We obtained a high-resolution monitoring dataset of ²²²Rn (half-life: 3.8 days), NO₃^-, and humic-like fluorescent dissolved organic matter (FDOM_H) using a newly developed real-time monitoring system to evaluate the influence of tides on submarine groundwater discharge (SGD)-derived nutrient supply in the intertidal and subtidal areas of a macrotidal coastal system in the Yellow Sea. Field observations were conducted in June and August 2024, corresponding to spring tide conditions (tidal amplitudes of 5.1–5.5 m) and a neap-to-spring tidal transition (tidal amplitudes of 3.1–5.2 m), respectively. During the June sampling period, excess ²²²Rn activities and NO₃^- concentrations were approximately seven- and six-fold higher than those during the August sampling period, respectively, suggesting enhanced groundwater-derived inputs under stronger tidal forcing. In addition, mass balance model results showed that SGD-derived NO₃^- input in June (11.8 mmol m^-2 d^-1) was approximately eight-fold higher than that in August (1.5 mmol m^-2 d^-1). In contrast, FDOM_H was supplied mainly by riverine inputs during both observation periods. These findings demonstrate that tidal variability strongly regulates SGD-derived nutrient supply in dynamic macrotidal coastal systems.
 

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