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Greenhouse gas emissions from wetlands with different vegetation type

Jeroen de Klein1, Frits Gillissen1, Chih-Chung Wu1, Irene Paredes Losada2, Annelies Veraart31Aquatic Ecology and Water quality management group Wageningen University, Wageningen, The Netherlands 2Estación Biológica de Doñana, Sevilla, Spain 3Radboud University, Nijmegen, The Netherlands

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Area of free-floating plants on wetlands is increasing effect on fluxes of CO2 and CH4

Eichornia cover BrasilAzolla cover Doñana Spain

Introduction

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Introduction

(Contrasting) mechanisms of floating plants on GHG emission

• Oxygen depletion under floating vegetation: Anoxic decomposition; more CH4

• Temperature increase lower oxygen (decomposition more enhanced than production)

• However, with floating plants less exchange with atmosphere entrapment and oxidation of CH4 bubbles in rootzone

Veraart at al. 2010 Biogeochemistry

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Air/Water gas exchange rate

• Effect of floating biomass on air/water gas exchange rate• Effect of floating biomass on CH4-ebulition • 3 free-floating species (Azolla, Salvinia, Eichhornia)

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Gas exchange rate K Eichhornia

Azolla

Air/Water gas exchange rateFr

actio

n of

Ope

n W

ater

K (

-)

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Micro-cosms experiments

• Microcosms (submerged, floating (Azolla, Lemna), controls, n=4)• Temperature range 10-25 °C (measured in light and dark; 12/12h)• Gasfluxes measured with Innova TGA

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Results CH4 fluxes cosm-experiments

Accelerated effect of temperature on DOVeraart A.J. and de Klein J.J.M. (2011), PLoS ONE, 6(3), 2-7

Temperature experiment

-0.01

0

0.01

0.02

0.03

0.04

10 15 20 25

Gas

flux

(mm

ol m

-2h-

1 )

Temperature °c

CH4 subm

Dark

Light

CH4 submerged plants

-0.01

0

0.01

0.02

0.03

0.04

10 15 20 25

Gas

flux

(mm

ol m

-2h-

1 )

Temperature °c

CH4 floatCH4 floating vegetation

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0

2

4

6

8

10

12

14

16

18

-4

-3

-2

-1

0

1

2

3

4

5

6

Lemna Azolla Elodea No Plants

Diss

olve

d O

xyge

n (m

g/l)

Prod

uctio

n (m

mol

m- ²

hr-1

)

CO2darklightDO DarkDO Light

Results gas fluxes cosm-experiments

continuous experiment (average fluxes 13 weeks, 20-25°C)

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Results gas fluxes cosm-experiments

continuous experiment (average fluxes 13 weeks, 20-25°C)

0

2

4

6

8

10

12

14

16

18

0

0.05

0.1

0.15

0.2

0.25

Lemna Azolla Elodea No Plants

Diss

olve

d O

xyge

n (m

g/l)

Prod

uctio

n (m

mol

m- ²

hr-1

)

CH4darklightDO DarkDO Light

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• 9 shallow lakes and ponds in marshland (single measurement, 6 experiments per lake)• Different cover of submerged and floating vegetation• Gas fluxes measured with floating chamber (Innova and LGR)

Field measurements Doñana Wetlands

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-1.0

-0.5

0.0

0.5

1.0

1.5

low medium abundant

gas f

lux

(mm

ol m

-2h-

1 )

CO2

0.0

0.1

0.2

0.3

low medium abundant

CH4

Average gas fluxes (daytime) related to macrophytes density

Field measurements Doñana Wetlands

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To summarize

GHG fluxes from microcosms and shallow vegetated lakes

- Clear temperature effect on CH4 with floating plants (temperature

threshold ?)

- With increasing floater dominance: shift from carbon sink to source

- In field conditions: highest CH4 emissions with median vegetation cover

- DO depletion effect of floaters seem to prevail above gas exchange

limitation

- However, overall effect is variable (species, temperature, local

conditions)

CO2CH4

GHG potential

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