Phytoplankton Community Dynamics and Evaluation of Trophic State in the Lake Unmoon

doi:2003.18.2.135

Algae > Volume 18(2); 2003 > Article

Algae 2003;18(2): 135-143. doi: https://doi.org/10.4490/ALGAE.2003.18.2.135

Jung-Kwan Seo, Jae-Jeung Yu, Jay-Jung Lee, Sang-Yong Yang, Ik-Kyo Chung

Nakdong River Water Quality Research Laboratory, National Institute of Environmental Research, Division of Earth Environmental system, Pusan National University

ABSTRACT

The seasonal dynamics of phytoplankton and trophic State were evaluated weekly at three sites in the Lake Unmoon from May to November 2001. The seasonal succession pattern of phytoplankton community in the Lake Unmoon showed that the dominant species were; ⅰ) diatoms during the late spring, ⅱ) dinoflagellates in June, ⅲ) blue green algae, diatoms and dinoflagellates in July, ⅳ) green algae and blue green algae in August, ⅴ) blue green algae in September and early November, and ⅵ) diatoms in November. Members of Microcystis were dominant from middle August to late October and members of Aulocoseira appeared as important species in autumn in the Lake Unmoon. The concentration of chlorophyll-a ranged from 2.4 to 23.0 mg?m〈sup〉-3〈/sup〉(average: 8.6 mg?m〈sup〉-3〈/sup〉) during the study period. Concentrations of total phosphorus were high during the period from July to November with the maximum of 0.028 mg?l〈sup〉-1〈/sup〉. The average N/P ratio was 121, indicating that concentrations of phosphorus may determine the high algal biomass in the Lake Unmoon. Concentrations of silicate were higher in the Lake Unmoon(average value: 10.016 mg?l〈sup〉-1〈/sup〉) than in other lakes (average value: 1.074-4.408 mg?l〈sup〉-1〈/sup〉), suggesting high potential of diatom growth. The average trophic state index in the Lake Unmoon was 52, which was close to eutrophic state, and the trophic state trend was increasing steadily since 1999.

Key words: chlorophyll-a, phytoplankton, Trophic State Index, Unmoon Lake