Nitrogen loading resulting from major floods and sediment resuspension to a large coastal embayment

Alistair Grinham; Tony Costantini; Nathaniel Deering; Cameron Jackson; Carissa Klein; Catherine Lovelock; John Pandolfi; Gal Eyal; Michael Linde; Matthew Dunbabin; Brendon Duncan; Nicholas Hutley; Ilha Byrne; Craig Wilson; Simon Albert

doi:10.1016/j.scitotenv.2024.170646

Nitrogen loading resulting from major floods and sediment resuspension to a large coastal embayment

Sci Total Environ. 2024 Mar 25:918:170646. doi: 10.1016/j.scitotenv.2024.170646. Epub 2024 Feb 5.

Authors

Affiliations

¹ School of Civil Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. Electronic address: a.grinham@uq.edu.au.
² Urban Utilities, Brisbane, QLD 4001, Australia.
³ School of Civil Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia.
⁴ School of the Environment, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia.
⁵ School of the Environment, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia; The Mina & Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat Gan 5290002, Israel.
⁶ Port of Brisbane Pty Ltd., Brisbane, QLD 4178, Australia.
⁷ Biopixel Oceans Foundation, Fortitude Valley, QLD 4006, Australia.

PMID: 38325481
DOI: 10.1016/j.scitotenv.2024.170646

Abstract

Major floods pose a severe threat to coastal receiving environments, negatively impacting environmental health and ecosystem services through direct smothering with sediment and nutrient loading. This study examined the short and long-term impacts of the February 2022 major flood event on mud extent and sediment nitrogen flux in Moreton Bay (the Bay), a large, sub-tropical embayment in Southeast Queensland, Australia. Short-term impacts were assessed three days after the flood peak by sampling surface water at 47 sites in the direction of the predominant circulation pattern. Longer-term impacts were assessed by undertaking an intensive sediment survey of 223 sites and a nutrient flux experiment using sediment core incubations to simulate calm and resuspension conditions for the four key sediment classes. Short-term impacts revealed elevated turbidity levels extended across the Bay but were highest at the Brisbane River mouth, ammonium concentrations varied inversely with surface turbidity, whereas nitrate concentrates closely tracked surface turbidity. The sediment survey confirmed fine sediment deposition across 98 % of the Bay. Porewater within the upper 10 cm contained a standing pool of 280 t of ammonium, with concentrations more than three orders of magnitude higher than overlying surface waters. The nutrient flux experiment revealed an order of magnitude higher sediment ammonium flux rate in the sandy mud sediment class compared to the other sediment classes; and for simulated resuspension conditions compared to calm conditions for sand, muddy sand, and mud sediment classes. Scaling across the whole Bay, we estimated a mean annual sediment flux of 17,700 t/year ammonium, with a range of 13,500 to 21,900 t/year. Delivery of fine sediments by major floods over the last 50 years now impact >98 % of the benthic zone and provide a major loading pathway of available nitrogen to surface waters of Moreton Bay; representing a significant threat to ecosystem health.

Keywords: Ammonium; Australia; Catchment management; Flood; Moreton Bay; Nitrogen budget; Sediment distribution; Sediment flux; Sub-tropics; Turbidity.