Riparian zones act as critical interfaces for carbon cycling, yet quantifying their greenhouse gas (GHG) emissions is challenging due to the mismatch between continuous soil respiration and episodic methane pulses. Traditional models often fail to reconcile these distinct temporal dynamics. This study proposes a Point-Event Dual-Scale Framework based on high-frequency monitoring of tidal riparian soils to address this gap.
For CO2, we leveraged a comprehensive seasonal dataset to construct a continuous point-scale model. Results confirmed a robust water-limited aeration mechanism: groundwater drawdown significantly enhances aerobic respiration by increasing the vadose zone thickness. This seasonal model demonstrated high explanatory power (R2=0.48) and strong generalizability, successfully capturing the dominant biological response to water level and temperature variations throughout the year.
For CH4, given the stochastic nature of ebullition, we focused specifically on identifying the triggering mechanisms for moments of intense gas release. We revealed a hierarchical Two-Stage control: while biological methanogenesis initiates at a deep threshold of -1.3m, explosive emissions are only triggered when the water table breaches a shallow physical threshold of -0.91m. Crucially, these high-intensity events manifested as instantaneous pulses driven by hydrostatic unloading (physical shock) rather than cumulative biological production.
The proposed framework successfully decouples these processes: using a continuous approach for the stable CO2 baseline and an event-based approach for sporadic CH4 outbursts. We identify -0.91 m as a critical Safety Line for eco-hydrological regulation, providing a scientific basis for optimized sluice scheduling to mitigate carbon pulses.