Carbon dioxide and methane dynamics in estuaries

(1)

Carbon dioxide and methane dynamics in estuaries

Alberto V. Borges

1 _{and Gwenaël Abril}

2

1 _{Université de Liège (BE)}

2 _{Université de Bordeaux 1 (FR)}

Vienna, 02 – 07 May 2010 http://www.co2.ulg.ac.be/

*

_{Due in 2011 if all goes well…}

(2)

Vienna, 02 – 07 May 2010

(3)

River inputs

of CO

₂

In-situ CO

₂

production

= net ecosystem production

Emission of CO

₂

to the atmosphere

(4)

Vienna, 02 – 07 May 2010

(5)

(1) Increasing ratio of

allochtonous inputs

of inorganic nutrients :

organic matter

(1)

(2)

(2) Decreasing size

(3)

(3) increasing light limitation

(6)

(1) allochtonous inputs of CO

₂

(riverine and lateral)

(2) anoxic production of CO

₂

(1)

(2)

(1)

(2)

(3) more rapid equilibration of O

₂

than CO

₂

(3)

1641 measurements in 24 estuarine environments

Net community production in estuaries

(7)

Vienna, 02 – 07 May 2010

http://www.co2.ulg.ac.be/

CO

2 River inputs

• terrestrial organic matter

inputs (DOC) sustaining net

heterotrophy in the rivers

(pCO

₂

)

• Inputs of both DOC and

CO

₂

from soils by

ground-waters and surface run-off

more refractory DOC

lower buffer

capacity

HCO

₃

-

_{0 to 775 µM}

(8)

Vienna, 02 – 07 May 2010

CO

2 River inputs

In-situ CO

₂

production

CH

₄

degassing

and bacterial

oxidation

(9)

Vienna, 02 – 07 May 2010

CO

2 River inputs

• input of CO

₂

from

rivers ~10% of total CO

₂

emission from estuaries

• increases in low

(10)

Vienna, 02 – 07 May 2010

Physical settings - size

Mangrove creeks of Ca Mau (Vietnam)

decreasing size

• Larger impact on smaller systems of inputs of pore waters rich in CO

₂

& CH

₄

• Higher production of CO

₂

and CH

₄

in the water column and sediments sustained by

(11)

Vienna, 02 – 07 May 2010

Physical settings - stratification

(1) Stratified systems

= transfer of O.M. across the pycnocline

= decrease of CO

₂

in surface waters

= promoting anoxia in bottom waters

= favourable for methanogenesis

(1)

(2) Rhine

= high freshwater discharge

= short residence time

= low loss of riverine CH

₄

by evasion to the

atmosphere and by bacterial oxidation

= lesser CO

₂

production due net

heterotrophy

(2)

(3) Well-mixed systems

= increase of allochtonous

carbon inputs

= increase of both CO

₂

&

CH

₄

production

(3)

(4) Sado

= very extensive inter-tidal

areas and marshes

= higher lateral inputs of

CH

₄

from pore waters

(4)

(5) Small mixed systems

= lateral inputs of CH

₄

from

pore waters

= high allochtonous inputs

sustaining methanogenesis

(5)

(12)

CH

4 fluxes

Low tide

High tide

Ebullition (3)

Tidal pumping

Transport

through plants (2)

Aerobic oxidation

Water-air diffusion (4)

Labile OM

CH

₄

Sulfate depletion depth

hydrostatic

pressure

hydrostatic

pressure

Sediment-air

Diffusion (1)

Tidal flats and marshes

O

₂

CH

₄

O

₂

o

xi

d

at

io

n

Vegetation roots

A. Freshwaters and low salinity regions

Sediment-water diffusion

Estuarine Turbidity Maximum

Deposition & Resuspension

10-6_-10-7 10-2_-10-3 10-7_-10-8

1.5±1.2

10-2_-10-3 Anaerobic oxidation ? 10-8_-10-9

14.5±17.5

1.5±1.2

0.1±0.1

Low tide

High tide

Ebullition (3)

Tidal pumping

Transport

through plants (2)

Aerobic oxidation

Water-air diffusion (4)

Labile OM

CH

₄

Sulfate depletion depth

hydrostatic

pressure

hydrostatic

pressure

Sediment-air

Diffusion (1)

Tidal flats and marshes

O

₂

CH

₄

O

₂

o

xi

d

at

io

n

Vegetation roots

A. Freshwaters and low salinity regions

Sediment-water diffusion

Estuarine Turbidity Maximum

Deposition & Resuspension

10-6_-10-7 10-6_-10-7 10-2_-10-3 10-2_-10-3 10-7_-10-8 10-7_-10-8

1.5±1.2

10-2_-10-3 10-2_-10-3 Anaerobic oxidation ? 10-8_-10-9 10-8_-10-9

14.5±17.5

1.5±1.2

0.1±0.1

mmol m

-2

_d

-1

_{mol L}

-1

(13)

B. High salinity regions

Low tide

High tide

Tidal pumping

Transport

through plants (6)

