Task 3a: Transport and sequestration of dissolvedorganic C in contrasting soils amended with

C-14 enriched leaf litter

Philip JardineDonald ToddPaul HansonJana Tarver

Chris Swanston

Oak Ridge National LaboratoryLawrence Livermore National Laboratory

Objectives

• Use 14C enriched litter as a well defined source to quantifydissolved organic C flux through soil profiles as a function ofstorm events.

• Quantify the impact of coupled hydrological and geochemicalprocesses on the fate and transport of dissolved organic C throughcontrasting soil profiles being used in the Enriched BackgroundIsotope Study at ORNL.

• Quantify the mechanisms that control enhanced carbonaccumulation within deep subsoils of forested Ultisols andInceptisols.

Widespread, highly developed mature soils such as Ultisols and some Inceptisolshave deep soil profiles that have a tremendous capacity to sequester organicC that has been made soluble from surface horizons.

Mineral stabilized organic C within the subsoil decreases the rate of carbon turnover byorders of magnitude relative to upper A/B and E/B horizons.

Competing geochemical and hydrologic processes (e.g. sorption and micropore protectionvs. preferential flow and biodegradation) control organic C accumulation or loss throughsoil profiles.

Ultisol devoid of organic Cdue to agricultural abuse

Ultisol enriched with organic C throughimproved management technologies

Background

Anthropogenically enrichedsoil of the Amazon Adjacent unenriched soil

These soils are from the same physiographic position and have the sameclay content and clay mineralogy. The soil on the left was enriched byancient human occupation centuries ago; the right is unenriched. This illustratesthat such soil enrichments can be maintained for several centuries.

Example of deep profile organic C sequestration

Approach• Two background and two enriched plots from each of the four EBIS sites (16

plots) were each instrumented with four tension lysimeters and four tension-free lysimeters. Two of each type were placed within the A- and B-horizonsof the soil profiles (8 samplers per plot).

• Besides the addition of enriched and background litter, a nonreactive Br tracerwas evenly applied over each of the instrumented areas using a backpacksprayer (i.e. distributed initially to the soil matrix porosity).

• Solution samplers were monitored during all storm events and analyzed for Br,TOC, inorganic anions, and pH. Numerous select samples were analyzed for14C.

• Bulk soil samples from each plot were characterized for select physical andchemical properties and organic C sorption isotherms were quantified for eachsubsoil.

Inceptisols

Ultisols

Monitoring scheme

Ultisols on WB and TVA

Inceptisols onPR and HR

Zero/low tension solution samplerfor monitoring macropore and

mesopore domains

High tension solutionsampler for monitoring

primarily microporedomains

Multi-porosity sampling capabilities

Funds lacking to do an adequate investigationof large pore organic C fluxes

Results: Organic C sorption isotherms

ß A shake-batch method was utilized to construct dissolved organic carbonisotherms on the Ultisol and Inceptisol subsoils from the various EBIS plots.

ß Select physical and chemical properties of the subsoil samples weredetermined in an effort to cross-correlate soil properties with differences inDOC solid-phase adsorption.

))((

TVA Site Adsorption IsothermHA: GT-NOM

-500

0

500

1000

1500

2000

2500

0 20 40 60 80 100 120

Equil. Soln. Conc (mg-DOC L-1)

DO

C s

orb

ed (

mg

kg

-1)

T1BE

T1B21t

T3BE

T3Bt

T4E/B

T4B

T4B2t

T7A/E/B

T7Bt

Walker Branch Adsorption IsothermHA: GT-NOM

-500

0

500

1000

1500

2000

2500

0 20 40 60 80 100 120

Equil. Soln. Conc (mg-DOC L-1)

DO

C s

orb

ed

(m

g k

g-1)

New W3Bt

New W4Bt

W6A/B

W6B

W7B

W3B22t MM Soil samples from lowerB-horizons have significantlylarger carbon sorption capacitiesrelative to upper A, E, A/E,and B/E horizons.

Upper horizons

Lower horizons

Upper horizons

Lower horizons

Typical soil profile

Carbon sorption isotherms on Ultisol soil profiles

Typical soil profile

Low organic C sorptionon sandy inceptisols withlow Fe-oxide content andsignificant indigenous solidphase O.M. (i.e. Haw Ridge).

High organic C sorptionon clayey inceptisols withhigh Fe-oxide content (i.e.Pine Ridge).

