Purpose: To provide participants with an understanding of the sinks of carbon and sources of methane...

Purpose: To provide participants with an understanding of the sinks of carbon and sources of methane and nitrous oxide emissions in land based systems.

Source: University of Melbourne (UoM) June 2013

THE MANAGEMENT OF AGRICULTURAL SOURCES AND

SINKS

The management of soil based sinks

• Carbon sequestration in soils under a range of agricultural practices

• Drivers of soil carbon change• Management effects on soil carbon • Soil carbon monitoring

Desert soils: < 1% Agric soils: 1-5% Forest soils: 1-10%Organic soils:

up to 100%

In top 15 cm SOM typically ranges:

• Carbon forms in soil– Inorganic forms

• carbonates, graphite, CO2 (carbon dioxide), HCO3

(hydrogen carbonate ion)

– Organic• living, dead; labile, non-labile

What is Soil Carbon?

• Soil Organic Matter (SOM) – The sum total of all organic carbon-

containing substances in soils: – Living biomass, decomposed residues and

humus• Soil Organic Carbon (SOC)

– Carbon component of the SOM• Total Organic Carbon (TOC)

– SOC


• Crop residues– Shoot and root residues greater than 2 mm found

in the soil and on the soil surface– Energy to soil microbes

• Particulate Organic Carbon (POC)– Individual pieces of plant debris that are smaller

than 2 mm but larger than 0.053 mm– Slower decomposition than residues– Provides energy and nutrients for microbes


400 m400 m400 m

Source: Jeff Baldock

• Humus – Decomposed materials less than 0.053 mm that

are dominated by molecules stuck to soil minerals– All soil processes, source of N

• Recalcitrant or resistant organic carbon (ROC)– Biologically stable; typically in the form of

charcoal.


10 m10 m10 m

20 m20 m Source: Jeff Baldock

Why is it important?

- Biochemical energy

- Reservoir of nutrients

- Increased resilience

- Biodiversity

Biologicalroles

- Structural stability

- Water retention

- Thermal properties

- Erosion

Physicalroles

Chemicalroles

- Cation exchange

- pH buffering

- Complexes cations

Roles of organic carbon (and associated elements) in defining soil productivity

1567 to 2700 Pg of C stored in soils worldwide


Tropical forests

Temperate forests

Boreal forests

Tropical savannas

Temperate grass & shrublands

Deserts & Semi-deserts

Tundra

Croplands

Plants Soils Area

2 115 5.6

Global Carbon Stock (Pg C) Mill km2

57 338 13.7

139 153 10.4

340 213 17.5

79 247 27.6

23 176 15.0

10 159 27.7

4 165 13.5

Total 654 1567

Saugier et al (2001)

How does soil carbon compare to other sinks globally?

• A big, slow-changing input : output equation– Inputs: Plant residues & fire residues– Outputs: Decomposition & mineralisation

• Limited by – Climate, soil type, management & nutrients– Water is usually most limiting

• Good seasons = more soil C• Drought = less soil C

What determines soil organic carbon content?


How fractions differ between soils

Soil 1

Soil 2

Soil 3

Soil 4

Soil 5

Soil 6

Soil 7

So

il or

ga

nic

carb

on

sto

ck (

Mg

C/h

a)

10

20

30

40

50

Particulate organic carbon

Humus organic carbon

Resistant organic carbon

0

Understanding composition provides information on the vulnerability of soil organic carbon to change


Can we quantify changes?

Longest experimental evidenceSoil-C increase often greatest soon after land-use or management change

Rate of change decreases after new equilibrium is reached.

BUT

1.2% to 2.7% in 110 years = 0.013% /yr

Maximum of 0.4% in 25 years

Arable land grass

The management of carbon in vegetation

• Carbon sequestration in trees• Drivers of tree carbon change• Management of tree carbon • Monitoring of carbon stored in trees and woody

vegetation

Carbon sequestration in trees

Carbon stock/pools

Carbon sequestration

Carbon balance

How much C at one point in time

Change of C stock over time

Exchange of C fluxes over time

Carbon sequestration in trees

Measurement of forest carbon pools

Aboveground biomass

Belowground biomass

Soil carbon

Litter & coarse woody debris

• Easy, tree allometrics, • remote sensing

techniques• good inventories• Often ignored• Not many data• Often small pool

• Difficult• Not many data• Mostly expansion factors

(i.e. 25% of aboveground)

