# Presentation: 906573

## A new AmeriFlux site in the Florida Everglades: characterizing response of carbon dioxide, water, and energy exchange of peat and marl wetlands to changes in hydroperiod

- Florida Everglades are highly productive, though oligotrophic
- Productivity is maintained by a tolerant emergent macrophyte, sawgrass (*Cladium jamaicense*), and abundant algal mat communities (periphyton) (Fig. 1)
- Periphyton NPP in the Everglades reported at some sites as 20,599 g C m-2 yr-1 (Ewe et al. 2006)
- Hydroperiod (days with water above the surface) is central in differentiating Everglades wetlands:
**Long hydroperiod**: continuous water above the surface, peat soils, and low periphyton biomass
- Everglades peat soils were formerly the world’s largest single body of organic soils (Stephens and Johnson 1951)
- Drainage and other agricultural activities have led to substantial loss of this organic carbon
**Short hydroperiod**: 6 months or less with water above the surface, marl soils, and high periphyton biomass
- Geochemical carbon fixation – large amounts of carbon are precipitated as calcium carbonate as CO2 is reduced during photosynthesis: 	CO2 + H2O ⇌ H2CO3 ⇌ HCO3ˉ + H+  	Ca2+ + 2HCO3ˉ ⇌ CaCO3 + CO2 + H2O
- Everglades water levels vary seasonally and with water management (regulated quantity and timing of water delivery), but evaporative losses are not well characterized
- Historical slow sheet flow to be restored: Comprehensive Everglades Restoration Plan ($8 billion over 50 yrs)
- Everglades ecoregion is poorly represented by the current AmeriFlux network (Hargrove et al. 2003)

- Steven F. Oberbauer1, Evelyn E. Gaiser1, Gregory Starr2, and Jessica L. Schedlbauer1
- 1Department of Biological Sciences, Florida International University, Miami, FL, 2Department of Biological Sciences, University of Alabama, Tuscaloosa, AL

**Question 1.** What are the CO2 balances of Everglades peat and marl forming wetlands?

**Question 3.** What are the responses of the CO2 exchange processes to the dominant control, hydroperiod?

**Question 2.** What are the relative contributions of physiologically-based exchange and abiotic carbon precipitation to the net CO2 flux?

**Introduction**

**Question 4.** How does the contribution of macrophyte CO2 flux vary with hydroperiod across the landscape?

- Figure 2. Location of study sites (yellow dots) in long (1) and short (2) hydroperiod Everglades wetlands.  Sites will be co-located with existing sites in the Florida Coastal Everglades Long Term Ecological Research program (FCE-LTER).

- Eddy covariance and microclimatic measurements will be made at two sites: long (peat) and short (marl)  hydroperiod wetlands (Fig. 3)
- Everglades freshwater ecosystems are well-suited for the collection of such data with low, even canopies on flat terrain with frequent nighttime wind

- Data will allow us to:
- Make direct comparisons of CO2 fluxes in short and long
- hydroperiod wetlands
- Investigate coupling of CO2 and water fluxes at wet-dry
- season transitions
- Characterize inter- and intra-annual variations in CO2 flux

**Acknowledgements:** Funding for this project is provided by NICCR grant No. 07-SC-NICCR-1059.
**References:**
- Ewe, S.M.L., E.E. Gaiser, D.L. Childers, V.H. Rivera-Monroy, D. Iwaniec, and R.R. Twilley, 2006.  Spatial and temporal patterns of aboveground net primary productivity (ANPP) in the Florida Coastal Everglades LTER (2001-2004). Hydrobiologia 569: 459-474.
- W.W. Hargrove, F.M. Hoffman, and B.E. Law. 2003. New analysis reveals representativeness of AmeriFlux network. EOS Transactions 84:529-531.
- Lodge, Thomas. 1994. The Everglades Handbook. St. Lucie Press.
- Stephens, J.C. and L. Johnson. 1951. Subsidence of Peat Soils in the Everglades Region of Florida. United States Department of Agriculture Soil Conservation Service. 47 p.

- Chambers will be used to measure plot-level CO2 exchange and ecosystem dark respiration, providing a check of ecosystem GEP
- Macrophyte/periphyton removal treatments will be used to determine the contribution of macrophytes/periphyton to NEE and ecosystem respiration
- Geochemical techniques will be used to estimate the magnitude of net calcification and subsurface photosynthesis
- Net fluxes will then be partitioned into three components: macrophyte above water photosynthesis/respiration, submerged photosynthesis/respiration, and calcification/decalcification
- Stable carbon isotope analyses of periphyton organic carbon, macrophyte carbon, and carbonates will be coupled with nighttime Keeling Plots to estimate the contribution of these components to ecosystem respiration

- Figure 1. (a) Long hydroperiod marsh with light colored periphyton mats floating on surface and below water. (b) Short hydroperiod marsh dominated by sawgrass.

- Flux data will be related to microclimate and water level data supplemented with water quality and periphyton biomass data from the Florida Coastal Everglades LTER (FCE-LTER)
- Controls on fluxes will be evaluated with an approach that includes structural equation modeling, response models and residuals analysis, and a process model (MAESTRA)
- This will enable us to:
- Predict the contribution of sawgrass to seasonal flux patterns and estimate the flux proportion attributable to other components
- Examine the influence of hydroperiod and other controls on fluxes

- Bi-annual airboat transects across the Everglades landscape will be made where:
- Macrophyte leaf tissue will be collected to determine N concentration
- N:photosynthesis relationships will be used to estimate photosynthetic capacity
- Vertical distribution of leaf area will be determined
- These data and an Everglades hydroperiod mapping tool will be used to estimate above-water macrophyte leaf area along transects
- Landscape-scale estimates of macrophyte flux in response to intra- and inter-annual hydroperiod variation due to climate change or water management will be made with MAESTRA

- Figure 3. Highly horizontally compressed schematic of Everglades wetlands and flux processes.  Adapted from Lodge (1996).

**Objective:** To determine the total CO2 balance and the relative magnitudes of the biotic and abiotic CO2 exchange processes in peat and marl forming wetlands of the Florida Everglades in response to changes in hydroperiod

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