Soil CO2 production and transport in the drought experiment in Caxiuana

National Forest, Para, Brazil.

Eleneide Doff Sotta Antonio Carlos Lola Rosiene Keila da Paixao Edzo Veldkamp Brenda Rocha Guimaraes Patrick Meir Alessandro Rosario Maria de Lourdes RuivoLuitgard Schwendenmann

Purpose of the study

• Estimate soil CO2 production in deep soil

• Test which model of soil gas diffusivity better work for Caxiuana soils

• Show how CO2 production rate varies with seasons and under drought

conditions

Background:

CO2 Transpo

rt

CO2

Emission

Microbial respirati

on

CO2 Diffusion

CO2 concentration

in soil airRoot

respiration

Soil water contentSoil total porositySoil air pore spaceField capacity

Soil water content Soil temperatureLitterfallRadiation

Environmental factors

Drought experiment: site description

Period of the measurements:from Jan to Dec 2002 Bi-weekly and from Jan to Nov 2003 monthly

ControlTreatment

~ 90% water exclusion

Experimental design: 2 plots of 1 ha each• 16 efflux chambers per plot • 4 soil shafts per plot

Localization:Caxiuana National Forest, Para, Brazil

Forest type: Terra firme

Soil type: oxisol and ultisol

Sampling and sample processing

Soil CO2 efflux• PVC rings covered with a lid for 5 min. • Closed dynamic system (LiCor 6262)

Soil air CO2 concentration• 30 mL plastic syringes • 0.5 mL samples injected in a gas chromatograph

Rn measurementsRn concentration:• soil gas samples same depth (Lucas cells)• Impulses counted with a Radon monitor Rn activity:• incubation of soil samples for 4 weeks (wet and dry conditions)

Pits instrumentation

• Stainless steel tubing • Thermocouple T-probes

Depths (cm) : 5 10 25 50100200300

• Soil moisture sensors

(TDR) Depths (cm):0-30 (vertically) 50 100 200 300

1) Calculation of diffusion coefficient through empirical formulas:

Non-aggregated porous media Millington & Quirk (1961)Aggregated porous media Millington & Shaerer (1971)

Parameters given: Total pore space, soil water content, Air pore space, field capacity

Method: CO2 production rates

P CO2 production (mg C m-2 h-

1)

2) Validation of diffusion coefficient with the help of Radon concentration profileNumerical solution of transport for Radon in the soil air

Parameters given: Radon production, diffusion coefficient

PCO2 per layer is calculated from Fick’s first law

Topsoil PCO2 (including litter layer)

PCO2 topsoil = soil CO2 efflux – PCO2 modelled.

0 – 50 cm

50 - 300 cm

PCO2 topsoil

PCO2 modelled

Soil CO2 efflux

d Diffusion coefficient (m2 h-1)

Pi

Fi+1 [Ci+1]

[Ci]

[Ci-1]

Fi

Fi-1

di-1

di

di+1

[C] CO2 concentration in soil air (mg C m-3)

F CO2 flux between layers (mg C m-2 h-1)

i Layers

Davidson & Trumbore (1995)

Simulated vs. measured Radon concentration

A dry season

0

50

100

150

200

250

300

350

400

450

0 10000 20000 30000

222Rn activity (Bq m -3)

so

il d

ep

th (

cm

)

measured Rn concentration

Simulated Rn concentrationnon-aggregated model

aggregated model

B dry season

0

50

100

150

200

250

300

350

400

450

0 10000 20000 30000

222Rn activity (Bq m -3)

soil

dep

th (

cm)

B wet season

0

50

100

150

200

250

300

350

400

450

0 10000 20000 30000

222Rn activity (Bq m -3)

soil

dep

th (

cm)

Results: Soil CO2 concentrationJa

n-02

Feb

-02

Mar

-02

Apr

-02

May

-02

Jun-

02

Jul-0

2

Aug

-02

Sep

-02

Oct

-02

Nov

-02

Dec

-02

Jan-

03

Feb

-03

Mar

-03

Apr

-03

May

-03

Jun-

03

Jul-0

3

Sep

-03

Oct

-03

Nov

-03

0.05

0.10

0.25

0.50

1.00

2.00

3.00

So

il d

epth

(m

)

Control

0-1

1-2

2-3

3-4

4-5

5-6

6-7

CO2 (%)

Jan-

02

Feb

-02

Mar

-02

Apr

-02

May

-02

Jun-

02

Jul-0

2

Aug

-02

Sep

-02

Oct

-02

Nov

-02

Dec

-02

Jan-

03

Feb

-03

Mar

-03

Apr

-03

May

-03

Jun-

03

Jul-0

3

Sep

-03

Oct

-03

Nov

-03

0.05

0.10

0.25

0.50

1.00

2.00

3.00

So

il d

epth

(m

)

