Minerogenic Salt Marsh Soil Responses to Increasing Rainfall Intensity and Soil CO2: Implications for Alkalinity Generation

Salt Marshes and other vegetated coastal ecosystems play a crucial role in sequestering anthropogenic CO2 by storing carbon as organic matter within the ecosystem. Additionally, these ecosystems have been identified as potential hotspots for alkalinity generation, via anaerobic respiration and dissolution of carbonate minerals within sediments. In this way, they enhance the capacity of the ocean for CO2 removal. Quantitative insights into alkalinity generation at small scales, particularly those where rhizosphere processes and associated feedback take place, still remain limited. Our study addresses this gap by conducting a two-factorial lab-based column experiment coupled with water chemistry analysis to elucidate the influence of increased rainfall intensity and elevated soil CO2 levels on alkalinity generation in organic-poor minerogenic salt marsh soil. The results revealed a significant positive effect of increased rainfall intensity and elevated soil CO2 levels on alkalinity generation. Carbonate mineral dissolution was identified as the dominant driving force, with an additional dissolution of silicate minerals. Together, this study advances the understanding of rhizosphere environments characterized by relatively high CO2 levels as potential hotspots for alkalinity generation through mineral dissolution processes. Moreover, it indicates a clear association between intensified rainfall and heightened alkalinity generation, underlining an implication for future climate scenarios.