Bubble Bubble and maybe not Toil and Trouble.

As atmospheric carbon dioxide (CO₂) levels rise, very few coastal marine ecosystems will be spared the impacts of ocean acidification. Localized natural and human influences result in large diel variations in the oceans carbon chemistry which have negative impacts across a range of marine taxa: with the greatest impact on respiration, motility, and fertility.

With the increasing knowledge of anthropogenic stressors in coastal ecosystem many studies have tried to establish mitigation strategies. However these approaches have been limited in scope and results have been disappointing. Currently CO₂ bubble stripping technology can be found in aquacultures, however the concept has been largely ignored for natural coastal environments.

Koweek and his team (2016) set out to evaluate a new geochemical engineering approach to reduce aqueous pH, pCO₂, and Ω, through pumping air into the water as bubble plumes, as CO₂ will natural diffuse into the air bubbles if the CO₂ Concentration is lower, effectively removing the CO₂ from the water.

Three models were developed before experimentation, the first model predicted that the amount of air-sea CO₂ flux would be far greater when bubble stripping was implemented in a biologically active shallow coastal ecosystem. The second model found that high levels of water advection reduced the ability of the bubble stripping, however this could be overcome by increasing gas flow rates. The final model predicted that bubble stripping technology would work more efficiently in predicated marine conditions for the end of the century.

Experiments were then carried out replicating the models in closed tanks, the results closely matched the predictions from the computer models, giving the team confidence in their accuracy. The bubble stripping technology increases the transfer rate of CO₂ between the ocean and the air up to 30 times faster than natural processes. The results from the model and experiment show that the installation of bubble stripping may prove useful for protecting small sections of shallow coastline that are ecologically or commercially important. 

Experimentally there were very few problems, however conceptually there are some major hurdles surrounding the implementation of bubble stripping. Would it be possible to comprehensively evaluate the ecological responses of the bubbling system in the natural environment? How would the equipment survive the variable conditions found in these environments? And where would the team obtain funding for large scale implementation? It should also be noted that the CO₂ that bubble stripping removes from the seawater will increase the concentration in the air. That will in turn increase the rate of diffusion/solution back into the water so bubble stripping technology is only a temporary local solution unless combined with carbon capture technology which sequesters carbon in solid form or as liquefied CO₂.

There haven’t been any significant publications in the same area released since this publication, however the obvious next step would be to conduct in-situ experiments which will be highly anticipated. Koweet and his team also made a passing comment mentioning that this technique may be applicable not only for coral habitats but for many other shallow coastal environments such as salt marshes and mangroves, opening up more areas of potential research.

The future of bubble stripping as a re-mediation technique is uncertain at this point as there are many factors that may derail this emerging technology. However this study has established an important foundation for bubble stripping technology and if this technique is as beneficial as promised, this could be a pivotal moment in shallow coastal water conservation and management.

Paper Reviewed 

Koweek, D., Mucciarone, D. and Dunbar, R. (2016). Bubble Stripping as a Tool To Reduce High Dissolved CO 2 in Coastal Marine Ecosystems. Environmental Science & Technology, 50(7), pp.3790-3797.