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 combined denitrification and coupled nitrification–denitrification accounted approximately 96% of the N₂ production, while DNRA accounted for 9% of total NO₃⁻ reduction pathways in the Noosa River Estuary. The macroalgae habitat contributed 76% of total N removal via N₂ production and 65% of N retention via DNRA, despite accounting for only 25% of the total surface area. We show a strong relationship between seagrass and macroalgae area and N₂ production (r² = 0.8; p < 0.01), and as such, the capacity to mitigate reactive N loads in estuaries may decrease with the large‐scale loss of seagrass and other vegetated habitats.

中文翻译：

---

在河口底栖生境的马赛克上将反硝化，厌氧氨化和异化硝酸盐还原为铵

河口在调节氮向海洋生态系统的流动中起关键作用。然而，由于存在底栖生境，河口内和河口之间氮的去除量会发生巨大变化。在这里，我们在澳大利亚亚热带的努萨河河口底栖生境的马赛克上比较了反硝化，硝化-反硝化，厌氧氨氧化和异化硝酸盐还原成铵（DNRA）。使用^15个Ñ示踪技术和被动孔隙水取样器，我们表明，耦合硝化-脱硝是N的主要途径₂的生产在所有的生境，在植被栖息地更高的速率（10-70  μ摩尔的N米^-2 ħ ^-1）相比裸沉积物（0.9-2 μ摩尔的N米^-2 ħ ^-1）。在大型海藻沉积物不寻常的孔隙水型材建议NH的硫驱动缺氧硝化的存在₄ ⁺为NO ₃ ^-和N ₂。甲底栖Ñ预算表明，组合的脱硝和耦合硝化-脱硝占所述N个的约96％的₂生产，而DNRA占总NO 9％₃ ^-在努萨河口减少通路。大型藻类栖息地通过N ₂去除了总N的76％尽管仅占总表面积的25％，但通过DNRA仍可生产65％的氮，但氮的保留量却高达5％。我们显示海草和大型藻类面积与N ₂产量之间存在很强的关系（r ² = 0.8；p  <0.01），因此，随着海草和其他生物的大量损失，减轻河口活性氮负荷的能力可能会降低。植被栖息地。