• Journal of Soil and Groundwater Environment
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• v.20 no.7
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• pp.121-134
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• 2015

Spatial and temporal changes in algal population in Yongdam reservoir and ecological factors that induced the changes in the size and composition of algal population were investigated by monthly sampling at ten locations in the reservoir. Nutritional state of the reservoir was identified to be phosphorus-limited with nitrogen to phosphorus (N : P) ratio much greater than 17 in most samples. Algal population was dominated by three taxonomic groups, diatoms, chlorophytes and cyanobacteria. Although explosive algal growth was not observed in the summer, algal population showed transition with time of the dominant algal type from diatoms in the winter to cyanobacteria in the summer. Chlorophyta was not the dominant group in the reservoir although they maintained relatively stable number of cells in the reservoir and showed increase in population from March to May. The application of statistical methods revealed that the factors inducing changes in cell number of each group were water temperature for diatoms and cyanobacteria and phosphorus concentration for chlorophyte. Fluctuation of cyanobacterial population was mainly observed near the inlet of tributaries while diatoms showed higher variation inside the reservoir.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.20 no.4
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• pp.1-13
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• 2017

The purpose of this study is to analyze a term of decade of water quality data of the Mulgum intake station on the Nakdong river(dam) to find the cause of algal blooms and to set an alternative to prevent artificial lake water pollution. Our study shows that water quality changes have regular periodic regularity and there was a certain correlation between specific analytical items. According to the analysis results of each factor, the decline in precipitation was not the main reason for algal blooms. TP concentration had a slight effect on Chl-a concentration but was not a limiting nutrient of a bloom. TN concentration had a strong correlation with Chl-a and strongly negative correlation with temperature, but was not a bloom's limiting nutrient, and was only a dependent variable. As the temperature was negatively correlated with the Chl-a concentration, it is found that the aspect of the ecological influence of the temperature was the most important factor of the phytoplankton concentration change. The N/P ratio lies under a power function with a high degree of reliability by the TP concentration, and the phenomenon appeared to be the same as the results of two other comparative areas. This result confirms that TN is dependent on TP and the biota in the lake that TN is a dependent variable whose concentration is determined by TP it. In conclusion, the increase in lake bloom is the result of a food chain change, and it is necessary to control the ecosystem by the food chain in the lake in order to reduce the lake's bloom. In particular, it is important to keep the benthic ecosystem as wide as possible in the aerobic state.

• Korean Journal of Ecology and Environment
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• v.37 no.4 s.109
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• pp.368-372
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• 2004

The development of a benthic filamentous green algal community formed by Spiro gyra sp. in early summer has been observed in the littoral zones in the north basin of Lake Biwa since the 1980s. The development of a Spirogyra sp. community may have an effect on the increase in the biomass of the benthic algal community in early summer and on the alterations in seasonal fluctuation patterns of the biomass. In this mini-review, the causes underlying the development of the Spirogyra sp. community are discussed on the basis of studies in the seasonal fluctuations of benthic algal communities in littoral stony zones carried out in 1963-1964, 1995-1996 and 2000-2001, especially those focusing on the nutrient concentration $(NO_3^--N)$. $NO_3^--N$ concentrations in June were higher than $100{\mu}g\;L^{-1}$ in 1995 and 2000 in contrast to a concentration in June 1964 of only $20{\mu}g\;L^{-1}$. These results show that $NO_3^--N$concentrations throughout in 1963-1964 period were considerably lower than those in 1995-1996 and 2000-2001, suggesting that the $NO_3^--N$concentration may have served as a limiting factor on Spirogyra sp. growth in 1963. $NO_3^--N$ concentrations in the pelagic zone in the north basin of Lake Biwa have clearly increased from the 1950s under the impact of economic growth and the increasing population in the watershed. The development of the Spirogyra sp. community seems to be the result of a heady increase in the nutrient supply from human activities.

• Korean Journal of Ecology and Environment
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• v.50 no.3
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• pp.337-354
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• 2017

Cyanobacteria Aphanizomenon population is widely distributed in the world, and well known as harmful algae by producing toxins and off-flavor materials, thus belonging to one of the taxa that became more interested in the field of limnoecology. In this study, the frequency, intensity, and duration of Aphanizomenon occurrence were increased with the abnormal drawdown of water level in the winter in Boryeong Reservoir, and the spatial and temporal characteristics of them are compared with each other in the perspective of hydrometeorology (1998 to 2017) and limnology (2010 to 2017). In Korea, Aphanizomenon flourished mainly in high temperature, and the appearance in the low temperature was rare in total five times. The harmful cyanobacteria Aphanizomenon was observed in the low temperature (December to February) in Boryeong Reservoir from 2014, and then reached a maximum value of $2,160cells\;mL^{-1}$ in January 2017. In addition, the period exceeding $1,000cells\;mL^{-1}$ at this time was more than 3 months. This was simultaneously associated with abnormal water level fluctuation in the low temperature ($<10^{\circ}C$). The large drawdown of water level in the winter season has the potential to promote or amplify the germination and development of harmful algae. Also, subsequent water quality and ecological impacts(e.g., algal toxins and off-flavor substances) need to be considered carefully.