moisture controls on trace gas fluxes from semiarid soils dean a. martens and jean e. t. mclain swrc...

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Moisture Controls on Moisture Controls on Trace Gas Fluxes From Trace Gas Fluxes From Semiarid Soils Semiarid Soils Dean A. Martens and Jean Dean A. Martens and Jean E. T. McLain E. T. McLain SWRC – Tucson and Water SWRC – Tucson and Water Conservation Laboratory – Conservation Laboratory – Phoenix Phoenix

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Page 1: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Moisture Controls on Trace Moisture Controls on Trace Gas Fluxes From Semiarid Gas Fluxes From Semiarid

SoilsSoils

Dean A. Martens and Jean E. T. Dean A. Martens and Jean E. T. McLainMcLain

SWRC – Tucson and Water SWRC – Tucson and Water Conservation Laboratory – Phoenix Conservation Laboratory – Phoenix

Page 2: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Semiarid ConceptsSemiarid Concepts• Due to limited rain and high seasonal

temperatures that limit plant productivity, semiarid systems are not important in global C dynamics?

• Semiarid ecosystems do not contribute to or mitigate atmospheric C concentrations involved in potential climate disruptions

Page 3: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Study site was the San Pedro Riparian zone near Tombstone AZ.

The San Pedro is the last nearly perennial, non dammed semiarid stream in the southwest.

It occupies an important avian – North – South flyway between the Rio Grande and the Colorado Rivers

Open

Mesquite

Sacaton

Page 4: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Vegetation Response to Vegetation Response to Seasonal MoistureSeasonal Moisture

15 mm rain in 7 months 200 mm rain in 1 month

July 2002 August 2002

Page 5: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Three Vegetation SitesThree Vegetation Sites

Annual grasses and forbes

Sacaton site

Mesquite Community

Page 6: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Instrumentation and Methods

Trace gas sampling

Ambient CO2 and soil factors

CO2 flux and isotope collection

Page 7: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Organic TotalSoil Depth C δ13C N C/N

(g kg-1) (‰) (g kg-1)

________________________________________________Mesquite Plant -- -27.1 -- --

O-H -- -22.7 -- -- 0-5 cm 29.9 -20.2 3.08 9.7 5-10 12.7 -18.9 1.36 9.4 10-20 10.5 -18.7 1.01 9.8

Open Plant -- -19.9 -- -- O-H -- -18.4 -- -- 0-5 cm 5.83 -18.3 0.63 9.2 5-10 6.04 -18.8 0.58 10.3 10-20 3.76 -17.1 0.37 10.3

Sacaton Plant -- -13.5 -- -- O-H -- -13.4 -- -- 0-5 cm 17.6 -16.0 1.81 9.7 5-10 11.6 -15.3 1.21 9.6 10-20 10.9 -14.5 1.23 11.0

Soil Properties

Page 8: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Ambient COAmbient CO22 Response to Rainfall Response to Rainfall

0

5

10

15

20

25

30

35

40

156

161

166

171

176

181

186

191

196

201

206

211

216

221

226

231

236

241

246

251

256

261

Julian Day

CO

2*10

0 (p

pm

) :

Rai

n (

mm

)

-1500

-1000

-500

0

So

il M

ois

ture

(kP

a)

CO2*100 (ppm) Rain (mm) Soil Moisture (kPa)

A

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

156

161

166

171

176

181

186

191

196

201

206

211

216

221

226

231

236

241

246

251

256

261

Julian Day

CO

2*10

0 (p

pm

) :

Rai

n (

mm

)

-1500

-1000

-500

0

So

il M

ois

ture

(kP

a)

CO2*100 (ppm) Rain (mm) Soil Moisture (kPa)

C

Open annual grass site – 697 ppm average

Mesquite site – 448 ppm average

Jan 1 – July 2002 = 15 mm; 2002 monsoon = 238 mm; Total for 2002 = 293 mm

Jan 1 – July 2003 = 40 mm; 2003 monsoon = 95 mm ; Total for 2003 = 232 mm

Page 9: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Date

18-J

ul

2-Aug

22-A

ug

11-S

ep9-

Oct

10-D

ec

19-F

eb

5-M

ay

16-J

ul

29-J

ul

15-A

ug

2-Sep

Ca

rbo

n D

ioxi

de

Pro

du

ctio

n (m

g C

O2 m

-2 h

-1)

0

40

80

120

160

200

240

280

320

360

400

Pre

cip

itatio

n (

mm

)

0

10

20

30

40

50

MesquiteOpenSacatonRainfall

2002 2003

Figure 3. Carbon dioxide efflux from three SPRNCA vegetation sites on measurement dates during 15-month monitoring period (July 2002 through September 2003). Symbols are averaged values from 2 or 3 flux collars installed at each site.