• Relatively easy to measure• Not many data in forests• Very difficult to assess

change of soil C over time

Carbon stocks in ecosystems

Habitat

Boreal1 Temperate1

Wet Tropical1

Wet-dry Tropical2

Evergreen coniferous

Deciduous Broadleaf

Rainforest Tall-grass savanna

forest forest

Carbon stocks (t C ha-1)

Above-ground biomass 49.2 79 217 34

Below-ground biomass 18.2 50 105 17

Total Biomass 67.4 129 322 51

Soil carbon 390.4 56 162 150

Ecosystem total 458 185 484 201

Productivity (t C ha-1 y-1)

GPP 9.6 17.3 30.4 20

NPP 5.2 9.4 15.6 10.1

Respiration 9.0 11.4 24.6 17.2

NEP 0.7 5.8 5.8 2.8

NPP/GPP 54% 55% 51% 51%

1) Malhi et al (1999) PCE 22: 715 & 2) Chen et al. (2003) Oecol 137:405

Drivers of tree carbon change

Chapin, Matson, Mooney (2002)

Carbon stocks are only one small part of the carbon ecosystem processes

What will matter long-term is ecosystem production:inputs - outputs

CO2

Gross Primary Productivity GPP (photosynthesis)

Litter(foliage, branches, etc)

Net Primary Productivity NPP

= GPP - Ra

Soil microbialrespiration (Rh)

Soil carbon

CH4 N2O

Non-CO2 greenhouse gas (trace gas exchange) Canopy, wood & root

CO2 respiration (Ra)

Net Ecosystem Productivity NEP= GPP - Ra - Rh


Habitat

Boreal1 Temperate1

Wet Tropical1

Wet-dry Tropical2

Evergreen coniferous

Deciduous Broadleaf

Rainforest Tall-grass savanna

forest forest Carbon stocks (t C ha-1)

Above-ground biomass 49.2 79 217 34

Below-ground biomass 18.2 50 105 17

Total Biomass 67.4 129 322 51

Soil carbon 390.4 56 162 150

Ecosystem total 458 185 484 201

Productivity (t C ha-1 y-1)

GPP 9.6 17.3 30.4 20

NPP 5.2 9.4 15.6 10.1

Respiration 9.0 11.4 24.6 17.2

NEP 0.7 5.8 5.8 2.8

NPP/GPP 54% 55% 51% 51%

1) Malhi et al (1999) PCE 22: 715 & 2) Chen et al. (2003) Oecol 137:405


Main drivers that influence tree carbon change:

Drivers that influence tree carbon uptake (photosynthesis):• Light • Water availability • Temperature • Atmospheric CO2 • Nutrients

Drivers that influence tree carbon loss (respiration):• Water availability • Temperature • Nutrients

Drivers that influence ecosystem carbon loss (disturbance):• Fire • Pests & diseases • Storms• Floods


Photosynthesis > Respiration

Net carbon gain

Healthy mature forest Healthy young forest/plantation

Photosynthesis > Respiration

Net carbon gain

Forest is a carbon sink Forest is a carbon sink


Photosynthesis = Respiration

Small carbon gain

Old growth forest Disturbance / Deforestation

Net carbon loss

Photosynthesis < Respiration

Forest is carbon neutral or small sink

Forest is a carbon source

Management of tree carbon

Important: Distinction between C-stocks and C-fluxesC-stocks need to be conservedC-fluxes should results in sinks not sources

IPCC 2007 WG III


Mitigation options for the forest sector


Four general categories

1. Maintain or increase forest area

2. Maintain or increase stand level carbon density (t C/ha)

3. Maintain or increase landscape level carbon density

4. Increase off-site carbon stocks

IPCC 2007 WG III

Largest short-term gains – avoid emissions avoid forest degradation, fire protection once emission is avoided C stocks increase only slightly

Long term gains – afforestation up-front cost

Largest sustained mitigation benefit: maintain or increase C-stocks produce annual yield of timber, fibre, energy


1. Maintain or increase forest area reduce deforestation and forest degradation

IPCC 2007 WG III

Protection from harvest reduces wood and land supply income for local communities socially acceptable?

