Appendix B: What is the actual occurrence or probability ...



The cost of soil degradation in England and WalesAppendix B: What is the actual occurrence or probability of soil degradation in England and Wales?To evaluate the consequences (impacts and costs) of soil degradation, it is first necessary to identify the actual or potential probability of degradation in terms of degree (intensity) and extent (spatial distribution). Appendix A details our present level of understanding of the extent and intensity of the 6 identified soil degradation processes for England and Wales. Appendix B provides estimates of probability of degradation occurring in different soilscapes, under different land uses based on available information. Soil erosionOf the four identified types of soil erosion (water, wind, tillage and co-extraction) in England and Wales, erosion by water is the most extensive. Wind erosion mainly affects sandy and peaty soils in the eastern and middle counties of England, and upland areas of England and Wales. However, erosion by tillage and through co-extraction remains poorly understood with almost no available scientific data for England and Wales.Our understanding of soil erosion, which is estimated to affect 17 per cent of the land in England and Wales, is limited to certain landscapes, including farmed land and upland areas. Our understanding of erosion occurring in other landscapes is limited. Estimates of intensity of soil erosion that cover more than a field in general tend to be based on model predictions with only limited verification from actual measurements of soil erosion. However, while erosion by water may be spatially more dominant, erosion by wind can cause greater lost of soil per unit of land. Table C SEQ Table \* ARABIC 1. Review of the extent and intensity of soil erosion in England and WalesErosionExtentIntensityThe soils in England and Wales most susceptible to water erosion are sandy soils in south west and south east England, East Anglia, the Midlands and South Wales; chalky soils on the South Downs, Wolds and in East Anglia (Defra, 2005). Wood et al. (2006) conclude that brown earths were the major soil group with the highest soil erosion vulnerability overall. In upland areas, peat soils and podzols (particularly the wetter stagnoposzols) were at the highest risk of erosion. Factors affecting erosion in these areas include wind splash erosion of blanket peat (Foulds and Warburton, 2007). In a recent Farm Practices Survey (2007), 50 per cent of farmers said they observed at least some soil erosion on their land. The ‘State of the Environment’ (Environment Agency, 2005) estimated that 17 per cent of the land in England and Wales is affected by erosion.Wind erosion has mainly been recorded on sandy and peaty soils in the eastern and middle counties of England e.g. East Midlands and East Anglia, and parts of the uplands of England and Wales (Figure 6). In comparison to water erosion, the area of England affected by wind erosion is small (Chappell and Warren, 2003). However, the rate of erosion can be greater by wind than by water. This is partly due to the fact that wind erosion is likely to impact on a whole field area while erosion by water is limited to where the water flow is concentrated (Evans, 1996; Owens et al., 2006a).Uplands are at risk of wind erosion, especially on exposed bare soils and peat, where overgrazing can expose soil and peat (McHugh et al, 2002). Drier summers may increase the risk from wind erosion as soils dry out and become friable. Peat soils in particular will become more vulnerable to wind and water erosion, both through drier conditions (leading to vegetation loss and increased susceptibility to wind erosion), and from extreme rainfall events in the winter. Critically, erosion of peat will lead to a loss of carbon back into the atmosphere.The extent and magnitude of soil loss by tillage erosion in England and Wales is poorly understood (Owens et al., 2006a). There are almost no easily available (i.e. published) data on the magnitude of tillage erosion in England and Wales. Exceptions include field data from Dalicott Farm in Shropshire (Govers et al., 1993; Quine and Walling, 1993; Quine et al., 1994, 1996) and Coombe Barton Farm in Devon (Quine and Zhang, 2004a, b). The extent of tillage erosion will be limited to arable land that is conventionally tilled. According to Owens et al. (2006a), there have been almost no scientific studies of soil loss due to co-extraction with root crops and associated farm machinery in England and Wales. Brazier (2004) provides a summary of available data describing rates of erosion by water from the hillslope scale to the large catchment scale. Measurements are reported from erosion plots, overflight and field surveys, Cs137 data, reservoir sedimentation and suspended sediments monitoring. Evidence suggests that soil erosion rates in excess of acceptable thresholds occur on a wide range of soils and under a wide range