UK losses of soil
carbon – due to climate
change?
Pat Bellamy
Natural Resources Department
Cranfield University
UK
Outline
• Brief overview of Carbon losses from all soils across
England and Wales 1978-2003 published in Nature
2005
• Potential causes of carbon loss
• Changes that have occurred in UK over the twenty
years between samplings
• How we are investigating what is driving the
change in soil carbon
• Preliminary results based on simple models
• Work in progress
The National Soil Inventory
of England & Wales
The National Soil Inventory was made
to obtain an unbiased estimate of the
distribution of the soils of England and
Wales and of the chemistry of the topsoil
(0–15 cm depth)
• Whole of England & Wales
sampled at each intersect of a 5 km
x 5 km grid – 1979-1983.
• Soil profiles described and topsoil
(0-15cm) samples taken
• For each sample organic carbon,
pH, metal concentrations and
nutrients measured.
• Site properties such as land use,
slope, aspect recorded.
20m
20m
Sampling at each site
Soil organic carbon
content c.1980
Resampling of NSI
• Proportion of NSI sites were re-sampled:
1994-1996 (cropland and managed
grassland)
2002-2003 (forestry, moorland,
extensive grazing land)
• Sampling scheme designed to detect changes of organic
carbon ± 2 g kg-1
Resampling of the NSI
Protocols verified for:
• Original surveyor
• Field sampling – methods
and tools
• Site location
• Laboratory analyses
© Bellamy et al (2005)
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Roane d hass
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Up
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m s
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Rate of change
(g kg-1 yr-1)
Results from
resampling of NSI
Annual change in carbon
– grouped by land use
2
0
-2
-4
-6
Results from NSI
across all land uses
Annual change in carbon (g/kg/yr)
All land uses
Rate of change
(g kg-1 yr-1)
2
0
-2
-4
-6
Eqn (1)
-8
0
© Bellamy et al (2005)
100
200
300
400
500
Corg (g kg-1)
Eqn (1): Rate of change = 0.6 - 0.0187 × Corg
Changes in soil carbon
1978-2003
Annual change in carbon g/kg/yr
•Carbon lost from soils at a
mean rate of 0.6 gm of
organic carbon per kg of
soil per year.
•For soils with more than
100 gm per kg carbon rate
of loss greater than 2 gm
per kg per year
Annual changes in soil
carbon stocks
Organic Carbon (%)
No Data
0-1
1-2
2-5
5 - 10
10 - 25
25 - 35
> 35
Estimated annual soil C loss:
ƒ England & Wales
≈ 4.4 million tonnes
ƒ UK ≈ 4.4 x UK / E&W C stock
≈ 13 million tonnes
For comparison:
ƒ UK industrial CO2 emission
≈ 140 million tonnes
ƒ Reduction since 1990
≈ 13 million tonnes
Potential causes of
carbon losses
Land use/management
ƒ Extension of agriculture
- e.g. grassland and woodland
conversion to cropland
ƒ Intensification of land use
- e.g. drainage, increased nutrient
loading, pesticide use
ƒ Non-agricultural land uses
- e.g. afforestation on wet land,
managed burning
Environmental change
ƒ Atmospheric
- e.g. decreased acid rain,
increased nitrogen
deposition
ƒ Climatic
- e.g. temperature and
precipitation
20
16
Tmax
15
rain
14
12
Tmin
10
10
5
0
8
1
2
3
4
5
6
7
8
Rainfall (cm)
Temperature (oC)
Mean monthly UK temp
and rainfall
1978-2003
(a) Annual pattern
6
9 10 11 12
Month of year
1.5
1.0
1.0
0.5
0.0
-0.5
-1.0
-1.5
0.5
0.0
-0.5
-1.0
-1.5
0
5
10
15
20
∆ monthly precip (cm)
1.5
∆ monthly Tmin (oC)
∆ monthly Tmax (oC)
(b) Changes since 1978
0
5
10
15
Year after 1978
20
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
4
2
0
-2
-4
0
5
10
15
20
Jan
Changes in soil pH
between NSI samplings
Original pH
Annual change
in pH
(over 12-25 yr)
How do we investigate
what is driving the
change in soil carbon?
• We do not have detailed information on many of the
potential drivers of soil carbon change at the NSI sites
• An alternative approach is to use simple models of soil
carbon turnover to evaluate possible explanations for
the observed trends based on changes in land
management or environmental change including
climate change
• We can reject explanations for the changes that
require unrealistic parameters to deliver the measured
magnitudes of change
Soil carbon dynamics
Plant
carbon
Atmosphere
CO2
Soil carbon
immobilization
mobilization
Soil C accumulates if
immobilization > mobilization
Lost if
mobilization > immobilization
Leached
carbon
Simple carbon model
Rate of change = Input – k x organic carbon
(k = decomposition rate constant)
• Assume Input & k changed some time before first sampling –
i.e. soils are adjusting to earlier change - Input & k independent of
OC, dependant on land use only
• Assume change in decomposition rate, k, (proportional to
organic carbon) – i.e. decomposition rate changes in response to
climate change
• Assume change in Input (proportional to carbon content) – i.e.
Input changes in response to environmental change
The model fitted to data for each land use class
Simple
carbon
model:
results
1.0
0.8
Arable
0.6
0.4
Arable and
rotational
grassland
0.2
0.0
-0.2
-0.4
-0.6
observed
predicted
-0.8
-1.0
-1.2
0
2
4
6
8
10
12
14
16
18
-1
0.6
Rate of change (kg C m y )
0.8
-2
1.0
Permanent grass
0.4
Permanent
grassland
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
0
2
4
6
8
10
12
14
16
18
1.0
0.8
Non-agricultural
Non-agricultural
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
0
2
4
6
8
10
12
14
-2
Mean soil carbon content (kg C m )
16
18
Simple carbon model:
results
• The model parameter estimates were assessed against
known effects of land use/management change, climate
change and environmental change
Simple carbon model:
results
• Estimates of k and Input obtained for each land use
• If k changed proportional to OC the large changes
required suggest climate change cannot be sole driver
• Large changes in Input required suggest environmental
changes not a major driver
Initial conclusions
Results so far indicate the dominant driver of soil carbon
losses was changes in land use/management, but climate
change was responsible for part of the losses, and is likely
to cause increased losses in future
Further work in
progress
• More sophisticated models of carbon change are
being developed which will represent the whole range
of soils in England and Wales
• These models are being validated using the NSI data
• These will allow more precise estimation of the
contribution of climate change to the change in soil
carbon observed in the NSI data
Acknowledgements
• Funding for the National Soil Inventory of England and
Wales came from Defra (Department for Environment Food
and Rural Affairs UK)
• I would like to thank past and present colleagues at the
National Soil Resources Institute at Cranfield University
including Ian Bradley, Guy Kirk, Peter Loveland, Richard
Andrews, Ilkka Leinonen and Bob Jones, also Murray Lark
at Rothamsted Research.
Carbon losses from all soils across England and Wales 1978-2003 (2005) Pat H. Bellamy, Peter J.
Loveland, R. Ian Bradley, R. Murray Lark & Guy J.D. Kirk Nature 437 pp245 - 248