Wastewater-based ocean alkalinity enhancement alleviates effluent-induced disturbance on coastal bacterial community.

Wastewater-based ocean alkalinity enhancement (OAE) has emerged as a promising, wastewater-infrastructure-enabled pathway for atmospheric carbon dioxide removal. However, its ecological assessment, especially on coastal bacterial communities, which serve as fundamental regulators of marine biogeochemical cycles, remains poorly studied. Here, we assessed the response of bacterial communities to alkalinized wastewater effluents through a 30-day microcosm experiment. Our results showed that alkalinized wastewater increased seawater total alkalinity (TA) and pH by approximately 140 μmol kg-1 and 0.1 units upon mixing, respectively. Additionally, alkalinized wastewater effluents reshaped bacterial succession dynamics and community structure (P < 0.05), with enrichment of taxa such as Nitrincolaceae that are potentially involved in carbon and nitrogen cycling. Compared to non-alkalinized wastewater effluents, wastewater-based OAE improved bacterial network stability as reflected by higher robustness and lower vulnerability. Overall, our findings provide an upper-bound exposure assessment of potential ecological impacts of wastewater-based OAE, highlighting the need for field-scale studies to fully evaluate its ecological effects under real-world conditions.