Floating flowers: Screening cut-flower species for production and phytoremediation on floating treatment wetlands in South Florida

Floating treatment wetlands (FTWs) are artificial ecosystems designed to mimic the nutrient removal capabilities of natural wetlands through the hydroponic cultivation of plants on floating rafts, thereby utilizing the process of phytoremediation. This approach provides plants with protection against submersion, creating an optimal environment for the growth of valuable hydroponic crops. To ensure the removal of nutrients absorbed and incorporated into plant biomass from aquatic systems, the implementation of routine plant harvesting serves as an effective management strategy. This practice prevents the decomposition and subsequent release of nutrients back into the water. Furthermore, the cultivation of crops for commercial purposes can serve as an incentive to enhance biomass harvesting and replanting efforts, which may be financially impractical otherwise. This study aimed to assess the growth success and nutrient remediation capacities of five cut-flower species on FTWs in controlled mesocosm systems at Florida International University in Miami, Florida. The surviving species were evaluated based on growth metrics, bloom count, and nutrient removal abilities, specifically for total phosphorus (TP) and total nitrogen (TN). Among the five species tested, only marigold (Tagetes erecta) survived throughout the 12-week trial on the FTWs. The marigold-planted treatment exhibited a significant enhancement in nutrient reduction efficiencies compared to the control treatment, removing 52% more TP and 33% more TN mass from the mesocosm system. This resulted in a nutrient removal rate of 0.062 g of TP ‧ m2 ‧ day−1 and 0.321 g of TN ‧ m2 ‧ day−1 in the marigold-treated mesocosm. Additionally, the marigold treatment yielded an average of 65 market-quality blooms per m2, with mean widths of 6.4±1.8 cm and lengths of 27.6±7.3 cm. Given the substantial nutrient removal and the production of marketable blooms, marigold (Tagetes erecta) shows promising potential as a commercially viable remediating crop cultivated on FTWs in South Florida. Statement of Significance: This study demonstrated that marigolds grew successfully on an FTW, removed a comparable amount of nutrients from the water as other wetland plants tested on FTWs in previous studies, and produced a high number of blooms for market. This species is worth testing at a field scale to see how well they thrive in application. Future studies should increase the thickness of the FTW for roots to anchor better and help stabilize the growth of additional cut-flower species. Specifically, the production of cut-flowers on FTWs in South Florida could take advantage of the floral industry infrastructure in Miami, FL while also helping to address increasing water quality issues in the region.