Abstract: As a basic work for establishing China water environment ecological criteria, an investigation was conducted on the phytoplankton community structure and water quality in Daliaohe river system in July 2010, based on relevant guidelines. A total of 124 phytoplankton species were recorded, most of which belonged to Chlorophyta and Bacillariophyta, occupying 43.55% and 31.45% of the total, respectively. The total cell density at different sampling sites varied from 2.05×10⁵ to 1.46×10⁷ ind·L^-1, with an average of 6.35×10⁶ ind·L^-1 and dominated by Chlorophyta and Bacillariophyta. At all sites,Melosira granulata var. angustissim of Bacillariophyta was the dominant species. Forty-four indicator species of water pollution were detected, and most of them were of β-mesosaprobic, with 36 species and occupying 81.81% of the total. The Shannon index of the phytoplankton community was 1.43-2.68, Margalef index was 1.00-1.78, and the Pielou index was 0.52-0.83. Based on this investigation, it was considered that the Daliaohe river system was in eutrophic state and at moderate pollution level.

Key words: Adenophora potaninii population, Root system biomass, Growth and development, Habitat conditions