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)