Balancing methane emission and alkalinity conservation: Insights from mineral amendments in coastal sediments.

With global climate warming and ocean acidification, mineral amendments in coastal areas have emerged as a promising strategy to bolster carbon sinks and alkalinity. However, most research has predominantly focused on carbon dioxide (CO₂) absorption, with limited exploration of methane (CH₄) reduction despite its more potent greenhouse effect. To address this gap, our study conducted a microcosm manipulative experiment employing coastal wetlands sediments to elucidate the regulatory effects of various mineral amendments on greenhouse gas emissions (including CO₂ and CH₄) and seawater alkalinity. The findings unveiled that olivine application effectively absorbed CO₂, achieving a 175 % reduction (-342.0 mmol L^-1 h^-1) in the late stage, while gypsum application significantly reduced CH₄ by 53 % (-6.06 mmol L^-1 h^-1) in the early stage. Nevertheless, applying gypsum led to a marked decrease in seawater alkalinity, potentially exacerbating ocean acidification and posing risks to marine ecosystems. Interestingly, the simultaneous application of both minerals showed promise in reducing CH₄ emissions without compromising seawater alkalinity. This study presents a pioneering endeavor that contributes to the sustainable management of coastal wetlands and supports future initiatives at reducing CH₄ emissions and alleviating ocean acidification.