Hypotheses and Proposed Work for FCE III (2007-2018)
General Question: How do changing freshwater inflows, tidal and storm cycles, and climate patterns affect the magnitude, rates, and pathways of C sequestration, loss, storage, and transport across the land-water continuum?
Hypothesis 1: Temporal variability in C uptake, storage, and transport in the mangrove ecotone reflects the pulsed dynamics of marine water, nutrient, and sediment supplies driven by tides and storms, and freshwater supply driven by seasonal rainfall and water management.
Approach - We will integrate our C cycle measurements following the analytical approaches and field methods of Chapin et al. (2006), Engel et al. (2011), and Rivera-Monroy et al. (2012b) utilizing continuous estimates of NEE from our flux towers, regular above and belowground NPP values, OM accretion from sediment elevation and paleoecological studies, DIC and CO2 fluxes across the land-water-air continuum, and measurements of dissolved and particulate C tidal fluxes (including riverine fluxes using Lagrangian tracer techniques). This framework will be newly applied in the dwarf mangrove system in TS/Ph, and comparisons between the SRS and TS/Ph datasets will enable rigorous tests of this hypothesis. Integration will be accomplished through a dedicated post-doc and subannual workshops of contributing working groups. We will collaborate with the Scenarios CCT to further refine biospheric-hydrodynamic models needed to quantify and predict C dynamics and ecosystem function.
Hypothesis 2: Landscape patterns in C fluxes reveal legacies of exposure of the marsh, mangrove, and seagrass ecosystems to long-term changes in the balance of fresh and marine water supplies.
Approach - We will coordinate a large-scale initiative to determine landscape variability in the patterns and controls on C budget components, including the expansion of our eddy flux network to include a tower in the dwarf mangrove forest of TS/Ph-7 and underwater O2-based gas flux in Florida Bay. We will use the framework described above to calculate and cross-validate C cycling measurements from plot-based and tower-based methods. We will work with the Legacies CCT to extend our site-based measures to the landscape using satellite imagery. By coordinating cross-site and international meetings we will enable this comprehensive C budget to be used to increase our understanding of the future of coastal C dynamics in a global context. This includes integration with other Atlantic coastal LTER sites, ongoing and expanding international research projects in coastal Panama, Shark Bay, Australia, and locations throughout Central America to assess vulnerability of C budgets in a variety of coastal wetlands to climate change and human impacts.