Transverse distribution of cyanobacteria in a regulated urban river

Abstract

River eutrophication and CyanoHABs are severe problems that are often ignored because of high current speed and strong self‐purification. In this paper, Liangxi River, Taihu Basin, was selected as the research area. Combined with field investigation, a 2D water environment mathematical model was developed to simulate the chl‐a distribution in Liangxi River. An indicator (Transverse Distribution Center, TDC) and its normalized form (NTDC) to quantitatively represent material transverse distribution in rivers is proposed and coupled in the model. The calculation showed that TDC and NTDC had the property of random fluctuation, seasonal consistency, and water transfer dependence. The multiple regression equation with normalized data indicated that the maximum offset, average variation rate, and average reverting rate of Liangxi River chl‐a NTDC were most affected by the chl‐a dry matter flux ratio between tributaries and the mainstream, followed by flow and chl‐a concentration ratio. From the perspective of river morphology, for different river width change modes and river bending directions, when water flows into and out of these river sections, the chl‐a transverse distribution is subject to different specific effects. In addition, the position of nutrients and dissolved oxygen significantly affected the position of chl‐a growth when the N/P ratio was not very high. Conversely, a high N/P ratio may contribute to decrease of the chl‐a concentration. Proliferation with abundant nutrients may cause the settlement of chl‐a resulting in a decrease of chl‐a in the water column.

Flow velocity and light intensity combination is important for Microcystis aeruginosa physical suppression

“…Previous research on the effects of flow velocities on cyanobacterial growth had inconsistent results; the variations in experimental environments may be one of the reasons. Additionally, water flow alters the effect of light intensities on cyanobacteria by changing their distribution (Yan et al, 2021). This interaction between water flow and light intensity has not been thoroughly investigated in controlled laboratory settings, although some field studies have examined both water flow (or wind) and light intensities (Hamagami et al, 2019; Li et al, 2013).…”

“…Previous studies have reported a range of critical flow velocities for cyanobacteria, varying from 0.06 to 0.3–0.5 m s −1 (Gao et al, 2007; Zhang et al, 2015). Cyanobacterial presence has been recorded under higher flow velocities, as evidenced in the Liangxi River of the Taihu Lake Basin, China (Yan et al, 2021), and the Yeongsan River, Korea (Kim et al, 2019), where outbreaks are more frequent during periods of high flow than in dry periods. The flow velocity in the Liangxi River can reach up to 17.72 cm s −1 (Wang et al, 2021), whereas in the Yeongsan River, a maximum of 49.80 cm s −1 near the Chucksan weir has been recorded (Sin & Lee, 2020).…”