Unveiling the nitrogen and phosphorus removal potential: Comparative analysis of three coastal wetland plant species in lab-scale constructed wetlands

It is well accepted that tidal wetland vegetation performs a significant amount of water filtration for wetlands. However, there is currently little information on how various wetland plants remove nitrogen (N) and phosphorus (P) and how they differ in their denitrification processes. This study compared and investigated the denitrification and phosphorus removal effects of three typical wetland plants in the Yangtze River estuary wetland (Phragmites australis, Spartina alterniflora, and Scirpus mariqueter), as well as their relevant mechanisms, using an experimental laboratory-scale horizontal subsurface flow constructed wetland (CW). The results showed that all treatment groups with plants significantly reduced N pollutants as compared to the control group without plants. In comparison to S. mariqueter (77.2-83.2%), S. alterniflora and P. australis had a similar total nitrogen (TN)removal effectiveness of nearly 95%. With a removal effectiveness of over 99% for ammonium nitrogen (NH4+-N), P. australis outperformed S. alterniflora (95.6-96.8%) and S. mariqueter (94.6-96.5%). The removal of nitrite nitrogen (NO2--N)and nitrate nitrogen (NO3--N)from wastewater was significantly enhanced by S. alterniflora compared to the other treatment groups. Across all treatment groups, the removal rate of PO43--P was greater than 95%. P. australis and S. alterniflora considerably enriched more N-15 than S. mariqueter, according to the results of the N-15 isotope labeling experiment. While the rhizosphere and bulk sediments of S. alterniflora were enriched with more simultaneous desulfurization-denitrification bacterial genera (such as Paracoccus, Sulfurovum, and Sulfurimonas), which have denitrification functions, the rhizosphere and bulk sediments of P. australis were enriched with more ammonia-oxidizing archaea and ammonia-oxidizing bacteria. As a result, compared to the other plants, P. australis and S. alterniflora demonstrate substantially more significant ability to remove NH4+-N and NO2- -N/NO3--N from simulated domestic wastewater.