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Determining the role of different
wetland plant communities on
the export of dissolved organic
carbon (DOC) in the Florida
Everglades - a mesocosm
experiment
Jorge A. Villa, William J. Mitsch
The Ohio State University, Columbus, OH, USA
ENVIRONMENTAL SCIENCE GRADUATE PROGRAM
DOC
DOC
Leaching
Microbial Biomass Detritus
Peat
Leaching
Microbial Biomass
CO2
Production of DOC in the wetland ecosystems
Export
downstream
from
upstream
INTRODUCTION
The use of C stable Isotopes as a tracer
e.g. Natural abundance of
Carbon Isotopes
12C = 98.892%
13C = 1.108%
Stable Isotopes:
Isotopic signature (13C): Rsample = 13C/12C
13Csample = [(Rsample – Rreference)/ Rreference] * 1000‰
Fractionation (α): • Evaporation-condensation
• Kinetic effects (e.g. Biological mediated reactions,
like photosynthesis)
• Diffusion
• Others
DOC
DOC
Leaching Detritus
Peat
Leaching
CO2
Flow of C from and Isotopic perspective
α
α
α
α
Initial 13C 13C mixture
Microbial Biomass
Microbial Biomass
13C
Aboveground
Biomass
Flow of C from and Isotopic perspective
Initial DOC 13C mixture DOC 13C
13C
Belowground
Biomass
13C microbial
decomposition
13C microbial
decomposition*
Why DOC?
Source of carbon (C) for microbial growth
Decomposition, humification and stabilization of Organic matter
DOC is a stable component of Dissolved Organic Matter (DOM)
DOM is crucial to assess ecosystem functioning, especially in
regards to the biochemical cycling of nutrients
Important in the design of functional constructed wetlands
Mode for organic C, nitrogen (N) and phosphorus (P) export
Transport and toxicity of metals
Why DOM?
0 10 20 30 40 50 60
Everglades National Park
WCA3
WCA2
Loxahatchee (WCA-1)
Hillsboro Canal
STA-3/4
STA-2
STA-1W
Lake Okeechobee
DOC mg C L-1
Adapted from: Chimney and Goforth (2006) Data from: Aiken et al. (2011)
Average DOC in the Everglades
(North – South)
Storm Treatment Area (STA)
What is the contribution of different
wetland plant communities to the bulk
DOC exported from a mesocosm
experiment to remove Phosphorus in
the Florida Everglades?
DOC and 13C of DOC in inflow and outflows of each treatment
13C and 15N of biomass
and soils
Contribution of each source
METHODS Study Site:
18 fiberglass tanks
(6 m L x 1 m W x 1 m D)
Retention time: 14 d
Soils: Hisotosols
(from STA -1W)
6 plant communities:
•Typha domingensis (Cattail)
•Cladium jamaicense (Sawgrass)
•Nymphaea sp. (Water lily)
•Nymphaea sp. + Eleocharis sp.
(Spikerush)
• Najas sp. + Charas sp.
• Self Design (Najas sp.)
Field Sampling:
Water Soil
Biomass
3.3
3.6
3.9
4.2
4.5
4.8
J F M A M J J A S O N D
Wa
ter
Le
ve
l (m
.a.s
.l.)
Component 3/24/11 6/02/11 9/02/11
Water (Inflow/Outflow) X X X
Biomass (Above/belowground) X X
Soils (0-2 cm, 2-10 cm) X X
Analytical methods:
Water Samples
TOC/IRMS
DOC / 13C-DOC
Biomass
Dried at 55 o C
Milled to
powder
13C/15N
Soils
Dried at 55 o C
Grinded to
powder
Fumed with
HCl
ANCA-GSL/IRMS + 0.6‰
< 0.2‰
Filtered 0.45 micron
RESULTS (Water)
Average change in DOC concentrations
between inflow and treatment outflows
-2
0
2
4
6
8
10
12
14
16
Net
me
an
(+
SE
) D
OC
ch
an
ge
(m
g/L
)
-26.5
-26.0
-25.5
-25.0
-24.5
13 C
+ S
E (
‰)
13C values for the inflow and treatment outflows
* *
RESULTS (Biomass and Soils)
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
-30 -28 -26 -24 -22 -20 -18 -16
15N
(‰
)
13C (‰)
Aboveground
Roots
Soil (0-2)
Soil (2-10)
Average 13C/13N ratios for biomass
and soils for all the treatments
SAV
Emergent macrophytes
DOC
DOC
Leaching Detritus
Peat
Leaching
CO2
Export
downstream
α
α
α
α
Inflow 13C-DOC Outflow 13C-DOC
Microbial Biomass
Microbial Biomass
13C
Aboveground
Biomass
Initial 13C- DOC Outflow 13C-DOC
13C
Belowground
Biomass
RESULTS (Isotope Mixing Model)
13C-DOCoutflow = (ƒinflow) (13C-DOCinflow ) + (ƒbiomass) (13C-DOCbiomass) (1)
1 = ƒinflow + ƒbiomass (2)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Typha domingensis
Cladium jamaicense
Nymphaea sp.
Nymphaea sp./
Eleocharis sp.
Najas sp./ Charas sp.
Najas sp.
Contr
ibution (
fraction)
Inflow
Biomass
Inflow and biomass contributions to the outflow from each treatment
SUMMARY
All the treatments, except the Najas sp./Charas sp. were net exporters of
DOM in the period evaluated.
Emergent vegetation has a considerable greater effect on DOM exports
than submerged vegetation.
IMPLICATIONS
In the short term, recently constructed wetlands in the Everglades area will
function as exporters of DOM and possibly other dissolved organic nutrients.
AKNOWLEDGEMENTS
To Shili Miao from the SFWMD that made this project possible. Also to Li
Zhang, Keunyea Song, Blanca Bernal, Diana Lombana, Darryl Marois,
and staff members from SFWMD working in the mesocosm experiment
for their help with the logistics and sampling. To the Olentangy Wetland
Research Park for trip and meeting expenses.
Thanks for your Questions!!
REFERENCES: Aiken, G.R., Gilmour, C.C., Krabbenhoft, D.P., Orem, W., 2011. Dissolved Organic Matter in the Florida Everglades: Implications for Ecosystem Restoration. Critical Reviews in Environmental Science and Technology 41, 217–248. Chimney, M.J., Goforth, G., 2006. History and description of the Everglades Nutrient Removal Project, a subtropical constructed wetland in south Florida (USA). Ecological Engineering 27, 268–278. Reddy, K.R., DeLaune, R.D., 2008. Biogeochemistry of wetlands, science and applications. CRC, Boca Raton, FL..
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