Dissolved organic carbon release from surface sand of a high energy beach along the Southeastern Coast of North Carolina, USA

The purpose of this study was to determine the flux of dissolved organic carbon (DOC) from high-energy beach sand to the coastal ocean. The DOC concentration of seawater was measured before and after exposure to the beach sand in laboratory experiments. Increases were observed in all experiments (n = 36) conducted on seawater and high-energy beach sand collected on a monthly basis for one year. Final dissolved organic carbon in seawater after exposure to surface sands were positively correlated with water column DOC concentrations measured in the surf zone at the same time of sand collection for laboratory experiments. Increases in DOC during laboratory experiments displayed marked seasonality with larger increases observed during summer with a corresponding low DOC carbon to nitrogen ratio (C:N) suggesting phytoplankton as the source of DOC during this time of year. Higher DOC C:N was observed during winter indicating a more aged organic material as the source of DOC during this time of low flux. Sandy beach sediments release over an order of magnitude more DOC per meter squared compared to coastal shelf sediments and rainwater suggesting that in locations where there are no direct river inputs these beach environments play a significant, previously unrecognized role as an external source of DOC to the immediate coastal ocean. It is likely that DOC released from these environments has a significant effect on surf zone biogeochemistry potentially affecting oxygen concentrations in coastal regions.