Enhancing carbon sequestration through flocculation of harmful algal blooms by modified clay technology

ABSTRACT Global efforts to mitigate climate change emphasize the critical need to enhance carbon sinks. Harmful algal blooms (HABs) areas represent hot spots for labile organic carbon production, yet their carbon sequestration capacity is diminished by rapid microbial mineralization. Modified clay (MC) technology, used for HABs mitigation, could enhance the sedimentation and influence the transformation dynamics of algal-derived organic carbon. Nevertheless, the impacts of MC on the mineralization of algal-derived organic carbon and the mechanisms involved remain inadequately understood. In this study, employing ¹³C-labeled batch incubation experiments, we demonstrated that algal-derived organic carbon undergoes rapid mineralization, with 46%–59% of the total organic carbon (TOC) being mineralized within 30 days. MC substantially reduced the mineralization rate of algal-derived organic carbon from 0.68–0.80 mg/(L·d) to 0.09 mg/(L·d), thereby boosting organic carbon sequestration potential by approximately 55-70% compared to the control group. Multiple lines of evidence, including microscopic imaging, fluorescence spectroscopy, and microbial analysis, revealed that MC promoted organic carbon downward export, reduced bioavailability through flocculation and encapsulation, and suppressed heterotrophic bacteria. Notably, the MC treatment group exhibited a significant reduction, with the abundance of heterotrophic bacteria decreasing by approximately 60% and the functional genes associated with microbial mineralization dropping by 50%. Overall, this study presents direct evidence and mechanistic insights that demonstrate the feasibility of employing MC to enhance carbon sequestration in mitigating HABs.