pCO2 decrement through alkalinity enhancement and biological production in a shallow-water ecosystem constructed using steelmaking slag

• Published in: Marine environmental research 2023-11, Vol.192, p.106223-106223, Article 106223
• Main Authors: Nakamura, Wataru, Kosugi, Chika, Yoshimura, Ko, Kato, Toshiaki, Sasaki, Jun, Nakamura, Yoshiyuki
• Format: Article
• Language: English
• Subjects: alkalinity; Alkalinity enhancement; Basic oxygen furnace slag; biological production; Blue carbon; calcium; carbon dioxide; climate change; CO2 uptake; Coastal enhanced weathering; ecosystems; habitats; macroalgae; Mesocosm; Ocean based CDR; seagrasses; slags; soil; Steelmaking slag; turbidity; Zostera marina
• ISSN: 0141-1136; 1879-0291
• DOI: 10.1016/j.marenvres.2023.106223

Ocean-based carbon dioxide removal has gained immense attention as a countermeasure against climate change. The enhancement of ocean alkalinity and the creation of new blue carbon ecosystems are considered effective approaches for this. To evaluate the function of steelmaking slag from the viewpoints of CO2 reduction and creation of new blue carbon ecosystems, we conducted a comparative experiment using two mesocosms that replicated tidal-flats and shallow-water ecosystems. Initially, approximately 20 seagrasses (Zostera marina) were transplanted into the shallow-water area in the mesocosm tanks. The use of steelmaking slag is expected to increase the pH by releasing calcium and mitigate turbidity by solidifying dredged soil. In the experimental tank, where dredged soil and steelmaking slag were utilized as bed materials, the pH remained higher throughout the experimental period compared with the control tank, which utilized only dredged soil. As a result, pCO2 remained consistently lower in the experimental tank due to mainly its alkaline effect (March 2019: −10 ± 6 μatm, September 2019: −130 ± 47 μatm). The light environment in the control tank deteriorated due to high turbidity, whereas the turbidity in the experimental tank remained low throughout the year. The number of seagrass shoots in the experimental tank was consistently approximately 20, which was higher than that in the control tank. Additionally, more seaweed and benthic algae were observed in the experimental tank, indicating that it was more conducive to the growth of primary producers. In conclusion, tidal-flat and shallow-water ecosystems constructed using dredged soil and steelmaking slag are expected to enhance CO2 uptake and provide a habitat for primary producers that is superior to those constructed using dredged soil only. [Display omitted] •Steelmaking slag was examined as a bed material for the creation of BC ecosystems.•Alkalinity enhancement by steelmaking slag decreased pCO2 in water.•The use of steelmaking slag had no apparent negative impact on primary producers.