Pilot Experiments on Air-Water Exchange of Carbon Dioxide in

the Amazon Basin

Simone Alin – University of Washington

Scott Miller – University of California Irvine

Alex Krusche – CENA, Universidade de São Paulo

Jeff Richey – University of Washington

Helber Freitas – Universidade de São Paulo

How much CO2 is evaded from the rivers of the Amazon Basin?pCO2 -> Outgassing

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

pC

O2 (

x 10

3

atm

)

0

4

8

12Jt

Jr

Sol

Ic

Md

Pr

Ng

Jp

atm

15

0

5

10

20

25

30

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

CO

2 E

vasi

on

(T

g C

mo

-1) T (>100m)

S (<100 m)MF

MC

10

15

20

25

%

1.77 x 106 km2

Inundation

1.2 ± 0.3 Mg C ha-1 y-1 or

0.5 Gt C y-1 for the whole Amazon Basin

Richey et al., 2002

Estimating Air-Water CO2 Exchange

• Floating “domes” – measure increase in CO2 in

enclosed space– smaller footprint– more easily deployed in various

environments

• Eddy covariance – simultaneous measurements of air

turbulence and CO2 concentration

– integrates flux measurements over larger footprint

Floating Dome

Scales of Sampling

Eddy CovarianceEquipment

4

32

CO2 Accumulation in the Dome

0

200

400

600

800

1000

10:27 10:30 10:33 10:36Time (minutes)

CO

2 (

ppm

)

Reserva Ducke

Evasion Rates vs. River pCO2

0

5

10

15

20

25

30

35

0 2000 4000 6000 8000

DuckeCatuaba

HumaitáIacoPurús

TapajósNegroSolimões

Amazônas

pCO2 (water) (ppm)

CO

2 e

vasi

on (

umol

m-2 s

-1)

Low wind (fan: 2.0 m/s)r 2 = 0.7137

Evasion Rates vs. River pCO2

0

5

10

15

20

25

30

35

0 2000 4000 6000 8000

Ducke

Catuaba

Humaitá

Purús

Tapajós

Negro

Solimões

Amazônas

High wind (fan: 6.5 m/s)

CO

2 e

vasi

on (

umol

m-2 s

-1)

r 2 = 0.8503

pCO2 (water) (ppm)

Gas Transfer Velocity

FCO2 = k s (pCO2(water) – pCO2 (air) )

where:

k = gas transfer or piston velocity (cm hr-1)

s = solubility of CO2

Wind speed experiment – Rio Negro

0

10

20

30

40

50

60

0 2 4 6 8

Wind (fan) speed (m s-1)

k = 7.2675 wind speed + 1.3109r 2 = 0.7203

Wind speed <3 m/s >3 m/s

Gas

tra

nsfe

r ve

loci

ty,

k (c

m h

r-1)

k values used by Richey et al., 2002

Wind speed experiment – Rio Solimões

0

10

20

30

40

50

60

0 2 4 6 8

Gas

tra

nsfe

r ve

loci

ty,

k (c

m h

r-1)

k = 8.5004 wind speed - 19.559r 2 = 0.9435

Wind (fan) speed (m s-1)

Wind speed <3 m/s >3 m/s

k values used by Richey et al., 2002

Eddy Covariance Calculations

FCO2 = c΄w΄

where:

c = atmospheric CO2 mixing ratio

w = vertical wind speed

΄ = fluctuation about the mean

Tapajós-Amazônas Data

FCO2 estimate: 1.7 umol m-2 s-1

- 30-60 minutes- upwind transect across river

system boundary

Conclusions

• Eddy covariance looks promising for measuring CO2 fluxes over freshwater systems with large pCO2 gradients

• Previous estimates of CO2 outgassing from the Amazon Basin (0.5 Gt C y-1) may be conservative, based on the underestimation of gas transfer velocity, pCO2 in Rio Negro, etc.

Acknowledgments• Technical/design assistance: Patrick Crill, John Kumph, Randy Fabro

• Funding: NASA-LBA and NSF

• Logistics: LBA staff in Santarém, Palmas, and Manaus

•Field and lab assistance: Anthony Aufdenkampe, Erin Ellis, Cleber Salimon, Chris Doughty, Hillândia Brandão da Cunha, Tania Pimentel, Daniel Amaral, Dariusz Kurzatkowski, Rita da Mata Ribeiro, Erich Collicchio, Fernando Frickmann, Walter, Luis, Jean Ometto, Michael Goulden

S. Denning (RAMS): Tapajós River Evasion Signal ~ 5 mol m-2 s-1

Next Phase

• Improvements to the floating dome:

– ADV (Acoustic Doppler Velocimeter) to measure micro-scale, water-side turbulence

– Anemometers– Thermistors

CO2 evasion rate vs. pH

0

5

10

15

20

25

30

35

4 5 6 7 8 9

pH

CO

2 e

vasi

on (

umol

m-2 s

-1)

evasion = 8825.2 pH-4.2688

r 2 = 0.621

Wind Speed and Temperature Effects on Gas Transfer Velocity

0

2

4

6

8

10

12

14

15 20 25 30 35 40Water temperature (°C)

Gas

tra

nsfe

r ve

loci

ty

(k ,

cm h

r-1)

0123

4

5

6

7

Wind speed(m s-1)

Wanninkhof (1992), Cole et al. (1998)

Evasion Rates vs. River pCO2

y = 0.0013x + 1.1784

R2 = 0.7137

0

5

10

15

20

25

30

35

0 2000 4000 6000 8000

Ducke

Linear(Ducke)

pCO2 (ppm)

CO

2 e

vasi

on (

umol

m-2 s

-1)

Low wind

Evasion Rates vs. River pCO2

y = 0.003x + 2.7976

R2 = 0.8503

0

5

10

15

20

25

30

35

0 2000 4000 6000 8000

Ducke

Catuaba

Humaitá

Iaco

Purús

Tapajós

Negro

Solimões

AmazônasLinear(Ducke)

pCO2 (ppm)

High wind

CO

2 e

vasi

on (

umol

m-2 s

-1)