Quantifying inorganic carbon fluxes in temperate seagrass meadows

Understanding the carbon sequestration potential of blue carbon ecosystems is a crucial component for developing nature-based solutions to combat climate change. Alkalinity generation is an often-overlooked carbon sequestration mechanism, especially in seagrass meadows. Here, we quantified alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes at temperate seagrass meadows in Sweden, using 24-hour in-situ chamber incubations during the late part of the productive season in early September. Observed net TA fluxes to the water column of 22 ± 10 mmol m^-2 d^-1 were 19% lower than DIC fluxes (27 ± 6 mmol m^-2 d^-1). Both fluxes were largely related to day-night cycles. A sink of TA during the day was counteracted by a 3-times stronger source at night. DIC fluxes displayed a highly variable source, being 3 to 50-times higher at night compared to daytime. TA and DIC fluxes were slightly lower than those reported for seagrasses in warmer climates and for other coastal wetlands, i.e., mangroves and saltmarshes. Nonetheless, alkalinity generation in temperate seagrasses contributes to their carbon sequestration potential and warrants consideration in future investigations.