Variations in the Temporal and Spatial Distribution of Microalgae in Aquatic Environments Associated with an Artificial Weir

The construction of weirs causes changes in the aquatic environment and affects several aquatic organisms. To understand the ecosystem in the Sangju Weir, Gyeongsangbuk-do Province, variations in the spatiotemporal distribution and composition of microalgae communities were analyzed. Microalgae were collected fortnightly from April to November 2018 from six sites in the Nakdonggang River. There was significant variation in environmental factors, microalgal community structure, and flora. Microalgae communities were dominated by diatoms (e.g., Fragilaria crotonensis , Ulnaria acus , and Aulacoseira ambigua ), green algae (e.g., genera Eudorina and Desmodesmus ), cyanobacteria (e.g., genera Anabaena and Microcystis ). Multidimensional scaling indicated that species composition and diversity were generally similar among sites but varied between the bottom and the surface and middle water layers. Vertical migration of microalgae was difficult to investigate because of the thermocline in the study area and high turbidity in the lower layer. The distribution of microalgae was little affected by the construction of the weir, but the formation of thermocline changed microalgae communities in the water layer.