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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 2 Department for Environment, Food and Rural Affairs 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. 4 3 Department for Environment, Food and Rural Affairs 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 4 Department for Environment, Food and Rural Affairs 24 September 2009 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. 5 Department for Environment, Food and Rural Affairs 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. 6 Department for Environment, Food and Rural Affairs 24 September 2009 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. 7 Department for Environment, Food and Rural Affairs 24 September 2009 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. 8 Department for Environment, Food and Rural Affairs 24 September 2009 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. 9 Department for Environment, Food and Rural Affairs 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. 10 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 11 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. 12 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. 13 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. 14 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. 15 Department for Environment, Food and Rural Affairs 24 September 2009 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. 16 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. 17 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 18 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 19 Department for Environment, Food and Rural Affairs 24 September 2009 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 20 Department for Environment, Food and Rural Affairs 24 September 2009 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. 21 Department for Environment, Food and Rural Affairs 24 September 2009 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. 22 Department for Environment, Food and Rural Affairs 24 September 2009 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 23 Department for Environment, Food and Rural Affairs 24 September 2009 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 24