Carbon sorption isotherms on Inceptisol soil profiles

Pine Ridge Adsorption IsothermsHA: GT-NOM

-500

0

500

1000

1500

2000

2500

3000

0 20 40 60 80 100

Equil. Soln. Conc (mg-DOC L-1)

DO

C s

orb

ed (

mg

kg

-1)

P3B

P4B2t

P5B

P6B2

Haw Ridge Adsorption IsothermsHA: GT-NOM

-300

-200

-100

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120

Equil. Soln. Conc (mg-DOC L-1)

DO

C s

orb

ed (

mg

kg

-1)

H3B

H4B

H5B

H7B*

Influence of soil Fe-oxides on organic C sorption

Fe-oxide content (mg Fe / g)

0 5 10 15 20 25 30 35

C sorption m

ax. (mg C

/ kg)

0

500

1000

1500

2000

2500

3000

3500

Low Fe-oxides High Fe-oxides

Organic C sorption on the 22 soils usedin this study was strongly correlated withthe Fe-oxide content of the media.

C sorption = 316 + 74*Fe-oxider2 = 0.74

Fe-oxide coatings on mineral surfacesstrongly sequester pore water organic Cwhich can potentially limit bioavailabilityand transport to groundwater.

2D Graph 2

Fe-oxides

0 5 10 15 20 25 30 35

ST

0

500

1000

1500

2000

2500

3000

3500

Fe mg/g vs ST mg/kg Fe vs ST-Hobcaw Col 13 vs Col 11 Plot 3 Regr

C sorption = 214 + 67*Fe-oxider2 = 0.67 n=168

Fe-oxide content (g Fe / kg)

C s

orpt

ion

max

(m

g / k

g)

Sandy Coastal Plain Ultisols

Clayey Inland Ultisolsand Inceptisols

Regional Importance of Fe-oxides on Organic C Sequestration

C sorption = 316 + 74*Fe-oxider2 = 0.74 n=22

Storm driven transport of organic C

Example storm driven Br breakthrough in Inceptisol soil profiles

Haw RidgePlot 3- Bromide

0

50

100

150

200

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

Date

(mg

/L)

Pine RidgePlot 3- Bromide

0

20

40

60

80

100

120

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

Date

(mg

/L)

Pine RidgePlot 5- Bromide

0

20

40

60

80

100

120

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

Date

(mg

/L)

Haw RidgePlot 5- Bromide

0

20

40

60

80

100

120

140

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

Date

(mg

/L)

A-horizons

B-horizons

A-horizons

B-horizons

A-horizons

B-horizons B-horizons

A-horizons

Clayey

Sandstonedominant

2002

2002

2002

2002

Rapid breakthrough Rapid breakthrough

Delayed breakthrough Delayed breakthrough

Non-reactive Br tracer provides useful data for quantifying flow and transport processes at the various sites.

Haw Ridge exhibits the most rapid infiltration characteristics which is consistent with its more highly structuredmedia and lower microporosity relative to the more clayey Pine Ridge and Ultisol soils.

Example storm driven Br breakthrough in Ultisol soil profiles

TVAPlot 1- Bromide

0

50

100

150

200

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

Month, 2002

(mg/L

)

TVAPlot 3- Bromide

0

50

100

150

200

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

Month, 2002

(mg/L

)

Walker BranchPlot 3 Bromide

0

20

40

60

80

100

120

140

160

J F M A M J J A S O N DMonth, 2002

(mg/L

)

Walker BranchPlot 5 Bromide

0

20

40

60

80

100

120

140

160

J F M A M J J A S O N DMonth, 2002

(mg/L

)

A-horizons

B-horizons

A-horizons

B-horizons

A-horizons

B-horizons

A-horizons

B-horizons

Delayed breakthrough Delayed breakthrough

Sort-of delayed breakthrough Delayed breakthrough

Example storm driven DOC concentrations in Inceptisol soil profiles

Pine RidgePlot 3- TOC

0

1

2

3

4

5

6

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

Date

(mg/

L)

Haw RidgePlot 5- TOC

0

5

10

15

20

25

30

35

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

Date

(mg

/L)

Haw RidgePlot 3- TOC

0

10

20

30

40

50

60

70

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

Date

(mg/

L)

Pine RidgePlot 5- TOC

0

5

10

15

20

25

30

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

Date

(mg/

L)

A-horizons

B-horizons

A-horizons

B-horizons

A-horizons

B-horizons

A-horizons

B-horizons

Clayey

Sandstonedominant

2002

2002

2002

2002

High organic C High organic C

•DOC concentrations higher for A-horizons relative to B-horizons.

