Effects of Aquatic Plant Diversity and Cipangopaludinas chinensis on Nitrogen Removal and Its Stability in Constructed Wetlands

In constructed wetlands (CWs), aquatic plant diversity can enhance system nitrogen (N) removal. However, the impact of aquatic plant diversity with different life forms and benthic animals on the N (NO3−-N, NH4+-N, TIN) removal and its stability has been neglected. This study established 42 simulated CWs, selecting three aquatic plant species with different life forms to establish plant species diversity, with benthic animals (Cipangopaludinas chinensis) added or not added at each diversity level. The results indicated that (1) the presence of the aquatic plant Pistia stratiotes increased the effluent nitrate nitrogen (NO3−-N) concentration. (2) In systems with or without C. chinensis, the plant species richness increased the temporal stability of the effluent NO3−-N concentration; the presence of the aquatic plant Vallisneria natans increased the temporal stability of the effluent total inorganic nitrogen (TIN) concentration in systems without C. chinensis and the temporal stability of the effluent NO3−-N concentration in systems with C. chinensis. (3) Adding C. chinensis significantly reduced the temporal stability of the effluent TIN concentration in the monoculture of V. natans. The rational establishment of aquatic plant diversity with benthic animals can improve the effluent’s water quality while ensuring the water quality’s temporal stability.