Ecosystem CO2 fluxes and landscape dynamics in response to hydrologic modification in the Everglades ridge-slough mosaic

Background/Question/Methods

The ridge-slough mosaic in the central Everglades, which comprised large areas of the pre-drainage landscape, is a patterned peatland with elongated ridge patches embedded in a matrix of hydraulically interconnected sloughs. Hydrologic modification over the last century has led to widespread loss of this historic patterning, as evinced by changes in both the corrugated topography of the peat surface as well as broad changes in vegetation type and prevalence. As a peat accreting wetland, carbon dynamics play a pivotal role in ecosystem stability and landscape processes.  We sought to test the hypothesis that water management changes have altered net peat accretion and thus profoundly affected feedbacks that previously maintained distinct ecosystem patches. We predicted approximately equal net autotrophy in ridges and sloughs in the most hydrologically well-preserved part of the landscape, and a loss of net autotrophy in ridges with both drainage and impoundment. We present CO₂ fluxes obtained using closed-path chamber systems in ridges and sloughs in four 2x4 km landscape blocks spanning hydrologic conditions from drained through well-conserved to impounded, including soil and water column CO₂ respiration measurements (2009 through early 2011) and ecosystem CO₂ fluxes (July 2011 through June 2012).

Results/Conclusions

Soil/water column respiration measurements showed that CO₂ is more strongly controlled by water depth than air or water/soil temperature. While soil/water column respiration showed no significant differences by community type, ecosystem-level CO₂ respiration measurements did exhibit significant community differences, likely because of differential short-term autotrophic respiration. Wet season analyses of net ecosystem CO₂ fluxes suggest significant differences between communities and landscape blocks, with net heterotrophy even during the wet season in the drained and impounded blocks, but net autotrophy in the more hydrological well-preserved blocks. We present modifications to the standard rectangular hyperbola function for extrapolating flux rates that consider the effects of water levels on both net ecosystem production (NEP) and ecosystem respiration (R_eco). We ultimately suggest that, in this subtropical wetland, changes to hydrology (specifically, hydroperiod and water depths) has significant consequences on landscape biogeomorphology via direct hydrologic controls on ecosystem carbon dynamics.