WHO WINS? COMPARISON BETWEEN EMERGENT MACROPHYTES AND PONTEDERIA CRASSIPES (WATER HYACINTH) AS NATURE-BASED SOLUTIONS FOR NUTRIENT PHYTOREMEDIATION AND CYANOBACTERIA MITIGATION
Authors: Filho Cesar Macedo Lima , Santos Allan Amorim , de Lima Daniel Vinícius Neves , de Oliveira Silva Luan , Pacheco Ana Beatriz Furlanetto , Azevedo Sandra M. F. O. 
Published: July 2024

AbstractEmergent 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,andUrochloa muticain controlling eutrophication and inhibiting cyanobacterial growth, compared to the floating macrophytePontederia 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 ofMicrocystis aeruginosa. WhileP. crassipesreduced SRP concentration by 86% in 14 days, the tested macrophytes reduced SRP concentration by > 94%, except forT. domingensis,which showed a reduction of 64%. NH4+and NO3−removal in 14 days were 96% and 62%, respectively, forP. crassipes. These values corresponded to 96% and 63% for the five tested macrophytes. Root exudates ofA. philoxeroides, L. leptocarpa,andP. ferrugineumcaused inhibition ofM. aeruginosagrowth with no detection of Chl-aafter 7 days. Thus, three emergent macrophytes were more efficient in removing nutrients thanP. 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 abstractHighlightsEmergent macrophytes were similarly efficient toP. crassipesin nutrient removalLudwigia leptocarpawas the most efficient in SRP removal in 7 daysAllelopathy on cyanobacteriumM. aeruginosabyA. philoxeroides, L. leptocarpa, andP. ferrugineumroot exudatesAdapting emergent macrophytes in CFW structures can be helpful in in situ phytoremediation.Statement ofNoveltyThis 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 outperformP. crassipesin reducing soluble reactive phosphorus (SRP) concentrations and exhibit substantial nitrogen removal efficiencies. Furthermore, the allelopathic potential ofA. philoxeroides,L. leptocarpa, andP. ferrugineumagainst the harmful cyanobacteriumMicrocystis aeruginosashowcases their dual functionality in mitigating eutrophication and inhibiting harmful algal blooms.