Coupling High Frequency Atmospheric Carbon Flux Measurements with Seasonal Sedimentary Carbon Deposition to Constrain Short-Term Carbon Accumulation: Preliminary Data from a Restored Coastal Wetland in San Francisco Bay

Coastal wetlands play a significant role in global carbon cycles, where carbon sequestration is roughly comparable to forests even though the spatial extent is much smaller. These coastal wetlands therefore present a huge opportunity as a blue carbon ecosystem, yet measuring and modelling carbon exchanges in coastal wetlands is difficult given the complexities of the physical and biogeochemical processes operating within these systems. Understanding short-term carbon dynamics in coastal wetlands will be critical to understanding ecosystem response to climate change, and assessing ecosystem services within these valuable blue carbon ecosystems. Herein we present preliminary data from a restored coastal wetland in San Francisco Bay where we have coupled high-resolution atmospheric carbon flux measurements with seasonal sedimentary carbon deposition over >1 year to improve estimates of the Net Ecosystem Carbon Budget for the wetland. Ecosystem exchange of CO₂ and CH₄ between plant canopies and the atmosphere were determined from the micrometeorological eddy covariance method, while seasonal sedimentary carbon depositional was determined using the short-lived radioisotope ⁷Be to measure seasonal sediment mass accumulation and the carbon content of newly deposited material was measured using an elemental analyzer. Preliminary results showed that annual atmospheric carbon uptake in the wetlands was 408 g C-CO₂ m^-2 yr^-1, while seasonal carbon burial was estimated at ~220 g C m^-2 yr^-1 suggesting that 40-50% of the annual carbon uptake may be lost to hydrologic transport within or out of the wetland. To our knowledge, the coupling of these measurements is unprecedented. This work is ongoing, with the next phase incorporating hydrologic carbon flux measurements within the tidal channels. From this work we aim to improve biogeochemical models for carbon sequestration in coastal wetlands, and provide valuable information concerning coastal wetland ecosystem services.