Responses of wetland plants to ammonia and water level

Constructed wetland systems receiving animal wastewater may enhance water quality when designed, operated, and maintained properly. In the case of wetlands designed to treat animal waste, system effectiveness may be limited by high ammonia concentrations and inundation, conditions that can adversely affect macrophytic vegetation. We conducted a 4-month greenhouse experiment to assess the impact of ammonia concentration and water level on plants commonly used in constructed wetlands for treating animal waste. We examined the effects of ammonia concentration (0, 50, 100, 200 and 400 mg/l) on the growth and biomass production of Juncus effusus, Sagittaria latifolia, Schoenoplectus tabernaemontani, Typha angustifolia, and Typha latifolia. We also explored interactions between ammonia concentration (0, 50, 100, 200 and 400 mg/l) and water level (flooded and nonflooded conditions) for S. tabernaemontani and T. latifolia. We found that ammonia levels in excess of 200 mg/l inhibited growth for J. effusus, S. latifolia, and T. latifolia after a period of weeks, and levels in excess of 100 mg/l similarly inhibited growth for S. tabernaemontani. Ammonia levels in the range studied had an ambiguous effect on T. angustifolia. Affected species demonstrated similar fertilization/inhibition responses to increased ammonia, but important differences were noted between species. Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia. Our results emphasize the need for careful consideration of the species used in treatment wetlands, and suggest that management of ammonia concentration may enhance plant growth and system function.