Soil carbon accounting:options to measure, monitor, and

address project-level issues

Forestry & Agriculture Greenhouse Gas Modeling ForumShepherdstown, West Virginia

8-11 October 2002

Tris WestEnvironmental Sciences DivisionOak Ridge National Laboratory

OAK RIDGE NATIONAL LABORATORY

U.S. DEPARTMENT OF ENERGY

Potential trade-offs between environmental integrity and economic incentives

Issues that may arise in efforts to maintain

environmental integrity

What is accuracy of soil C measurements or estimates?

Are changes in land use and climate considered?

Are other environmental effects (e.g., changes in GHG emissions) considered?

Additionality, permanence, saturation, & leakage

Consider simplicity & flexibility

Issues that may arise if incentives for C

sequestration are provided

What level of accuracy is desired?

What are acceptable amounts of time and costs associated with measuring and monitoring?

What are acceptable levels of economic risk (e.g., risk of not meeting sequestration obligation)?

Who is eligible for incentives (targeting)?

Consider simplicity & flexibility

Focus: soil C changes in agricultural soils

Conventional Tillage(CT)

No-Till(NT)

Photos courtesy of Donald Tyler, Univ. of TN, West TN Ag. Exp. Station

Presentation outline

I. Current options for measuring and monitoringA. Summary of measurement optionsB. Issues associated with measurement optionsC. Discussion of carbon management response curves

1. Project-level issues2. Accounting for other greenhouse gases

II. Comparison of options

III. Conclusions

Option 1: Measuring soil carbon change

Ex situ – soil sampling (analyzed in lab)

In situ – soil sampling (analyzed in field) Laser Induced Breakdown Spectroscopy

(Cremers et al. 2001, Martin et al. 2002) Surface-Enhanced Raman Scattering

(Stokes & Vo-Dinh 2001) Inelastic Neutron Scattering

(Wielopolski et al. 2000)

Eddy Covariance – net ecosystem exchange

Option 2: Estimating soil carbon change

Remote sensing capabilities

Process models

Database accounting

See also:Post et al. 2001. Monitoring and verifying changes of organic carbon in soil. Climatic Change 51:73-99.

Option 3: Incentive based on practice

Approach similar to Conservation Reserve Program:

Payments for cropland “set aside” for a fixed time period.

Decreases in soil erosion are not measured.

Carbon accounting issues related to carbon measurements (Option 1)

Is it reasonable to provide an incentive based on natural variability of soil carbon measurements?

How do we know when soil C has reached saturation or a new equilibrium?

Do we know that all change in soil C is due to the change in practice (is there a control plot or baseline estimate)?

Example: Comparison between measured and estimated changes in soil carbon

0

500

1000

1500

2000

2500

0 10 20 30 40Time (year)

Estimated mean change in soil C from West & Post (2002). SSSAJ 66:1930-1946.

95% C.I.

Measured change in soil C (in red)Illinois corn/soybean (Kitur et al. 1994)

Cum

ulat

ive

C s

eque

ster

ed in

soi

l w

ith a

cha

nge

from

con

vent

iona

l til

lage

to

no-t

ill (

g m

-2)

-400

-200

0

200

400

600

800

1000

1200

1400

0 10 20 30 40

Time (year)

Cum

ualti

ve C

seq

uest

ered

in

soil

with

a c

hang

e fr

om

conv

entio

nall

tilla

ge t

o no

-till

(g m

-2)

Measured change in soil C (in red)Kentucky continuous corn (Ismail et al. 1994)

Example: Comparison between measured and estimated changes in soil carbon

95% C.I.

Estimated mean change in soil C from West & Post (2002). SSSAJ 66:1930-1946.

0

500

1000

1500

2000

2500

0

200

400

600

800

1000

1200

1400

0 10 20 30 40Time (year)

Cum

ula

tive

C s

eque

ste

red

in s

oil

with

a

chan

ge f

rom

co

nve

ntio

nal t

illag

e to

no-

till

(g m

-2)

Ohio corn/soybean rotation

Ohio continuous corn

Example: Comparison between measured and estimated changes in soil carbon

Measured change in soil C (in red) Dick et al. (1997)

Estimated mean change in soil C from West & Post (2002). SSSAJ 66: 1930-1946.

Campbell et al. 2001. Canadian Journal of Soil Science 81:383-394.

Changes in soil carbon due to climate suggest the need to consider issues of additionality and saturation

Option 4: Estimate change in C based on practice using average measured responses

Approach is a hybrid between options 1, 2 and 3:

Development of Carbon Management Response Curves

Option 1: Measuring soil carbon change

Option 2: Estimating soil carbon change

Option 3: Incentive based on practice

Introducing Option 4

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 10 20 30 40

Time (years)

Mean95% C.I.