of land uses throughout the country. It has been estimated that the annual soil erosion rate for the UK is 2.2 million tonnes of topsoil (SSLRC, 2000; Environment Agency, 2007). Considering that the agricultural area in the UK is 18.7 million hectares (Agristats, 2009), this would result in an average soil loss of 0.7 Mg ha-1 yr-1 on land affected by erosion. However, Evans (2002) estimated that 29% of the farmland was affected by erosion at an average rate of 1.9 Mg ha-1 yr-1 during the period 1982-1986 (Table 1). He noted that soil loss may be considerably higher on individual fields causing considerable on- and off-site damage. Other studies have estimated typical erosion rates at 1 to 20 Mg ha-1 yr-1, but erosion rates are thought to be less than 1 Mg ha-1 yr-1 for most fields (Defra, 2009a). Other estimates of erosion rates include work by Wood et al. (2006). They estimated that annual erosion rates across England and Wales were extremely low for a rain event with a 1 in 1 year return probability. However, for the 1 in10 year return period, annual erosion rates were estimated to be 0.52 Mg ha-1 (≤12o slope) and 1.56 Mg ha-1 (>12o slope) in some parts of England and Wales (Figure 1). The results of Wood et al. (2006) correspond well with observations made by Evans (1998) and Boardman (1998). These predictions and estimates should be verified by actual measurements of soil erosion, but these have been ad hoc in the UK. Based on field experiments, Morgan (1980) measured low rates of annual soil loss (0.23 to 0.98 Mg ha-1 yr-1) on agricultural fields under natural rainfall. The rate of soil loss on bare soils, however, was very high at 11 Mg ha-1 yr-1. More severe rates of soil erosion have been measured during storm rainfall events, resulting in soil loss between 2 and 8.6 Mg ha-1 yr-1. Morgan (1980) thus concluded that soil erosion is typically associated with rainfall events of moderate magnitude. For the majority of rainfall events rates of soil loss are thus negligible. Soil loss rather takes place during moderate to high magnitude rainfall events, and local conditions (soil conditions, land cover, slope) determine whether any particular field is susceptible to erosion processes. Boardman et al. (2003) measured average erosion rates between 0.65 to 6.5 Mg ha-1 yr-1 in South East England during the 1980s. However, rates on individual fields reached over 260 Mg ha-1 yr-1 in occasional years. In a more recent study, erosion rates of 31 to 234 Mg ha-1 were measured on fields prone to erosion in South East England during the 2006 – 2007 winter season (Boardman et al., 2009). Walling et al. (2005) assessed net erosion rates from arable and pasture fields in South West England and calculated that the median net rates of soil loss were 4.1 Mg ha-1 yr-1 and 0.6 Mg ha-1 yr-1, respectively. The net erosion rates were about half of the gross erosion rates. Within-field storage of sediments is thus significant in the gentle rolling terrain that characterizes most arable fields in this region. This has implications for soil protection as it implies that a significant amount of soil erosion is ‘invisible’ – i.e. soil and its functions are being lost at source, but with no visible evidence (e.g. turbid runoff, muddy floods and sedimentation in streams).Farmers in East Anglia expect moderate damage to crops from wind erosion once every three or four years and severe damage once in 10 years (Chappell and Thomas, 2002). The mean rate of wind erosion has been estimated at the order of 0.1 to 2 Mg ha-1 yr-1, although maximum values for fields can be one or two orders of magnitude higher. Evans (1996) reported that the value of the crop in wind eroded fields is often higher than that affected by water erosion, so the on-site cost of wind erosion is often greater (five times or more) than when fields suffer from water erosion. The national annual cost of agricultural inputs lost because of wind erosion in the mid-1980s was estimated at ?210,000 and the loss of crop at ?705,000: equivalent values for water erosion were ?285,000 and ?940,000 respectively, due to the larger area affected by water erosion (Quine et al., 2006).These limited studies suggest that within-field movement by tillage operations can be similar or greater than that due to water and wind erosion, and tentatively within the range 0.1 to 10 Mg ha-1 year-1. Van Oost and Quine (2006) produced a map of simulated tillage erosion rates (Figure 7).It is estimated that 2 Mg ha-1 year-1 is eroded during the harvesting of sugar beets (= c.4% of the total crop land of England and Wales at present) and potatoes (Figure 8). It has been estimated that this represents the loss of about 1% of the topsoil of beet fields per century. Annually British Sugar receives around 450,000 t of soil with the 9 x 106 t of sugar beet it purchases from UK farmers. The available information suggests that for sugar beet of the order of 1-3 Mg ha-1 year-1 may be lost from the field on crop