Artemisinin sustained-release algaecides for the prevention of cyanobacteria recovery: dose effects and microbial processes

Climate change has made on-site bloom control increasingly challenging. Therefore, it is necessary to study whether it is possible to control the outbreak of summer cyanobacterial blooms by early prevention of cyanobacterial recovery. This study used artemisinin sustained-release algaecides (ASAs), a typical allelochemical for in-situ cyanobacterial control, to evaluate recovery effects and microbial-ecological impacts through microcosm experiments. All doses inhibited the recovery and bloom of cyanobacteria (Chl-a < 66μg/L), prevented spore germination to varying degrees (especially at the low and high doses), and reduced the ecological niche of cyanobacteria (1.6–2.6). The results demonstrated that low-dose ASAs effectively prevented cyanobacterial recovery with minimal microbial-ecological impacts. Higher ASAs doses reduced bacterial diversity (shannon index dropped from 5 to around 2.8), enhanced environmental selection (the proportion increased from 15 % to 67 %), and loss of native species. The bacterial community underwent a pronounced shift: dominant cyanobacterial genera such as Limnothrix declined substantially, whereas Proteobacteria increased to 60–95 % phylum-level relative abundance. Conversely, eukaryotes enhanced heterogeneous selection (the proportion = 50 %–83 %), smaller diversity changes (Chao1 = 1000–1600), moderate community succession, and widespread microbial cooperation. The effects of ASAs on microbial networks were limited, but the effects of high doses were not negligible, especially the low occupancy module, which accounted for only 8.79 %, was more affected by the DOC/pH changes caused by high-dose. Moreover, ASAs prevented cyanobacterial recovery through bacterial-eukaryotic cooperation and functional microbes, provided the microbial community had not undergone severe environmental stress. Our findings emphasize the importance of considering the nonlinear microbial-ecological responses to dosing and the necessity of low-dose strategies during both in-situ control and prevention, as low-dose result in less changes in microbial community structure and lower risk of secondary cyanobacterial blooms.