Carbon Management Response Curves —carbon accumulation under no-till

Targeting

Uncertainty

Mean sequestration and duration

Ave

rage

ann

ual C

seq

uest

ratio

nra

te f

ollo

win

g a

chan

ge f

rom

CT

to

NT

(%

/yr)

Estimate: 11 ± 2% (normalized to original land use)Source: West & Post (2002). Soil Sci. Society of Am. J. 66:1930-1946

Carbon Management Response Curves —carbon accumulation following afforestation

Estimate: 37±12% (normalized to original land use)Sources: Gao & Gifford (2002), Paul et al. (2002), Post & Kwon (2000)

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60

Time (years)

Ave

rage

ann

ual C

seq

uest

ratio

n ra

te fo

llow

ing

a ch

ange

from

cu

ltiva

ted

land

to fo

rest

(%

/yr)

Mean95% C.I.

Carbon Management Response Curves —soil carbon loss following cultivation

Estimate: -30 ± 5% (normalized to original land use)Sources: Mann 1986, Post & Mann 1990, Davidson & Ackerman 1993, Murty et al. 2002

-14

-12

-10

-8

-6

-4

-2

0

0 5 10 15 20

Years in cultivation

Ave

rage

ann

ual l

oss

of s

oil C

fo

llow

ing

culti

vatio

n of

fore

sted

la

nd (

%/y

r)

Carbon Management Response Curves —Integrating changes in land use

“…there are not enough data available to perform a meta analysis of the land use change from pasture or forest to no-tillage crop.”

- Guo & Gifford (2002)

Years

Estimating carbon stocks following changes in land management using CMR curves

-10

0

10

20

30

40

0 20 40 60 80 100

-4

-20

2

4

68

10

12

Conventional tillageNo-tillForest

-4-20

2468

1012

0 20 40 60 80 100

Scenario: Deforest, cultivate with CT for 20 yr, change to NT for 10 yr, use CT for 1 year, change back to NT for 10 yr, reforest at year 50.

Ave

rage

ann

ual r

ate

of C

flu

x to

the

atm

osph

ere

(%/y

r)

Years

Ave

rage

cum

ulat

ive

C

flux

to th

e at

mos

pher

e (%

)

Change in soil C with change in land use Integration over time

Permanence

Deforestation (CT)No-till (NT)Afforestation

Accounting of changes in GHG emissions assumes:• Soil C sequestration of 570 ± 140 kg C/ha/yr [normal distribution]• Average US production inputs and associated emissions

• Estimated relationship between N fertilizer and N2O

emissions of 2.66 kg Ceq / kg N applied (2% of N applied)

• Potential change in N2O emissions of 7 ± 15% with

change from CT to NT [uniform distribution]• Potential change in yield of ± 6% [uniform distribution]• Change in cropped area that ranges from full compensation for

the change in crop yield to no response to the change in yield

[uniform distribution]

Estimating changes in GHG emissions associated with soil C sequestration using CMR curves

-8000

-6000

-4000

-2000

0

2000

4000

0 10 20 30 40 50

Time (year)

Change in N2O emissionsChange in SOCChange in CO2 emissions

Savings in CO2 and N2O emissions are permanent while

C sequestered in soil may be temporary

Cum

ulat

ive

chan

ge in

SO

C a

nd

CO

2 an

d N

2O e

mis

sion

s to

the

at

mos

pher

e (k

g/ha

)

Temporary

Permanent

-10000

-8000

-6000

-4000

-2000

0

0 10 20 30 40 50Time (year)

Change in SOC, CO2, and N2OChange in SOCChange in SOC and CO2

Emissions that are released as a result of an implemented carbon sequestration strategy may represent a future liability

Temporary

Liability

Credit

Cum

ulat

ive

chan

ge in

net

GH

G f

lux

to t

he a

tmos

pher

e (k

g/ha

)

Permanent

Carbon management response curves — Summary

Upon further development, CMR curves may effectively address:

• Integration of practices over time• Duration of C sequestration rates (saturation)• Uncertainty in C sequestration rates• Additionality (cancels out climate effect)• Possible inclusion of net carbon/GHG accounting• Targeting• Permanence• Temporal and spatial variability

Cost of Measuring & monitoring

Accuracy of change in C stock

Account for saturation or seq. duration

Risk of not meeting seq.

obligation

Simplicity and flexibility of accounting

Direct

(in situ)Medium High

Low-Medium

Medium-High

Low-Medium

Direct

(ex situ)High High

Low-Medium

Medium-High

Low-Medium

Practice Low Low Low Low High

Hybrid (avg. estimate)

Low Medium High Low High

A general and qualitative comparison of some options to measure/estimate changes in soil C stocks

Concluding remarks

Options to measure & monitor partly depend on ability to address project-level issues

Costs, simplicity, predictability, flexibility, as well as saturation, additionality, and permanence all appear to be more effectively addressed by the use of average sequestration or loss rates (CMR curves) rather than direct C measurements

In addition, CMR curves allow for integration of several practices over time and possible inclusion of net GHG accounting

Similar comparison could be done with economic/ incentive options and combined with measuring & monitoring options to develop a comprehensive carbon accounting framework

Acknowledgments

Consortium for Research on Enhancing

Carbon Sequestration in Terrestrial Ecosystems

OAK RIDGE NATIONAL LABORATORYU.S. DEPARTMENT OF ENERGY