The influence of oyster reefs and surrounding sediments on nitrogen removal - An in-situ study along the East coast of Australia

Giulia Filippini; Ana B Bugnot; Angus Ferguson; Paul E Gribben; Julia Palmer; Katherine Erickson; Katherine A Dafforn

doi:10.1016/j.envres.2023.116947

The influence of oyster reefs and surrounding sediments on nitrogen removal - An in-situ study along the East coast of Australia

Environ Res. 2023 Nov 15;237(Pt 1):116947. doi: 10.1016/j.envres.2023.116947. Epub 2023 Aug 22.

Authors

Giulia Filippini¹, Ana B Bugnot², Angus Ferguson³, Paul E Gribben⁴, Julia Palmer⁵, Katherine Erickson⁶, Katherine A Dafforn⁷

Affiliations

¹ School of Natural Sciences, Macquarie University, North Ryde, NSW, 2109, Australia. Electronic address: giulia.filippini@mq.edu.au.
² CSIRO Environment, St. Lucia, QLD, 4067, Australia; School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW, 2006, Australia.
³ Department of Planning, Industry and Environment, Lidcombe, NSW, 2141, Australia.
⁴ Centre for Marine Science and Innovation, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia; Sydney Institute of Marine Science, Mosman, NSW, 2088, Australia.
⁵ School of Natural Sciences, Macquarie University, North Ryde, NSW, 2109, Australia.
⁶ Centre for Marine Science and Innovation, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, 2052, Australia.
⁷ School of Natural Sciences, Macquarie University, North Ryde, NSW, 2109, Australia; Sydney Institute of Marine Science, Mosman, NSW, 2088, Australia.

PMID: 37611788
DOI: 10.1016/j.envres.2023.116947

Abstract

Oyster reefs play a crucial role in the removal of nitrogen (N) from aquatic systems by facilitating nutrient regeneration and denitrification, both in their tissues and shells and surrounding sediments. However, we still have a limited understanding about the contribution of each component of the reefs (e.g. oysters vs sediments) to N processes, and whether rates are dependent on site-specific characteristics. To address these knowledge gaps, we conducted an experiment across six oyster reefs along 1080 km of the Eastern Australian coast with different sediment characteristics. By using in-situ clear and dark incubation chambers, we assessed how benthic metabolism, nutrient and dinitrogen gas (N₂) fluxes varied among the following treatments: 'oysters', 'sediments', and 'sediments + oysters' that were used to represent components of the whole reef habitat (i.e. reef matrix vs surrounding sediments vs the interaction among them, respectively), and sites. We found that during dark conditions and at siltier sites, N₂ effluxes from oysters can be up to 23 times higher than sediments, while N₂ effluxes from chambers with both sediments and oysters were similar to sediment treatments, and lower than oyster treatments. These results can be explained by sediment processes including nutrient assimilation by benthic microalgae and/or lower nutrient diffusion into interstitial space. Additionally, oyster treatments showed an uptake of nitrate (NO₃^-) that was likely converted into N₂, whereas sediment treatments showed an overall release of NO₃^-. In dark conditions, ammonium (NH₄⁺) fluxes remained consistent across treatments and sites, indicating that any exports from oyster excretion (in those treatments including oysters) were either counterbalanced by or comparable to exports from sediments. This study provides evidence that the crucial contribution of oyster reefs to N removal is dependent on interactions between reef components and environmental factors.

Keywords: Benthic metabolism; Denitrification; Nutrient flux; Oyster reef; Sediment characteristics.