Download 1 soil strategy for england supporting evidence paper

Department for Environment, Food and Rural Affairs
24 September 2009
SOIL STRATEGY FOR ENGLAND
SUPPORTING EVIDENCE PAPER
1
Department for Environment, Food and Rural Affairs
24 September 2009
1. This document provides a detailed analysis of the evidence on why soils are important
and the pressures being faced; it is being published alongside the Soil Strategy. It is
organised initially by soil function and then the information is reanalysed by soil threat.
Contents
Introduction ...................................................................................................................... 2 Provision of food, fuel and fibre ........................................................................................ 2 Storing soil carbon and climate change interactions ........................................................ 7 Buffering pollution .......................................................................................................... 13 Water and flood regulation ............................................................................................. 16 Supporting biodiversity ................................................................................................... 19 Supporting our Cultural heritage .................................................................................... 20 Summary of Soil threats ................................................................................................. 21 Historic contamination .................................................................................................... 23 Total costs relating to key pressures .............................................................................. 24 Introduction
2. Soil is a fundamental and irreplaceable natural resource and provides an essential link
between the components that make up our environment (i.e. air, geology, water and
biota). It is also a non-renewable resource (in that renewal is extremely slow and not
always possible) and needs to be utilised in a way that does not endanger it for future
generations. Soil provides a range of functions or ecosystem services fundamental to
our well-being and prosperity and the diversity and versatility of England's soils help
shape the landscape including above ground biodiversity.
3. The key functions provided by our soils are:
• support of food, fuel and fibre 1 production;
• environmental interaction functions (e.g. regulating the flow of and filtering
substances from water, emitting and removing atmospheric gases, storing
carbon);
• support of habitats and biodiversity;
• protection of cultural heritage and archaeology;
• providing a platform (for construction); and
• providing raw materials.
4. Soil functions can also be described in terms of the ecosystem services defined by the
Millennium Ecosystem Assessment (MA) 2 . The MA is an international assessment
process that provides a tool to assess the benefits of ecosystems for human wellbeing. It provides a useful system for quantifying the value of different soils in different
areas with regard to the service(s) they provide.
Provision of food, fuel and fibre
1
Fibre here refers to timber and non-food agricultural crops.
Millennium Ecosystem Assessment: (2005) Ecosystems and Human Well-being: Synthesis. Island Press,
Washington, DC.
2
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24 September 2009
5. Soil is vital to the provision of food and fibre. It is one of the fundamental assets of most
farms, but mismanagement can result in its loss as well as physical degradation. 3 This
reduces the ability of soils to perform this service as well as impacting on the provision
of other ecosystem services.
6. In 2008, the value of total agricultural output for the UK (at market prices)was £19.8
billion 4 . Whilst many other factors contribute to this level of output, we are reliant on
good soil quality for these high outputs.
7. Good soil management and soil quality can increase the incomes of farmers. For
example, evidence suggests that by improving management of soil organic matter
financial returns for farmers can be improved by a total of £31 to £66 per hectare 5 (as a
result of ease of tillage, fertiliser saving, and higher yields). The financial benefits are
generally significantly higher than the costs involved in improving the management of
soil organic matter.
8. Poor management of soil during food and fibre production can lead to soil degradation
and impact the wider environment; moreover, soil degradation in turn can impact on the
production of food and fibre. There are a number of key pressures and degradation
processes and their interaction with the function of food and fibre provision is explored
below.
Soil erosion
9. Erosion is a major issue. In the 2007 Farm Practices Survey for England, farmers
assessed the extent of soil erosion on their farms. In all, 50% of farmers stated that
they had experienced some indicator of soil erosion on their land – indicators included
discoloured runoff entering ditches and water courses, sediment deposited in ditches
and water courses, sediment deposited on roads and formation of gullies and rills 6 .
Typical soil erosion rates are in the order of <1-20 tonnes/hectare/year 7 with most
fields experiencing <1 tonnes/hectare/year 8 , but erosion rates as high as 100
tonnes/hectare have been reported 9 .
10. Available information for England and Wales suggests that non-water erosion
processes (i.e. wind, tillage, soil loss due to crop harvest) may be equally as important
as erosion caused by water, although their spatial extent will differ 10 . In 2002 a survey
of farmers in East Anglia showed that they expected moderate damage to crops from
wind erosion once every three or four years and severe damage once in 10 years 11 .
The value of the crop in wind eroded fields (e.g. field vegetables) is often higher than
3
IPCC (2003): Good practice guidance for land use, land use change and forestry.
Defra, DARDNI, SG, WAG (2009): Agriculture in the UK 2008.
5
Gaunt et al (2004): To develop a robust indicator of soil organic matter status. Defra Project SP0310.
6
http://statistics.defra.gov.uk/esg/publications/fps/default.asp
7
Defra (2003): Strategic review of diffuse water pollution from agriculture: Stakeholder discussion paper.
8
Harrod et al (1998): A systematic approach to national budgets of phosphorus loss through soil erosion and
surface runoff at National Soil Inventory nodes. Defra project NT1014.
9
Defra (2003): Strategic review of diffuse water pollution from agriculture: Stakeholder discussion paper.
10
Owens et al (2006): Scoping study of soil loss through wind erosion, tillage erosion and soil co-extracted
with root vegetables. Defra project SP08007.
11
Chappell, A. and Thomas, A.D. (2002): Modelling to reconstruct recent wind erosion history of fields in
eastern England. In: Proceedings of ICAR5/GCTE-SEN Joint Conference, Lee, J.A. and Zobeck, T.M. (Eds),
International Center for Arid and Semiarid Lands Studies, Texas Tech University, Lubbock, Texas, USA
Publication 02-2 p. 309.
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24 September 2009
that affected by water erosion, so the cost to the farmer is much (five times or more)
greater than when fields suffer from rill erosion (small channels formed by the action of
water) 12 .
11. The key monetized costs of erosion are the water treatment costs associated with the
presence of phosphate and sediment in sources of drinking water due to agriculture.
The Environment Agency has compiled data on the costs of environmental damage
caused by agriculture (based on 2004/05 prices) 13 . It estimates the water treatment
cost of soil erosion to be £21.17 million per year, based on an assumption that 50% of
the cost is attributable to agriculture. More recent work suggests that on average
agriculture is only responsible for 25% of the phosphorus 14 but 75% of the sediment 15 .
12. The additional off-farm costs incurred as a result of soil erosion (or costs of damage to
property and dredging stream channels) were estimated to be £9 million per year, with
on farm costs of soil erosion (due to wind and water) also estimated at £9 million per
year 16 . On top of this, during 2006/07, a further £5.5 million was spent on managing
accumulated sediment in watercourses managed or owned by British Waterways in
England 17 .
13. These costs therefore approximate an annual total cost of the impacts of soil erosion
due to agriculture of £45 million. This figure is likely to be an underestimate as it does
not take into account the long-term impact on soils and the risk of reaching a situation
where soil functionality has been severely diminished by the cumulative effect of
erosion (particularly where the rate of erosion is greater than that of soil formation 18 ), or
the costs of restoring degraded habitats.
14. In the 2008 Farm Practices Survey for England, farmers reported the actions they had
taken over the previous year to prevent run-off, water and wind erosion. The most
common actions taken were working across rather than down slopes, loosening
tramlines and fencing watercourses to prevent stock eroding banks with 71%, 66% and
50% of farmers carrying out these practices respectively 19 .
Compaction
15. Compaction of soils occurs as a result of the use of heavy machinery or the action of
livestock and is expressed as an increase in bulk density. The impact of compaction on
other ecosystem services such as water and flood regulation is explored in a later
section, but compaction also has a consequence for food and fibre production.
Reynolds et al (2007) 20 observed that for fine-textured soils, the optimum bulk density
range for field crop production appears to be in the order of 0.9–1.2 milligrams per
12
Evans, R. (1996). Soil erosion and its impacts in England and Wales. Friends of the Earth, London.
EA (2007): The total external environmental costs and benefits of agriculture in the UK.
14
Hammond et al (2006): Updating the estimate of the sources of phosphorus in UK waters.
15
Anthony et al (2006): Sediment Gap Analysis to Support WFD. Defra Project WQ0106.
16
Evans, R. (1996): Soil Erosion and its Impact in England and Wales. Friends of the Earth Trust.
17
British Waterways (2008): Consultation response.
18
Average world soil formation rates, based on the conversion of parent rock into soil, are estimated to be
between 0.05 and 10 mm/100 years. These numbers have large error bars. (Ragnarsdottir, V. (2006): The
state we are in – understanding the life-cycle of soils. Research Review March 2006.)
19
http://statistics.defra.gov.uk/esg/publications/fps/default.asp
20
Reynolds et al (2007): Land management effects on the near-surface physical quality of a clay loam. Soil
and Tillage Research 96, 316-330.
13
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cubic metre. Bulk density values <0.80 may provide insufficient root–soil contact, water
retention and plant anchoring, while bulk density values >1.20 may impede root
elongation or reduce soil aeration. The upper bulk density limit for adequate aeration of
fine-textured soils appears to be in the order of 1.25–1.30, while mechanical resistance
to root elongation in fine-textured soil often becomes excessive for bulk density >1.40.