roots, depending on its occurrence within crop rotations. Owens et al. (2006a) found no literature on the magnitude of soil co-extracted on farm machinery. However, a first attempt based on typical information on farm machinery, for example tyre dimensions, suggest that the maximum likely loss of soil associated with a tractor and trailer for sugar beet harvesting is c. 1-2 Mg ha-1 per pactionField measurements of the extent and severity of soil compaction in England and Wales are limited and mainly come from work by Palmer (2004). Maps of estimated vulnerability and risk of compaction for grasslands across England and Wales have been produced but are limited by the available data sets, both in terms of accuracy and sensitivity. Table C SEQ Table \* ARABIC 2. Review of the extent and intensity of compaction in England and WalesCompactionExtentIntensityStalham et al., 2005 survey 602 potato fields in UK between 1992 and 2004, in two thirds of fields, a soil resistance sufficient to limit root growth was presentTowers et al. (2006) found localised compaction on cultivated soils in ScotlandWork by Palmer (2004) using a technique developed during work on flood-affected catchments in 2000 provides the most significant body of evidence of the extent of compaction (12 catchments)Maps of vulnerability and risk for grasslands across England and Wales in Defra (2007)In Scotland - No clear evidence that it poses a serious threat to soil quality nationally (Towers et al. 2006)In England and Wales - Palmer (2004) less than 1% sites had Severe degradation, 21 % had high degradation, 60 % in ModerateLoss of organic matterThe extent of the total stock of carbon is reasonably well known for Wales and for agricultural areas in England and Wales. The intensity of loss of organic matter has been estimated from the Soil Surveys archive that compares soil samples taken in the original survey and those collected in a partial resurvey. The changes in soil carbon across England and Wales measured in the National Soil Inventory have not been detected in the Countryside Survey. The reasons for this are being investigated in a continuing project funded by Defra (SP1101 Comparison of soil carbon changes across England and Wales estimated in the Countryside Survey and the National Soil Inventory).Table C SEQ Table \* ARABIC 3. Review of the extent and intensity of organic matter in England and WalesLoss of organic matterExtentIntensityBellamy et al. (2005): over last 25 years been a general decline in soil OM in agriculturally managed soils. Some small increases in intensively farmed arable soils.Carey et al. (2008b): between 1978 and 2007 Broadleaved, Mixed and Yew Woodland (increase OM), Arable and Horticulture (decrease OM) and Bracken (increase OM)Smith et al. (2007): Organic soils (peats and organo-mineral soils) cover about 20% of the area of Wales and contain 50% of the carbon, equivalent to 195.6 MtCBradley et al. (2005): total stocks of soil carbon 1740 Mt England and 340 Mt Wales.Bradley et al. (2005): Stocks of carbon: England: semi-natural (310 Mt), woodland (108 Mt), pasture (686 Mt), arable (583 Mt) and gardens (54 Mt); Wales: semi-natural (121 Mt), woodland (45 Mt), pasture (162 Mt), arable (8 Mt) and gardens (3 Mt).Defra (2009): Eastern England peat shrinkage rates of 1-2 cm per year have been noted following drainage and cultivationBellamy et al. (2005): carbon lost from UK soils at an annual rate of 13 million tonnes.Countryside survey (Carey et al., 2008a): found no significant change in carbon concentration in soils (0-15 cm depth) between 1978 and 2007POST (2006):Around 18% of organic matter present in arable topsoils in 1980 had been lost by 1995 (grasslands ploughed for arable use)Holden et al. (2007): Land use changes impacting on organic soils13% upland Wales and 6% of England afforested.Holden et al. (2007): soil erosion in the southern Pennines, on peat soils, has been very severe over the past 200 years. Many heavily eroding catchments are producing 200 to 500 t km-2 a-1 of sediment.Holden et al. (2007): reported rates of surface retreat measured on bare peat by erosion pins ranged between 5.4 and 40.9 mm a-1.Jones et al. (2003) more than half of the total Welsh resource of blanket bog mapped as bearing semi-natural vegetation cover exhibited symptoms of degradation.Loss of soil biodiversityThe potential threat to soil biodiversity in most parts of England and to a less extent in Wales is high primarily because of the effect of high intensity agriculture, soil compaction, risk of erosion and loss of soil organic matter content (Jeffery et al., 2010). Table C SEQ Table \* ARABIC 4. Review of the extent and intensity of loss of soil biota in England and WalesLoss of soil biodiversityExtentIntensityVery little information available.The Thematic Strategyfor Soil Protection in Europe (European Commission 2006) identifies loss in biodiversity as one of the main threats to soil.Diffuse contamination of soilThe spatial extent