Combining Eddy Covariance and Chamber Methods to Better Constrain CO 2 and CH 4 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 CH 4 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 CO 2 and CH 4 at a restored tidal saltmarsh across spatial and temporal scales. Eddy covariance data revealed that the site was a strong net sink for CO 2 (−387 g C‐CO 2 m −2 yr −1 , SD = 46) and a small net source of CH 4 (0.7 g C‐CH 4 m −2 yr −1 , SD = 0.4). After partitioning net ecosystem exchange of CO 2 into gross primary production and ecosystem respiration, we found that high net uptake of CO 2 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 CO 2 emission was from higher elevation mudflat soils (0.5 μmol m −2 s −1 , SE = 1.3) and CH 4 emission was greatest from lower elevation Spartina foliosa soils (1.6 nmol m −2 s −1 , SD = 8.2). Overall, these results highlight the importance of the relationships between wetland plant community and elevation, and inundation for CO 2 and CH 4 fluxes. Future research should include the use of high‐resolution imagery, automated chambers, and a focus on quantifying carbon exported in tidal waters. At the ecosystem level, a restored tidal salt marsh in the South San Francisco Bay California took in more carbon dioxide (CO 2 ) from the atmosphere through photosynthetic activity than it emitted through respiration, and it emitted very small amounts of methane (CH 4 ). This site appears to be a stronger sink for CO 2 compared to other tidal marsh sites due to the very low rate of CO 2 being lost through respiration to the atmosphere, rather than strong photosynthetic rates. We also found that ecosystem level CO 2 emissions and the responses to temperature and light varied based on land cover type. By measuring soil surface emissions from each of the main land cover types of pickleweed, cordgrass, and mudflats we found that on average soils with lower elevation where cordgrass grows were stronger sources of CH 4 while mudflat soils with greater elevation were stronger sources o