Soil erosion was identified as one of the main threats to Scotland’s soils in the comprehensive ‘State of Scotland’s Soil Report’ (2011). The Scottish Soils Framework sets out a vision for soils to be “safeguarded for existing and future generations”. Soil erosion can result in significant costs, not only to immediate users of soils but also to society as a whole. Climate change projections for Scotland indicate more heavy rainfall days and an increase in winter rainfall, leading to greater risks of soil erosion in the future, making the status of ‘Soils and agriculture’ in Scotland of ‘high concern’ (Committee on Climate Change, 2019).
The literature review demonstrates that evidence on soil erosion rates, impacts, mitigation and costs in Scotland tends to be sparse, and anecdotal rather than quantitative. These estimates may have some uncertainty, given the paucity of data.
For the economic analysis, rates of soil erosion had to be estimated from empirical data primarily derived for England and Wales. However, the probability of erosion taking place in any one year / field was based on Scottish field observations and analysis of the Soil Erosion Risk Classes, derived for Scottish conditions.
The ecosystem services framework adopted here assesses the economic costs of soil erosion in terms of its effects on the services provided by soils: provisioning, regulating, supporting and cultural. Inevitably, gaps in the evidence remain, whether it is capturing all the ways in which soil erosion impedes the delivery of ecosystem goods and services; how to put a cost to that effect; and understanding any feedback mechanisms between the erosion process, soil properties and soil functions. Even so, the framework is robust and flexible enough to incorporate more evidence as and when it becomes available. For example, although costs of mitigation have been reported in the Literature Review, they were not included in the economic analysis at the catchment or national scale, because there was no information on the numbers of measures used or their geographical location. This would require mapping these measures at a much finer resolution than used in the present study (e.g. location of field buffer strips; identification of minimum tillage use; etc.).
The present study estimated that the total costs of soil erosion in Scotland per annum are £49,498,461 (including drinking water treatment costs) or £30,972,155 (not including water treatment costs). Annual off-site costs of soil erosion always exceeded those associated with on-site costs for all the 5 study catchments. The same was true at the national scale.
Understanding the impacts and costs of soil erosion will inform national policies and local practices designed to value the soil resource in delivering a range of ecosystem goods and services that support a broad spectrum of human activities and associated benefits.