• Increasing methane (CH4) and carbon dioxide (CO2) emissions represent a global environmental issue.

• Wetlands (especially peatlands) are recognized as important components in the global carbon cycle, for both sequestration and emission potential.

• Over the last 130 years, land development and agriculture have severely impacted the Everglades.

• As part of restoration efforts, increasing water inputs to Everglades soils can stall decomposition and reduce CO2 emissions, but increase CH4 emissions.

Carbon, Climate Change, and the Florida Everglades

Bradley R. Schonhoff1,2, Leonard J. Scinto1,2, Alexandra Serna1,2, Eric Cline3, Thomas Dreschel3, and Fred Sklar3

1Southeast Environmental Research Center, Florida International University, Miami, FL2Department of Earth & Environment, Florida International University, Miami, FL 3South Florida Water Management District, Everglades Systems Assessment Section, West Palm Beach, FL

Objectives• To quantify emission rates for CH4 and CO2 under

prolonged wet and dry conditions in a recreated, peat-based Everglades wetland with varying topographic features; tree island, ridge and slough.

• To determine the effects of water levels and elevation on overall CH4 and CO2 emissions.

• To compare CO2/CH4 emission ratios across five main Everglades landscape components.

Hypotheses• Areas of lower elevation – and therefore higher

water levels over longer periods – were predicted to exhibit the highest concentrations of CH4 (as anaerobic conditions lead to CH4 production).

• The highest CO2 concentrations were expected to occur at the highest elevations, which experience the least flooding (and the greatest exposure).

• CO2/CH4 ratios were likewise hypothesized to be highest at higher elevations. Distance (m)

Levee

Ridge

Shallow sloughDeep sloughEl

eva

tio

n (

m N

GV

D)

Levee

Tree IslandHead High (HH)

Tree IslandHead Low (HL)

McVoy et al., 2011

Greenhouse Gases (GHGs) and Global Warming Potential (GWP)

• Trapped solar radiation in atmosphere has a warming effect on the planet.

• Recent increases in the atmospheric concentrations of both CO2 and CH4 (linked to industrial revolution)

• Flooded soils saturation (pore spaces filled).

• Under anaerobic (low-oxygen) conditions, further decomposition leads to CH4 production, as anaerobic microbes break down organic materials.

Methanogenesis in Wetlands Study Site Loxahatchee

Impoundment Landscape

Assessment (LILA)

CH4 has a GWP 72x greater than CO2 in short-term spans

LILA Stage Inundation (cm) Days Flooded

-.405** -.168** .218**

.000 .006 .000

.425** .376** .047

.000 .000 .445

.420**

.205**

-.126*

.000 .001 .038

-.440** -.415** -.177**

.000 .000 .003

CO2 mmol L-1

CO2/CH4 ratrio

*. Significant at the 0.05 level.**.

Statistical Correlations (Pearson 2-tailed) N = 271

Redox (mV)

CH4 umol L-1

**. Significant at the 0.01 level.

Figure 2. Cross-section of LILA macrocosm with pore-water sippers installed

Figure 1. LILA Hydrograph with Sampling Events

Stage (water level)

Fig. 3: CH4 Concentrations Across SitesFig. 4: CO2 Concentrations Across Sites Fig. 5: CH4/CO2 Ratios, with GWP markers

ACKNOWLEDGEMENTSThank you to Dr. Leonard Scinto and to my committee; Dr. Tom Dreschel, Dr. René Price, and Dr. John Kominoski. Thanks to Eric Cline and the South Florida Water Management District, Dr. Alexandra Serna and Diana Johnson with the FIU Freshwater Biogeochemistry lab.

REFERENCESCharman, D.J., 2002. Peatlands and Environmental Change. John Wiley and Sons Limited, Chichester.Gorham, E. 1991. Role in the carbon cycle and probable responses to climatic warming. Ecol. Apps 1. Light, S.S., Dineen, J.W., 1997. Water Control in the Everglades: A Historical Perspective. In: Davis, S.M., Ogden, J.C., Eds. Everglades: the ecosystem and its restoration. Boca Raton (FL): St. Lucie Press. pp 47–84.McVoy, C.W., Said, W.P., Obeysekeran, J., Arman, J.V., Dreschel, T.W., 2011. Landscapes and Hydrology of the Pre-Drainage Everglades. Gainesville, FL: University Press of Florida.Reddy, K.R., & DeLaune, R.D., 2008. Biogeochemistry of Wetlands. CRC Press, Boca Raton, FL.United States Environmental Protection Agency (US EPA), 2014. Climate Change, Greenhouse Gas Emission Data. Retrieved from: http://epa.gov/climatechange/ghgemissions/

Discussion

• Flooding influenced the production of both CH4 and CO2 in this re-created Everglades landscape.

• Significant differences were found primarily between the two end-points along the elevation gradient; between the Tree Island Head High and the Deep Slough sites (Figure 3).

• Flooding and drying had an inverse relationship with average CO2 efflux rates (Figure 6).

• Stage (water levels), Inundation (depth of flooding), and Days Flooded correlated as expected with Redox Potentials, CH4 and CO2 concentrations, and CO2/CH4 ratios (Figure 7).

• The average CO2/CH4 ratio across all sites within a macrocosm: 22 (mol:mol). Given the GWP of each GHG, CH4 had a disproportionately greater impact than CO2, for at least a 100-year span.

• Water management in wetlands should therefore consider the disproportionate GHG effect of CH4 compared to CO2 in these areas.

• Future study of carbon inputs would give a sense of the overall carbon balance of the system.

Results

Fig. 7: Statistical Correlations

CH

4µ

mo

l L-1

HH = Tree Island Head High HL = Tree Island Head Low MR = Middle Ridge SS = Shallow Slough DS = Deep Slough

CO

2m

mo

l L-1

CO

2/C

H4

mm

ol L

-1

GWP: 8x @ 500 years

GWP: 25x @ 100 years

GWP: CH4 72x more effective than CO2 (20 years)

Fig. 6: Average CO2 Efflux Rates (LICOR)

• Large-scale physical model

• Elevation gradient important for flooding, and CH4 production