REDD Policy

Largest and most immediate impact!!! large C stocks are not emitted if forest is maintained

Mitigation cost depends on: cause of deforestation (wood extraction, agriculture, settlement) associated returns from non-forest land-use returns from potential alternative forest uses (tourism) compensation payments


2. Maintain or increase stand level carbon density (t C/ha) Silviculture (fertilisation, uneven-aged stand management, site prep) tree improvement (breeding, molecular)

IPCC 2007 WG III

Harvest systems that maintain partial forest cover minimize losses of dead organic matter minimize losses of soil C by reducing soil erosion avoid slash burning and high emission activities

Economic constraints leaving carbon on site delays revenue

Forest fertilisation potential N2O losses


3. Maintain or increase landscape level carbon density forest conservation longer rotations, fire management, protection against insects

Landscape level changes usually sum of stand level changes


4. Increase off-site carbon stocks wood products substitute products with high fossil fuel requirements increase biomass energy to replace fossil fuel

IPCC 2007 WG III

Duration in wood products variable days (biofuels) years/decades (landfill) centuries (furniture, houses)

Replacement of fossil fuel intensive construction materials aluminium, steel, concrete, plastics

Wood-fuels can provide sustained carbon benefits replacement of fossil fuels

Monitoring of carbon stored in vegetation

Assess and monitor the extent, state and development of forests and woodlands

All forest areas in Australia– Minimum 2m height and 20% canopy cover

Two main components:– Ground based inventory (Tier 1)– Remote sensing (Tier 2 & 3)


Measurement of forest carbon

• Tree (diameter and height)• Other vegetation (understorey)• Coarse woody debris• Stumps and dead vegetation• Soil and litter

Remote sensing:High resolution images (2 x 2 km)Medium resolution images (wall-to-wall)


Annual change in carbon stocks in biomass(stock-difference method)

where


C = total carbon in biomass (tonnes, at time t1)

Ai,j = Area of land in forest type i and climate zone j (ha)

Vi,j = Merchantable volume (m3 ha-1)

BCEFsi,j = biomass conversion and expansion factor

(merchantable volume to aboveground biomass in tonnes)

Ri,j = ratio of belowground to aboveground biomass

Cfi,j = carbon fraction of dry biomass (default 0.5)

IPCC 2006


Vi,j = Volume of tree biomass in forest type i and climate zone j

• Define plot area

• Measure over-bark diameter at breast height (1.3 m) and tree height calculates tree stem volume

• Convert plot level volume to biomass using biomass conversion and expansion factors (BCEF’s)

• Or convert tree level dimensions to biomass using allometricequations then aggregate to plot level


How many plots do I need to measure?

Voluntary Carbon Standard (VCS) and REDD+ require carbon pool estimates with 95% confidence that results are within 10% of the true mean

Coefficient of variation(SD / mean, %) in a pilot survey

t is student’s t value for a specified degree of certainty

E is the specified precision(e.g. 10% of true mean)

Total tree biomass carbon of 35 plots: mean = 92 t C/ha, SD = 27.3

• CV = 27.3 / 92 = 30%• t (student’s t value, 95%, CI, 35-1 df) = 1691• E = within 10% of true mean• Required plot number for tree carbon: n = 25


Design of a biomass carbon estimation program will depend on objectives

• Within 10% of true carbon stock within a forest stratum: pilot survey and sample intensity formula temporary plots

• Wall to wall prediction of carbon stocks:temporary plots combined with spatial data (e.g. remote sensing)

• Carbon stock change: repeat measurement of permanent sample plots (+ spatial data)

Methane from ruminants and monogastrics

• Introduction and background to methane emissions• Global warming potential• Methanogenesis in the rumen • Factors affecting methanogenesis

Methane from animal production

Global Trends in Atmospheric Methane

IPCC 2007


Australian Trends in Atmospheric Methane

CSIRO 2011


Unexpected rise in global methane concentrations from 2007

Mascarelli (2009)


DCCEE 2011

Dairy C

attle

Non-Dairy

Cattle

Alpaca

sDeer

Ost

riches

and Em

us

Buffalo

Sheep

Goats

Camels

and Lla

mas

Horses

Donkeys

Swine

0

5000

10000

15000

20000

25000

30000

35000

40000

Gt

CO

2e

Australian Methane Emissions


• Global warming potential– Shorter lifetime in atmosphere

• 8 to 12 years

– Concentrations• Pre-industrial - 700 ppb • Current - 1745 ppb

– High GWP • 72 x CO2 on a 20 year time horizon

• 21 x CO2 on a 100 year time horizon (AR2 – DCCEE)

