Characteristics of algal bloom and its threshold of ecological flow in the middle and lower Hanjiang River

Based on the hydrological, water environment, and water ecology data in the middle and lower Hanjiang River from 2015 to 2019, this paper uses principal component analysis and redundancy analysis to identify the key factors for the prevention and control of algal bloom outbreaks in the river, and obtained their regulatory thresholds by fitting. Then the ecological flow rate for inhibiting algal bloom outbreaks in the river was calculated by using the cross section flux method and the velocity inhibition method. The results showed that: Algal blooms in the middle and lower Hanjiang River mainly occurred in the dry season. In the dry season, the dominant algal populations were Bacillariophyta, chlorella were the dominant species. In the wet season, the dominant algal populations were Chlorophyta and Bacillariophyta, Chlorella sp. were the dominant species. Flow velocity is the dominant controlling factor affecting algae growth. We found the flow velocity exceeding 0.462m/s will inhibit algae growth. The ecological flow thresholds for controlling algal blooms in the middle and lower Hanjiang River during the dry season were 890m3/s in the Shayang section, 918m3/s in the Qianjiang section, 953m3/s in the Xiantao section and 1075m3/s in Hanchuan section. © 2024 Chinese Society for Environmental Sciences. All rights reserved.