Effects of flushing flow on periphytic algal community at different colonization stages

Global climate change has led to periphytic algal overgrowth in water diversion canals, causing clogging issues and water quality deterioration. Flushes with high water velocity can effectively detach periphytic algae, but little information can be found on the association of flush-periphyton interactions. To fulfill the gap, flush experiments were carried out at the different colonization stages of periphytic algal community (Stage 1: initial colonization stage, Stage 2-1: early community formation stage, Stage 2-2: late community formation stage, and Stage 3: primary succession stage) with varied flushing time (0 d, 2 d, 4 d). The results demonstrated that periphytic algal community at Stage 2-1 had weak resistance to flushing-flows and the lowest biomass accumulation ability after the flush. Besides, flush suppressed the growth of periphytic filamentous algae at Stage 2-1, reducing clogging issues. Short-term (less than 2 days) flushing-flows with high velocities (v = 0.8 m/s) inhibited algal proliferation and reduced species diversity with temporary scour effects. The algal species (Navicula, Achnanthes, and Fragilaria) with strong scouring resistance became dominant species and proliferated extensively after the flush. This study laid the groundwork for hydraulic regulation, and the flushing strategy would reduce the threat of periphytic algae in the water transportation canals.