Temporal and Seasonal Variations in a Phytoplankton Community Structure in Artificial Lake Uiam, South Korea

Lake Uiam is situated midway through a basin with dams at both the upstream and downstream ends; considerable environmental fluctuations have been observed here. However, studies on changes in environmental factors and plankton community fluctuations remain limited. This study analyzed the seasonal physicochemical factors and changes in the phytoplankton community structure in Lake Uiam (2015–2016). Organic matter, phosphorus, total suspended solids (TSS), and Chl-a concentrations were high in the summer. Seasonal changes in the dominant taxa followed the typical succession pattern of temperate phytoplankton, with Bacillariophyceae (Ulnaria acus) being dominant in spring and Cyanophyceae (Pseudanabaena limnetica) dominant in summer. However, Cryptophyceae (Rhodomonas sp.) showed unusually high dominance in autumn. Cell abundance showed no seasonal differences. Rhodomonas sp. was negatively correlated with water temperature, suggesting its dominance in spring and autumn. Cryptophyceae showed a significant correlation with Chl-a (0.708 **), indicating its contribution to spring Chl-a concentrations. Cryptophyceae (Rhodomonas sp. and Cryptomonas spp.) commonly appear in spring but are dominant in autumn in Lake Uiam. Despite disturbances from various environmental factors, they showed higher adaptability than other algae, resulting in their consistent appearance and dominance, differing from the general succession patterns of temperate phytoplankton.