[Periphytic Algae Community Structure and Its Relation to Environment Factors in the Main Stream of the Songhua River from 2014 to 2019].

Periphytic algae are often used as an indicator to evaluate water quality. Here, the community structure of periphytic algae and its relationship with environment factors were analyzed in the main stream of the Songhua River during the summers of 2014 to 2019. The status and trends in ecological water quality were also evaluated based on bioassessments. Phytoplankton species belonging to 4 phyla and 58 genera were recorded, including 28 Bacillariophyta genera, 17 Chlorophyta genera, 10 Cyanophyta genera, and 3 Euglenophyta genera; Bacillariophyta, Chlorophyta, and Cyanophyta accounted for 48.28%, 29.31%, and 17.24% of the community, respectively. Cell densities varied between 1.29×10 ⁴ and 8.42×10 ⁴ ind·cm ^-3 , with an average of 4.35×10 ⁴ ind·cm ^-3 . The dominant genera were Cyclotella, Melosira, Asterionella, Cymbella, Synedra, Pinnularia, Navicula , and Scenedesmus . The physicochemical water quality showed notable changes during the past six-year monitoring period. Specifically, the dissolved oxygen content increased year on year; ammonia nitrogen, total phosphorus, and total nitrogen first increased and then decreased; and, overall, water quality significantly improved in 2019. Relationship between periphytic algae and environmental factors was further examined using redundancy analysis (RDA), which showed that time was the main factor driving the succession of algal community structure. Dissolved oxygen (DO), ammonia nitrogen (NH ₄ ⁺ -N), total nitrogen (TN), total phosphorus (TP), five-day biochemical oxygen demand (BOD), and chemical oxygen demand (COD) were also important environmental variables affecting algal community structure.