of diffuse contamination of soil is mainly limited to discussion regarding zinc and copper contents related to the application of animal manures, domestic sludge and paper waste on agricultural land. However, risk of sea level rise and therefore salt water intrusion has also been estimated. Deposition of airborne pollutants is limited to discussions relating to the Chernobyl disaster and acidification from industrial pollution. Intensity of diffuse contamination is limited to estimates of potential increases in heavy metal contents from animal manures, domestic sludge and paper waste.Table C SEQ Table \* ARABIC 5. Review of the extent and intensity of diffuse contamination in England and WalesDiffuse contamination of soilExtentIntensityGuardian 2009: 370 farms in Britain (mostly in Wales) are still restricted in the way they use land and rear sheep because of radioactive fall out from Chernobyl. A reduction of 95% since 1986 when 9700 farms were restricted across the UK. Chambers et al., (1998): see Figures 2 and 3 for spatial distribution of Zn and CuAlloway (1995): Although all sludges contain a wide range of metal and other contaminants in varying concentrations, those from industrial catchments generally have higher metal contents than those from suburban domestic areas.Natural England (2009): 60% of England’s highest quality Grade 1 agricultural land lies below 5m AOD and is at risk of loss or degradation due to sea level riseNicholson and Chambers (2006): Heavy metal contamination in areas where sewage sludge is spread.Nicholson and Chambers (2006): Atmospheric deposition of heavy metals likely to be greater in forest and woodland soils than agricultural or ‘natural’ soils because tree foliage is more efficient at scavenging metal ions from the atmosphere.Nicholson and Chambers (2008): During 1996/7, approximately 50% of sludge production (480,000 t of dry solids) was applied to 73,000 ha of agricultural land in England and WalesCCW (2007): 59% of Welsh soils exceed ‘critical loads’ for acid pollutants. Acidification of soils in Wales is extensive because of a combination of high acid deposition rates and soils with low calcium and magnesium content.EA: In the UK, 100 million tonnes of organic waste, such as sewage sludge and compost, is applied to land each year. 30% of total annual inputs of Zn and Cu in soil come from livestock manures and a further 6 to 16% from sewage sludgeChambers et al., (1998): Heavy metal contents of a range of animal manures led to the prediction that the highest loadings of Zn (up to 3.3 kg ha-1) and Cu (up to 2.2 kg ha-1), corresponded with the main pig farming areas in East Anglia and Humberside. Highest loadings of other metals were: nickel (up to 0.08 kg ha-1), chromium (up to 0.064 kg ha-1), cadmium (up to 0.007 kg ha-1) and lead (up to 0.073 kg ha-1).Chambers et al., (1998): Heavy metal analysis of animal manure samples showed that pig manure typically had Zn concentrations of ca. 40 mg kg-1 dry matter (dm) and Cu ca. 350 mg kg-1 dm. Poultry manures had Zn ca 400 mg kg-1 dm and Cu 80 mg kg-1 dm. Cattle manures were Zn 130 mg kg-1 dm and Cu 30 mg kg-1 dm. Dairy cattle manures had higher concentrations of most metals than beef cattle manures.Nicholson and Chambers (2006): estimated that it would take87 years of sewage sludge addition to raise Zn to the limit value (200 mg Zn kg-1 dry soil), 94 years for composts, and 149-177 years for pig slurry. Paper sludge would also raise soils to the Zn limit value after 128-313 yearsAlloway (1995): in UK sludges 62% of Cu and 64% Zn were from domestic sources.Defra (2009): Soils degrade or retain more than 99% of the pollutants that they receiveDefra (2009): Concentrations of metals in urban and industrial soils (UK) were on average 1.5-2.5 times those in rural soils, reflecting both historical legacies and current emissions.Surface sealingThe extent of surface sealing is seen through the growth of urban areas and settlements, and the communication networks that link these areas. Recent growth in surface sealing has mainly occurred in pre-existing urban areas and only small areas of greenfield land have been developed (i.e. in England 5,000 ha per annum between 2000 and 2006; FLUFP, 2010).Table C SEQ Table \* ARABIC 6. Review of the extent and intensity of surface sealing in England and WalesSurface sealingExtentIntensitySoil sealing has greatest impact in urban and metropolitan areas. The importance of the extent of sealing to soil performance is recognised widely (Van Camp et al., 2004)On average, the area of soil surface covered with an impermeable material is around 9% of Europe (Scalenghe and Marsan, 2009). Highest % occurs in Denmark, Belgium and the Netherlands (16-20%) (Burghardt et al., 2004)Globally it is estimated at 500,000km2 (Elvidge et al., 2007)). Over the past 20 years the extent of built-up areas in European countries has increased by 20%, while the population has increased by only 6% (Huber et al., 2008; Burghardt