Our study has focused on carbon dynamics along a landscape hydrologic gradient from upland pine flatwoods (Pinus palustris), to depression marshes (Eleocharis interstincta) and a significant peat accumulating marsh dominated by sawgrass (Cladium jamaicense). Across the hydrological gradient, inhibited decomposition within flooded organic soils of subtropical peatlands may result in a sink for carbon dioxide, while methane production also impacts the greenhouse gas balance of these ecosystems. Carbon dioxide and methane fluxes have been measured since 2010 by eddy covariance. In this paper we compare components of carbon balance of these ecosystems and focus on the long-term carbon dynamics in the sawgrass marsh.
Results/Conclusions
Across the landscape gradient, net ecosystem exchange in pine flatwoods showed little seasonality and totaled 96 g m-2 of carbon uptake for the period of comparison (May 2013 – May 2014). The Eleocharis marsh showed seasonality driven by hydroperiod (length of time flooded) averaging 131 g m-2 of carbon uptake. The sawgrass marsh showed seasonality driven by water level and phenology resulting in 177 g m-2 of carbon uptake. Over the period 2010-2015, the sawgrass site experienced hydroperiods ranging from nine to twelve months. Net ecosystem productivity was (65-97 g C m-2) in years with periodic drying events and higher (284-597 g C m-2) during years with continued flooding. In 2013, methane emissions totaled 44 g m-2 y-1 of carbon release to the atmosphere, varying seasonally with temperature and water level. A 3000 hectare fire occurred in the sawgrass marsh in the spring of 2014, and it consumed approximately 85% of the aboveground biomass (963 g C m-2) within the measurement footprint. Simulations of a long-term carbon balance that included fire indicate the wetland is an annual sink with 131 g m-2 y-1 of carbon uptake. These results demonstrate the importance of the subtropical peatland ecosystems for regulating atmospheric greenhouse gas concentrations.