Work

Dual pathways of tide-driven greenhouse gas emissions via porewater advection and surface exchange in mudflat and sandy beach

Year: 2025

Type: article

Abstract: Intertidal subterranean estuaries (STEs), as a critical component of the Earth's Critical Zone, are biogeochemical hotspots for greenhouse gas (GHGs: N2O, CH4, and CO2) emissions. Tidal forcing fundamentally controls carbon and nitrogen cycles that driving the production/consumption of GHGs in muddy and sandy intertidal STEs. However, the sediment-dependent source/sink dynamics of GHGs and tidal responses remain poorly constrained. Through high-resolution spatiotemporal observations across sediment types in intertidal STEs, we show that the mudflat acted as a net GHGs source to coastal waters, whereas the sandy beach was a net sink of N2O but a source of CH4 and CO2. Both types were net atmospheric GHGs sources, with CO2 accounting for 79.05-99.88%. The comparable magnitude of GHGs fluxes between sandy and muddy systems underscores the previously underestimated contribution of low-organic sandy coasts to marine GHGs budgets. Our analyses further identify pronounced tidal modulation of dissolved GHGs storage and transport pathways, including lateral (porewater exchange) and vertical (sediment/water-air interfaces) fluxes, with particularly strong tidal phase dependence in sandy environments. Global extrapolation of these observations estimates intertidal zones emissions at approximately 0.06±0.14 Tg N2O, 0.53±1.11 Tg CH4, and 191.22 ± 123.69 Tg CO2 annually. These findings enhance mechanistic understanding of tidal-scale GHGs variability in coastal aquifers, highlighting the necessity to integrate hydrology and biogeochemistry into global GHGs budget to refine climate predictions.

Source: Water Research X

DOI: 10.1016/j.wroa.2025.100468