Increased Organic Carbon Burial in Northern Florida Mangrove-Salt Marsh Transition Zones

Blue carbon habitats like salt marshes and mangroves bury large amounts of carbon with limited area; however, they also are increasingly susceptible to current climate change. Combined effects of rising temperatures, decreasing freeze frequencies, and increasing sea level rise rates are resulting in mangrove replacement of salt marshes along the southern United States. Surface soils analyzed here from wetlands along northern Florida Atlantic and Gulf Coasts showed higher apparent sedimentation rates in mangrove-dominated sites (1.5-3.2 mm yr(-1)) and where mangroves are migrating into the marsh (termed transition sites, 2.3-3.8 mm yr(-1)). Average carbon burial rates were higher in transition sites for both coasts (27-47 g C center dot m(-2)center dot yr(-1)) compared to the respective mangrove (10-22 g C center dot m(-2)center dot yr(-1)) and salt marsh (4-7 g C center dot m(-2)center dot yr(-1)) sites. Lignin biomarker data (?-6, ?-8, and C/V) indicated that mangrove and transition sites had higher lignin inputs from woody vascular plants compared to salt marsh sites, which may slow decadal- to centennial-scale decay. Higher amino acid concentrations in mangrove soils relative to mangrove biomass (1.8-2.3 mmol g C-1 vs. 0.2-0.9 mmol g C-1) and lower C/N indicated that these mangrove sites receive higher algal inputs than the transition and salt marsh sites, attributed to greater tidal inundation in the mangrove sites given their position near the shoreline. Overall, increased accretion, carbon burial, and lignin in mangrove transition sites indicate that this migration may increase carbon burial and increase the stability and residence time of buried soil carbon. Future studies on mangrove migration in northern Florida can verify this through replication and elevation analysis.