Nutrient removal, biomass accumulation and nitrogen-transformation functional gene response to different nitrogen forms in enhanced floating treatment wetlands

Enhanced floating treatment wetlands (EFTWs) were established to treat water with different concentrations of ammonia and nitrate, the ratios of which were set at 0:3, 1:2, 2:1 and 3:0, respectively. The results showed that the average total nitrogen (TN) removals were 80.7%, 79.2%, 47.0% and 10.1% in those four treatments, respectively. EFTWs had much better removal ability of NO3−-N (82.8-98.1%) than that of NH4+-N (25.1-59.4%). Canna indica L. in the water containing both NH4+-N and NO3−-N experienced higher relative growth rate and absorption capacity of N (7.7 g/m2) and P (1.5 g/m2) than those with the sole N source. The relative abundance of narG and nirK on the plant roots and biofilm carriers in the six nitrogen functional genes accounted for 71.1-85.6% and 58.5-90.3%, respectively, leading to high denitrification in EFTWs. Therefore, N forms in water could affect biomass accumulation and attached microorganisms, and thus affect the water purification efficiencies of EFTWs.