Groundwater modulates nutrient dynamics in a freshened saltmarsh tidal creek

IF 2.5 3区地球科学 Q2 CHEMISTRY, MULTIDISCIPLINARY

Marine Chemistry Pub Date : 2025-09-27 DOI:10.1016/j.marchem.2025.104566

Jianan Liu , Xueqing Yu , Tong Peng , Xinyi Lin , Jinzhou Du

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引用次数: 0

Abstract

Saltmarsh tidal creeks play a critical role in coastal nutrient cycling, yet submarine groundwater discharge (SGD), as a key driver, remains poorly understood. Research on SGD-derived outwelling of multiple nutrient species is notably scarce in low-salinity estuarine saltmarshes influenced by large rivers. Utilizing long-lived radium isotopes (²²⁶Ra and ²²⁸Ra) combined with high-frequency monitoring encompassing the most comprehensive species of dissolved nutrient to date during both spring and neap tides, we quantified SGD fluxes and their contribution to nutrient outwelling in a low-salinity saltmarsh tidal creek system of the Yangtze River Estuary. Results showed that driven by tidal pumping, SGD flux during spring tides (12 ± 5.9 cm d⁻¹) was significantly greater than during neap tides (0.77 ± 0.42 cm d⁻¹), along with corresponding differences in nutrient transport fluxes. SGD served as a source of dissolved inorganic nitrogen (DIN) and dissolved silicate (DSi) to the tidal creek system. Specifically, NH₄-N contributed approximately 93 % of the outwelling flux, while SGD-derived DSi accounted for 31–36 % of the DSi outwelling. Conversely, SGD functioned as a sink for dissolved phosphorus (inorganic + organic), capable of removing phosphorus in the tidal creek waters. More importantly, due to nitrogen input via SGD and its retention of phosphorus, both groundwater and ebbing tidal creek waters exhibited nitrogen-to‑phosphorus (N/P) ratios significantly exceeding the Redfield ratio. Although the saltmarshes partially mitigated the elevated N/P ratio during the outwelling process, the imbalanced N/P ratio in SGD-driven outwelling still poses risks of inducing coastal eutrophication and harmful algal blooms. This study unveils the crucial regulatory role of SGD in nutrient dynamics within low-salinity saltmarshes, emphasizing the necessity to incorporate groundwater-surface water interactions into coastal nutrient management and ecological conservation.

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地下水调节新鲜盐沼潮汐溪的营养动态

盐沼潮汐溪在沿海养分循环中起着关键作用，但作为关键驱动因素的海底地下水排放（SGD）仍然知之甚少。在受大河影响的低盐度河口盐沼中，对sgd衍生的多种营养物质外溢的研究尤其缺乏。利用长寿命镭同位素（226Ra和228Ra），结合迄今为止春潮和小潮期间最全面的溶解营养物种类的高频监测，我们量化了长江口低盐度盐沼潮汐溪系统的SGD通量及其对营养物外移的贡献。结果表明，在潮汐泵送的驱动下，春潮期间的SGD通量（12±5.9 cm d - 1）显著大于小潮期间的SGD通量（0.77±0.42 cm d - 1），同时营养物运输通量也存在相应差异。SGD是潮汐溪系统中溶解无机氮（DIN）和溶解硅酸盐（DSi）的来源。具体而言，NH4-N贡献了约93%的外溢通量，而sgd衍生的DSi占DSi外溢的31 - 36%。相反，SGD作为溶解磷（无机+有机）的汇，能够去除潮溪水体中的磷。更重要的是，由于SGD的氮输入及其对磷的滞留，地下水和退潮溪水的氮磷比（N/P）显著超过Redfield比。尽管盐沼在外溢过程中部分缓解了氮磷比的升高，但sgd驱动的外溢中氮磷比的不平衡仍然存在诱发沿海富营养化和有害藻华的风险。本研究揭示了SGD在低盐度盐沼营养动态中的重要调节作用，强调了将地下水-地表水相互作用纳入沿海营养管理和生态保护的必要性。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Marine Chemistry 化学-海洋学

CiteScore

6.00

自引率

3.30%

发文量

审稿时长

4.5 months

期刊介绍： Marine Chemistry is an international medium for the publication of original studies and occasional reviews in the field of chemistry in the marine environment, with emphasis on the dynamic approach. The journal endeavours to cover all aspects, from chemical processes to theoretical and experimental work, and, by providing a central channel of communication, to speed the flow of information in this relatively new and rapidly expanding discipline.