Tidal freshwater marshes are threatened by seawater intrusion globally due to freshwater discharge reduction and sea-level rise. However, terrestrial nitrate (NO₃⁻) transport responding to seawater intrusion remains poorly understood in tidal marshes. After validation against laboratory experiments, numerical simulations were conducted to analyze seawater intrusion effects on terrestrial NO₃⁻ transport and transformation in tidal marsh aquifers. Results reveal that seawater intrusion noticeably affects NO₃⁻ transport from the marsh aquifer to the tidal creek. Seawater intrusion results in an upper saline plume and a saltwater wedge within the aquifer, which markedly narrows the discharge outlet width of the NO₃⁻ plume and intensifies the peak NO₃⁻ flux across the creek bank. Consequently, both the NO₃⁻ removal efficiency and total nitrogen gas load to the creek decrease substantially after seawater intrusion. This is because the reduction of the transit time and the mixing zone width of the NO₃⁻ plume after seawater intrusion weakens denitrification. Sensitivity analyses indicate that the difference of the NO₃⁻ removal efficiency before and after seawater intrusion depends on soil properties. A larger unsaturated flow effect, saturated hydraulic conductivity or effective porosity leads to a greater difference of the NO₃⁻ removal efficiency before and after seawater intrusion. The predicted decrease of the NO₃⁻ removal efficiency after seawater intrusion is consistent with existing field data.

中文翻译：

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海水入侵抑制潮汐沼泽含水层中硝酸盐的去除


由于淡水排放量减少和海平面上升，潮汐淡水沼泽在全球范围内受到海水入侵的威胁。然而，人们对潮汐沼泽中响应海水入侵的陆地硝酸盐（NO ₃ ^- ）迁移仍知之甚少。经过实验室实验验证后，进行数值模拟来分析海水入侵对陆地NO ₃ ^-迁移和潮汐沼泽含水层转化的影响。结果表明，海水入侵显着影响NO ₃ ^-从沼泽含水层到潮汐溪的输送。海水入侵导致含水层内出现上部盐水羽流和盐水楔，这显着缩小了NO ₃ ^-羽流的排放出口宽度，并增强了穿过溪岸的峰值NO ₃ ^-通量。因此，海水入侵后，NO ₃ ^-去除效率和小溪的总氮气负荷均大幅下降。这是因为海水入侵后NO ₃ ^-羽流的传输时间和混合区宽度减少，反硝化作用减弱。敏感性分析表明海水入侵前后NO ₃ ^-去除效率的差异取决于土壤性质。较大的非饱和流动效应、饱和导水率或有效孔隙率导致海水入侵前后NO ₃ ^-去除效率差异较大。 海水入侵后NO ₃ ^-去除效率的预测下降与现有的现场数据一致。