WHO WINS? COMPARISON BETWEEN EMERGENT MACROPHYTES AND PONTEDERIA CRASSIPES (WATER HYACINTH) AS NATURE-BASED SOLUTIONS FOR NUTRIENT PHYTOREMEDIATION AND CYANOBACTERIA MITIGATION

A bstract Emergent macrophytes are commonly used to control eutrophication in Constructed Floating Wetlands (CFW) systems. However, tropical emergent macrophyte species, particularly from South America, are underrepresented in these applications. This study aims to investigate the potential of five emergent macrophytes, Alternanthera philoxeroides, Ludwigia leptocarpa, Polygonum ferrugineum, Typha domingensis, and Urochloa mutica in controlling eutrophication and inhibiting cyanobacterial growth, compared to the floating macrophyte Pontederia crassipes, the most studied macrophyte for this purpose. Phytoremediation experiments were performed ex-situ in mesocosms (50 L) with high soluble reactive phosphorus (SRP) concentration (400 µg L −1 ). Allelopathic effects of the macrophytes root exudates on cyanobacteria were tested in vitro using a strain of Microcystis aeruginosa . While P. crassipes reduced SRP concentration by 86% in 14 days, the tested macrophytes reduced SRP concentration by > 94%, except for T. domingensis, which showed a reduction of 64%. NH 4 + and NO 3 − removal in 14 days were 96% and 62%, respectively, for P. crassipes . These values corresponded to 96% and 63% for the five tested macrophytes. Root exudates of A. philoxeroides, L. leptocarpa, and P. ferrugineum caused inhibition of M. aeruginosa growth with no detection of Chl- a after 7 days. Thus, three emergent macrophytes were more efficient in removing nutrients than P. crassipes . and showed allelopathic potential against cyanobacteria, indicating that using local emergent macrophytes in CFW systems can be a valuable and sustainable tool to mitigate eutrophication and its consequences in aquatic environments. Graphical abstract Highlights Emergent macrophytes were similarly efficient to P. crassipes in nutrient removal Ludwigia leptocarpa was the most efficient in SRP removal in 7 days Allelopathy on cyanobacterium M. aeruginosa by A. philoxeroides, L. leptocarpa , and P. ferrugineum root exudates Adapting emergent macrophytes in CFW structures can be helpful in in situ phytoremediation. S tatement of N ovelty This study lies in its comparative analysis of underrepresented tropical emergent macrophytes from South America against the widely studied floating macrophyte, Pontederia crassipes (water hyacinth). By focusing on these local emergent macrophytes, the research addresses a significant knowledge gap. It provides insights into their potential application in Constructed Floating Wetlands (CFWs) for nutrient removal and cyanobacteria control. Key findings demonstrate that the selected emergent macrophytes outperform P. crassipes in reducing soluble reactive phosphorus (SRP) concentrations and exhibit substantial nitrogen removal efficiencies. Furthermore, the allelopathic potential of A. philoxeroides , L. leptocarpa , and P. ferrugineum against the harmful cyanobacterium Microcystis aeruginosa showcases their dual functionality in mitigating eutrophication and inhibiting harmful algal blooms.