Investigation into ammonia stress on Cyperus alternifolius and its impact on nutrient removal in microcosm experiments

• Gaussian cosine model fits the kinetics of ammonia stress on Cyperus alternifolius.
• Ammonia stress has 50% inhibition at 168 mg N/L and lethal effects at 307 mg N/L.
• The stress of one-time ammonia concentration up to 400 mg N/L is reversible.
• Ammonia concentrations constantly above 219 mg N/L exert irreversible stress.
• Ammonia stress did not affect N removal, but limited plant phosphorus uptake.

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.

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