16. Countryside Survey measured bulk density for the first time in 2007. The average
topsoil (0-15 cm) bulk density for the arable and horticulture broad habitat in Great
Britain was 1.23 grams per cubic centimetre (equivalent to 1.23 milligrams per cubic
metre). 21
17. In the 2008 Farm Practices Survey for England, farmers reported the actions they had
taken over the previous year to address compaction: 69% of farmers removed
compaction from headlands after harvest, 61% used low ground pressure set-ups and
48% improved drainage 22 .
Organic matter decline
18. Soil organic matter (SOM) increases the capacity of soils to bind chemicals, buffers the
release of pollutants, regulates the supply of nutrients, improves soil structure, is a
store of carbon, and makes soil more resistant to drought and erosion.
19. Cultivation is one of the main causes of SOM loss, with the most dramatic losses
occurring as a result of the ploughing up of grasslands and the drainage and cultivation
of organic soils. For example, in Eastern England peat shrinkage rates of 1-2 cm per
year (due to consolidation and oxidation) have been noted following drainage and
cultivation, resulting in up to 3 m of peat loss since the 17th Century 23 . The evidence
for a decline in soil carbon (SOM typically contains up to 58% carbon) and its
interaction with climate regulation is discussed in a later section, but a decline in
organic matter is also significant for food and fibre production due to its influence on
soil properties.
20. Organic matter can hold up to 20 times its weight in water and can, therefore, directly
affect soil water retention, which makes soil more resistant to drought and erosion, as
well as indirectly through its effects on soil structure 24 . Recent studies have shown that
a small change in total organic carbon content can have an effect on soil physical
properties and functions. A small increase in organic carbon content has a
considerable benefit in terms of water infiltration capacity. The small increase in total
organic carbon content resulting from using nitrogen fertiliser for many years was also
shown to considerably decrease the energy required for tillage 25 and have benefits for
21
Carey, P.D., Wallis, S., Chamberlain, P.M., Cooper, A., Emmett, B.A., Maskell, L.C., McCann, T., Murphy,
J., Norton, L.R., Reynolds, B., Scott, W.A., Simpson, I.C., Smart, S.M., Ullyett, J.M. (2008): Countryside
Survey: UK Results for 2007.
22
http://statistics.defra.gov.uk/esg/publications/fps/default.asp
23
Hodge et al. (1984): Soils and their use in Eastern England. Soil Survey of England and Wales Bulletin
No.13. Harpenden, 450pp.
24
Dick et al (2004): Developing and maintaining soil organic matter levels. In: Managing Soil Quality
Challenges in Modern Agriculture. (Eds. P. Schjonning, S. Elmholt & B.T. Christensen)., CABI Publishing,
Wallingford, Oxen. pp.103-120.
25
Watts et al. (2006): The role of clay, organic carbon and long-term management on mouldboard plough
draught measured on the Broadbalk wheat experiment at Rothamsted. Soil Use and Management 22, 334341.
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24 September 2009
aggregate stability 26 . Soil organic matter also increases the capacity of soils to bind
chemicals, buffers the release of pollutants and regulates the supply of nutrients.
21. Recent research has shown that farmers can be encouraged to change their soil
management when presented with information on the likely benefits to their farm of
increasing soil organic matter 27 . This project developed and used case studies and soil
organic matter interpretation tools to convey the impact of management on soil organic
matter and the likely benefits of increasing this to farm businesses.
22. Farmers are taking action to manage soil organic matter. In the 2008 Farm Practices
Survey for England, farmers reported the actions they had taken over the previous year
to improve soil organic matter: 75% of farmers had applied FYM or other bulky
materials, 59% returned straw or other crop residues after harvest, and 43% included
grass leys and/or short term cover crops in rotation 28 .
Climate change impacts
23. According to the recently published climate change projections (UKCP09), the UK will
continue to get warmer; summers will get hotter and drier and winters milder and
wetter 29 . We will also experience sea level rise and increased frequency and intensity
of extreme weather events, such as summer heat waves and heavy winter
precipitation. These climatic changes are likely to have an impact on the capacity of
soil for food and fibre production due to changes in soil moisture balance, lengths of
growing seasons and the suitability of crops and farming systems to altered
temperature and rainfall patterns.
24. Whilst increased temperatures may raise certain crop yields, greater flood risk may
reduce the area of land available for agriculture. The need to use machinery on wet
land is likely to result in poor and damaged soil structure, and erosion risk is likely to
increase due to changes in soil water content. 30 Changes in soil moisture content affect
several soil forming processes and it is uncertain how this, and changes in
temperature, will affect carbon turnover. 31 Less summer rainfall means that salinisation
may occur from groundwater being drawn upwards by vegetation and surface
evaporation (depositing salts on the soil surface and root zone) 32 and from the potential
loss of surface water 33 . Drought has the potential to reduce soil moisture content and
increase frequency of shrink-swell in clays; this encourages by-pass flow increasing the
risk of groundwater contamination 34 .
25. A further issue which needs to be borne in mind is that, with 57% of the UK’s Grade 1
agricultural land lying below the 5 metre contour, climate change induced sea level rise
26
Blair et al. (2006): Long-term management impacts on soil C, N and physical fertility. Part 1: Broadbalk
experiment. Soil and Tillage Research 91, 30-38.
27
Gaunt et al (2008): Soils within the Catchment Sensitive Farming Programme: Project to deliver
improvements in soil management. Defra project SP08014.
28
http://statistics.defra.gov.uk/esg/publications/fps/default.asp
29
Defra (2009): Adapting to Climate Change: UK Climate Projections.
30
Bradley et al (2005): Impacts of climate change on soil functions. Defra project SP0538.
31
ADAS (2001): The timescale of potential farm level responses and adaptations to climate change in
England and Wales. Defra project CC0333.
32
Food and Agricultural Organisation of the United Nations (1988): Soils Bulletin 39 - Salt affected soil and
their management.
33
Bradley et al (2005): Impacts of climate change on soil functions. Defra project SP0538.
34
Bradley et al (2005): Impacts of climate change on soil functions. Defra Project SP0538.
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will also have a significant effect. UKCP09 gives projections of UK coastal absolute sea
level rise (not including land movement) for 2095 that range from approximately 12-75
centimetres. 35 Taking vertical land movement into account gives slightly larger sea
level rise projections relative to the land in the more southern parts of the UK where
land is subsiding.
26. The indirect impacts of climate change due to changes in cropping 36 are likely to in turn
also exacerbate the risks of erosion, organic matter decline and compaction. This may
turn out to be more significant than the direct impacts of changing temperature and
rainfall patterns alone.
27. Some research has been undertaken using the occurrence of extreme climatic events
to represent future climatic conditions. For example, the rainfall conditions of autumn
2000 presented an opportunity to examine the potential effects of one aspect of climate
change on soil erosion: i.e. increased duration and intensity of rainfall. Erosion extent
on arable and upland field sites was assessed shortly after one of the wettest periods
in England and Wales since records began in 1766 and compared with data from
previous surveys of the same sites 37 . The project concluded that the impacts of climate
change on soil erosion were likely to be complex and composed of both direct impacts,
such as changed land use practices, and indirect impacts, including changes in
vegetation composition, growth and recovery.
Pressures on land
28. Changes in cropping and agricultural practices are driven by more than climate change
and will have significant impacts on the soil. In particular, increasing demand for arable
crops from the food, feed and fuel sectors will increase the pressure on agricultural
land as UK farmers respond to market demand and increase arable production.
29. There are also pressures to bring areas of non-arable land into production, such as the
ploughing up of grassland for biofuels and the use of more marginal land for cereal
production, both of which will have a similar, if not greater impact on soil carbon as well
as biodiversity and landscapes.
30. In addition, population growth and the need for more housing and infrastructure means
an increasing demand for land for development. This is unlikely to lead to large scale
loss of agricultural land at present rates of growth but this is still an issue that needs to
be monitored.
Storing soil carbon and climate change interactions
35
Lowe, J. A., Howard, T., Pardaens, A., Tinker, J., Jenkins, G., Ridley, J., Met Office, Leake, J., Holt, J.,
Wakelin, S., Wolf, J., Horsburgh, K., Proudman Oceanic Laboratory, Reeder, T., Environment Agency, Milne,
G., Bradley, S., University of Durham, Dye, S., Marine Climate Change Partnership (MCCIP)(2009): Marine
& coastal projections. UK Climate Projections.
36
The potential for soils to support agriculture, and the future distribution of land use, will be strongly
influenced by changes in the soil water balance. Drier soil conditions may favour arable agriculture in the
currently wetter regions of the UK as a result of improved soil workability, and diminished poaching risk in
grassland areas. The range of current crops is expected to move northward and marginal crops such as
maize may increasingly penetrate southern UK. (Defra (2000): Climate change and agriculture in the UK.)
These spatial changes will impact on the distribution of pressures and threats to soil associated with these
agricultural practices and crops.
37
McHugh et al (2002): Arable and upland NSI erosion resurvey. Defra Project SP0407.
