Integration of Ocean Alkalinity Enhancement Processes with Coastal Industries: Ecotoxicity Assessment for Local Environmental Impacts

Bringing carbon dioxide (CO₂) removal approaches from the laboratory to the industrial scale in the following years is imperative to reaching Net Zero goals. Ocean Alkalinity Enhancement (OAE) is a promising approach that introduces alkalinity into surface waters, slightly modifying the carbonate equilibrium and thus increasing the seawater’s CO₂ removal capacity. The co-location of OAE with existing coastal industries (e.g., desalination plants) is a way to accelerate their deployment.

Recognizing the importance of balancing climate mitigation strategies with environmental stewardship, our study focuses on the outcomes of comprehensive ecotoxicity tests conducted to discern the effects of return flows from desalination plants (concentrated seawater or brine) enriched with alkalinity (carbonates). To simulate real conditions, we investigated three scenarios: (i) brine alone, (ii) alkalinity alone, and (iii) brine with added alkalinity. The ecotoxicity tests were designed to capture the responses of key marine organisms across various trophic levels. Bacterial assays illuminated the microbial community's sensitivity to different scenarios, while diatom assessments provided insights into primary producers' adaptive capacity. Copepod and crustacean tests explored the cascading effects on higher trophic levels, elucidating potential ramifications for marine food webs.

Our findings shed light on the intricate interplay between alkalinity-enhanced brines and local ecosystems, providing valuable insights into potential stressors and their implications for marine biota. The ecotoxicity results at different dilutions are combined with the knowledge of mixing zones for ocean outfall technologies, putting forward the environmental impact at different distances from the alkalinity addition.

By addressing the specific challenges posed by integrating OAE with desalination, this research contributes to the ongoing dialogue on responsible and sustainable climate mitigation strategies. It offers a nuanced understanding of the potential trade-offs and synergies between addressing climate change and preserving or benefitting local marine environments. At a time when environmental testing at scale is needed, this study assesses the potential risks of such research. Ultimately, this work facilitates dialogue among OAE companies, desalination experts, policymakers, and organisms for environmental control and protection.