• 25 x CO2 on a 100 year time horizon (AR4)

IPCC 2007


• Ruminants (cows, sheep)– 95% breathed and eructated– 5% from flatus

• Non-Ruminants (pigs, poultry, horses)– Mainly from flatus– Horses, rabbits

• Extended caecum for microbial digestion

• Effluent ponds– Anaerobic ponds = more methane

Eckard 2011

Enteric Fermenta-tion (64.59)

Manure Manage-

ment (3.91%)

Rice Cul-tivation (0.05%)

Agricul-tural Soils (16.75%)

Prescribed Burning of Savannas (14.33%)

Field Burning of Agri-cultural Residues

(0.18%)


• Microbes in the microbial digestion– Bacteria, protozoa, fungi, archaea, and

viruses• 40-60% bacteria, protozoa• 5-10% fungi• 3% Archaea (methanogens)

– Normal component of the rumen– Many species yet to be identified!

Eckard 2011


• Methanogensis – A form of anaerobic respiration

• 4H2 +CO2→CH4 +2H2O

– Uses H2 to reduce CO2 to form CH4

– Volatile Fatty Acid (VFA) production produces H2 • BUT H2 can also affect VFA production

– Interspecies hydrogen transfer • From bacteria and protozoa to methanogens

Klieve & Ouwerkerk 2007; Attwood & McSweeney 2009; McAllister & Newbold 2009


• Volatile Fatty Acid production– More propionate, less H2, thus less CH4

– More butyrate and acetate, more H2, thus more CH4

Jansen 2010


• Waste management systems– Piggery > Dairy > Poultry

Dairy

Cattle

Non-D

airy

Cattle

Alpaca

sDee

r

Ostric

hes

and

Emus

Buffa

lo

Sheep

Goats

Camels

and

Llam

as

Horse

s

Donke

ys

Swine0

5000

10000

15000

20000

25000

30000

35000

40000

Animal

Waste

Gg

CO

2e

DCCEE 2011


• Waste management systems– % of total on farm CH4 from waste

management• 7% of Dairy farm• 95% of Piggery

DCCEE 2011

Enteric Fermenta-tion (64.59)

Manure Management

(3.91%)

Rice Cultiva-tion (0.05%)

Agricultural Soils (16.75%)

Prescribed Burning of Savannas (14.33%)

Field Burning of Agricultural Residues (0.18%)


• Less CH4

– Faster rumen passage– More O2

– Less methanogens– Less H2

– Carbon– Lower temperature

• More CH4

– Slower rumen rate– Less O2

– More methanogens– More H2

– Acid rumen pH– Higher temperature

Factors affecting methanogenesis

Eckard 2011

Animal Class Methane (kg/year)

MJ CH4 lost /hd/day

Effective annual grazing days lost

Potential km driven in 6-cylinder car

Mature ewe 6 to 10 0.9 to 1.5 26 to 43 54 to 90

Beef steer 50 to 90 7.6 to 13.6 33 to 60 450 to 800

Dairy cow 90 to 146 13.6 to 22.1 25 to 40 800 to 1350


• Largest inefficiency in animal production– Methane energy content - 55.22 MJ/kg – 6 to 10% of GEI lost as CH4

But: we cannot abate 100%Eckard, Grainger & de Klein 2010

Methane Measurement

• Measurement – in vitro– Test tubes – Continuous Culture

AgResearch, New Zealand

Methane Measurement

• Measurement– SF6 (sulphur hexafluoride)Tracer

• Individual animals in the field

Permeation tubes

Grainger, Eckard et al. 2007

Evacuated yolk/canister

Methane Measurement

• Measurement– Chambers/Calorimeters

• Individual Animals

Grainger, Eckard et al. 2007

Methane Measurement

• Measurement– Open Path laser or FTIR tracer

Wind

Reflector

Reflector

FTIR

Griffiths et al. 2007; Phillips et al. 2009

Laser FTIR

Methane from landfill and waste treatment

• Introduction to methane production in landfill and waste• Factors affecting methanogenesis• Measurement of methane