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31. Soils are a major reservoir of carbon, with the order of 10 billion tonnes of carbon being
stored in UK soils 38 , 39 . Dawson and Smith (2007) have estimated that the carbon
stored in soils in Great Britain was 9.8 ± 2.4 billion tonnes, with 6.9 billion tonnes in
Scotland and 2.8 billion tonnes in England and Wales 40 . This is more than the 9.5
billion tonnes of carbon stored in all of the trees (biomass) in the forests of Europe
(excluding Russia) 41 . The soils of the English uplands contain more carbon than all the
trees in the UK and France added together 42 . Loss of soil carbon will be to the
detriment of soil functions as well as contributing to greenhouse gas emissions and
climate change. A number of key issues relating to soil carbon storage and its
interaction with climate change are dealt with below.
Greenhouse gas emissions and targets
32. Loss of soil carbon as carbon dioxide (CO2) to the atmosphere contributes to climate
change. The UK Greenhouse Gas Inventory 43 , is consistent with internationally agreed
Intergovernmental Panel on Climate Change methodologies to calculate likely additions
and removals of greenhouse gases (GHG) from soil, estimates that in 2007, 21.8
million tonnes carbon dioxide were emitted from UK soils and 11.6 million tonnes
carbon dioxide were added to the soils. A further 0.43 million tonnes carbon dioxide
were emitted directly from peat extraction 44 .
33. Work by Natural England suggests that the GHG inventory may underestimate the
losses of carbon from peat 45 . They estimate that English lowland peatlands could be
emitting between 2.8 and 5.8 million tonnes of CO2 a year, which is significantly higher
than the 1.15 million tonnes of CO2 currently recorded in the inventory. They attribute
the discrepancy to an under-estimate of the area of deep peatlands.
34. Under the Kyoto Protocol, the UK is committed to reduce its greenhouse gas emissions
by 12.5% below 1990 base year levels over the 2008-2012 commitment period.
Although the Kyoto target does not take account of agricultural soils the UK is already
projected to reduce greenhouse gas emissions by nearly double its commitment under
Kyoto 46 , and more is required to meet challenging new domestic targets. The 2008
Climate Change Act sets out a strong new legal framework to underpin the UK's
contribution to tackling climate change. It commits the UK to at least an 80% reduction
in greenhouse gas emissions, including emission from soils, through domestic and
international actions by 2050.
38
Milne, R.; Brown, T. A.. (1997): Carbon in the vegetation and soils of Great Britain. Journal of
Environmental Management, 49. 413-433.
39
Tomlinson, R. W.; Milne, R.M.. (2006): Soil carbon stocks and land cover in Northern Ireland from 1939 to
2000. Applied Geography, 26. 18-39.
40
Dawson, J.J.C., Smith, P., (2007): Carbon losses from soil and its consequences for land-use
management. Science of the Total Environment 382, (2-3), 165-190
41
MCPFE and UNECE/FAO (2003): State of Europe’s Forests 2003: The MCPFE Report on Sustainable
Forest Management in Europe.
42
H M Government (2006): Climate Change: The UK programme 2006.
43
Under the UN Framework Convention on Climate Change, the UK is committed to producing annual
reports which account for all greenhouse gas emissions and removals.
44
Jackson et al (2009): UK Greenhouse Gas Inventory 1990 to 2005: Annual Report for submission under
the Framework Convention on Climate Change.
45
Thompson, David (2008): Carbon Management by Land and Marine Managers. Natural England Research
Reports, Number 026.
46
Chapter 4 of the UK’s 5th National Communication to the United Nations Framework Convention on
Climate Change shows UK greenhouse gas emissions in 2010 at 23.3 percent below the base year level.
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Trends in soil carbon
35. A study by Bellamy et al (2005) suggested that over the last 25 years there had been a
general decline in soil organic matter in agriculturally managed soils, although small
increases had been observed in some intensively farmed arable soils. It reported that
carbon had been lost from UK soils at an annual rate of 13 million tonnes, equivalent to
about 8% of the UK’s current carbon emissions from consumption of fossil fuels 47 . If
this is correct, this is a significant contribution to GHG emissions. However, there is
significant uncertainty surrounding the Bellamy et al findings, in particular on the
causes 48 and fate of the lost carbon and contradictory evidence from other surveys
which require further investigation.
36. The Countryside Survey of 2000 found an increase, in the average carbon
concentration of the soil (0-15 cm depth) across Great Britain over the period 1978 to
1998. 49 The 2007 survey found that there was a decrease in the average carbon
concentration between 1998 and 2007. Overall Countryside Survey found no significant
change in carbon concentration in soils (0-15cm) between 1978 and 2007. 50 The only
broad habitats for which a significant change in soil carbon concentrations was found
between 1978 and 2007 were Broadleaved, Mixed and Yew Woodland (increase),
Arable and Horticulture (decrease) and Bracken (increase). 51
37. It has been estimated that the annual cost, in terms of treatment, prevention,
administration and monitoring, of the carbon lost due to soil cultivation in the UK
amounts to £82 million. 52 It is important, therefore, to determine whether any loss is
preventable and how this can be achieved.
38. Further losses of soil carbon could also occur as a result of climate change, due to
changes in temperature and soil moisture which speed up the decomposition of organic
matter 53 . However, there is evidence to suggest that carbon from deep in the soil would
not provide enough energy to sustain active microbial populations and this could
reduce or cancel the effect of future changes in temperature on the decomposition of
this large pool of deep carbon 54 . Moreover, increased decomposition may be
counteracted by the higher uptake of carbon dioxide by plants, as they grow faster in
47
Bellamy et al (2005): Carbon losses from all soils across England and Wales 1978–2003. Nature Vol
437:245-8.
48
Smith et al (2007): Climate change cannot be entirely responsible for soil carbon loss observed in England
and Wales, 1978-2003. Global Change Biology 13, 2605-2609.
49
Black, H. I. J., Garnett, J. S,, Ainsworth, G., Coward, P. A., Creamer, R., Ellwood, S., Horne, J., Hornung,
M., Kennedy, V. H., Monson, F., Raine, L., Osborn, D., Parekh, N. R., Parrington, J., Poskitt, J. M., Potter,
E., Reeves, N., Rowland, A. P., Self, P., Turner, S., Watkins, J., Woods, C. and Wright, J. (2002): MASQ:
Monitoring and Assessing Soil Quality in Great Britain. Countryside Survey Module 6: Soils and Pollution.
Environment Agency R&D Technical Report E1-063/TR
50
Carey, P.D., Wallis, S.M., Emmett, B.E., Maskell, L.C., Murphy, J., Norton, L.R., Simpson, I.C., Smart, S.S.
(2008): Countryside Survey: UK Headline Messages from 2007.
51
Carey, P.D., Wallis, S., Chamberlain, P.M., Cooper, A., Emmett, B.A., Maskell, L.C., McCann, T., Murphy,
J., Norton, L.R., Reynolds, B., Scott, W.A., Simpson, I.C., Smart, S.M., Ullyett, J.M. (2008): Countryside
Survey: UK Results for 2007.
52
EA (2007): The total external environmental costs and benefits of agriculture in the UK.
53
Schlesinger, W. H. & Andrews, J. A. (2002): Soil respiration and the global carbon cycle. Biogeochemistry
48, 7–-20.
54
Fontaine et al (2007): Stability of organic carbon in deep soil layers controlled by fresh carbon supply.
Nature Vol 450: 277-80.
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24 September 2009
warmer conditions and store carbon as biomass 55 . A recent European review of
information on the interrelations between soil and climate change was unable to find
strong and clear evidence for either an overall combined positive or negative impact of
climate change (raised atmospheric CO2, temperature, precipitation) on soil carbon
stocks 56 .
Carbon storage and degradation of peat soils
39. In addition to the carbon losses from agriculturally managed soils there is also
evidence to show that upland organic soils (peat) are being degraded and losing large
amounts of carbon. For example, the amount of dissolved organic carbon (DOC) in
water is increasing in the uplands due to losses from peat soils. Since 1988, there has
been, on average, a 91% increase in DOC concentrations of UK lakes and streams in
the Acid Waters Monitoring Network 57 . Removal of colour from water represents one of
the major operational costs of any treatment plant 58 and can run into millions of pounds
per annum. United Utilities are restoring approximately 6,000 hectares of peatland as
part of their Sustainable Catchment Management Programme (SCaMP) 59 . They
anticipate saving between £1.2 and £2.4 million per year in avoided water treatment
costs. 60
40. Peat is also extracted for use in growing media for the professional and amateur
markets. This requires the peat bog to be drained, the removal of vegetation and the
levelling of the peat surface before machinery is used to mill and harvest the peat. In
2007 1.31 million cubic metres of the peat used in growing media and soil improvers
were from UK sites (43% of the total) 61 . This has reduced from a recent peak volume
of peat from UK sources in 2001 of 1.52 million cubic metres. This reduction in volume
could be due to a range of factors including weather (affecting harvesting) or changes
in the sourcing of peat.
