View article

Estuaries play a key role in moderating the flow of nitrogen (N) to marine ecosystems. However, the magnitude of this N removal can vary dramatically both within and between estuaries due to the benthic habitats present. Here, we compare denitrification, coupled nitrification–denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) across a mosaic of benthic habitats in the subtropical Noosa River Estuary, Australia. Using ¹⁵N tracer techniques and passive pore‐water samplers, we show that coupled nitrification–denitrification was the dominant pathway for N₂ production across all habitats, with higher rates in vegetated habitats (10–70 μmol N m⁻² h⁻¹) compared to bare sediments (0.9–2 μmol N m⁻² h⁻¹). Unusual pore‐water profiles in the macroalgal sediments suggest the presence of sulfur‐driven anoxic nitrification of NH₄⁺ to NO₃⁻ and N₂. A benthic N budget showed that …