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..