41. Wind farm development on peatland is an increasing area of concern as it can result in
habitat degradation and an increase in carbon losses 62 . Carbon may be lost during the
construction process as excavated peat and from areas affected by drainage (the effect
of which lasts beyond the construction phase) 63 . The extent of drainage effects varies
widely and distances ranging from 2 to 50 metres around the site of disturbance have
been reported.
55
Kirschbaum, M. U. F. (2000): Will changes in soil organic carbon act as a positive or negative feedback on
global warming. Biogeochemistry 48, 21–-51.
56
Schils, R., Kuikman, P., Liski, J., Van Oijen, M., Smith, P., Webb, J., Alm, J., Somogyi, Z., Van den Akker,
J., Billett, M., Emmett, B., Evans, C., Lindner, M., Palosuo, T., Bellamy, P., Jandl, R. & Hiederer, R. (2008):
Review of existing information on the interrelations between soil and climate change. European Commission
Service contract No 070307/2007/486157/SER/B1.
57
Evans et al (2005): Long-term increase in dissolved organic carbon: observations, possible causes and
environmental impacts. Environ. Pollut.137, 55-71.
58
http://www.uk-adapt.org.uk/find/index.html?action=project&id=67
59
http://www.unitedutilities.com/?OBH=5056
60
A land fit for the future - David Miliband’s speech to the Campaign to Protect Rural England Conference, 9
March 2007.
61
Holmes et al (2007): Monitoring of peat and alternative products for growing media and soil improvers in
the UK 2007. Defra project WC04019.
62
Holden et al (2007): Vulnerability of organic soils. Defra Project SP0532.
63
Nayak et al (2008) Calculating carbon savings from wind farms on Scottish peat lands – a new approach.
Final report. Project funded by the Rural and Environment Research and Analysis Directorate of the Scottish
Government.
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Department for Environment, Food and Rural Affairs
24 September 2009
42. When in pristine condition, active peat bogs can accumulate up to 0.7 tonnes of carbon
per hectare per annum 64 . Studies indicate that most blanket peat development began
5000-6000 years ago and on average the depth of UK peat is 0.5-3 metres, though
depths in excess of 5 metres are not unusual. There is approximately 215,000 hectares
of blanket peat soil in England, though significant proportions no longer support blanket
bog vegetation. Additionally England has 500 hectares of lowland raised bog, down
from 37,000 hectares at the start of the nineteenth century. 65 Even when they are not
actively accumulating carbon, peat bogs are an important store of carbon. However,
these habitats can become a source of carbon when disturbed and climate change
may increase the rate of degradation, e.g. through increased risk of fire 66 and repeated
summer droughts 67 . Losses of carbon from peats can occur in various forms, including
as DOC, eroded particulates and gaseous CO2 or methane.
43. In addition, degradation of peat can lead to losses of biodiversity, wetland archaeology
and palaeoenvironmental records. It can also speed up the flow of water across the
landscape, potentially increasing the risk of flooding downstream.
Increasing soil carbon
44. Current policy is to maintain levels of SOM and, where appropriate, to increase levels,
as well as to protect certain habitats such as peat bogs which contain large stores of
soil carbon. Government is currently involved in a range of direct and indirect activities
which maintain levels of SOM and protect and restore habitats that store carbon such
as peat bogs.
45. The quantity of carbon that can be stored in any soil is dependent on the land-use, soil
type and climate. After a change in land use or management practice, SOC in mineral
soil increases or decreases towards an equilibrium value (after c.100 years or more)
that is characteristic of the soil type, land use and climate. 68 Rates of change are
generally slow, but soil carbon is lost more rapidly than it accumulates 69 .
46. There has been increasing interest in the potential of reduced tillage (also known as
non-inversion tillage) and organic matter additions to mitigate climate change by
increasing the levels of carbon in the soil. A recent study critically reviewed the extent
to which both reduced tillage practices (including zero tillage) and organic matter
returns (farm manures, biosolids, composts, paper waste, etc.) could increase the
carbon content of arable soils under English and Welsh conditions 70 . This raised
questions as to whether the international evidence in support of the sequestration
potential of reduced tillage compared to conventional tillage 71 was reliable. These
64
Holden et al (2007): Vulnerability of organic soils. Defra Project SP0532
UK Biodiversity Group Tranche 2 Action Plans - Volume VI: Terrestrial and freshwater species and
habitats (October 1999, Tranche 2, Vol VI).
66
O’Brien et al (2007): Review of Blanket Bog Management and Restoration. Defra project BD1241.
67
Sowerby et al (2008): Contrasting effects of repeated summer drought on soil carbon efflux from hydric
and mesic heathland soils. Global Change Biology.
68
Bhogal et al (2007): Climate change critical review. Defra Project SP0561.
69
Freibauer et al (2004): Carbon sequestration in the agricultural soils of Europe. Geoderma 122, 1-23.
70
Bhogal et al (2007): Climate change critical review. Defra Project SP0561.
71
It is suggested that rather than increasing SOC, zero and reduced tillage were responsible for
redistributing SOC within the soil profile. Whilst zero-tillage increased SOC concentrations in the upper
layers of the soil, when the whole profile was examined these soils did not store more SOC than
conventionally tilled (ploughed) soils. (Baker et al (2007): Tillage and soil carbon sequestration-What do we
really know? Agriculture Ecosystems and Environment, Vol 118:1-5).
65
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Department for Environment, Food and Rural Affairs
24 September 2009
concerns have recently been confirmed by Lal (2008) 72 who found no differences in
SOM between different tillage practices when the whole soil profile was considered.
47. On the basis of the evidence available, which was found to be very sparse and
inconclusive, the study concluded that the amount of carbon that could potentially be
sequestered under zero tillage in England and Wales was likely to be small, with a best
estimate of 310 (±180) kilograms of carbon per hectare per annum, with experimental
values ranging from -140 to 760 kilograms of carbon per hectare per annum. If all
arable farms were to convert to zero tillage (assuming this was practical) this could
mean sequestering carbon equivalent to only 0.034% of the UK’s carbon emissions
and reduced tillage is assumed to have only half these benefits. However, even these
small gains in carbon might be completely offset by an increase in direct nitrous oxide
emissions, or reversed through conventional ploughing which is in the UK generally
undertaken every 3-4 years for compaction, weed, disease and pest control purposes
even when reduced tillage is used. The report concluded that reduced tillage should,
therefore, be considered as a method for protecting existing soil carbon, rather than
increasing its concentration in soil.
48. The report on farming practices also suggested that small increases in soil carbon
could be achieved by applying organic materials to land, raising typical soil carbon
levels from 91 tonnes of carbon per hectare 73 to 91.6 – 92.5 tonnes of carbon per
hectare 74 . However, it suggested that only materials diverted from landfill should be
regarded as genuine additional carbon storage, as the application of other materials to
land was already part of good land management.
49. Research has shown that the biggest potential for increasing soil carbon comes from
land-use change (e.g. arable to woodland) rather than changes in land management 75 .
However, if this results in food production being transferred to other areas of the
country or world the net benefits may be low.
50. Carbon uptake associated with the creation of new woodland can only make a limited
additional contribution to countering greenhouse gas emissions in a country such as
England, where land availability is limited. Nevertheless, carbon sequestration remains
an important benefit of woodland management and creation 76 . Planting trees on peat
soil can lower the soil carbon content and thus the net amount of carbon sequestered
from timber production, but on other soils, trees contribute to woodland soils as a
carbon sink 77 . Soil carbon levels are generally higher under forests and semi-natural
vegetation than under more intensive land uses such as arable agriculture. In England,
land under arable cultivation or pasture have on average 153 and 170 tonnes of carbon
per hectare respectively, whilst under woodland, the carbon content of soil increases to
72
Lal et al (2008): No-Tillage and soil-profile carbon sequestration: An on-farm assessment. SSSAJ Vol 72:
693-701.
73
91 tonnes is the typical carbon content of an arable soil in England and Wales assuming 28 g/kg soil
organic carbon, 1.3 g/cm3 bulk density and 25 cm soil depth.
74
This is based on application rates of 250 kg/ha total nitrogen (N) for livestock manures, digested biosolids
and green waste compost, 150 kg/ha total N for primary or secondary chemical/physically treated paper
crumble (equivalent to 75 t/ha fresh weight) and 7.5 t/ha of straw.
75
King et al (2004): Carbon sequestration and saving potential associated with changes to the management
of agricultural soils in England. Soil Use and Management, Vol. 20 (4), 394-402
76
Defra (2007): A Strategy for England’s Trees, Woods and Forests.
77
Willis et al (2005) Review of evidence for the formulation of forestry policy in England. Final report for
Defra.
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Department for Environment, Food and Rural Affairs
24 September 2009
217 tonnes of carbon per hectare (and 487 tonnes of carbon per hectare under seminatural vegetation including moorland, heathland and scrub vegetation) 78 . Certain
management activities, such as excessive soil disturbance from harvesting, can
release stored carbon back into the atmosphere 79 , whilst the end product of the timber
determines how long carbon remains ‘locked up’ beyond the end of the rotation or
whether it is released back into the atmosphere shortly after the end of the rotation 80 .
Particular benefits arise when woodfuel and wood products are directly or indirectly
substituted for fossil fuels.
