Monitoring alkalinity enhancement in intertidal environments – A field study –

Global warming is the greatest threat for humankind today. Despite all efforts to reduce CO₂ emissions, the undertaken measures are not sufficient to stop the temperature rise. One recently proposed and promising approach to actively remove CO₂ from the atmosphere is carbon dioxide removal through marine alkalinity enhancement. This technique increase the natural CO₂ uptake capacity of seawater through weathering of fine-grained alkaline minerals in marine environments. Even through this method has been extensively tested and verified by numerical models, field experiments scaling the CO₂ uptake under natural conditions and assessing the impact on the environment and biota are still lacking. To bridge this gap of knowledge a monitored 2-year in-situ experiment was established in September 2022 at the Ria Formosa Coastal Lagoon, southern Portugal.

The experiment was installed in the pioneer vegetation zone of the saltmarsh with three replicate plots.  Each plot contain deployments of coarse olivine, fine olivine, coarse basalt and fine basalt and an unchanged area as control. Supernatant and porewater from each treatment are analysed monthly for temperature, salinity, oxygen concentration, pH, total alkalinity, nutrients, and trace metals. Sediment samples are analysed quarterly for faunal and floral composition to evaluate the impact on the biota.

The first  months of the experiment showed an increase in total alkalinity in the supernatant and porewater of the treatments. Other environmental parameters remained stable among the different treatments and control. The total alkalinity decreased through time although remained on higher levels as compared to the natural background level.

Acknowledgment. Research supported by the Portuguese Science Foundation, with the projects PTDC/CTA-CLI/1065/2021, UID/00350/2020CIMA and contracts DL57/2016/CP1361/CT0009.