Multi‐Year Continuous Lateral Fluxes of Dissolved Carbon From a Microtidal Saltmarsh

Tidal salt marshes play a critical role in coastal carbon cycling, yet quantifying lateral carbon fluxes remains challenging due to strong spatial and temporal variability. We combined multi‐year continuous sensor data with discrete water‐chemistry measurements to quantify dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and total alkalinity (TA) fluxes in a tidal creek draining a salt marsh in the Barataria Basin, Louisiana, USA. Multiple linear regression models trained with discrete carbon measurements and in situ sensor data were used to generate continuous DOC, DIC, and TA concentration time series from November 2021 to September 2024. Coupled with high‐resolution discharge data, these estimates revealed strong tidal control on carbon exchange. Instantaneous fluxes ranged from −13,120 to 16,203 g C m −2 yr −1 for DOC, −95,290 to 93,834 g C m −2 yr −1 for DIC, and −63,703 to 62,766 g C m −2 yr −1 for TA, with mean fluxes of 56, 326, and 298 g C m −2 yr −1 , respectively, indicating net export. Lateral dissolved carbon export substantially exceeded sediment carbon burial (204 g C m −2 yr −1 ), with mean DIC flux exceeding the burial rate by 60%. Inorganic carbon dominated lateral exports, accounting for ∼85% of total dissolved carbon flux. Although TA fluxes were lower than DIC fluxes, TA outwelling still exceeded burial by approximately 50%. Pronounced interannual and monthly variability underscores the importance of hydrological and biogeochemical controls at various scales. These results highlight how continuous multi‐year observations can be used to constrain lateral carbon exchange and coastal carbon budgets.