Turn the potential greenhouse gases into biomass in harmful algal blooms waters: A microcosm study

Carbon sources are a critical requirement for the proliferation of algae and the occurrence of harmful algal blooms (HABs), but are often turned into methane (CH₄) after the collapse of severe HABs. Here, we attempt to remove HABs, reduce algal-derived CH₄ emissions, and repair the broken carbon biogeochemical cycle in aquatic systems using an integrated ecological approach including flocculation, capping, and submerged macrophyte induction, preliminary at a microcosm scale. This strategy sustainably reached 98% algal removal after 65 days of incubation and resulted in an aerobic microenvironment (ORP = +12 mv) at the sediment-water interface. The approach contributed to an approximate 60% decline in CH₄ released from the aquatic environment into the atmosphere jointly through assimilation of mineralized organic carbon by submerged macrophytes, production of carbon dioxide (CO₂) under aerobic conditions, and aerobic CH₄ oxidation. Some of the CO₂ produced in the aquatic phase contributed to inorganic carbon and formed the submerged macrophytes biomass. A combination of flocculation, capping, and submerged macrophyte incubation were significant contributors to altering the carbon budget and sealing nearly 99% of the carbon in the simulated ecosystem (the majority in sediment, followed by submerged macrophytes), providing a sustainable way to reuse algal-derived carbon and reduce CH₄ emissions.