Methane from landfill and waste

• Methane in landfill or waste– Decomposition of organic matter – Anaerobic conditions (moisture)

• Typically contains – 50% to 75% methane– 25% to 50% carbon dioxide – impurities such as hydrogen sulphide &

ammonia


• Basic approach– Covering effluent lagoons to prevent the

release of methane into the atmosphere– Collecting the biogas from the covered

lagoons• Methane can then be

– Flared to convert CH4 to CO2 (lower GWP)– Used to generate heat– Drive a steam turbine or modified

combustion engine to replace fossil fuel energy


• Some types of digesters for livestock effluent ponds– Covered anaerobic lagoon

• Work at ambient temperatures• Less efficient in winter• Suits total solids up to 3%

– Anaerobic Filter• Film increases surface area for digestion• Suits total solids up to 3%

– Continuously Stirred Tank Reactor• increases contact between bacteria and organic matter• Suits total solids up to 3 to 11%

– Plug flow Anaerobic Digester• A long concrete tank loaded at one end and plugged at the

other• Suits total solids up to 11 to 13%


• Digester options for livestock effluent as determined by solids content

(source: US EPA nd).

Factors affecting methanogenesis in waste and landfill

• Organic matter content• Anaerobicity

– Oxygen content– Moisture content

• Temperature– Optimum 20 to 50ºC

Estimating methane from waste or landfill

• Calculated– Piggery waste - PigBal model– Dairy waste – DGAS Calculator – Landfill gas –

• Baseline = methane from pond prior to any covering

• Project = methane after covering

Richard Eckard

Dairy Greenhouse Gas Abatement Strategies

Problems with methane collection from waste and landfill

• Water vapour• Hydrogen sulphide is corrosive• Methane is not easily compressed

– On site consumption needed• Explosive at 5 to 15% of air• CO2 and H2S can collect in confined

spaces

Methane from waste and landfill

• In Summary: – Collecting methane from waste and landfill

can be a valuable alternative source of energy, but does require specialist expertise and equipment for safe operation.

Nitrous oxide from cropping and animal production

• Introduction and background to nitrous oxide emissions• Global warming potential• Sources from soils, fertilisers, legumes and animal

waste• Factors affecting nitrous oxide formation in soils• Measurement of nitrous oxide


• Atmospheric Concentrations– Pre-industrial - 270 ppb – Current - 323 ppb

• 0.25% per year

IPCC 2007


Australian Atmospheric nitrous oxide

CSIRO 2011


• Nitrous Oxide– ∼10% of global greenhouse gas emissions

• ∼90% from agriculture

– 2.5% of Australian national emissions• 76% from agriculture in Australia

Smith et al. 2007; de Klein & Eckard 2008


• Global Warming Potential– N2O = 298 x CO2 (used in AR4)

• Note 310 x used in Australian inventory (and AR2)

– Long residence time in atmosphere• Inert in the troposphere

– But absorbs radiation

• Stratosphere– Cause ozone depletion

– Atmospheric concentration• 0.3 ppm (0.00003%)

IPCC 2007


• Denitrification– Warm, water-logged soils– Excess N in soil

• Nitrification– Warm, aerobic soils– Minor losses

• Inefficient use of nitrogen– >60% N lost from grazing– >30% N lost from cropping

Eckard 2011


Fertili

sers

Grazin

g

Atmos

pher

ic Dep

ositio

n

Leac

hing

and

Run

-Off

Anim

al W

aste

Nitrog

en F

ixing

Cro

ps

Crop

Resid

ue

Cultiv

atio

n of

Hist

osol

s0

500

1000

1500

2000

2500

3000

3500

4000

Gg

CO

2e

DCCEE 2011

18%

4%6%

26%

5%

41%

25%

17%

[Sources of N2O and % contribution


• Factors affecting nitrous oxide formation in soils– N (NO3)

– Soil Temperature– Soluble C– Soil pH– Anaerobicity

Granli & Bøckman 1994

Nitrous oxide measurement

• Measurement of N2O– Manual and automatic chambers

Nitrous oxide measurement

• Measurement of N2O– Micrometeorological methods

Purpose: To provide participants with an understanding of the sinks of carbon and sources of methane...

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Transcript of Purpose: To provide participants with an understanding of the sinks of carbon and sources of methane...