Winter-Spring dynamics of dissolved organic carbon fluxes driven by precipitation in a North Carolina tidal marsh

The lateral transport of dissolved organic carbon (DOC) is crucial in tidal marsh carbon budgets, but estimating DOC remains a challenge due to the dynamic nature of terrestrial-aquatic interfaces and limitations of in situ observations. This study used a linear model to correlate DOC and chromophoric dissolved organic matter (CDOM) absorption coefficient at 440 nm ( $a_{\text{CDOM}}\left(440\right)$ ; $r^2=0.75$ ) in Bald Head Creek, North Carolina, USA. Modeled DOC concentrations were merged with current velocity derived from the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) to estimate daily DOC fluxes from January to April 2021, representing winter and spring in the mid-latitude northern hemisphere. DOC flux depended on season and tide, where negative values represent DOC import into the marsh and positive values represent export to the estuary. Results showed that DOC was exported from the marsh in February and March after peak rainfall. While tidal inundation and increased river flow from precipitation influenced DOC flux, the average daily DOC import of -13.6 ± 6.0 g C m^-2 d^-1 was greater than the average daily DOC export of 9.4 ± 8.3 g C m^-2 d^-1 during the study period, showing that the marsh was a net sink for DOC during the early spring. This study demonstrated that field measurements with models like SCHISM provided a synoptic representation of DOC flux, where rainfall-induced river discharge impacts DOC mobilization and export to coastal systems like Bald Head Creek.