Combining eddy covariance and chamber methods to better constrain CO2 and CH4 fluxes across a heterogeneous restored tidal wetland

Tidal wetlands play an important role in global carbon cycling by storing carbon in sediment at millennial time scales, transporting dissolved carbon into coastal waters, and contributing significantly to global CH₄ budgets. However, these ecosystems' greenhouse gas monitoring and predictions are challenging due to spatial heterogeneity and tidal flooding. We utilized eddy covariance and chamber measurements to quantify fluxes of CO₂ and CH₄ at a restored tidal saltmarsh across spatial and temporal scales. Eddy covariance data revealed that the site was a strong net sink for CO₂ (−387 g C-CO₂ m⁻² yr⁻¹, SD = 46) and a small net source of CH₄ (0.7 g C-CH₄ m⁻² yr⁻¹, SD = 0.4). After partitioning net ecosystem exchange of CO₂ into gross primary production and ecosystem respiration, we found that high net uptake of CO₂ was due to low respiration emissions rather than high photosynthetic rates. We also found that respiration rates varied between land covers with increased respiration in mudflats compared to vegetated areas. Daytime soil chamber measurements revealed that the greatest CO₂ emission was from higher elevation mudflat soils (0.5 μmol m⁻²s⁻¹, SE = 1.3) and CH₄ emission was greatest from lower elevation Spartina foliosa soils (1.6 nmol m⁻²s⁻¹, SD = 8.2). Overall, these results highlight the importance of the relationships between wetland plant community and elevation, and inundation for CO₂ and CH₄ fluxes. Future research should include the use of high-resolution imagery, automated chambers, and a focus on quantifying carbon exported in tidal waters.