Treatment

0-1

1-2

2-3

3-4

4-5

CO2 (%)

SeasonalityBoth plots had higher concentration during wet season

Wet = up to 2.0 % upper layers

Drought effect Treatment plot had lower CO2 concentration

Control = 3.2 %Treatment = 1.0 %

Results: CO2 concentration profile

Control

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6

CO2 concentration in soil air (%)

So

il d

epth

(cm

)

Treatment

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6

CO2 concentration in soil air (%)

So

il d

epth

(cm

)

w et season

dry season

Wet season: Big difference on the first 5 cm depthAlmost no change in [CO2] in the profile

Drought effect: ~50 % lower [CO2] in the profile

Results: estimates of soil CO2 production

Average CO2 production rate:Control = 170.1 ± 4.7 mg C m-2 h-1 Treatment = 137.3 ± 5.8 mg C m-2 h-1

No difference during wet season

0

50

100

150

200

250

Jan-02 Mar-02 May-02 Jul-02 Sep-02 Oct-02 Dec-02 Feb-03 Apr-03 Jun-03 Aug-03 Oct-03 Dec-03

CO

2 p

rod

uc

tio

n (

mg

C m

-2 h

-1)

Control 0 - 0.5 m Control 0.5 - 3.0 m

Treatment 0 - 0.5 m Treatment 0.5 - 3.0 m

dry seasonwet season dry seasonwet season

Results: Profile CO2 production rate

Wet season

0 50 100 150 200

Soil CO2efflux

0 - 50

60 - 100

110 - 200

210 - 300

De

pth

s in

terv

als

(c

m)

CO2 (mg C m-2 h-1)

Control

Treatment

SeasonalityControl - no difference between wet and dry season

Control Wet and Dry season

0 – 50 cm = 76 %60 – 300 cm = 24 %

Treatment Wet season Dry season0 – 50 cm = 84 % 71 %60 – 300 cm = 16 % 29 %

168.7159.9

Dry season

0 50 100 150 200

Soil CO2efflux

0 - 50

60 - 100

110 - 200

210 - 300

De

pth

in

terv

als

(c

m)

CO2 (mg C m-2 h-1)

171.5113.4

Drought effect Treatment – almost 30% less during dry season

Correlations: PCO2 and environmental factors

PCO2

SoilMoistur

e

SoilTemperatu

re

AirTemperatu

reRadiatio

nRainfal

l

Litter (1 month lag)

Soil depth Total Leaves Flowers Twigs

0 - 0.5 m

-0.23n.s. 0.33n.s. -0.16n.s. -0.08n.s.

-0.21n.s.

0.23n.s.

-0.04n.s.

0.59* 0.47n.s.

0.6 - 1 m

0.82** -0.60** -0.22n.s. 0.63**

-0.14n.s.

-0.61** -0.55*

-0.28n.s.

-0.24n.s.

1.1 – 2 m

-0.12n.s. 0.24n.s. 0.72** -0.51* 0.72**

-0.37n.s.

-0.16n.s.

-0.68**

-0.06n.s.

2.1 – 3 m -0.55** 0.47* 0.81** -0.81** 0.66** 0.11n.s. 0.34n.s. -0.58* 0.03n.s.

PCO2

Soil Moisture

SoilTemperatur

e

AirTemperatu

reRadiatio

nRainfal

l

Litter (without lag)

Soil depth Total Leaves Flowers Twigs

0 - 0.5 m

0.76** -0.41n.s. -0.70** 0.84** -0.73**

-0.37n.s.

-0.62* 0.52* 0.67**

0.6 - 1 m

0.57** -0.47* -0.26n.s. 0.59**

-0.35n.s.

0.14n.s.

-0.05n.s.

0.65** 0.00n.s.

1.1 – 2 m

-0.43* 0.47* 0.81** -0.67** 0.71** 0.63* 0.68**

-0.10n.s.

-0.35n.s.

2.1 – 3 m

-0.53* 0.45n.s. 0.91** -0.76** 0.78** 0.45n.s. 0.60*

-0.33n.s.

-0.45n.s.

(a) Control plot

(b) Treatment plot

** P < 0.01* P < 0.05n.s. no significance

Conclusions

1. There was seasonality in [CO2] in soil profile

2. [CO2] was lower in drought conditions

3. The cumulative PCO2 in topsoil was affected by drought but not by season

4. ~76 % of the PCO2 happened in the topsoil

5. During the dry season in the drought plot the deep soil compensated for the CO2 production.

6. Apparently the capacity of water storage is limited, which makes the forest more susceptible to drought. The PCO2 in deep soil may not recover during the wet season.

7. A lower soil respiration can be expected during El Nino due to the limited capacity of compensation of the deep soil.