A Spatial Model Comparing Above- and Belowground Blue Carbon Stocks in Southwest Florida Mangroves and Salt Marshes

Blue carbon ecosystems such as mangroves and salt marshes store large amounts of carbon (C) in the form of plant biomass and soils that are often rich in organic matter. These C stocks have a high degree of spatial variability within and among coastal wetland ecosystem types, but quantifying location-specific C stocks is both labor intensive and time-consuming. Above- and belowground C stock data were compiled from field efforts in Southwest Florida and from published georeferenced C data. These data were used in conjunction with ecosystem maps, remote-sensing parameters, and existing vegetation models to create 30-m resolution spatial models quantifying aboveground C stocks and belowground C stocks up to 1-m depth in mangroves and salt marshes along 360 km of coast in Southwest Florida (Tampa Bay to the Everglades). Based on modeling results, mangroves and salt marshes in Southwest Florida store an average of 393.9 ± 107.1 and 286.7 ± 71.9 Mg C ha−1, respectively, in above- and belowground C stocks. Soil C density and belowground C stocks increased at lower latitudes within the study region. Total C stocks in mangroves increased from 265.1 ± 43.2 Mg ha−1 in Tampa Bay and Sarasota Bay to 409 ± 104.4 Mg ha−1 in the Everglades. Substrate stability and C stocks are susceptible to impacts from climate change, sea-level rise, hydrologic changes, and episodic disturbances such as tropical cyclones. The long-term storage of C in these ecosystem types depends on ecosystem stability in the face of these stressors.