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• 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