51. More novel means of increasing soil carbon are also being considered, for example,
the precipitation of carbonates 81 and the incorporation of biochar (a product formed
from the partial combustion of biomass). Whilst there is increasing interest in its
potential for use in the UK to mitigate greenhouse gas emissions, there are large gaps
in the evidence base relating to its application and impact on soils and the wider
environment. Recent research has, in particular, highlighted significant losses of
biochar during application totalling around 30%. 82 Defra and DECC have jointly
commissioned a review of the available evidence which will report later this year.
Buffering pollution
52. Soils play an important role in buffering and transforming chemicals that could
otherwise cause water or air pollution and/or contaminate our food. Soil microbes are
capable of degrading and consuming a variety of contaminants, which can be
exceedingly harmful in the wider environment. Soils degrade or retain more than 99%
of the pollutants that they receive 83 . However, when the buffering capacity of a soil is
exceeded or the transformation ability compromised, further additions of chemicals will
have a negative impact on soils and the wider environment.
53. Contaminants can enter the soil from many point and diffuse sources, including
atmospheric deposition, inorganic fertiliser and organic manure applications to maintain
agricultural soil fertility, and deposition by floodwaters. Soil contamination can have
long-term implications for soil quality and the ability of a soil to fulfil a wide range of
functions (e.g. food and fibre production, filtering/buffering of water supplies,
conserving biodiversity and cultural heritage). Key contaminants and sources are
explored below as well as the impact on the provision of other ecosystem services.
Heavy metals and persistent organic pollutants
54. Leaching losses and plant uptakes of heavy metals are usually small compared with
the total quantities entering the soil from different sources, so they tend to slowly
accumulate in topsoils over time 84 . Long-term heavy metal additions to land may mean
78
Broadmeadow and Matthews (2003). Forests, carbon and climate change: the UK contribution.
Information Note 48. Forestry Commission, Edinburgh.
79
Forestry Commission (2003) Forests and water guidelines – 4th Edition.
80
Willis et al (2005) Review of evidence for the formulation of forestry policy in England. Final report for
Defra.
81
Manning, D. A. C. (2008): Biological enhancement of soil carbonate precipitation: passive removal of
atmospheric CO2. Mineralogical Magazine. April 2008, v72, No 2, p639-649
82
BlueLeaf Inc. (2009) Preliminary Evaluation of Biochar in a Commercial Farming Operation in Canada
83
EA (2006): Soil quality indicators. IPSS Meeting, Leeds.
84
Nicholson et al (2007): Sources and impacts of past, current and future contamination of soil. Defra
Project SP0547.
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Department for Environment, Food and Rural Affairs
24 September 2009
that some soils cannot be used for food production where they exceed maximum
permitted concentrations in food products (e.g. for cadmium and lead). Biomass
production may also be affected by decreased nutrient uptake leading to yield
reductions. Additions of heavy metals to natural and semi-natural soils can also affect
their ability to support ecosystems, habitats and biodiversity. Research in the mid
1990s concluded that metals, especially zinc 85 , affect soil respiration rates, the soil
microbial biomass and fixation of atmospheric nitrogen. More recently, studies have
shown that elevated soil zinc can affect the functional diversity of microbial
communities 86 , 87 .
55. Persistent organic pollutant (POP) ingestion by grazing animals is considered to be the
pathway which holds the greatest risk of POPs entering the food chain. Since the 1977
UK ban on polychlorinated biphenyls (a POP) the concentration in the soil has
decreased and the risk of transfer into the human food chain is minimal 88 . Soil heavy
metal impacts on soil processes are not yet fully understood, but can have profound
implications for sensitive ecosystems, especially in conjunction with acidification or
eutrophication. 89
56. Levels of some contaminants in soils are falling; for example the UK Soil and Herbage
Survey (UKSHS) 90 revealed that concentrations of dioxins, one of the most toxic and
persistent group of contaminants, have fallen in the UK by about 70% since the late
1980s when restrictions on emission from major industries were introduced. The
UKSHS also revealed higher levels of many contaminants in urban and industrial soils
compared to rural soils. For example, concentrations of metals in urban and industrial
soils were on average 1.5 – 2.5 times those in rural soils, reflecting both historical
legacies and current emissions.
57. Research was undertaken to identify the major past, current and future sources of soil
pollutants 91 . It recommended that the issue of heavy metal loading of soil should be
revisited and that there was a need to consider the ‘new’ materials (diverted from
landfill) being spread to land that can contribute to this. The results of various other
pieces of research looking at the impact of metal additions 92 and the effectiveness of
regulatory regimes in achieving their soil protection goals 93 support this
recommendation.
Land application of organic materials
85
McGrath SP (1996): Effects of heavy metals from sewage sludge on soil microbes in agricultural
ecosystems. In: Toxic Metals in Soil-Plant Systems, ed. SM Ross, Wiley Chichester.
86
Moffett et al (2003): Zinc contamination decreases the bacterial diversity of agricultural soil. FEMS
Microbiology Ecology 43, 13-19.
87
Lock K & Janssen CR (2005): Influence of soil zinc concentrations on zinc sensitivity and functional
diversity of microbial communities. Environmental Pollution, 136, 275-281.
88
Nicholson et al (2007): Sources and impacts of past, current and future contamination of soil. Defra
Project SP0547.
89
Nicholson et al (2007): Sources and impacts of past, current and future contamination of soil. Defra
Project SP0547.
90
Environment Agency (2007): UK Soil and Herbage Pollutant Survey.
91
Nicholson et al (2007): Sources and impacts of past, current and future contamination of soil. Defra
Project SP0547.
92
Gibbs et al (2007): Effects of sewage sludge on agricultural productivity and soil fertility (Phase III). Defra
Project SP0130.
93
Nicholson et al (2008): Road testing of ‘trigger values’ for assessing site specific soil quality: Phase 1 –
Metals. EA Science Report SC050054SR1.
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Department for Environment, Food and Rural Affairs
24 September 2009
58. Applying sewage sludge (biosolids) to land provides valuable plant nutrients and
maintains soil organic matter which plays a key role in retaining good soil structure and
water holding capacity. Application of sludge and other organic materials to land, for
agricultural benefit or ecological improvement, is likely to be the Best Practicable
Environmental Option in most circumstances, and when carried out in accordance with
good practice. However, recent results from long term field experiments have indicated
that metal-rich sewage sludges applied at vastly accelerated loading rates can have
detrimental impacts on some fractions of the soil microbiota. 94
59. These experimental results give a preliminary indication of potential, worst case, long
term scenarios. Although research is in place, we do not yet have the information to
know whether the observed impacts are those of the high application rates over a short
time period in this experimental set-up, or of the resulting total soil metal
concentrations. Such total soil concentrations would occur only after applying sludges
to agricultural land over the very long term, as sewage sludge is applied at much lower
rates in practice, and in the present day has a lower metal content. We also do not
know if the microbial community would adapt when subject to operational
practice rates. It is important that we understand the significance of these results
before making large changes to the current regulatory regime. Metals may be
introduced into soil from a wide variety of different organic materials. However, until
further data on the bioavailability of metals from other organic materials is available, we
do not know if metals from other sources would have similar effects; or if the effects
observed to date in the Long Term Sludge Experiments are unique to metal-containing
sewage sludges.
Atmospheric deposition
60. Deposition of atmospheric emissions of air pollutants such as sulphur and nitrogen
compounds can have significant effects on sensitive ecosystems and on human health.
Ammonia, sulphur dioxide and nitrogen oxides can lead to acidification, and in the case
of nitrogen oxides and ammonia, also to eutrophication, of terrestrial (soil) and aquatic
ecosystems. Deposition results in damage to biodiversity in semi-natural
environments 95 and upland rivers and lakes - many of which are of high conservation
value (Sites of Special Scientific Interest and Natura 2000 sites). The acidification of
mineral soils can lead to enhanced levels of aluminium in the soil solution. In many
cases this can have significant effects on ecosystems 96 , damage plants roots and
inhibit nutrient uptake 97 and reduce nitrogen fixation 98 , leading to decreased plant
growth or changes in plant communities. Populations of other soil biota may also
change, shifting towards acid tolerant species. As a result, a number of soil processes
can slow down (e.g. the breakdown of plant litter becomes slower) 99 .
94
Gibbs et al (2007): Effects of sewage sludge on agricultural productivity and soil fertility (Phase III). Defra
Project SP0130.
95
Bobbink et al (1998): The effects of air-borne nitrogen pollutants on species diversity in natural and seminatural European vegetation. Journal of Ecology 86, 717-738
96
Bareham S.A. (1996): Acid deposition and soils: a perspective for nature conservation. In: Taylor, A.G.,
Gordon, J.E. and Usher, M.B. (Eds) Soils, Sustainability and the Natural Heritage. HMSO, Edinburgh, 105120.
97
Kennedy I.R. (1992): Acid Soil and Acid Rain. Second edition. Research Studies Press.
98
Slattery, J.F., Coventry, D.R. and Slattery, W.D. (2001): Rhizobial ecology as effected by the soil
environment. Aust. J Exp. Agric. 41 289-298.
