Ammonia stress on plants has been investigated at discrete ammonia concentrations in constructed
wetlands. This study introduced a Gaussian model to simulate the kinetics of ammonia stress and
investigated reversible and irreversible ammonia stress on Cyperus alternifolius in wetland-like microcosms.
Ammonia stress on plant weight increase and oxygen release potential started at weekly
ammonia concentrations of 27 and 28 mg N/L, reached 50% inhibition at 178 and 158 mg N/L, and
resulted in lethal effects at 311 and 303 mg N/L, respectively. The stress of one-time ammonia concentrations
up to 400 mg N/L could be reversible. Ammonia concentrations constantly above 219 mg N/L
exerted irreversible stress. In the microcosms with ammonia concentrations above the 50% inhibition
levels, plants played a minor role in nitrogen removal. Nitrogen removal performance was not affected
considerably by ammonia stress. Orthophosphate removal was suppressed by ammonia stress due to less
plant uptake. Design and operation of constructed wetlands should consider wastewater ammonia
concentration so that the integrity of constructed wetland ecosystems can be maintained.