Season Dynamicsof Phytoplankton Community in the Naktong River Estuary, Korea

Algae > Volume 8(1); 1993 > Article

Algae 1993;8(1): 15-28.

Kyung-Je Cho, Ik-Kyo Chung, Jin-Ae Lee

Department of Biology and Department of Environmental Science, Inje University, Department of Marine Science, Pusan National University

ABSTRACT

The floral composition and seasonal variation of phytoplankton in the Naktong and Sonaktong river, which have an estuarine barrage at each river mouth, were studied from June 1991 to August 1992. The phytoplankton community consisted of four algal group: diatoms, blue-green algae, green algae and cryptomonads. Eutrophic indicator algae such as Melosira, Stephanodiscus, Fragilaria, Scenedesmus, Microcystis, Phormidium predominate over the freshwater zones, which are upper part of both estuarine barrage. Stephanodiscus hantzschii persistently bloomed from October to md-May in the freshwater area of Naktong river estuary. In the Sonaktong river, diatom Extubocellulus spinifer and cryptmonad Chroomonas species succeeded Stephanodiscus. Microcystis aeruginosa coincided with the disappearance of cryptomonads and diatoms such as Stephanodiscus and Extubocellulus, and Microcystis outbreaks were primarily monospecific blooms. Phytoplankton had spring-early summer peaks in the algae biomass of the river. However, phytoplankton community of Naktong river unusually had a early winter bloom in November. Cell density and chlorophyll concentration of phytoplankton at the Naktong river were 2-3 fold higher than before the barrage construction. Phytoplankton biomass of the Sonaktong river was 2-3 fold higher than that of the Naktong river. Eutrophic indicator species and blue-green algal dominance in the phytoplankton composition considerably increased more than before the construction. Viewed from algal biomass increase and persistent bloom of eutrophic indicator species, the Naktong estuarine ecosystem was more fertilized than previously and would progress towards further fertilization in the future.

Key words: phytoplankton, eutrophic indicator species, seasonal variation, chlorophyll