The effects of bottom water oxygen concentration on sediment oxygen uptake, oxygen penetration depth, nitrate and ammonium fluxes, anammox, denitrification, dissimilatory nitrate reduction to ammonium, nitrification, and mineralization were investigated off the Changjiang estuary and its adjacent East China Sea, by combining a seasonal comparison with three artificially induced bottom water oxygen conditions (oxic, ambient, and severe hypoxia). A 50% decrease in in‐situ bottom water oxygen concentrations between May and August, led to decreases in the average sediment oxygen uptake and oxygen penetration depth by 23% and 29%, respectively. Anammox rates decreased by a factor of 2.5, and the relative contribution of anammox to the total benthic N‐loss decreased from 20% to 7.4%. However, denitrification rates increased, leading to an overall benthic N‐loss rate of 0.85 mmol N m⁻² d⁻¹. At the same time, an increasing contribution of dissimilatory nitrate reduction to ammonium to total nitrate reduction led to higher recycling of inorganic nitrogen during hypoxia in August. Under artificially induced conditions of severe hypoxia, there was a sharp decrease in both sediment oxygen uptake and benthic N‐loss rates by 88% and 38%, respectively. Nitrate and ammonium fluxes showed complex behavior at different sites which could be related to the repression of sedimentary nitrification below a bottom water oxygen threshold of 9.7 μM and increasing dissimilatory nitrate reduction to ammonium. Taken together, our results indicate that changes in benthic nutrient cycling under seasonal hypoxia enhance the retention of both organic and inorganic nitrogen, thereby exacerbating oxygen deficiency.

中文翻译：

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底栖氮循环对河口缺氧的响应

结合长江河口及其邻近东海，研究了底水氧浓度对沉积物氧吸收，氧渗透深度，硝酸盐和铵通量，厌氧氨氧化，反硝化，硝酸盐异化还原成铵，硝化和矿化的影响。与三种人工诱发的底水氧气状况（有氧，环境和严重缺氧）的季节性比较。在5月至8月之间，原位底水中的氧气浓度降低了50％，导致平均沉积物氧气吸收量和氧气渗透深度分别降低了23％和29％。厌氧氨水的发生率降低了2.5倍，厌氧氨水对总底栖N损失的相对贡献从20％降低到7.4％。但是，反硝化率增加了，^-2 d ^-1。同时，异化硝酸盐还原对铵的贡献在总硝酸盐还原方面的增加，导致8月缺氧期间无机氮的循环利用率更高。在人为诱导的严重缺氧条件下，沉积物的摄氧量和底栖氮损失率分别急剧降低了88％和38％。硝酸盐和铵的通量在不同的位置表现出复杂的行为，这可能与抑制低于9.7 µm的底水氧阈值的沉积硝化作用有关。M和增加异化硝酸盐还原成铵。两者合计，我们的结果表明，季节性缺氧下底栖养分循环的变化会增强有机氮和无机氮的保留，从而加剧缺氧。