Blue carbon loss driven by the accelerating rate of sea level rise during the Anthropocene Marine Transgression, Southeast Saline Everglades, Florida

The Southeast Saline Everglades is an ephemeral wetland ecosystem supporting a gradient of salt-tolerant to freshwater plant communities, each with characteristic sediment organic carbon densities and accumulation rates. The accelerating rate of sea level rise has greatly increased the rate of saltwater encroachment resulting in the landward shift of coastal plant communities and their biogenic sediments, decreased plant production, and changes in annual sediment organic carbon accumulation and stock. The objectives of this study are to determine how the accelerating rate of sea-level rise has affected sediment organic carbon accumulation and stock and to predict the future contribution. The areas and volumes of each sediment type were determined and the annual sediment organic carbon accumulation and stock were calculated. The 2017 annual sediment organic carbon accumulation was 93.4 Gg and its total stock accumulated over the last ~3200 years, in the 92,720 ha Southeast Saline Everglades ecosystem, was 31.3 Tg. The annual average sediment organic carbon accumulation is 1.25 Mg SOC ha^-1 yr^-1 with the largest contribution from sawgrass peat-marl (81.5 %). The average sediment organic carbon stock is 419.2 Mg ha^-1. The average mangrove peat organic content contains 7.31 Mg ha^-1, but only contributes 15.6 % of the total stock. Since 1900 anthropogenic activities reduced natural wetlands area by 19.5 %, the annual SOC accumulation by 19.7 %, and stock by 4.8 %. At the present rate of SLR, the entire Southeast Saline Everglades will experience saltwater encroachment prior to 2100 and submergence by 2140.