The Scottish Soil Framework

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CHAPTER 4 : PRESSURES ON SOILS

4.1 In 2001 SEPA published the State of the Environment: Soil Quality Report( 12) which identified the main pressures on soils. Towers et al.( 1) undertook a comprehensive review on the state of and threats to the Scottish soil resource, which is summarised in Figure 4.1. Some of the impacts associated with these threats are also indicated.

Figure 4.1 Soil threats and impacts (from SPICe Briefing 06/53)

Figure 4.1 Soil threats and impacts (from SPICe Briefing 06/53)

4.2 Although man has clearly had an impact on the Scottish soil resource (including some large scale disturbances such as deforestation and urban growth), Towers et al.( 1) found that soils in Scotland are generally in good health due largely to the sustainable management employed by land managers over a prolonged period. The authors cautioned however that there was a lack, or in some areas absence of data from which to make robust conclusions. In particular there was a lack of trend data from which evidence of change in, and damage to soils might be determined.

4.3 Box 4.1 provides a summary of the analysis of national threats undertaken by Towers et al. ( 1).

Box 4.1 Threats to Scottish Soils after Towers et al. (2006)

To determine the overall importance of each threat for each function, the consequence, extent (national or local), uncertainty and reversibility was scored on a simple three point scale. Presented here is a summary of the relative ranking of the threats on the basis of the evidence available at time of publication of the report. The analysis presented is at a national scale, an assessment of threats occurring at a local level could lead to a different ranking at a particular location.

Ranking of threats to soils across all soil functions at national scale

Ranking of threats to soils across all soil functions at national scale

Climate change and loss of organic matter are the most significant threats to the functioning of Scottish soils. Both affect most soil functions with impacts which are national in their spatial occurrence and which are difficult to reverse. However, there are great levels of uncertainty associated with these linked threats.

Sealing is a serious threat in that once the soil is covered with an impermeable surface and development has taken place, it cannot perform any other functions.

Acidification & Eutrophication are most evident in water quality and above ground vegetation where the critical load approach has been used to determine the extent of damage to soils and ecosystems. Although there is evidence that pH in water is recovering due to sulphur abatement policies, it will take decades for soils to recover to previous levels. There have not yet been similar reductions in nitrogen emissions and deposition, so eutrophication remains a threat to upland soil quality.

Loss of soil biodiversity is difficult to assess due to the lack of an evidence base. But given that soil organisms are the driving force behind most soil processes, decline in soil biodiversity is thought to be a significant threat.

Contamination by heavy metals can be locally significant. Other contaminants such as persistent organic pollutants, pharmaceuticals, pesticides and hormones need to be considered in any future analysis.

Erosion, pesticides and compaction, associated with agricultural activity can be significant locally and it is local action that will resolve them. New evidence indicates that compaction may be a bigger threat than previously thought. There is also doubt about the effectiveness of ameliorative treatments. The risk of compaction is also likely to increase under a changing climate and with the use of heavier machinery (Hallet pers comm.).

Salinisation (the increased level of soluble salts in the soil profile) was not judged to be a current threat to Scottish soils. However, rising sea levels and the resulting impacts of seasonal incursion by sea water could also have a dramatic effect on coastal soils, and the integrity of many archaeological structures that are currently protected by soil.

4.4 The analysis undertaken by Towers et al. ( 1) does not recognise the interaction between the threats for example the relationship between soil organic matter levels and soil erosion, whereby organic matter may help to reduce erosion risk in many soils. It is also important to bear in mind that the threats listed above are not static, as they may vary in their intensity over time. Management techniques and technological advances, such as the use of poly tunnels and heavier machinery can also increase the likelihood of specific threats.

4.5 Due to lack of evidence, threats like depleted or excessive nutrient levels in soils were not considered ( 1). Emerging potential threats including nano-particles, acidification in previously cultivated land and moorland burning may require consideration in any future analysis.

4.6 Table 4.1 provides an indication of the relationship between the threats identified ( 1) and the primary function(s) of soil discussed in Chapter 3. This analysis provides the broad context for Chapter 7 where planned activities and outcomes aimed at minimizing these threats and maintaining soil functionality are set out.

4.7 A common thread in the assessment of the pressures on soils is the lack of systematic baseline data in some cases and a lack of trend data for nearly all cases. Long term baseline data from field sites and/or national datasets are clearly essential to detect change and trends in Scottish soils with a view to assess the effectiveness of policies in place to protect soils.

Table 4.1 Threats to soils and their potential impact on soil functions: a preliminary analysis.

Threats to Scottish soils (Towers et al. 2006)

Function impacted ( chapter 3)

Food & biomass production

Regulating water flow & quality

Carbon storage and gas balance

Habitats & biodiversity

Heritage

Raw Materials

Platform for building

Climate change

xx

xx

xx

xx

xx

x

Loss of organic matter

xx

xx

xx

xx

x

Sealing

xx

xx

xx

xx

xx

xx

Acidification and Eutrophication

x

xx

x

xx

x

Loss of biodiversity

x

x

xx

xx

Contamination by heavy metals

x

x

x

xx

X

Soil erosion

x

X 1

x

x

x

Pesticides

x 1

xx

Compaction and structure

x

x 1

x 1

x

x

Salinisation

X 1

XX

X 1

XX major effect
X minor effect
1 but locally important