99
Nicholson et al (2007): Sources and impacts of past, current and future contamination of soil. Defra
Project SP0547.
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Department for Environment, Food and Rural Affairs
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61. Projections indicate that under current policies, significant areas of habitats in England
will still be at risk (in exceedence of critical loads 100 ) from both acidification and
eutrophication in 2010 (65.6% of the area of sensitive habitat, for which critical loads
are mapped, are exceeded for acidity and 87.2% for nutrient N for 2010 101 ), despite
significant reductions in air pollution emissions 102 . Between 1990 and 2006 there has
been a decrease in UK sulphur dioxide and nitrogen oxides emissions by 82% and
46% respectively. Despite this decline, modelling and experimental data predict that
recovery by increasing base saturation will take decades and some acidic soils may
potentially not return to pre-industrial revolution levels 103 , 104 . However, there is some
evidence, from soil monitoring, that levels of soil acidity in England are
decreasing 105 , 106 , 107 .
Other sources of diffuse soil pollutants in the built environment
62. In 2005, over 4 million tonnes of soil were recovered from construction, demolition and
excavation waste 108 . Some of this screened soil is sold as an alternative to natural
topsoil for use in landscaping developments. However, it is often a mixture of topsoil,
subsoil, clay and numerous fragments of building waste materials – brick, concrete,
mortar, ash, clinker and, to a lesser extent, glass, metal, wood and plastic. In terms of
its physical and chemical properties, the material may often be extremely alkaline,
saline, infertile, and contain elevated levels of chemical contaminants (heavy metals
and hydrocarbons) and ‘sharps’, e.g. shards of glass or ceramics 109 .
63. Finding building rubble or other physical contaminants within soils in built environment
gardens and green spaces containing is all too common. A survey of 10 urban centres
in England, Scotland and Wales by the British Geological Survey found visible signs of
contamination in over 50% of the samples 110 .
Water and flood regulation
64. Soil plays an important role in storing and transporting water. A single hectare of soil
has the potential to store and filter enough water for 1000 people for 1 year 111 . We rely
on the ability of well-managed soils to absorb rainfall and reduce run-off and to reduce
100
Critical loads - are usually defined as “a quantitative estimate of exposure to one or more pollutants below
which significant effects on specific sensitive elements do not occur according to present knowledge” and
where pollutants are deposited to land or water. Exceedence of critical load is used as an indication of the
potential for harmful effects to ecosystems.
101
Defra (2007): The Air Quality Strategy for England, Scotland, Wales and Northern Ireland.
102
Defra (2006): The Air Quality Strategy for England, Scotland, Wales and Northern
Ireland: A consultation document on options for further improvements in air quality.
103
Defra (2008): UK Emissions on Air Pollutants 2006 results (see Defra web pages)
104
National Expert Group on Transboundary Air Pollutants (NEGTAP) (2001): Transboundary air pollution,
acidification, eutrophication and ground-level ozone in the UK.
105
Black et al (2002): MASQ: Monitoring and Assessing Soil Quality in Great Britain. Countryside Survey
Module 6: Soils and Pollution. Environment Agency R&D Technical Report E1-063/TR
106
NSRI (2004): Spatial analysis of change in organic carbon and pH using re-sampled National Soil
Inventory data across the whole of England and Wales. Defra project SP0545.
107
Carey, P.D., Wallis, S.M., Emmett, B.E., Maskell, L.C., Murphy, J., Norton, L.R., Simpson, I.C., Smart,
S.S. (2008): Countryside Survey: UK Headline Messages from 2007.
108
DCLG (2007): Survey of arisings and use of alternatives to primary aggregates in England, 2005.
Construction, Demolition and Excavation Waste.
109
British Association of Landscape Industries (2006): Topsoil. Landscape News. Summer 2006, p16-23.
110
British Geological Survey (2005): Geochemical Survey of Urban Environments.
111
EA (2006): Soil quality indicators. IPSS Meeting, Leeds.
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Department for Environment, Food and Rural Affairs
24 September 2009
the risk of flooding. When the infiltration capacity of soil is exceeded or compromised
(such as by compaction) then the ability of soil to provide this function is reduced.
Recent research has found that current rural land management practices, such as
cultivation practices and overstocking have led to increased surface run-off at the local
scale 112 .
65. The importance of protecting our natural environment within urban areas has been the
subject of various reports including the Royal Commission on Environmental Pollution’s
(RCEP) twenty-sixth report on the urban environment. It states that the natural
environment of towns and cities is under-recognised and undervalued. The RCEP has
stated that it would like to see more use of flexible green infrastructure including
permeable surfaces in preference to an over-reliance on the expensive, hard
engineering approaches of the past and recommends that planning policy recognises
and protects the role that urban ecosystems can play in improving towns and cities. 113
Flooding
66. The annual cost of flooding due to soil structural degradation is difficult to assess, with
estimates ranging from £24-51 million for the UK (1996 prices) 114 up to £115 million for
England and Wales alone (2000 prices) 115 . These estimates have been updated to
2004/05 prices to give a range of £29 million to £128 million 116 . This does not include a
valuation of the impact of flooding on health, well-being and quality of life. A study in
2006 showed that about two thirds of flood victims suffered from mental health
problems at some point after the flooding, while some also had long term mental health
effects 117 . According to the report, psychological effects were much more commonly
reported after flooding than physical ones, with anxiety when it rains the most
frequently mentioned symptom.
67. Climate change has the potential to increase the probability of flooding due to
increases in sea level and potential changes in the frequency, duration and intensity of
storms. In 2004, the Government's Foresight Future Flooding report 118 estimated that,
taking these and other factors into account, annual average flood damages could
increase by between 2 and 20 times by the end of the century. Changes would be
highly dependent on the actual impact of climate change and sea level rise, patterns of
growth, development (building etc) and future flood risk management activity. The
Foresight report was updated in 2008 119 . The key message from the update is that the
effects of climate change may be more extreme than had previously been thought. It
also highlighted the increased risk that we will face from surface water flooding in the
future and how land use is an important tool in managing that risk.
112
O’Connell et al (2004): Review of impacts of rural land use and management on flood generation: short
term improvement in modelling and research plan. Defra Project FD2114.
113
Royal Commission on Environmental Pollution (2007): Twenty-sixth report: The Urban Environment.
114
Evans, R. (1996): Soil Erosion and its Impact in England and Wales. Friends of the Earth Trust.
115
EA (2002): Agriculture and Natural Resources: Benefits, Costs and Potential Solutions.
116
EA (2007): The total external environmental costs and benefits of agriculture in the UK.
117
Tunstall et al (2006): The health effects of flooding: Social research results from England and Wales.
Journal of Water and Health, 4(3): 365-80.
118
Evans et al (2004): Foresight. Future Flooding. Scientific Summary: Volume I Future risks and their
drivers. Office of Science and Technology, London.
119
Evans et al (2008): An update of the Foresight Future Flooding 2004 qualitative risk analysis. Cabinet
Office, London.
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Department for Environment, Food and Rural Affairs
24 September 2009
68. Following the summer 2007 floods, the Government commissioned an independent
study to establish lessons that could be learnt from the event. The Pitt Review 120
affirmed the importance of combining hard flood defence management with softer
approaches working with natural processes such as managing the infiltration rate of
soil, slowing water flow and identifying areas with additional water storage capacity. In
July 2008, £1 million was made available to fund three demonstration projects that will
explore how land management can reduce the risk of flooding 121 .
Compaction and soil sealing
69. Soil compaction is an issue on agricultural land and also in the built environment as the
over-compaction of subsoil is an almost inevitable by-product of the construction
process. 122 Compaction at construction sites is very rarely removed or reduced before
topsoil is spread and this affects the long-term functioning of the soils. This may be
evident on-site, in the performance and visual quality of vegetated areas, as well as offsite through impacts on flooding, aquifer recharge and water quality. 123
70. Additionally, the sealing of soil in urban areas with impermeable materials such as
concrete and tarmac increases the amount of rainwater run-off (by as much as 50% 124 )
and increases the risks of urban flooding. For example, the Environment Agency
estimated that two-thirds of the 55,000 homes and businesses affected by the summer
2007 flooding were flooded because drains, culverts, sewers and ditches were
overwhelmed 125 , highlighting the rising incidence of flooding caused by urban drainage
problems. This would represent insurance claims totalling approximately £2 billion 126 .
The use of alternative surfacing materials (e.g. permeable paving and gravel) may offer
a solution in some situations as well as enabling soil to perform its role in groundwater
recharge.
71. When the London Assembly examined aerial photographs of the capital in 2005, it
found that 12 square miles (32 square kilometres) of front gardens were under paving;
this is 67% of the total area of front gardens in Greater London and 3% of the total land
area. This is the equivalent of 22 Hyde Parks 127 . Continued increases in soil sealing
are likely to add considerably to the pressure on our drainage systems and increase
the risk of urban flooding.
Climate change and changing soil water storage in the built environment
72. Climate change will have implications for soils in the built environment. This is as a
result of likely increases in winter rainfall, particularly the magnitude and frequency of
intense events, as well as increases in summer temperatures and the frequency of
drought. Such conditions are likely to have negative impacts on land stability and give
rise to landslips, increase subsidence and cause problems with drainage and flooding.
