Simultaneous nitritation/anammox and nitrification/denitrification (SNAND) is a promising method to increase nitrogen removal from ammonium- and nitrate-rich wastewater. This study examined the effects of influent nitrogen concentrations on plant assimilation and microbial nitrogen removal via SNAND in three free water surface wetlands. Anammox and denitrification contributed 78 and 22%, respectively, of microbial removal of total inorganic nitrogen (TIN). Nitrogen removal rates increased with influent concentrations in the low ranges of 17 to 105 mg N/L ammonium and 51 to 179 mg N/L TIN. However, nitrogen removal rates appeared to decrease with influent concentrations in the high ranges of 248 to 293 mg N/L ammonium and 348 to 391 mg N/L TIN. Plant growth was negatively affected when influent ammonium concentration exceeded 46 to 76 mg N/L. Plant assimilation contributed 11 to 47% toward TIN removal at low influent ammonium concentrations (42 to 76 mg N/L) and 4% at high influent ammonium concentrations (mean 264 mg N/L).