Water-air diffusion

Sulfate depletion depth

Sediment-air

Diffusion (5)

Mangroves and saltmarshes

Stratified Lagoons

and fjords (9)

Sediment-water diffusion

Anaerobic oxidation

10-7_-10-8 10-3_-10-4 10-8_-10-9

Creeks at low tide (7)

Open waters and plumes (8)

10-5_-10-6

Aerobic oxidation

10-2_-10-3

0.14±0.10

0.18±0.02

0.04±0.17

1.85±0.99

0.32±0.27

Oxicline

10-5_-10-6

Bubble dissolution

B. High salinity regions

Low tide

High tide

Tidal pumping

Transport

through plants (6)

Water-air diffusion

Sulfate depletion depth

Sediment-air

Diffusion (5)

Mangroves and saltmarshes

Stratified Lagoons

and fjords (9)

Sediment-water diffusion

Anaerobic oxidation

10-7_-10-8 10-7_-10-8 10-3_-10-4 10-3_-10-4 10-8_-10-9 10-8_-10-9

Creeks at low tide (7)

Open waters and plumes (8)

10-5_-10-6 10-5_-10-6

Aerobic oxidation

10-2_-10-3 10-2_-10-3

0.14±0.10

0.18±0.02

0.04±0.17

1.85±0.99

0.32±0.27

Oxicline

10-5_-10-6 10-5_-10-6

Bubble dissolution

CH

4 fluxes

mmol m

-2

_d

-1

_{mol L}

-1

(14)

CH

4 fluxes

0

20

40

60

0.01

0.1

1

10

100 Tidal flats (unvegetated)

Tidal marshes (vegetated)

Mangrove sediments

Salinity of surrounding w aters or porew aters

S

e

d

im

e

n

t

-

a

ir

C

H

4 f

lu

x

m

o

l.

m

-2

.d

-1

diffusion

ebullition

transport through plants

Increasing importance of

sulfate reduction

= out-competition

methanogenesis

(15)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

(16)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

Larger emission of CO

₂

and CH

₄

in the Northern Hemisphere

Related to surface area

(17)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

PgC yr

-1

_{mol m}

-2

_yr

-1

₁₀

6 _km

2 _Reference

0.60

36.5 1.40*

Abril and Borges (2004)

0.43

38.2 0.94**

Borges (2005)

0.32

28.6 0.94**

Borges et al. (2005)

0.36

32.1 0.94**

Chen and Borges (2009)

0.27

21.0 1.10***

this study

CO

₂

emissions

* Woodwell et al. (1973) including intertidal areas

** Woodwell et al. (1973) excluding intertidal areas

*** Dürr et al. (2010)

(18)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

TgCH

₄

yr

-1

_{mmol C m}

-2

_yr

-1

₁₀

6 _km

2 _Reference

0.8-1.3

36-59

1.40*

Bange et al. (1994)

1.8-3.0

79-132

1.40*

Middelburg et al. (2002)

6.8

385 1.10**

this study

CH

₄

emissions

* Woodwell et al. (1973) including intertidal areas

** Dürr et al. (2010)

(19)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

CH

₄

emissions

Natural sources (TgCH

₄

yr

-1

₎

Wetlands

100-231

Termites

20-29

Ocean

4-15

Hydrates

4-5

Geological sources

4-14

Wild animals

15 Wildfires

2-5

Estuaries

7

(20)

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

CH

₄

emissions

Aquatic sources (TgCH

₄

yr

-1

₎

Wetlands

100-231

Rice paddies

31-112

Hydroelectric reservoirs

70 Lakes

8-48

Ocean

4-15

Estuaries

7

(21)

}

Vienna, 02 – 07 May 2010

Global scaling of CO

2 & CH

4 fluxes

-1.4

-0.3

+0.3

+0.1

+0.2

(22)

Vienna, 02 – 07 May 2010

Conclusions

(23)

Vienna, 02 – 07 May 2010

(24)

Vienna, 02 – 07 May 2010

Conclusions

• Need of observations in more estuaries worldwide

(25)

Conclusions

months

2009

months

2008

d

is

ta

n

c

e

f

ro

m

o

u

h

t

(k

m

)

500 1500

2500

3500

4500

5500

6500

7500

120

110

100

90

80

70

60

50

40

30

20

10

0 J F M A M J J A S O N D

J F M A M J J A S O N D

River

North Sea

pCO

₂

(ppm)

7220 ppm

4880 ppm

100 ppm

210 ppm

Scheldt estuary

(26)

Vienna, 02 – 07 May 2010

Conclusions

• Need of observations in more estuaries worldwide

• Need of sustained observations to unravel inter-annual variations

(27)

Vienna, 02 – 07 May 2010

Conclusions

(28)

Range of pCO

₂

variations

(ppm)

Range of pCO

₂

spatial variations

(ppm 100km

-1

₎

Range of pCO

₂

seasonal variations

(ppm month

-1

₎

(29)

Vienna, 02 – 07 May 2010