Novel insight into ammonium, phosphate, and iron(II) dynamics in the sediment porewater of a constructed wetland under artificial aeration through the diffusive equilibrium in thin films technique

Danielle J Allen; Jianyin Huang; Mark Farrell; Luke M Mosley

doi:10.1016/j.envres.2023.116746

Novel insight into ammonium, phosphate, and iron(II) dynamics in the sediment porewater of a constructed wetland under artificial aeration through the diffusive equilibrium in thin films technique

Environ Res. 2023 Nov 1;236(Pt 1):116746. doi: 10.1016/j.envres.2023.116746. Epub 2023 Jul 29.

Authors

Danielle J Allen¹, Jianyin Huang², Mark Farrell³, Luke M Mosley⁴

Affiliations

¹ School of Biological Sciences, The University of Adelaide, Kaurna Country, Urrbrae, South Australia 5064, Australia; CSIRO Agriculture & Food, Kaurna Country, Gate 4 Waite Road, Urrbrae, South Australia 5064, Australia.
² STEM, University of South Australia, Mawson Lakes Blvd, Kaurna Country, Mawson Lakes, South Australia 5095, Australia.
³ CSIRO Agriculture & Food, Kaurna Country, Gate 4 Waite Road, Urrbrae, South Australia 5064, Australia.
⁴ School of Biological Sciences, The University of Adelaide, Kaurna Country, Urrbrae, South Australia 5064, Australia. Electronic address: luke.mosley@adelaide.edu.au.

PMID: 37517502
DOI: 10.1016/j.envres.2023.116746

Abstract

The analysis of porewater concentrations in constructed wetland sediments could help to understand biogeochemical processes, the sources and sinks of nutrients, and their effect on overlying water quality. In this study, we measured high-resolution porewater concentration profiles of ammonium (NH₄⁺-N), nitrate (NO₃N), phosphate (PO₄^3--P), and ferrous iron (Fe(II)) in-situ in the Laratinga constructed wetland in Mount Barker (South Australia) using diffusive equilibration in thin films (DET) techniques. Measurements were taken under light and dark conditions, and non-aerated and aerated conditions to determine the effect on sediment porewater nutrient concentrations. Baseline surface water nutrient concentrations (NH₄⁺-N > 36 mg L^-1, PO₄^3--P > 0.43 mg L^-1) greatly exceeded water quality guideline criteria. Aeration of the water column alleviated night-time hypoxic conditions (i.e. dissolved oxygen increased from a minimum of 0.7 mg L^-1 to a minimum of 4 mg L^-1), and increased the redox potential in the sediment. Significant differences were present for NH₄⁺-N, PO₄^3--P, and Fe(II) concentrations with depth in the sediment. Ammonium concentrations in the sediment reduced under aerated conditions, presumably due to enhanced nitrification. However it was observed that PO₄^3--P and Fe(II) concentrations increased significantly with aeration, especially under dark conditions, and were strongly correlated (R²>0.8). This was not what was hypothesised and points to complex interactions between Fe and P in the sediment. Nitrate concentrations in the sediment were below the detection limit (<0.9 mg L^-1) which suggests limited nitrification-denitrification is occurring. Overall the results suggest that DET techniques are useful tools for quantifying porewater concentrations of nutrients in constructed wetlands under various environmental conditions.

Keywords: Aeration; Constructed wetland; Diffusive equilibrium in thin films (DET); Domestic effluent; Porewater.