Isotopically resolved fate and processes of nitrogen in a constructed wetland treating domestic effluent
Date
2025
Authors
Allen, D.J.
Farrell, M.
Wong, W.W.
Huang, J.
Mosley, L.M.
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Journal article
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Science of the Total Environment, 2025; 969(178816):178816-178816
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Abstract
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<sub>4</sub><sup>+</sup> concentrations (54 mg L<sup>-1</sup>) at the inlet of the wetland. The decrease in NH<sub>4</sub><sup>+</sup> and increase in NO<sub>3</sub><sup>-</sup> concentrations, coupled with an increase in δ<sup>15</sup>N-NH<sub>4</sub> in the water along the flow path of the wetland, strongly indicates the significance of nitrification and assimilation processes. We also observed an increase in δ<sup>15</sup>N-NO<sub>3</sub><sup>-</sup><sub>,</sub> however, the lack of increase in δ<sup>18</sup>O-NO<sub>3</sub><sup>-</sup> suggested denitrification was either not a prominent process, or the δ<sup>18</sup>O-NO<sub>3</sub><sup>-</sup> signature was masked by the extent of nitrification. There was evidence of an influence of the wastewater on the plants in the riparian zone as their δ<sup>15</sup>N increased along the flow path, unlike the adjacent terrestrial plants. Similarly, this occurred with suspended solids, indicating progressive plant and algal assimilation of N in the CW. Further research is required to account for changes with seasonality and sediment processes and interactions.
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Data source: Supplementary data, https://doi.org/10.1016/j.scitotenv.2025.178816
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Copyright 2025 The Authors. This is an open access article under the CC BY license. (http://creativecommons.org/licenses/by/4.0/)