Coastal enhanced olivine weathering for climate change mitigation: investigating the CO2 sequestration potential and ecotoxicological risks
Drastic greenhouse gas emission reductions and gigaton-scale atmospheric carbon dioxide (CO2) removal are needed to keep global warming below 2°C. Silicate rock weathering has regulated climate on earth over geological time scales. Coastal enhanced silicate weathering (CESW) aims to accelerate this process by distributing large amounts of finely ground olivine-rich rock in dynamic coastal environments. Olivine is a proposed candidate mineral for this technique due to its abundance, relatively fast weathering rate, and theoretically high CO2 sequestration potential. However, the in situ CO2 sequestration potential remains uncertain and olivine’s high nickel (Ni) and chromium (Cr) content could be of potential ecological concern. This thesis aimed to advance our understanding of olivine dissolution and CO2 sequestration kinetics under the influence of hydrodynamics and assess potential ecotoxicological effects of CESW. First, we investigated the effect of continuous grain-grain collisions on olivine weathering rates in seawater. Physical agitation enhanced olivine dissolution by 8 to 19 times compared to stagnant conditions, likely due to advective pore water flushing. Therefore, olivine should ideally be supplied in coastal areas with sufficiently high bed shear stress and pore water exchange rates. Subsequently, a flume experiment was conducted to investigate the effect of current on olivine dissolution in permeable sediment. Olivine dissolution was more than one order of magnitude lower than expected, for reasons that could not be identified, highlighting the need for studies under environmentally realistic conditions. Next, a first assessment of the ecologically safe olivine deployment scale was made based on existing marine Ni and Cr environmental quality standards. Results indicated that 0.059 to 1.4 kg of olivine per m2 of seabed could be supplied without posing metal toxicity risks for benthic biota. Changes in sediment physicochemical properties may also lead to avoidance of olivine rich sediments by marine organisms. Short choice experiments with the gastropod Littorina littorea and amphipod Gammarus locusta indicated avoidance of pure olivine but tolerance to environmentally relevant olivine concentrations of 30% w/w and lower. Metal bioaccumulation and chronic olivine toxicity testing with Gammarus locusta further revealed concentration and grain size dependent effects, with adverse reproductive outcomes at olivine concentrations of 10% w/w and higher. These findings underscore the necessity for additional olivine toxicity data to derive accurate, site-specific olivine application guidelines. Overall, our work provides valuable novel insights into the stimulating effect of hydrodynamics on olivine reactivity in marine environments and shows possible trace metal-related adverse ecological impacts of CESW.
Antwerpen : Universiteit Antwerpen, Faculteit Wetenschappen, Departement Biologie , 2024
417 p.
Supervisor: Blust, Ronny [Supervisor]
Supervisor: Town, Raewyn M. [Supervisor]
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Creation 09.02.2024
Last edited 20.02.2024
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