CO2 fluxes in a recently restored salt marsh

Blue carbon ecosystems are not only known to be one of the most important carbon sinks, but also their restoration is considered a nature-based tool for mitigating climate change impacts. Further research on restored salt marshes is essential to understand the recuperation of natural carbon dynamics and provide insights into short-term effects and a basis for long-term monitoring. In this study, we assess the net CO 2 exchange with the atmosphere over a year in a recently restored salt marsh in Trebujena, southern Spain. We measured CO 2 fluxes every two months from bare and vegetated sediments that were terrestrialised, under both dark and light conditions, and examined their relationships with the environmental variables measured in situ (i.e. sediment temperature, moisture, salinity, pH, organic carbon, and inorganic carbon). Additionally, CO 2 flux measurements were taken on the flooded area at the water-air interface. Our results indicate that CO 2 fluxes were significantly influenced by sediment temperature, moisture, and salinity. Bare and vegetated sediments were CO 2 sources because the meadow's uptake was insufficient to offset emissions from terrestrialised sediments, suggesting a degraded physiological state of the vegetation. In contrast, the flooded area was a net CO 2 sink, suggesting that the recovery of the natural hydrological regime would be advisable to promote the restoration of the carbon dynamics. • The restored salt marsh was a net CO 2 source to the atmosphere for over an annual period. • The CO 2 emission was raised by the combined effects of drought, elevated temperature, and reduced salinity. • Findings suggest that restoring a natural hydrology regime could be crucial for effective salt marsh restoration projects.