of potentially toxic Microcystis is an important concern in Microcystis blooming because the intracellular microcystin concentration may reflect microcystin levels in the water. The prevalence of potentially toxic Microcystis was highly related to water temperature in Daechung Reservoir (r = 0.585, P < 0.01). Thus, temperature increase during Microcystis blooming may lead to more frequent toxic Microcystis blooms in eutrophic water bodies.