Constructed wetlands (CWs) are recognised as effective wastewater purification systems for the removal of contaminants, particularly nitrogen (N). However, the performance of a CW in N removal relies on complex biogeochemical interactions within and between various compartments. We assessed the concentrations and isotopic compositions of multiple N and C species in the water column, sediment, plants and soil in the riparian and adjacent terrestrial zones within a CW in South Australia. The major source of N supplied to the wetland is domestic effluent delivered via a municipal wastewater treatment plant resulting in high NH