The behaviour of soils, particularly those containing clay, under different rainfall
patterns will require changes in their management and the need to repair and underpin
120
Pitt, M (2008): The Pitt Review – Learning lessons from the 2007 Floods.
http://www.defra.gov.uk/news/latest/2009/flood-0318.htm
122
WSP Environmental Ltd (2006): The impact of subsoil compaction on soil functionality and landscape.
Defra project SP08005.
123
Land Research Associates Ltd (2006): Use of surplus soil at development sites. Defra project SP0701.
124
RHS (2005): Gardening matters: Front Gardens.
125
Environment Agency (2007): Review of 2007 summer floods.
126
Association of British Insurers (2007): Summer floods 2007 – Learning the lessons.
127
London Assembly (2005): Crazy paving: The environmental importance of London’s front gardens.
121
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Department for Environment, Food and Rural Affairs
24 September 2009
foundations. 128 The Association of British Insurers estimate that the annual future costs
of subsidence claims could increase due to climate change from the current £300
million - £600 million, to £600 million - £1,200 million by 2050. 129
Impact of urban soil erosion on water
73. In 2002, there were 345 recorded water pollution incidents in England and Wales
involving the unauthorised disposal or inadequate containment of soil during
construction. 130 The annual cost of dealing with problems related to sediment in the
urban drainage system is in the order of £50-60 million and individual companies have
been fined up to £18,000 as a result of water pollution incidents in recent years 131 .
Supporting biodiversity
74. Soil biota perform a major role in soil processes by decomposing organic residues,
recycling nutrients and contributing to soil structure through their living tissue, waste
products and remains. Decomposition by soil organisms is a central process for the
delivery of most ecosystem services. 132 These services include animal and food
production, the provision of biochemicals and medicines and the regulation of fresh
water. Soil organisms support carbon sequestration, trace gas composition, nutrient
cycling, soil formation and structural habitat provision. They also play a role in
detoxification and waste treatment and in erosion control. Soil ecosystems also support
biodiversity for a wide range of farmland birds and other predators and therefore
sustaining below ground ecology is important in retaining above ground biodiversity.
Having a range of soil organisms that respond differently to different environmental
perturbations, for example different pollutants, is more likely to enable ecosystems to
respond to disturbances and variations and to allow greater flexibility in management
practices whilst maintaining soil function. 133 Some studies have shown that a decline in
below ground biodiversity will reduce the ability of the soil to withstand and recover
from perturbations. 134
75. It has been estimated that only 1 to 5% of all biota on Earth have been named and
classified. A large proportion of these unknown species are thought to reside in the soil.
Estimates of the possible number of existing species of different groups are staggering:
1.5 million species of fungi, 300,000 species of bacteria, 400,000 species of
nematodes and 40,000 species of protozoa 135 . New molecular techniques have been
used to estimate that a single gram of good quality arable soil can contain as many as
600 million bacteria from up to 20,000 species. The microbial biomass from a hectare
of arable soil has the same mass as 300 sheep 136 . The vast unexplored biodiversity of
128
Bradley et al (2005): Impacts of climate change on soil functions. Defra project SP0538.
Association of British Insurers (2004): A changing climate for insurance.
130
EA (2004): The state of soils in England and Wales.
131
Reeves et al (2007): Code of practice for the sustainable use and management of soils on construction
sites. Report to Defra.
132
Stockdale et al (2006): Do farm management practices alter below-ground biodiversity and ecosystem
function? Implications for sustainable land management. JNCC report no. 364.
133
Stockdale et al (2006): Do farm management practices alter below-ground biodiversity and ecosystem
function? Implications for sustainable land management. JNCC report no. 364.
134
Griffiths et al (2001): Functional stability, substrate utilisation and biological indicators of soils following
environmental impacts. Applied Soil Ecology 16, 49-61.
135
SNH (2002): Soil Biodiversity. Information and Advisory Note No. 151.
136
Ritz (2005): Underview: origins and consequences of below-ground biodiversity. Biological Diversity in
soil, Bardgett et al (eds.), British Ecological Society publication.
129
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soils has potential for commercial exploitation in biotechnology, in areas such as
medicine, industrial processes, agriculture and bioremediation of polluted wastes,
waters and land. Most clinically relevant antibiotics today originate from soil-dwelling
actinomycetes 137 and the potential uses of other biota and their products are being
actively pursued. For example, enediynes are a natural toxin produced by soil bacteria
which have been found to be one the most effective known anticancer agents 138 .
76. Soil management strongly influences soil biota in the agricultural ecosystem. Different
practices cause a shift in habitat and in substrate availability, which results in changes
in abundance of individual species. 139 Fixed site factors also have a major effect on the
size and activity of soil communities 140 . Evidence of the threats to soil biodiversity and
opportunities from its conservation and improved management is mainly qualitative and
there is need for research that makes quantification of threats and potential lost
opportunities possible 141 . Whilst it is clear that farm management practices do alter
below-ground biodiversity and ecosystem function, it is much less clear what steps
could or should be taken to prevent or mitigate these effects. Best practice is likely to
be farm, and even micro-site, specific. 142
Supporting our Cultural heritage
77. Soils are a key component of the landscape and our cultural heritage. They must be
considered as part of the totality of the landscape and the broader historic environment.
The soil in England preserves a diverse range of archaeological remains which is a
vital resource in understanding anthropogenic history. As a matrix the soil holds
palaeoenvironmental data and anaerobic wetland soils preserve organic remains. 143
78. Archaeological remains often occur in areas of intense arable farming which have
always been favourable to human settlement 144 . The Monuments at Risk survey
demonstrated that 10% of destruction and 30% of damage to archaeological sites in
the last half century is attributable to agriculture and approximately 65% of monuments
in arable areas are at medium to high risk of damage 145 . Damage is caused by a
number of processes such as drainage, exposure due to erosion from repeat
cultivation, increase in stocking levels, physical plough damage and acidification by
applying fertilisers 146 . There are various means of reducing the rate of cultivation
damage (reversion of arable to grassland, direct drilling or minimum cultivation);
137
Kieser et al (2000): Practical Streptomyces Genetics. John Innes Foundation, Norwich, UK.
http://news.bbc.co.uk/1/hi/health/2196277.stm
139
Van-Camp et al (2004). Reports of the Technical Working Groups Established under the Thematic
Strategy for Soil Protection. EUR 21319 EN/3, 872 pp. Office for Official Publications of the European
Communities, Luxembourg.
140
Stockdale et al (2006): Do farm management practices alter below-ground biodiversity and ecosystem
function? Implications for sustainable land management. JNCC report no. 364
141
Van-Camp et al (2004). Reports of the Technical Working Groups Established under the Thematic
Strategy for Soil Protection. EUR 21319 EN/3, 872 pp. Office for Official Publications of the European
Communities, Luxembourg.
142
Stockdale et al (2006): Do farm management practices alter below-ground biodiversity and ecosystem
function? Implications for sustainable land management. JNCC report no. 364
143
Van de Noort et al. English Heritage (2002): Monuments at Risk in England’s Wetlands.
144
Oxford Archaeology (2002): The management of archaeological sites in arable landscapes. Defra Project
BD1701.
145
English Heritage (1995): MARS, Monuments at Risk Survey of England.
146
English Heritage (2003): Ripping up History, Archaeology under the Plough.
138
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however in many circumstances these are not practicable and cost effective
solutions. 147 Artefacts are also susceptible to damage from other events, the
Fylingdales fire (2003) burned approximately a square mile of moorland exposing
several pieces of rock art and another prehistoric site 148 . Climate change could further
influence the fate of archaeological remains by increasing soil moisture accelerating
biological decay, increasing flooding occurrences and degradation of water-logged
soils 149 .
Summary of Soil threats
79. Many of the threats to soil act upon more than one ecosystem service, but the means
of dealing with them are often the same irrespective of the service being provided.
Therefore, the evidence has also been analysed by key threats to soil.
80. Climate change: Whilst soils are responsible for greenhouse gas emissions that
contribute to climate change (and removals of carbon that help mitigate it) they are also
likely to be greatly impacted by climate change. These impacts will be both direct, due
to changes in temperature and moisture, and indirect, due to changes in land use and
cropping, with the indirect effects potentially being the more significant of the two.
Climate change is likely to lead to increases in soil erosion, compaction, organic matter
decline, salinisation, flooding, fire risk, damage to archaeological sites, degradation of
habitats and subsidence.
81. Soil erosion: The loss of soil due to erosion has received a lot of attention due to its
impact on water quality. However, it can also have an economic impact on farmers.
Additionally, erosion can lead to damage of valued habitats and archaeological sites,
sedimentation of navigation channels and loss of carbon, particularly from peat.
Typical soil erosion rates are in the order of <1-20 tonnes/hectare/year. Erosion by
water, wind, tillage and from crop harvest are all important mechanisms for soil loss but
with different spatial extents and distribution. Climate change may increase the risk of
soil erosion.
