Coastal oceans, known as the major nitrous oxide (N₂O) source to the atmosphere, are increasingly subject to eutrophication and concurrent near-bottom hypoxia. The natural nitrogen cycle is likely to be altered markedly in hypoxic coastal oceans. However, the processes responsible for N₂O production and emission remain elusive because of lacking field rate measurements simultaneously conducted in the water column and sediment. Here, we quantified N₂O production rates using a ¹⁵N-labeled technique in the water-column and surface sediments off the Changjiang (Yangtze) River estuary, the largest hypoxic zone in the Pacific margins. Our results showed that the estuarine surface sediments were the major source for N₂O production, accounting for approximately 90% of the total water-column accumulation and consequent efflux of N₂O in the hypoxic zone, whereas the water-column nitrification and denitrification combined only contributed <10%. More importantly, the coupling of nitrification and denitrification at the presence of abundant supply and remineralization of labile organic matter was the main driver of the N₂O release from the sediment-water interface in this region. This study highlights the dominant role of benthic processes occurring at the sediment-water interface controlling the coastal N₂O budget, as the anthropogenic eutrophication and hypoxia are expanding in coastal oceans.

沿海海洋被称为大气中的主要一氧化二氮 (N ₂ O) 来源，正日益受到富营养化和同时发生的近底缺氧的影响。在缺氧的沿海海洋中，自然氮循环可能会发生显着变化。然而，由于缺乏在水柱和沉积物中同时进行的场速率测量，导致 N _{2 O 产生和排放的过程仍然难以捉摸。}在这里，我们使用¹⁵ N 标记技术在太平洋边缘最大的缺氧区长江（长江）河口附近的水柱和表层沉积物中量化 N _{2 O 的产生率。}结果表明，河口表层沉积物是N _{2的主要来源。}O 产量约占缺氧区水柱总积累和 N ₂ O 流出的 90%，而水柱硝化和反硝化作用的总和仅贡献 <10%。更重要的是，在存在大量供应和不稳定有机物再矿化的情况下硝化和反硝化的耦合是该地区沉积物-水界面释放N _{2 O的主要驱动力。}这项研究强调了在控制沿海 N ₂ O 预算的沉积物-水界面处发生的底栖过程的主要作用，因为人为的富营养化和缺氧正在沿海海洋中扩大。