Under-the-radar creeks could be sweeping carbon out of salt marshes

Salt marshes, coastal wetlands that experience daily inundation and exposure due to tides, play a significant role in carbon cycling. However, understanding how these marshes store, transport, and release carbon remains uncertain. Researchers from Louisiana have now shed light on a previously overlooked aspect of salt marsh carbon dynamics by focusing on the role of tidal creeks in carbon transport.

By installing sensors and collecting water samples over a period of three years, the researchers were able to capture detailed data on water flow, water chemistry, and environmental parameters in a salt marsh creek. This provided a rare, continuous data set that captured daily, seasonal, and annual variability, something that is often missing in other studies that use short-term monitoring.

The data analysis revealed that more dissolved organic and inorganic carbon was exported from the marsh than was stored in its soils. This net flux was primarily driven by the differences in carbon concentrations between ebb and flood tides across different time scales, including daily, monthly, and seasonal variations. The lateral transport of carbon through tidal creeks can therefore act as a dynamic control on the salt marsh's carbon sequestration, either enhancing or reducing it depending on the tide.

Interestingly, the researchers also found that total alkalinity varied with the tides, indicating that salt marshes can influence the acidity of downstream waters. This new understanding of the role of tidal creeks in carbon transport suggests that these coastal features may have a greater impact on coastal carbon budgets than previously thought.

Incorporating lateral carbon transport into coastal carbon models and blue carbon assessments could improve their accuracy and deepen our knowledge of the role that salt marshes play in the global carbon budget.