Ecological risks of olivine with different particle sizes and dosages on planktonic ecosystems during ocean alkalinization.

With industrialization, global climate change has intensified. Ocean alkalinization via olivine addition enhances seawater alkalinity and carbon sequestration but its ecological risks remain poorly understood. In this study, Chlorella vulgaris and Brachionus plicatilis were used as model organisms. Olivine of different particle sizes (≤38 μm, 50-74 μm, ≥154 μm) and dosages (1‰, 2‰) was applied in laboratory experiments with molecular analyses and model evaluation to assess effects on planktonic ecosystems and carbon sequestration. Results indicate strong particle-size dependence, with finer particles causing more pronounced effects. In phytoplankton, small particles induced stronger growth inhibition and reduced photosynthesis, while larger particles showed weaker effects or slight stimulation. In rotifers, fine particles decreased locomotion, feeding, and carbon transfer fluxes, suggesting potential disruption of zooplankton-mediated carbon transport. Overall, particle size, together with suspension characteristics and mineral dissolution processes, likely governs planktonic responses, with suspended fine particles representing a major ecological risk source. Model evaluation further indicates that, under the experimental conditions and assessment framework of this study, larger olivine particles (≥150 μm) exhibited relatively lower ecological risk. However, practical ocean alkalinization applications should balance settling behavior, dissolution efficiency, carbon sequestration, and ecological impacts to optimize the trade-off between carbon removal and ecosystem safety.