NITROGEN CYCLING AND NITROUS OXIDE FLUXES IN A TIDAL WETLAND IN AUSTRALIA

Tidal wetlands can remove excess nitrogen through processes such as denitrification and anammox. Denitrification thereby generates nitrous oxide (N₂O), a potent greenhouse gas. While wetlands are often an N₂O source, some pristine systems can be sinks under certain conditions. Habitat complexity can enhance biogeochemical cycling and thereby increase N₂O fluxes. However, the underlying mechanisms are not well understood.   This study measured denitrification, anammox, DNRA and N₂O fluxes across different habitats, including mangrove bare sediment, crab burrows, pneumatophores, and salt marsh, in different seasons at a low-disturbance tidal wetland near Jacobs Well, QLD, Australia. Sediment-air N₂O fluxes were measured using static chamber incubations in exposed habitats and sediment-water fluxes were measured with benthic chamber when these habitats were inundated. Denitrification, anammox and DNRA rates were measured in situ using a novel whole-system ¹⁵NO₃^- labelling approach.   Results show substantial variation in N₂O fluxes across different habitats, tides, and seasons. Generally, sediment-air N₂O fluxes are higher than sediment-water N₂O fluxes, with the highest fluxes observed from pneumatophores and bare sediment sites. Denitrification rates are also highest in those habitats. Crab burrows and salt marsh sites generally have lower N₂O emissions or slight uptakes and the highest DNRA rates.   All fluxes and process rates will be upscaled using a hydrodynamic model and habitat map to construct an annual nitrogen budget, which will improve our understanding of nitrogen dynamics and N₂O fluxes in tidal wetlands.

Presentation Preference: Oral

Primary Presenter: Britte van Haastregt, Southern Cross University (b.van.haastregt.10@student.scu.edu.au)

Authors:

Britte van Haastregt, Southern Cross University  (b.van.haastregt.10@student.scu.edu.au)

Jacob Yeo, Southern Cross University  (jacob.yeo@scu.edu.au)

Dirk Erler, Southern Cross University  (dirk.erler@scu.edu.au)

Judith Rosentreter, Southern Cross University  (judith.rosentreter@scu.edu.au)

Matt Hipsey, University of Western Australia  (matt.hipsey@uwa.edu.au)

Bradley Eyre, Southern Cross University  (bradley.eyre@scu.edu.au)