Carbon Dioxide Flux 2002 – 2003

2002 Monsoon = 123 - 126 mg m-2

Winter = 80 -109 mg m-2

2003 Monsoon = 72 – 105 mg m-2

2002 vs. 2003 40% reduction, yet during the 2002 season the 5X difference in soil C did not impact fluxes

Page 10: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Date (2002)

13 C

of

Re

sp

ire

d C

O 2 (o

/ oo)

-30

-28

-26

-24

-22

-20

-18

-16

-14

Pre

cip

ita

tio

n (

mm

)

0

10

20

30

40

50

SacatonMesquiteOpenRainfall

Figure 4. Isotopic composition of carbon dioxide respired from soil surface in three SPRNCA vegetation sites on measurement dates during monsoon and post-monsoon (July through December) 2002. Symbols are averaged values of two carbon dioxide collections per site on each sampling date, plus or minus standard deviation.

Isotopic Composition of CO2 Flux

Mesquite site = 63 to 98% C3-C

Open and Sacaton site = 50 to 65% C4-C

Page 11: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Date

18-J

ul

2-Aug

22-A

ug

11-S

ep9-

Oct

10-D

ec

19-F

eb

5-M

ay

16-J

ul

29-J

ul

15-A

ug

2-Sep

Met

hane

Con

sum

ptio

n ( g

CH

4 m

-2 h

-1)

0

5

10

15

20

25

30

35

40

45

50

55

Pre

cipi

tatio

n (

mm

)

0

10

20

30

40

50

MesquiteOpenSacatonRainfall

2002 2003

Figure 6. Methane consumption in three SPRNCA vegetation sites on measurement dates during 15-month monitoring period (July 2002 through September 2003). Symbols are averaged values from 2 or 3 flux collars installed at each site.

Methane Oxidation Rates 2002 – 2003

2002 Monsoon = 29 – 61 mg m-2

Winter = 118 – 160 mg m-2

2003 Monsoon = 62 – 70 mg m-2

Page 12: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Methane Oxidation with Soil Depth

-55

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

0 500 1000 1500 2000 2500

Porespace Methane (ppb)

De

pth

(c

m)

MonsoonTwo Weeks Post-MonsoonSix Weeks Post-MonsoonTwelve Weeks Post-Monsoon

Cool season may limit surface oxidation, but warmer temps in the subsoil continue to promote oxidation – also when surface is dry, subsoil active

Page 13: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Impacts of Grazing on CHImpacts of Grazing on CH44 Oxidation Oxidation

Open

Julian Day

150 160 170 180 190 200 210 220

Dep

th

0

20

40

60

80

100

Open

Julian Day

150 160 170 180 190 200 210 220

Dep

th

0

20

40

60

80

100

200 400 600 800 1000 1200 1400 1600 1800 2000

100 yr exclosure “Moderate” grazing for 50 yr

Page 14: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Nitrous Oxide Fluxes 2002 – 2003 Nitrous Oxide Fluxes 2002 – 2003

Date

18-J

ul

2-Aug

22-A

ug

11-S

ep9-

Oct

10-D

ec

19-F

eb

5-M

ay

16-J

ul

29-J

ul

15-A

ug

2-Sep

Nitr

ous

Oxi

de P

rodu

ctio

n (

g N

2O

m-2

h-1

)

0

10

20

30

40

50

Pre

cipi

tatio

n (m

m)

0

10

20

30

40

50

MesquiteOpenSacatonRainfall

2002 2003

Figure 5. Nitrous oxide efflux from three SPRNCA vegetation sites on measurement dates during 15-month monitoring period (July 2002 through September 2003). Symbols are averaged values from 2 or 3 flux collars installed at each site.

2002 Monsoon = 4 to 38 mg m-2

Winter = 17 to 54 mg m-2

2003 Monsoon = 8 to 20 mg m-2

2002 vs. 2003 30% reduction

Page 15: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

δδ1515NN22O Flux From MesquiteO Flux From Mesquite

-5.00

0.00

5.00

10.00

15.00

20.00

25.00

10-Jul 20-Jul 30-Jul 9-Aug 19-Aug 29-Aug

Date (2003)

15 N

2O

Precipitation (mm)

delta 15-N2O

-6.0

-25

δ15N2O

Isotope values with dry surface soils suggests subsoil activity and during monsoon represents surface activity

Page 16: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

Greenhouse Gas ProductionGreenhouse Gas Production

• 2002 monsoon season averaged 303 mg CO2 equivalents m-2 (57 d)

• Cool season averaged 390 mg CO2 equivalents m-2 (307 d)

• 2003 monsoon season averaged 185 mg CO2 equivalents m-2 (57 d)

• 60% reduction of warm season rain reduced CO2 equivalents by 39%

Page 17: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

ImplicationsImplications• Recent work has emphasized the

increased contribution of terrestrial C sources to atmospheric C pools if temperatures increase – positive feedback to climate change

• For the SW region, climate change models differ on whether future climate scenarios will be wetter or drier and possible shifts from summer to winter rains

Page 18: Moisture Controls on Trace Gas Fluxes From Semiarid Soils Dean A. Martens and Jean E. T. McLain SWRC – Tucson and Water Conservation Laboratory – Phoenix

These Results SuggestThese Results Suggest

• If rainfall shifts to greater winter events, overall reductions in surface dominated CO2 and N2O fluxes and prolonged spring CH4 subsurface oxidation

• Higher warm season precipitation will increase CO2 and N2O fluxes due to rapid oxidation of labile C pools that would not be off set by higher CH4 oxidation rates