Effects of Enrofloxacin on Nutrient Removal by a Floating Treatment Wetland Planted with Iris pseudacorus: Response and Resilience of Rhizosphere Microbial Communities

Constructed wetlands (CWs), including floating treatment wetlands (FTWs), possess great potential for treating excessive nutrients in surface waters, where, however, the ubiquitous presence of antibiotics, e.g., enrofloxacin (ENR), is threatening the performance of CWs. In developing a more efficient and resilient system, we explored the responses of the FTW to ENR, using tank 1, repeatedly exposed to ENR, and tank 2 as control. Plant growth and nutrient uptake were remarkably enhanced in tank 1, and similar phosphorus removal rates (86 similar to 89% of the total added P) were obtained for both tanks over the experimental period. Contrarily, ENR apparently inhibited N removal by tank 1(35.1%), compared to 40.4% for tank 2. As ENR rapidly decreased by an average of 71.6% within a week after each addition, tank 1 took only 4 weeks to adapt and return to a similar state compared to that of tank 2. This might be because of the recovery of microbial communities, particularly denitrifying and antibiotic-resistance genes containing bacteria, such as Actinobacteria, Patescibacteria, Acidovorax and Pseudomonas. After three ENR exposures over six weeks, no significant differences in the nutrient removal and microbial communities were found between both tanks, suggesting the great resilience of the FTW to ENR.

Automated summary

Constructed wetlands, specifically floating treatment wetlands, have the potential to efficiently remove excessive nutrients from surface waters. However, the presence of antibiotics, such as enrofloxacin, threatens the performance of these wetlands. This study revealed that enrofloxacin exposure enhanced plant growth and nutrient uptake, while slightly inhibiting nitrogen removal. The wetland showed resilience and adapted to enrofloxacin within a month, with no significant differences in nutrient removal and microbial communities compared to the control.