Nutrient uptake and allelopathic effects of <i> Elodea <i>nuttallii</i> </i> for the biological control of a microcystis‒dominated bloom from <i>Lake Des Oiseaux</i> , eastern Algeria

Lake Des Oiseaux is an Algerian aquatic ecosystem of worldwide importance that faces serious eutrophication issues. Ecological restoration offers a promising approach for the prevention and management of harmful algae blooms. Allelopathic submerged macrophytes are known to exert strong inhibitory effects. In this study, water restoration potential of Elodea nuttallii on cyanobacteria was investigated including effect on cyanobacteria cells density, cyanobacterial composition, water transparency, chlorophyll-a concentration, and competition for nutrients (NH4+, NO2−, NO3−, PO43−, total nitrogen and total phosphorus). The allelochemicals were identified and quantified using HPLC‒DAD. E. nuttallii had a strong inhibitory effect on cyanobacterial growth (P < 0.001) and chlorophyll-a synthesis (P < 0.001). E. nuttallii inhibited 95.23% of cyanobacteria growth after 7 days of exposure and 99.99% after 30 days. Compared to the control experiment, E. nuttallii improved water transparency after day 7 (P < 0.001) and maintained very high water transparency until the end of the experiment. Nine allelochemicals, eight of which are polyphenols were identified among E. nuttallii metabolites. The dominant components are: (−)-epicatechin, naringenin and apigenin. E. nuttallii competes well with cyanobacteria for nutrients, especially nitrogen, and absorbs NO2− and NO3− when ammonium is low in the medium. Additionally, E. nuttallii reduces the phosphorus content to low concentrations in the medium. These findings suggest a combined effect of competition for nutrients and allelopathy.