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Periphytic algal colonization is common in aquatic systems, but its interspecific competition remains poorly understood. In order to fill the gap, the process of periphytic algal colonization in the Middle Route of the South to North Water Diversion Project was studied. The results showed that the process was divided into three stages: the initial colonization stage (T1, 3–6 days), community formation stage (T2, 12–18 days) and primary succession stage (T3, 24–27 days). In T1, the dominant species were Diatoma vulgaris (Bory), Navicula phyllepta (Kützing) and Fragilaria amphicephaloides (Lange-Bertalot) belonging to Heterokontophyta; these species boasted wide niche widths (NWs), low niche overlap (NO) and low ecological response rates (ERRs). In T2, the dominant species were Diatoma vulgaris, Cymbella affinis (Kützing), Navicula phyllepta, Fragilaria amphicephaloides, Gogorevia exilis (Kützing), Melosira varians (C.Agardh), Phormidium willei (N.L.Gardner) and Cladophora rivularis (Kuntze). These species displayed wider NWs, lower NO, and lower ERRs than those in T1. In T3, the dominant species were Diatoma vulgaris, Cymbella affinis, Navicula phyllepta, Fragilaria amphicephaloides, Achnanthes exigu (Grunow), etc. Among them, Heterokontophyta such as Diatoma vulgaris and Cymbella affinis had a competitive advantage based on NWs and ERRs. Cyanobacteria like Phormidium willei lost their dominant status due to the narrower NW and the increased NO. It could be concluded the interspecific competition became fiercer and shaped the colonization process; this study will be helpful in understanding the colonization of periphytic algal communities.

Cadmium ion (Cd2+) is a highly toxic metal in water, even at low concentrations. Microalgae are a promising material for heavy metal remediation. The present study investigated the effects of Cd2+ on growth, photosynthesis, antioxidant enzyme activities, cell morphology, and Cd2+ adsorption and accumulation capacity of the freshwater green alga Scenedesmus obliquus. Experiments were conducted by exposing S. obliquus to varying concentrations of Cd2+ for 96 h, assessing its tolerance and removal capacity towards Cd2+. The results showed that higher concentrations of Cd2+ (>0.5 mg L−1) reduced pigment content, inhibited algal growth and electron transfer in photosynthesis, and led to morphological changes such as mitochondrial disappearance and chloroplast deformation. In this process, S. obliquus counteracted Cd2+ toxicity by enhancing antioxidant enzyme activities, accumulating starch and high-density granules, and secreting extracellular polymeric substances. When the initial Cd2+ concentration was less than or equal to 0.5 mg L−1, S. obliquus was able to efficiently remove over 95% of Cd2+ from the environment through biosorption and bioaccumulation. However, when the initial Cd2+ concentration exceeded 0.5 mg L−1, the removal efficiency decreased slightly to about 70%, with biosorption accounting for more than 60% of this process, emerging as the predominant mechanism for Cd2+ removal. Fourier transform infrared correlation spectroscopy analysis indicated that the carboxyl and amino groups of the cell wall were the key factors in removing Cd2+. In conclusion, S. obliquus has considerable potential for the remediation of aquatic environments with Cd2+, providing algal resources for developing new microalgae-based bioremediation techniques for heavy metals.