•Haw Ridge (sandy inceptisol) consistently has highest pore water organic C concentrations that continueinto the B-horizon. Since infiltration is more rapid in these soils coupled with their lower organic Cretention capacity, greater losses of dissolved organic C may be expected in these systems.

Example storm driven DOC concentrations in Ultisol soil profiles

Walker BranchPlot 5 TOC

0

1

2

3

4

5

6

7

8

J F M A M J J A S O N DMonth, 2002

(mg/L

)

TVAPlot 3- TOC

0

5

10

15

20

25

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

Month, 2002

(mg

/L)

Walker BranchPlot 3 TOC

0

5

10

15

20

25

30

J F M A M J J A S O N DMonth, 2002

(mg/L

)

TVAPlot 1- TOC

0

1

2

3

4

5

6

7

8

9

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

Month, 2002

(mg

/L)

B-horizons

A-horizons

B-horizons

A-horizons

A-horizons

B-horizons

A-horizons

B-horizons

DOC flux higher for A-horizons relative to B-horizons.

Haw Ridge (sandy inceptisol) has highest C flux relative to Pine Ridge and Ultisol soils which is consistent with itsmore labile C source and rapid flow and transport characteristics.

Organic C flux through soil profiles

Walker Branch Haw Ridge

Estimated organic C inputs in the Walker Branch Ultisol and Haw Ridge Inceptisol B-horizonsshowing that these lower horizons typically receive more C than they lose.

Walker Branch

Net organic C inputs into the B-horizons

Haw Ridge

Haw Ridge

Enriched

41S 42S 61S 62S 41D 42D 61D 62D 31S 32S 51S 52S 31D 32D 51D

Delta C

-14

-100

0

100

200

300

400

5005/29/2002 10/4/2002 10/24/2002 12/31/2002 2/03/2003 3/18/2003 5/28/2003 8/04/2003 8/13/2003

Background

Blue is last sampling prior tosecond litter addition

Enriched plots have higher D14C signatures in pore water than background plots.

Pore water from Haw Ridge has a higher D14C signatures relative to Walker Branch which is consistent with the

more rapid flow and transport characteristics and lower organic C retention capacity of HR. Elevated D14C

values continue into the B-horizon.

D14C signatures in select pore water from Haw Ridge Inceptisol soil profile

Walker Branch

Enriched

31S 32S 31D 32D 41S 42S 51S 41D 42D 51D

Delta C

-14

-200

-100

0

100

200

300

400

500

600 5/29/2002 10/4/2002 10/24/2002 12/31/2002 2/3/2003 3/18/2003 4/14/2003 5/28/2003 8/04/2003 8/13/2003

Background

Blue is the last sampling priorto second litter addition

D14C signatures in select pore water from Walker Branch Ultisol soil profile

Pore water from WB has a lower D14C signature relative to HR with B-horizon samples showing no

evidence of enrichment. This may be related to the higher organic C retention capacity of WB.Trends for WB similar to the other clayey soils Pine Ridge and TVA.

Walker Branch

Average shallow and deep pore water delta C-14 signituresfor both enriched and background plots

Soil type

HR WBW PR TVA

Delta C

-14

0

100

200

300

400

500Enriched shallow Background shallow Enriched deep Background deep

A-horizon B-horizon A-horizon B-horizon A-horizon B-horizon A-horizon B-horizon

Average D14C signatures of all pore water from each site

Possible pre-enrichment of Pine Ridge and TVA prior to EBIS experiment.

Enriched A- and B-horizons have consistently higher D14C porewater than background A- and B-horizons for all

sites.

Enriched porewater moves deeper in the Inceptisols relative to the Ultisols.

Summary

• Non-reactive Br tracer provides useful data for quantifyingflow and transport processes at the various sites.

• Dissolved organic C fluxes at each site are consistent withthe soil hydrodynamics and labile nature of the A-horizonorganic matter.

• Net organic C accumulations observed in the B-horizonwhere organic C sorption was strongly correlated with thesoil Fe-oxide content.

• Pore water D14C signatures look promising. Enriched plotsclearly show higher values than background plots, and thedata is consistent with site hydrological and geochemicalcharacteristics.