75°0'0"W

75°0'0"W

70°0'0"W

70°0'0"W

65°0'0"W

65°0'0"W

60°0'0"W

60°0'0"W

55°0'0"W

55°0'0"W

50°0'0"W

50°0'0"W

20°0'0"S 20°0'0"S

15°0'0"S 15°0'0"S

10°0'0"S 10°0'0"S

5°0'0"S 5°0'0"S

0°0'0"N 0°0'0"N

5°0'0"N 5°0'0"N

Legend

Rivers

Amazônia

Rondônia

Basin of Ji-Paraná

COM-1

PB-1

COM-2

PB-2

JIP-1

JIP-2

JIP-3

JIP-4

JIP-5

63°0'0"W

63°0'0"W

62°0'0"W

62°0'0"W

61°0'0"W

61°0'0"W

60°0'0"W

60°0'0"W

13°0'0"S 13°0'0"S

12°0'0"S 12°0'0"S

11°0'0"S 11°0'0"S

10°0'0"S 10°0'0"S

9°0'0"S 9°0'0"S

8°0'0"S 8°0'0"S

0 40 80 120 16020Kilometers

Legend

Sites

Rivers

Basin Ji-Paraná

­Average of discharge from Ji-Paraná river (1978 to 2001)

(Agência Nacional das Águas – ANA)

0200400

600800

100012001400

160018002000

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

Month

Dis

char

ge (

m3.s

-1)

pC

O2

(µat

m)

JJJ F MM AA S O N D

atm equilibrium tributaries Ji-Paraná

pCO

2 (

µat

m)

0

500

1000

1500

2000

F M A M J J S N D4.0

4.5

5.0

5.5

6.0

6.5pCO2 pH

Average COM-1 and PB-1

pH

Low waterHigh water

2.7

38,0 24,3

4,2

pC

O2 (

µa

tm)

Average JIP-2,3

pH

High water Low water

177,5166,8

24,2

240,5

pCO

2 (

µat

m)

Average JIP-1, 4, 5

High water Low water

156,9

84,124,4

185,9

CO2* (µM)

HCO3-(µM)

CO2* (µM)

HCO3-(µM)

pH

0

500

1000

1500

2000

2500

3000

3500

4000

F M A M J J S N D

5.0

5.5

6.0

6.5

7.0pCO2 pH

Machadinho

105,4

29,4 87,184,3

pCO

2 (

µat

m)

High water Low water

Pimenta Bueno -2

pCO

2 (

µat

m)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

F M A M J J S N D

5.5

6.0

6.5

7.0

7.5

pCO2 pH

pHHigh water

177,2154,7

Low water

36,1

219,7

Base Saturation

( % ) Urupá

pH

0

2000

4000

6000

8000

10000

12000

F M A M J J S N D

5.0

5.5

6.0

6.5

7.0

7.5

8.0pCO2 pH

610,8

60,3

High water Low water

215,6

264,3

pCO

2 (

µat

m)

INTRODUCTION

OBJECTIVE

STUDY­AREA

Fev/00

Mar/01

Abr/02

May/99

Jun/00

Jul/01

Sep/00

Nov/99

Dec/01

The partial pressures of dissolved CO2 (pCO2) in the Ji-Paraná and its tributaries are a

function of respiration and mineral weathering. Although rivers draining eutrofic soils

(Rolim, Urupá, Jarú and Pimenta Bueno-2) show the highest DIC concentrations and

outgassing (evasion) of CO2, pH changes lead to a pronounced seasonality in evasion.

The outgassing is higher during the rising water, because the dilution of ground water by

rain water, and probably also changes in metabolism, result in lower pH values, thus

increasing the partial pressures of dissolved CO2 (pCO2) and evasion process. In the

falling water, groundwater stay longer in contact with the substrate and weathering, which

consumes H+ and converts carbonic acid into bicarbonate, increases pH and lowers pCO2

and the evasion process.

The rivers draining distrofic soils (Comemoração, Pimenta Bueno-1, Preto e Machadinho)

show lower DIC concentrations and lower pH, and the potential evasion of CO2 is limited

by lower pCO2.

CONCLUSION

The influences of total dissolved inorganic carbon (DIC) concentrations and pH on potential outgassing from rivers

in Rondônia.Maria de Fátima F. L. Rasera1; Alex Vladimir Krusche1; Nei K. Leite1; Jeffrey E. Richey2; Anthony K. Aufdenkampe3

1 Universidade de São Paulo –CENA. Lab. de Ecologia Isotópica. Piracicaba/SP – Brasil mrasera@cena.usp.br2 School of Oceanography, University of Washington, USA

3 Stroud Water Research Center - USA

Recent studies point to the importance of CO2 outgassing from rivers of the Amazon,

suggesting that a significant part of the carbon fixed by forest return to the

atmosphere through this pathway. Gas exchange between the atmosphere and

waters is a funcion of gaseous gradients across the air-water interface, and the water

pCO2 is strongly determined by the concentrations of dissolved inorganic carbon

(DIC) and pH, which, in turn, are a funcion of physical, chemical and biological

processes. This study focus on the influence of DIC concentrations and the pH on

potencial CO2 outgassing to atmosphere from rivers of the Ji-Paraná basin,

Rondônia.

METODOLOGY

RESULTS

River Water

Field

Laboratory FiltrationDissolved Inorganic

Carbon - ( DIC )

Calculated

Theoretical diffusion model :

F = D.(Cwater - k.Pair) / Z (Broecker, 1974)

Where:

D = gas- and temperature-specific diffusion coefficient;

Cwater = concentration of gas in the water;

k.Pair = concentration of gas in equilibrium with the atmosphere

Z = thicness of the boundary layer

Total Organic Carbon Analyser

(Shimadzu, 5000A)

Infrared gas analyser,

non dispersive

Thermodynamic equilibrium equations

[CO2*] = DIC .(10pH)2 .

(10pH)2+ k1.(10pH) + k1.k2

(Stumm & Morgan, 1996)

DIC

(µ

M)

pH

temperature

pH

pH meter

condutivity

Condutivity meterAdd Thymol

[pCO2] = [CO2*] k0

Acknowledgements

CO

2 e

vasi

on

(m

ol

CO

2.m

-2.d

-1)

AVERAGE

HIGH WATER

LOW WATER

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

COM­1 COM­2 PB­1 PB­2 J IP­1 Rolim Urupá J IP­2 J IP­3 J aru Machad. J IP­4 J IP­5 Preto

* D/Z = K (exchange coeficient) = 1,2 m.d-1 (Richey et al, 2002)

SH 37.13

To expand the understanding of changes in pH and DIC concentrations in the Ji-

Paraná River Basin and its consequences for the outgassing of CO2.