82. Organic matter decline: Soil organic matter (SOM) increases the capacity of soils to
bind chemicals, buffer the release of pollutants, regulate the supply of nutrients,
improve soil structure and water infiltration and retention and makes the soil more
resistant to drought and erosion. SOM is lost due to mineralisation, erosion and land
use change. There is some evidence that soils in England are losing organic matter
especially our peat soils. However, there is also evidence that suggests levels are
increasing in some areas. The loss of SOM can contribute to climate change;
moreover, climate change itself may lead to increased losses. Levels of SOM can be
maintained in agricultural systems by maintaining grassland cover and application of
organic materials. In peat or organic soils, restoration of hydrology and/or semi-natural
habitats is often required to halt further organic matter loss.
83. Compaction: Soil compaction is an issue for arable and grassland soils, due to
machinery and livestock traffic, and for urban soils, particularly as a consequence of
147
Oxford Archaeology (2002): The management of archaeological sites in arable landscapes. Defra Project
BD1701.
148
English Heritage (2005) Research News - Out of the ashes: responding to the great Fylingdales fire.
149
Bradley et al (2005): Impacts of climate change on soil functions. Defra Project SP0538.
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construction. Compaction decreases the infiltration capacity of the soil and increases
the risk of runoff leading to flooding. It can also increase the risk of soil erosion, affect
crop yields, and have a negative impact on both above ground and below ground
biodiversity.
84. Soil pollution: Pollutants can enter the soil from many point and diffuse sources. The
main pollutants of concern are heavy metals, persistent organic pollutants, acidifying
and eutrophying substances, biocides and nanoparticles. Physical contaminants from
development, e.g. building rubble, are also a concern. The ability of soils to buffer or
transform pollutants is being exceeded in some areas with negative consequences for
soil. Impacts include damage and shifts in the populations of soil biota, damage to
crops and damage to semi-natural habitats. Soil contaminants can also enter the food
chain with implications for human health. Contaminated land is used to describe sites
where levels of contaminants present in the soil pose a significant possibility of
significant harm.
85. Acidification: Deposition of air pollutants can lead to acidification of the soil as can
high application rates of nitrogen fertilisers. Acidification damages biodiversity in seminatural environments and upland rivers and lakes; reduces the productivity of
agricultural soils by damaging plant roots, inhibiting nutrient uptake and reducing
nitrogen fixation; alters the population of soil biota with consequences for the soil
processes they perform; and damages archaeological sites. Despite falling levels of
acidifying pollutants, recovery will take decades and some acidic soils may never fully
recover. There is some evidence from soil monitoring that suggests that levels of
acidity in English soils are declining.
86. Land use change: Changing the use of a piece of land will have an impact on the soils
present, either favouring the delivery of certain ecosystem services over others, or
leading to the degradation and even loss of soil. Some land uses are associated with
greater levels of carbon storage in the soil, e.g. permanent grassland and woodland,
and changing land uses can lead to losses of soil carbon, e.g. grassland to arable, or
gains, e.g. arable to woodland. Development, with its associated soil sealing, leads to
the loss of soil, and associated functions, which can include our best quality agricultural
soils.
87. In England, between 2001 and 2003, around 5,860 hectares per year changed from
previously undeveloped land to developed land 150 . This represents an addition
of around 0.5% to the total developed land area and is a lower rate of change than in
the period 1995-97. This reflects various factors including more new housing being built
on previously developed land, in excess of the 60% target set by Government, and the
increased density of housing developments in accordance with Government policy. By
2005, 5.7% of England was developed 151 though this figure does not include smaller
rural settlements.
88. Soil sealing: Many of the ecosystem services provided by soil are linked to its
interaction with air and water. The sealing of soil with impermeable materials, such as
150
The term ’developed land‘ is used here in respect of an area of land of at least 20 hectares with a
population of 1000 or more.
151
DCLG (2007): Generalised land use database statistics for England 2005. The figure is lower than the
figure for ‘urban areas’ generally, because the figure for urban areas includes green space and other
categories.
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concrete and tarmac, increases the risk of run-off and urban flooding and reduces
aquifer recharge as well as adversely impacting other soil functions. The sealing of
front gardens to provide off-street parking has exacerbated these problems and
sustainable urban drainage systems mitigate the loss of some soil functions.
Historic contamination
89. Land contamination has the potential to pose serious risks to both human health and
the environment. There are many cases where soil-based contaminants have passed
into ground or surface waters and degraded them (e.g. to a point where the water is no
longer considered fit for human consumption). There have also been some instances
where explosions have occurred following the emission of flammable gases from
contaminated land 152 .
90. Evidence of direct impacts from soil-based contaminants on human health (e.g.
through long-term exposure causing illness) is less clear 153 . There have been some
cases globally where land contamination has been conclusively linked to serious health
effects 154 , but to date science has not established a widespread link. It is not yet clear
whether the small number of confirmed cases indicates the true scale of the problem
as it can be difficult to spot patterns in health problems and link them to a single cause.
We know from toxicological studies that many substances are able to cause harm to
laboratory animals when they are exposed at high enough concentrations. So
Government chooses to take a precautionary approach and seeks to identify those
sites where contaminants are present at concentrations which are believed to lead to a
significant possibility that significant harm could be caused. This definition of
contaminated land forms a key part of Part 2A of the Environmental Protection Act.
91. Assessing the risk posed by land contamination is a complex task which usually
depends on many site specific factors (it is not a simple case of measuring the amount
of contamination present). Judging whether the risk identified represents a significant
possibility of significant harm is also a difficult decision which can have serious
consequences for those affected. This coupled with the fundamental fact that soil is
very heterogeneous and contamination can be very localised means that it is not only
difficult to identify those sites with elevated levels of contamination but even harder to
say which sites are actually contaminated without carrying out a very detailed
investigation of each potential site 155 . Responsibility for doing this is given to the Local
Authority within whose area the each site is located.
92. To attempt to estimate the size of the contaminated land problem, the Environment
Agency carried out an exercise to estimate the number and extent of sites in England
and Wales where the current or previous usage could potentially lead to the site being
contaminated 156 . This revealed 325,000 sites where activities have taken place that
might conceivably lead to contamination. A small proportion of these “potential” sites
are likely to qualify as “contaminated land” (it is impossible to tell what proportion until
152
Gregson, E. M. (2000): Review of landfill gas: Incidents and Guidance, HSE.
Environment Agency (2009): Human Health Toxicological Assessment of Contaminants in Soil, Science
Report – Final SC050021/SR2.
154
Beck, E. C. (1979): The Love Canal Tragedy. US EPA Journal January 1979.
155
Environment Agency (2009): Dealing with contaminated land in England and Wales , A review of progress
from 2000-2007 with Part 2A of the Environmental Protection Act.
156
Environment Agency (2005): Indicators for Land Contamination, Science Report SC030039/SR.
153
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each site has been investigated and decisions have been taken Local Authorities in
each case, but previous experience suggest it may be somewhere in the region of
10%).
93. Once a site has been identified as contaminated, there is normally a legal responsibility
on Local Authorities to ensure it is remediated so that it no longer poses a significant
possibility of significant harm. There are numerous techniques for remediating
contaminated land. Which technique is used largely depends on the contaminant
involved and on site conditions. However, as many remediation techniques can have
serious environmental and social impacts themselves 157 , there are considerable
benefits to careful selection when more than one option is available.
Total costs relating to key pressures
94. It is difficult to come up with a precise value for the impact of soil degradation as many
of the impacts highlighted in the Soil Strategy have not been fully quantified (for
example, losses of cultural heritage and biodiversity, impacts of diffuse soil pollution.
However, based on the evidence we have gathered the total cost of soil degradation, in
the UK, will be at least £206 million-£315 million per year (see table 1). This does not
include the approximately £1 billion per year spent on contaminated land identification
and remediation or the cost of insurance and claims due to subsidence (£300-£600
million).
Table 1: Annual cost of soil degradation based on evidence presented in the
strategy (where values are available, but excluding contaminated land identification
and remediation)
Annual cost of soil
degradation (£M)
Soil erosion due to agriculture a
Loss of soil carbon due to cultivation b
Flooding due to structural damage to soil c
Sediment in urban drainage systems d
45
82
29-128
50-60
Total
206-315
a
soil erosion costs include: water treatment, damage to property and dredging stream
channels 158 ; damage to crops 159 ; removal of sediment from watercourses 160 .
b
loss of soil carbon costs include: treatment, prevention, administration and
monitoring 161
c
flooding costs include: property damage 162
d
urban sediment costs include: removal of sediment 163
157
English Partnerships (2006): The Brownfield Guide: A Practitioner’s Guide to Land Re-Use in England
EA (2007): The total external environmental costs and benefits of agriculture in the UK
159
Evans, R. (1996): Soil Erosion and its Impact in England and Wales. Friends of the Earth Trust.
160
British Waterways (2008): Consultation response.
161
EA (2007): The total external environmental costs and benefits of agriculture in the UK
162
EA (2007): The total external environmental costs and benefits of agriculture in the UK
163
Reeves et al (2007): Code of practice for the sustainable use and management of soils on construction
sites. Report to Defra.
158
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