Antibiotics and benthic fauna diversity affect nitrogen removal and greenhouse gas emissions in constructed wetlands by changing enzyme activity and microbial community

Antibiotic contamination in wastewater presents substantial ecological risks. However, the effects of antibiotics on nitrogen (N) removal and greenhouse gas (GHG) emissions in benthic fauna-enhanced constructed wetlands (CWs) remain poorly understood. In this study, 30 CW microcosms were established with three levels of benthic fauna richness (no fauna, three single-species, and one three-species), under conditions with or without sulfonamide antibiotics. Results showed that antibiotics significantly increased effluent N concentrations in single-species benthic fauna systems by plant and benthic fauna antioxidant capacity (superoxide dismutase, peroxidase, and catalase), plant biomass and N pool, the activities of N -transforming enzymes (e.g., hydroxylamine oxidoreductase, nitrous oxide reductase), and microbial community composition. In contrast, antibiotics reduced effluent nitrate N concentration by 42 % in fauna-free systems. Antibiotics and benthic fauna diversity also significantly influenced GHG emissions. Without antibiotics, the three-species systems exhibited the lowest total global warming potential (GWP CH4+N2O+CO2 ) per unit N removal, with a 265 % reduction relative to the control. With antibiotics, the Chironomus riparius systems showed the lowest GWP CH4+N2O+CO2 per unit N removal, reducing this indicator by 637 % compared to the control. Furthermore, antibiotics further enhanced this effect in C. riparius systems, resulting in a 372 % reduction. Results indicated that, without antibiotics, enhancing benthic fauna diversity can effectively improve pollutant removal and mitigate GHG emissions. Under antibiotic stress, however, introducing a tolerant keystone such as C. riparius may be a more effective strategy for achieving both water quality improvement and climate mitigation.