Comparison between American emergent macrophytes and Pontederia crassipes (water hyacinth) as nature-based solutions for nutrient phytoremediation and cyanobacteria mitigation

Emergent macrophytes effectively control eutrophication in constructed floating wetlands (CFW). However, tropical species from South America are underutilized. This study evaluates five emergent macrophytes-Alternanthera philoxeroides, Ludwigia leptocarpa, Polygonum ferrugineum, Typha domingensis, and Urochloa mutica-for their ability to control eutrophication and inhibit cyanobacterial growth, compared to the well-studied floating Pontederia crassipes. Phytoremediation experiments in 50 L mesocosms with high soluble reactive phosphorus (SRP) concentrations (400 µg L-1) showed that while P. crassipes reduced SRP by 76% in 14 days, compared to the control without macrophytes; other macrophytes reduced SRP by over 91%, except for T. domingensis at 40%. NH4+ and NO3- removal rates for P. crassipes were 90% and 47%, respectively, matching the performance of the tested macrophytes. Root exudates of A. philoxeroides, L. leptocarpa, and P. ferrugineum inhibited the growth of the cyanobacterium Microcystis aeruginosa, with no Chl-a detected after 7 days. Thus, three emergent macrophytes outperformed P. crassipes in nutrient removal and showed allelopathic potential against cyanobacteria. Utilizing local emergent macrophytes in CFW systems presents a valuable and sustainable approach to mitigating eutrophication and its consequences on aquatic environments such as cyanobacteria blooms.