Schematic showing CO2 uptake, transport, and storage (S) components and land-water-atmospheric fluxes that will be used to balance the FCE C budget.
Recent studies show that vegetated coastal systems can bury blue carbon - at rates up to 50 times higher than tropical forests, suggesting that continued coastal development and exposure to SLR and storms will have global biogeochemical consequences. The FCE transect approach is designed to examine long-term spatio-temporal patterns in ecosystem response to changing coastal pressures, and we have been gradually building our infrastructure to express change in terms of the C balance using multiple cross-validating tools. A central feature of this infrastructure are eddy covariance towers that measure net ecosystem-atmosphere CO2
exchange (NEE) and energy balance at three sites along our transects. Comparisons between NEE-derived estimates of net ecosystem productivity (NEP) and direct measurements of NPP provide important insights into the C balance, including the magnitude of C burial and transport. In FCE II, we determined that in short-hydroperiod freshwater marshes, low rates of CO2 exchange align with low NPP values indicative of oligotrophy. However, in the full-stature SRS mangrove forest, marine-derived P, year-round growth, low respiration rates, and intensive C burial and tidal export promote NEE levels (~1100 g C m-2 yr-1) that exceed forest records of NEP. In the seagrass ecosystem, we are just beginning to understand rates of C burial. In Florida Bay, ~37% of NPP is channeled into belowground, and eventually the sediments. New results suggest that C storage in seagrass sediments rivals that of tropical forests, and that Florida Bay sediments are C-rich compared to seagrass systems worldwide. By examining ecosystem metabolism from freshwater wetlands to the sea, using gas exchange, ground sampling, landscape analyses, and experiments, FCE is uniquely poised to address how C cycling is regulated across wide spatio-temporal scales to unravel, and improve predictions of subtropical wetland responses to SLR. We will synthesize WG results to create dynamic, spatially-explicit, and mechanistically-supported C budgets for the marsh-mangrove-seagrass ecosystem that can be used to drive simulation models to quantify how the C balance, and associated services (e.g., storm buffering, C sequestration) respond to, and mitigate, changes in water delivery, nutrient fluxes, and pressures of SLR in a highly vulnerable coastal ecosystem.