et al., 2004).Wood et al. (2005) identify different types and degrees of sealing and associated soil conditions. Degree of sealing is related to the type of land use (i.e. railway tracks, pavements, piazzas, vehicle parking areas, pathways, patios, etc) and population density (Scalenghe and Marsan, 2009). Building footprints (residential, commercial, industrial, sports stadiums; etc); highway surfaces;Burghardt et al., 2004 report intensity related to land use* (see table below)Estimates of the probability of soil degradationUsing this review of literature and data sources, a series of landscape and soilscape categories have been developed to represent the relative differences in degradation probability in England and Wales. It should be noted that these maps do not represent actual rates of degradation, but rather the relative level of risk within each land use type given the type of soil on which that land use is occurring. Table C SEQ Table \* ARABIC 7. The relative risk of erosion in each land use and soil type categoryLand useSoilscapesClaySiltSandPeatUrbanLHHn/aHorticultureLHHHArable intensiveLHHHArable extensiveLMHHGrassland improvedLMMHGrassland unimprovedLMMHRough grasslandLMMHForestryLLLMWoodlandLLLMWildscapeLLLMNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probabilityTable C SEQ Table \* ARABIC 8. The relative risk of compaction in each land use and soil type categoryLand useSoil typesClaySiltSandPeatUrbanHHHHHorticultureHHLHArable intensiveHHLHArable extensiveHMLMGrassland improvedHH?HGrassland unimprovedMMLMRough grasslandMMLMForestryHM?HWoodlandLLLLWildscapeLLLLNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probabilityForestry – High during planting, harvesting and extraction, low at all other timesTable C SEQ Table \* ARABIC 9. The relative risk of organic matter decline in each land use and soil type categoryLand useSoil typesClaySiltSandPeatUrbanHHHHHorticultureH*H*H***HArable intensiveH*H*H***H***Arable extensiveMMMMGrassland improvedMMMHGrassland unimprovedLLLRough grasslandLLLLForestryLLLLWoodlandLLLLWildscapeLLLLNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probability*, **and *** indicate that although high in all soil textures differences between soil textures can be recognized with * being smallest and *** being largest changes. Table C SEQ Table \* ARABIC 10. The relative risk of soil biodiversity decline in each land use and soil type categoryLand useSoil typesClaySiltSandPeatUrbanHHHHHorticultureHHHHArable intensiveHHHHArable extensiveLLLLGrassland improvedMMMMGrassland unimprovedLLLLRough grasslandLLLLForestryM/HLLM/HWoodlandLLLLWildscapeLLLLNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probability* Forestry – deciduous forest soil favour high soil biodiversity, high C:N ratios, fungal-dominated food webs, fungi-eating protists and nematodes and high densites of microarthropods and aneic earthworms (Bardgett 2005). Earthworm forest communities are not very diverse. Coniferous forest have lower biological activity, more heavilty fungal-dominated. Sewage sludge is used in forestry. The heavy metals in sewage sludge can reduce soil biodiversity, Clays and OM seem to be particularly vulnerable.Table C SEQ Table \* ARABIC 11. The relative risk of diffuse contamination in each land use and soil type category (heavy metals)Land useSoil typesClaySiltSandPeatUrbanHorticultureArable intensiveArable extensiveGrassland improvedHHGrassland unimprovedMMRough grasslandForestryHMLHWoodlandMLLMWildscapeLLLLNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probabilitySee Nicholson and Chambers (2008) for heavy metal accumulation in agriculture, urban and forestry.Table C SEQ Table \* ARABIC 12. The relative risk of diffuse contamination in each land use and soil type category (organic contaminants)Land useSoil typesClaySiltSandPeatUrbanHorticultureHLHArable intensiveHLHArable extensiveHLHGrassland improvedGrassland unimprovedRough grasslandForestryM1L1M1WoodlandWildscapeNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probability1lower pesticide use in forestry than agriculture or horticultureTable C SEQ Table \* ARABIC 13. The relative risk of surface sealing in each land use and soil type categoryLand useSoilscapesClaySiltSandPeatUrbanHHHHHorticultureMMMMArable intensiveMMMMArable extensiveHHHHGrassland improvedHHHHGrassland unimprovedHHHHRough grasslandHHHHForestryMMMMWoodlandLLLLWildscapeLLLLNote: H = high probability of soil degradation; M= moderate probability of soil degradation; L = low probability of soil degradation; ? = Uncertain probabilityAny soilscape is vulnerable to surface sealing, although restrictions and regulations exists due to:Planning system restrictionsAgricultural land classificationGreen BeltSSSIsBrownfield developmentThese categories were mapped using and the LCM2000 data and NSI soilscapes data to show where risks might occur in the landscapes (see Appendix D). ................
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